Date: Fri, 2 Jan 1998 01:18:25 -0500 (EST) From: Nigel Field Subject: Re: PROP-FAB: Spar (fwd) At 10:59 AM 12/31/97 EST, you wrote: > >Correct me if I'm wrong, but I believe that the prop produces much more >thrust at cruising speed than at TO/Climb (assuming a cruise prop, >anyway). I think this is because of the lower RPM at TO/Climb, as well >as the optimized Lift Coefficient for Cruise. I may very well be wrong >here - I have not done the analysis, and this is another region where my >intuition is weak. Yes that is correct as I understand it. The low RPM at static and TO results in lower developed shaft HP and the poor pitch distribution (helix) which is optimized for cruise, combine to give lower thrust. In fact on a fast airplane FP cruise prop the inner part of the blades can be stalled on TO roll. But this is the very problem we are attempting to overcome, how to improve the HP thus thrust at zero and low airspeed without compromizing cruise performance. If we use a variable pitch prop we can reduce the pitch to achieve rated HP and obtain much higher TO thrust, but we all know that. And then at the higher cruising speed we increase the pitch and _reduce power_ for cruise conditions. With a fixed pitch prop we just live with lower power/thrust at take off but we still _reduce power_ for cruise. This is done by reducing manifold pressure, thus torque which is basically linear to MAP, with the throttle or by climbing to cruise altitude, or a combination of both. Remember that at 8000 ft you only get 75% power with the throttle wide open due to the lower available MAP. Since torque drops with MAP then thrust goes down with it and we can capitalize on that to a small degree by using a scimitar shaped prop that can twist a little with power. If you are going racing for flat out speed down low at full throttle then a scimitar prop offers no advantage as it will continually be flexed into a slightly lower pitch, so you never see them used in racing for that reason. In fact they employ very stiff thin tipped unswept blades for better efficiency. But we don't cruise our Cozys and LE, VE at full power (not to be confused with wide open throttle) so we can obtain some CS effect by allowing some blade twist at high power. > >I wonder whether (given that we believe that the centrifugal loads are >two orders of magnitude more important than the thrust loads) what >actually causes the blade to twist is the aerodynamic loading under >power (which is only a few hundred lbs at best) or the centrifugal >loading as the RPM changes. It is purely the aerodynamic loads that twist the blade. RPM is part of that equation but only because the aerodynamic loads increase with V^2 . I can't see how centrifugal loads, which also increase with RPM, can be made to make the blade twist as the forces are 90 degrees apart in another plane. > As you state below, the "scimitar" tip can >cause a great deal of twisting (at the cost of higher stress levels) but >whether it's due to the offset thrust line (wouldn't the sweepback cause >a _lessening_ of pitch with high loading - exactly the opposite of what >you want?) Only if you do not reduce power for cruise by climbing or retarding the throttle or both. For example I use all I can get for TO at full throttle at 30 in MAP then reduce to 28 in for climb then set on 22 to 24 in MAP for cruise depending on what I am doing. At 10K I only get about 21 in MAP with the throttle wide open. The RPM is a result only, it is a variable and I get what I get along with the TAS, but typically 5200 RPM and 152 KTS at 22 in MAP. So the prop twist, such as it is, follows the torque which I control with MAP through throttle position and altitude. >or due to twisting caused by rotational speed changes - as the >rotations speed increases, even just a few hundred RPM, the forces on >the blade can change tremendously - isn't clear to me. Hopefully the >FEA can shed some light on these issues (actually, a closed form >solution could probably do just as well for a reasonable estimate). Its a bitch to model Marc. Prop design equations have 8 major variables( dia, pitch, RPM, area, airfoil, helix, compressibility, etc, and another half dozen minor variables ( cowl wake, density/cooling heat, fuselage interference, etc) which all _interact_ such that it can't be solved, at least with conventional algebra. Thats why they are designed using multiple iterative solutions changing only 1 or 2 variables at a time and tracking the results in a convergent algorithm. Thats what the propopt application does with 200 to 300 individual runs typical being made to derive an optimum (best compromise) solution. The power of a PC really shows here. BTW just for info it takes several hours to run a solution on a 386 PC with no math co-processor as opposed to 10 to 15 seconds on a 486 PC, thats how math intensive it is. I think an FEA stress analysis for all conditions would present the same kind of challenge. But for a fixed condition, say 75% power cruise with a given design, it could provide valuable information leading to better structural design. Looking forward to your findings here. Hope this sheds some light on a complex concept which I don't totally understand either. Happy New Year to all, Nigel From: Lee Devlin Subject: PROP-FAB: Wood density variations Date: Mon, 5 Jan 98 10:15:09 MST I was going to just send this to Nigel but I thought the others may also want to know of a problem I found with the wood I've been using for prop making. In handling the pieces of select grade pine, I 'felt' what seemed like a large variation in density of the wood. Sure enough, when weighing individual laminates, I found as much as 30% difference in individual part weights. It was difficult enough to get enough pieces without warps, knots, or cracking without having to 'judge by feel' for density as well. Next time I may add that to my list of properties to look for. I was able to mix and match the pieces to achieve ~2-3% (4.7-4.9 lbs) weight match of the three blanks, but more than 1/2 of the wood will be removed while shaping so I don't know how this will affect the finish match. I'm sure not all laminates will have equal amounts removed. Since blade balance is perhaps the most critical factor in a prop, I'm wondering what options I'll have available if one of the blades comes up exceptionally heavy or light. I could drill holes and add lead weight near the hub, but I don't know how that would affect the dynamic balance of the blades. I believe that the weight distribution as a function of radius matters. It's also possible to add more glass/epoxy to a light blade but I don't know how far off each blade might be from the others. Maybe Nigel can shed some light on this. Thanks, Lee Devlin From: lschuler@cellular.uscc.com Date: Mon, 05 Jan 98 15:52:36 -0600 Subject: PROP-FAB: Wood density variations --simple boundary Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Lee Wrote: >snip >Since blade balance is perhaps the most critical factor in a prop, I'm >wondering what options I'll have available if one of the blades comes up >exceptionally heavy or light. >snip My thoughts FWW: You point out one of the most basic characteristics of ALL wood. The small percent diference may or may not change after shaping; depends on the exact density/mass distribution of the wood and whether you trim away a light spot or a heavy spot. How do the manufacturers handle the density diferences??? Maybe cutting each board to exactly same dimensions and balancing each board prior to laminating would help to insure even mass distribution along each blade. Just a thought. In original notes, Nigel described some 'finessing' of the wood during shaping to balance. Could even add a layer of UNI on all blades out to the same point (say 40 to 50% so as not to upset scimitar affect by adding too much stiffness at tips). Use this "extra" ply as a balancing ply only. Sand away as necessary; not needed for structure. Neither of these ideas will garantee a perfectly matched mass distribution along length of all the blades. Is that even possible in metal blades??? Core weight is one reason I'd like to consider Balsa for the core. Supposedly the core is non-structural in this application. The Balsa would be lighter than the glass and epoxy and much easier to shape and balance. Also provide a lighter, thus an allowably thinner blade. Scary though; have'nt figured out how to get Balsa to stand up to torquing the hub bolts yet......maybe some inserts??? Just a thought. Larry Schuler Think'in is cheap; "doing" stuff gets expensive; especially if one is wrong. :-) --simple boundary Content-Type: text/plain; charset=US-ASCII; name="RFC822.TXT" Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename="RFC822.TXT" Received: from gatekeep.uscc.com by cellular.uscc.com (ccMail Link to SMTP R8.00.01) ; Mon, 05 Jan 98 11:19:04 -0600 Return-Path: Received: from www.uscc.com (www.uscc.com [204.179.101.2]) by gatekeep.uscc.com with ESMTP id MAA29293 for ; Mon, 5 Jan 1998 12:12:27 -0500 (EST) Received: from palrel1.hp.com (palrel1.hp.com [156.153.255.242]) by www.uscc.com with ESMTP id LAA28212 for ; Mon, 5 Jan 1998 11:13:29 -0600 (CST) Received: from hpwarhw.an.hp.com (hpwarhw.an.hp.com [15.57.193.122]) by palrel1.hp.com (8.8.6/8.8.5tis) with SMTP id JAA23195 for ; Mon, 5 Jan 1998 09:15:35 -0800 (PST) Received: by hpwarhw.an.hp.com (1.37.109.8/15.5+IOS 3.22) id AA18913; Mon, 5 Jan 1998 12:16:05 -0500 Received: from hpgrla.gr.hp.com by hpwarhw.an.hp.com with SMTP (1.37.109.8/15.5+IOS 3.22) id AA18908; Mon, 5 Jan 1998 12:16:03 -0500 Received: (from ldevlin@localhost) by hpgrla.gr.hp.com (8.8.5/8.8.5) id KAA03270 for prop_fab@hpwarhw.an.hp.com; Mon, 5 Jan 1998 10:15:10 -0700 (MST) From: Lee Devlin Message-Id: <199801051715.KAA03270@hpgrla.gr.hp.com> Subject: PROP-FAB: Wood density variations To: prop_fab@hpwarhw.an.hp.com (Prop Fab group) Date: Mon, 5 Jan 98 10:15:09 MST Mailer: Elm [revision: 70.85] Sender: owner-prop_fab@hpwarhw.an.hp.com Precedence: bulk Reply-To: Lee Devlin --simple boundary-- From: lschuler@cellular.uscc.com Date: Mon, 05 Jan 98 15:52:36 -0600 Subject: PROP-FAB: Wood density variations --simple boundary Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Lee Wrote: >snip >Since blade balance is perhaps the most critical factor in a prop, I'm >wondering what options I'll have available if one of the blades comes up >exceptionally heavy or light. >snip My thoughts FWW: You point out one of the most basic characteristics of ALL wood. The small percent diference may or may not change after shaping; depends on the exact density/mass distribution of the wood and whether you trim away a light spot or a heavy spot. How do the manufacturers handle the density diferences??? Maybe cutting each board to exactly same dimensions and balancing each board prior to laminating would help to insure even mass distribution along each blade. Just a thought. In original notes, Nigel described some 'finessing' of the wood during shaping to balance. Could even add a layer of UNI on all blades out to the same point (say 40 to 50% so as not to upset scimitar affect by adding too much stiffness at tips). Use this "extra" ply as a balancing ply only. Sand away as necessary; not needed for structure. Neither of these ideas will garantee a perfectly matched mass distribution along length of all the blades. Is that even possible in metal blades??? Core weight is one reason I'd like to consider Balsa for the core. Supposedly the core is non-structural in this application. The Balsa would be lighter than the glass and epoxy and much easier to shape and balance. Also provide a lighter, thus an allowably thinner blade. Scary though; have'nt figured out how to get Balsa to stand up to torquing the hub bolts yet......maybe some inserts??? Just a thought. Larry Schuler Think'in is cheap; "doing" stuff gets expensive; especially if one is wrong. :-) Date: Mon, 05 Jan 1998 16:52:10 -0500 (EST) From: Nick Ugolini Subject: PROP-FAB: Cutting the Helix Hi Nick, I'm curious how you cut the top and bottom of the airfoil on your bandsaw. How did you do it? Did you make a lot of small cuts? One twisting long cut? ... Thanks, Lee -------------- for the Prop Group Tomorrow, I will start on my jigs and tools for the prop construction. I plan to use a sanding guide and a special (home made) drum sander to shape the bottom surfaces very quickly. That way I can make sure all three are the same. (Measure once, cut 3 times) The upper surface should not be much of a problem. ------ The Helix When you cut the blank in the bandsaw you can also cut the top surface. Draw a line on the LE side of the block (before assembly) for the bottom and top surfaces. Build a guide for the bandsaw to hold the TE in the correct orientation to the blade. Cut the bottom blade surface first using the bottom LE line. Remove the TE guide. Use a guide block to hold the bottom blade surface at right angles to the saw table (I used a small can) so the blade will cut parallel to the bottom surface. Holding the blade flat against your guide block, and follow the LE upper surface line rotating as you cut. You will end up with a upper and lower helix. --- My Plan I plan cut the bottom surface, then finish shape the bottom by sanding to shape (my drum sander and guide). I will make each blade about 3" longer then necessary, and cut the blades LEAVING a few inches at the end of the blade square (this will help with the final assembly). THEN I will cut the upper surface helix. Tape the upper block back on and cut the LE of the blade. Assemble the blades together, utilizing the square blade block ends to help keep the bottom of the blade at the correct angle and elevation. Finally, hand shape the upper surfaces. Then I will cut off the square ends of the blade. I hope this helps with your blades... Nick Ugolini unick@mail.charleston.net Varieze N89RS LongEZ N29TM Cozy Mark IV #0264 From: CCady Date: Mon, 5 Jan 1998 18:54:07 EST Subject: Re: PROP-FAB: Cutting the Helix I think a prop duplicator like the GemInI would do the trick. Anyone have any idea what the price is? I'm afraid to ask! There are some good photos on their web site. Their web site is : http://www.wood-carver.com/ >>I'm curious how you cut the top and bottom of the airfoil on your bandsaw. How did you do it? Did you make a lot of small cuts? One twisting long cut? ...<< Date: Mon, 5 Jan 1998 22:28:21 -0500 (EST) From: Nigel Field Subject: Re: PROP-FAB: Wood density variations At 10:15 AM 1/5/98 MST, Lee wrote: >In handling the pieces of select grade pine, I 'felt' what seemed like a >large variation in density of the wood. Sure enough, when weighing >individual laminates, I found as much as 30% difference in individual >part weights. ................ >Maybe Nigel can shed some light on this. > > Sounds like I got lucky and Lee didn't. There is a great lumber supplier only 2 miles from home where I bought 8 ft lengths of 5 inch select pine completely knot free, straight grained, beautifull wood. The density seemed prety uniform between boards but I never weighed them to confirm this. I cut each of the 3 blade laminate sets from one board then the next 3 from a new board annd so on, so I guess I achieved a good density match. My 3 blade wood core came out well balanced and only took a little sanding to get it right on once skinned. The 2 blade that I made later from the same batch of lumber did not fair as well. I had to add 1 ply of 1.45 oz bid glass to one blade to get it in ballance. Wicks sells this as part number 1080. The weave was oriented span/chord wise so as not to upset the blade torsional properties. I think Lee has the right approach by weighing the laminates and trying to achieve the best density match. So certainly wood selection becomes important if you can find a supplier with a good selection. There are other soft woods that could be used also such as virola pine, or fir, and I looked at some poplar boards the other day which seemed about the same density as pine. All these should work fine if you can't find good pine. Perhaps we are spoiled up here in timber country -:) Larry mentioned the use of foam a couple of times and that is starting to look like another alternative. Possibly 8 to 12 lb density divinycell or clark foam would work with some wood re-inforcement at the hub for crush protection, but I have not researched this at all. I admit to being a bit nervous about trying it though. Lee mentions importance of blade CG, >I believe that the weight distribution as a function of radius matters. It's >also possible to add more glass/epoxy to a light blade but I don't know how far >off each blade might be from the others.> The centrifugal loads are M*V^2/ Radius of blade CG, so it certainly matters. This effect can be seen on the load calc spread sheet by arbitrarily changing the CG to a differenet value, say 30 % radius, while leaving the blade weight and everything else the same. You can observe it makes a big difference in blade load and therefore balance. I made my 3 blade cores to final shape _before_ I joined them at the hub and measured each for weight and then CG by balancing them on a screwdriver shank. They were within .2 inch of each other so again perhaps I got lucky. But it raises a good point on the importance of matching the blades before joining since once together I can't think of any way to accurately determine individual blade CG locations. The use of small lead weights drilled into the core is probably a workable solution to get the core in balance and CG. I have heard of this being done on wood props to correct for this problem. The skins should come out the same if the layups are done accurately with good resin control, and a little final sanding will get it right on. Just be certain the centre insert is drilled dead on centre or you will have a tough time getting it balanced. Mark it accurately and clamp it down when drilling in the press so it cant move around on you. BTW if anyone needs the spread sheet, let me know I can forward it. It is the one that says (modified by Marc Z.). I think that is the only one released. I sent the first version to Marc for review where he found and corrected an incorrect cell address which performed an incorrect calculation even though the answer turned out surprisingly accurate for the example. Its in Lotus .wk4 but I have Excel now also so if anyone needs it converted I could provide it in either format. Good to get early construction inputs from Lee and Nick. Good tip by Clif on the carving machine site, if one wants to make several then it may be the way to go. I plan to try Nick's band saw idea if I can figure out his method, just need to read it a few more times and then go stare at my band saw and it should all come to focus. Just can't quite see how to keep the blade cutting on both LE and TE reference lines when cutting the helix since you can't see the line on the table side??? Nick could you run over that bit again. Later, Nigel From: Marc J. Zeitlin Subject: Re: PROP-FAB: Wood substitutes Date: Tue, 6 Jan 98 9:26:43 EST Nigel/Larry wrote: >Larry mentioned the use of foam a couple of times...... as well as balsa wood.... >........ and that is starting to >look like another alternative. Possibly 8 to 12 lb density divinycell or >clark foam would work with some wood re-inforcement at the hub for crush >protection, but I have not researched this at all. I admit to being a bit >nervous about trying it though. I am more than nervous. Given the construction methodology of pure UNI on the blades, it is only the core material that performs any torsional resistance - we've discussed this a bit before in talking about ACS props. If this is really the case, I don't think I'd want a core made from foam or balsa - my guess is that the strength in torsion of either of these material would not be anything close to what we would need for a real prop. Many props are made from wood (although not pine, it's true) but neither balsa nor foam have anywhere near the stiffness of pine, not to mention hardwoods. It might be useful (hint, hint) for someone building a prop to build one blade from foam or balsa and then measure the torsional properties vs. the pine core prop blades (after glass layup). Now, with some BID skin material (or UNI on the 45 degree bias [like the canard or wing skins]) the torsional properties could be tailored, but this is a different kettle of fish than Nigel has cooked up for us here. Not to say that it couldn't be done - I'm certain it can. We just don't have a design for it (yet), and I wouldn't be comfortable using the current design with a different (read much lighter/weaker) core material. -- Marc J. Zeitlin Email: marcz@an.hp.com From: Marc J. Zeitlin Subject: Re: PROP-FAB: Cutting the Helix (fwd) Date: Tue, 6 Jan 98 9:39:01 EST Cliff Cady writes: >I think a prop duplicator like the GemInI would do the trick. Anyone have any >idea what the price is? I'm afraid to ask! There are some good photos on >their web site. > >Their web site is : http://www.wood-carver.com/ This does look cool - too bad we're distributed in cyberspace, or we could go in on one :-). It's basically a pantograph with a router on one arm - not particularly sophisticated..... There is an advert. in the back of Sport Aviation and Kitplanes each month (don't remember the name, but it's in the back in the classifieds under propellers or somesuch) for plans for a prop carving machine that you can build for ~$50 (it says). I think the plans are $15 or so, and was going to send for them at some point (what the hell, eh?). I assume that this is some device like the GemInI, but with cheaper (read 2x4) components. -- Marc J. Zeitlin Email: marcz@an.hp.com From: Lee Devlin Subject: PROP-FAB: Prop Duplicator Date: Tue, 6 Jan 98 9:08:08 MST Marc wrote: > There is an advert. in the back of Sport Aviation and Kitplanes each > month (don't remember the name, but it's in the back in the classifieds > under propellers or somesuch) for plans for a prop carving machine that > you can build for ~$50 (it says). I think the plans are $15 or so, and > was going to send for them at some point (what the hell, eh?). I assume > that this is some device like the GemInI, but with cheaper (read 2x4) > components. I have the plans. I bought those and the other plans advertised in the back of Sport Aviation when I first started considering making a prop. Basically, I wanted to see what others were doing. The duplicator is identical in operation to the one advertised at the website mentioned in previous postings except that it's made of much simpler materials (wood, pulleys, etc.). I think it would do the job quite well. One problem is that they show two completely finished blades which gives you the impression that this duplicator does it all. This month's AOPA Pilot has a picture in the back from a Sensenich shop which shows how the blade really looks when it comes out of a duplicator. There are scallops left on the blade you are cutting since you use a ball-end cutter so there's still the final shaping you must still do by hand. I think it would also be helpful to remove the big chucks of wood with a chisel (or bandsaw) first lest you fill your work area with wood chips. The first blade must be made by hand using the techniques we have been discussing on this mailing list in order to create the pattern. If you're doing a lot of props which are identical, a duplicator might be a good investment. I think the plans for the duplicator are $15 (by Gary McGill) and the other plans for carving your own prop (by Hess) are $7. The 'carving your own prop' is fine if you want to build one for a VW-powered Sonerai or KR-2. It uses virtually the same method that Nigel has explained for shaping the blades. One shortcoming is that you're stuck with only one pitch and diameter unless you have something like the Propopt application to generate some new ones. Lee Devlin From: Lee Devlin Subject: PROP-FAB: Selecting wood density Date: Tue, 6 Jan 98 9:40:55 MST In reading through Garth Hess's ($7 from the back of Sport Aviation) instructions, I think I found the source of my error in choosing wood. I quote: 'Avoid boards with noticeable bands of color other than the grain since you may be mixing heartwood with outer wood having different strengths and densities.' The 'heavy' boards had a reddish tint whereas the 'light' boards were also much lighter in color. Look for consistent color and parallel grain and you should also avoid this problem. Lee Devlin (I'm much too far away from timber country ) From: lschuler@cellular.uscc.com Date: Tue, 06 Jan 98 11:03:40 -0600 Subject: Re: PROP-FAB: Wood substitutes --simple boundary Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Marc wrote: >snip >Now, with some BID skin material (or UNI on the 45 degree bias [like the >canard or wing skins]) the torsional properties could be tailored, but >this is a different kettle of fish than Nigel has cooked up for us here. >Not to say that it couldn't be done - I'm certain it can. We just don't >have a design for it (yet), and I wouldn't be comfortable using the >current design with a different (read much lighter/weaker) core >material. My thinking exactly on adding torsional stiffners (ie BID), although I didn't state this. Hope I didn't leave the impression that the current design is adequate if the core were differant. It's not. The old saying always holds true: "Changing one thing changes everything". I'm not suggesting I'd glass up some foam or Balsa and go fly. At least not without wearing a diaper and a parachute. :-) Just mentally exploring the possibility of retaining the scimitar effect and relative cost while reducing mass and maybe thickness. Perhaps the results of Marc's number crunching can provide some insight as to the load distributions and such on the current design; which, in turn, may help determine a 'place to start' adjusting torsional stiffness "if" the core were changed. I'd certaily want to make some destructive test comparisons before jumping into the deep end of that pool. The impulse torsional loading from a reciprocating engine (more so with Lycosaureus engines than Subarus) and gyroscopic loads would be the most difficult to maintain or simulate over a long period of time. Lots of variables. Maybe I'm just getting ahead of the current design discussions... Larry Schuler From: lschuler@cellular.uscc.com Date: Tue, 06 Jan 98 12:20:42 -0600 Subject: Re[2]: PROP-FAB: Wood density variations Nigel wrote: >snip >Larry mentioned the use of foam a couple of times and that is starting to >look like another alternative. Possibly 8 to 12 lb density divinycell or >clark foam would work with some wood re-inforcement at the hub for crush >protection, but I have not researched this at all. I admit to being a bit >nervous about trying it though. I'd stear clear of the brittle foams such as the Urethanes. They'd probably turn to powder in short order. The PVC foams are more appealing due to relative toughness; may not be available in thickness/density needed though. I'd look for an 18 Lb PVC. May not be wise to try to laminate two or more sheets together in this application due to flexing. The change in stiffness between sheets (epoxy) would cause the joint to tear apart in time. One real nice feature of most foams is that they are manufactured and therefore are (at least in general) more tightly controlled than the stuff made in nature. The mass distribution (thus blade CG) can be more uniform than wood; similar in uniformity to metal. Balsa or BassWood might be very light alternatives in the wood family. Aspen may be another alternative. I wonder if there are more significant variations in the density and strength of these light woods than in the harder woods? Larry From: "norm & monda" Subject: Re: PROP-FAB: Wood substitutes Date: Tue, 6 Jan 1998 14:29:52 -0500 well foam must be good for a prop core material (yeah right) after all ivo prop uses it. and we all know how great these props are. From: Lee Devlin Subject: Re: PROP-FAB: Wood substitutes Date: Tue, 6 Jan 98 15:15:28 MST Norm wrote: > well foam must be good for a prop core material (yeah right) after all ivo > prop uses it. and we all know how great these props are. ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ (I am aware that you are being facetious.) Ivo has to have a very flexible prop in order to adjust the pitch using their unusual technique. Instead of rotating the blades at the hub, they have steel torque rods that run up through the center of each blade which applies a twisting force out near the center of the blade. This allows for very simple blade twisting mechanics. The downside is that the blades need to have very little torsional resistance which also means that they are quite flexible. The part of the IVO blade that mounts to the hub is made primarily of carbon to provide crush resistance. The hub portion of the blade has to be made of something quite substantial to provide very high compression strength. Most props are held on with friction between the crush plate and hub (or hub extension). The IVO has 3 independent blades which need to be torqued properly to prevent flailing of individual blades. They use some sort of metal tape as and indicator of this condition. My opinion is that if you have blade flailing, it will begin in the air. You can only check these tapes when you're on the ground. So it makes me a little uncomfortable. I have a LongEZ friend in Longmont, CO who put an Ivo on his plane about a year ago and he loves it. It gave him about 20 mph increase in cruise with no takeoff penalty. I am also aware of a number incidents with the Ivo so I'm still not convinced that it is a good prop for my plane. The only reasons to use foam is as a core material is 1:) to save weight, or 2.) to make the shaping of the core easier. If my wood core prop comes in at 9 lbs. like Nigel's, I'll be very happy. The IVO ground adjustable weighs 12 or 15 lbs even though it has a foam (micro, actually) core. The reason for this is that the hub portions of the blades are mostly pure carbon to provide crush strength and there is an elaborate aluminum hub section to hold it all together. I know that foam is easier to shape, but doing intricate sculpting like that needed for a prop core is likely to be very difficult with a fragile material like foam. Lee Devlin From: CCady Date: Tue, 6 Jan 1998 17:29:49 EST Subject: Re: PROP-FAB: Prop Duplicator In a message dated 98-01-06 11:09:52 EST, Lee wrote: << I think it would also be helpful to remove the big chucks of wood with a chisel (or bandsaw) first lest you fill your work area with wood chips. The first blade must be made by hand using the techniques we have been discussing on this mailing list in order to create the pattern. If you're doing a lot of props which are identical, a duplicator might be a good investment. >> Funny you should mention this, one of the pictures that they sent me by snail mail shows that they did make some cuts with a bandsaw first and chiseled off the excess material to cut down on the routing. The final product in the photos looked pretty smooth. I think something like this would be very helpful in making the blades more the same shape. Also I'll bet that one would want to make more than one prop till you got the one that worked the best. At least with the carver you could contemplate making more than one in a reasonable span of time. Also could you mounting pitch angle of the blank master blade and adjust the final pitch of the final prop? As far as the price for the carver whatever it is, it might save one from buying several expensive props especially if you like the 3 blades. I was wondering, do the professional prop carvers make their own wood blanks. I seem to remember a comment that they purchase their wood blanks from some source. If that is so and it could be located perhaps that would be easier than laminating your own. Cliff From: Marc J. Zeitlin Subject: Re: PROP-FAB: Prop Duplicator (fwd) Date: Tue, 6 Jan 98 17:45:01 EST Cliff Cady writes: >I think something like this would be very helpful in making the blades more >the same shape. Also I'll bet that one would want to make more than one prop >till you got the one that worked the best. At least with the carver you could >contemplate making more than one in a reasonable span of time. Very good points. >Also could you mounting pitch angle of the blank master blade and adjust the >final pitch of the final prop? If the "prop-opt" program told you that the pitch angle changed equally along the blade length (or at least equally out past the 30% (?) point, where it starts to matter) then you could do this. If however (as I suspect) the pitch changes for different propeller design points is NOT equal along the length of the blade, then you'll have a non-optimum blade at any rotated pitch angle other than the design point. It would certainly be an easy way to change the pitch, though, if it differences weren't too high ....... >As far as the price for the carver whatever it is, it might save one from >buying several expensive props especially if you like the 3 blades. I sent "Allred" some email asking for pricing info - maybe in a couple of days we'll find out just how shocked we should be. Also, Lee Devlin faxed me the 12 page instructions for building your own carving device, which (if you own a router) looks like it could be built in the $50 - $100 range, and be pretty decent, quality wise. I'm not absolutely sure that this article isn't copyrighted, however, so I'm leery of making it public until I find out. It's a reprint from a magazine, and although it doesn't have a (c) on it, the magazine may have an implied one. >I was wondering, do the professional prop carvers make their own wood blanks. >I seem to remember a comment that they purchase their wood blanks from some >source. If that is so and it could be located perhaps that would be easier >than laminating your own. Hmmm. This would be an interesting tradeoff of time vs. money. -- Marc J. Zeitlin Email: marcz@an.hp.com From: Lee Devlin Subject: PROP-FAB: Re: Simple prop question (fwd) Date: Tue, 6 Jan 98 16:29:57 MST I didn't know if this would be of interest to the group so I asked Nigel privately. He feels it's worth sharing with the group and so I'll forward it along. Lee Devlin > > At 09:13 AM 1/6/98 MST, you wrote: > >Hi Nigel, > > > >Pardon me for not posting this to the group. I am in the middle > >of chiseling out the bottom of my first blade. My recollection > >is that you didn't shape station 2 but rather blended everything > >from station 3 toward the hub. > > > >I'm wondering if I should make the flat saw cut on the bottom of > >the airfoil at station 2 or should I just stop at station 3 and > >shape by eye from there. > > > >The reason I'm asking is that it looking a little radical so close > >to the hub to have such a high angle of attack and I don't know if > >I'll have the room to blend it smoothly if I shape all the way > >to station 2. > > > >Thanks, > > > >Lee > > > > Hi Lee, > > Actually its a good question for the group as I probably did not explain it > fully initially. > > I had the same concern when I made my first one. I stopped chiseling out > wood at station 3 then switched to a belt sander using the nose of it to > form a natural curve into what later becomes the hub area. I marked the hub > circumference at the root in pencil so I would not go past that circle > (actually 1/3 circle). I did the first blade by eyeball in this area then > made the other 2 the same. Once the 3 blades were done and joined, I finish > blended the curves to the hub with the belt sander but it did not need too > much. I also had 3 small notches in the hub circumference from using 5 inch > boards that I filled in with flox just before skinning it. > > I carried the helix to as close as I could to the hub so it has about 70 > degrees of pitch at this point but you don't have to carry it that far as > the inner part contributes little in performance. Just blend it till it > looks natural with no abrupt curves then make the others the same. > > Glad you are making progress. The first one is the hardest, trying to > conceptualize just what it should look like, then it gets easy. > > Nigel > > Date: Tue, 13 Jan 1998 13:34:50 -0500 (EST) From: Nigel Field Subject: PROP-FAB: Prop Folks, FW as requested by Nick but without .dwg attachment. The autocad file is a combined dwg of Nick's prop design and his sanding machine. Apears that Nick plans to make a few to support his Ez stable. Nice work Nick on the design and dwgs. Now I really need to tackle that ever steepening autocad learning curve so I can make nice dwgs instead of just reading other's stuff. I think I better understand your blade cutting techniques as described below, thanks. >Nigel > >These are some email Lee and I have been have to help explain the helix.. >Attached is the prop dwg file. > >If you wouldn't mind, would you send this email to the rest of the prop >group.. I dont have the address at work. > >-- To Lee --------------- > >Tomorrow, I will start on my jigs and tools for the prop construction. I >have designed a built in self balancer for the center spindle (fig 4). I >plan to use a sanding guide and a special (home made, fig 3) drum sander to >shape the bottom surfaces very quickly. That way I can make sure all three >are the same. (Measure once, cut 3 times) The upper surface should not be >much of a problem. > >Since we have the same engine and design the Airfoil templates (fig 1) will >work for you too. Print out the airfoils in a 1 to 1 scale and you will >have full sized templates. I plan to glue the templates to Formica with >water based polyurethane, and cut out. The profiles and angle blocks are >exact sizes so you can use them for references (in addition to actual >measurements). The offset line is the undersized template for the core. >The outer line is the after glassing size. > > >Helix cutting > >When you cut the blank in the bandsaw you can also cut the top surface. >Draw a line on the LE side of the block (before assembly) for the bottom >and top surfaces (Fig 2 on the Acad dwg). Build a guide for the bandsaw to >hold the TE in the correct orientation to the blade. Cut the bottom blade >surface first using the bottom LE line. Remove the TE guide. > >Use a guide block to hold the bottom blade surface at right angles to the >saw table (I used a small can) so the blade will cut parallel to the bottom >surface. Holding the blade flat against your guide block, and follow the >LE upper surface line rotating as you cut. You will end up with a upper >and lower helix. > >This is my personal plan--- > >I plan cut the bottom surface, then finish shape the bottom by sanding to >shape (my drum sander and guide). I will make each blade about 3" longer >then necessary, and cut the blades LEAVING a few inches at the end of the >blade square (this will help with the final assembly). > >THEN I will cut the upper surface helix. Tape the upper block back on and >cut the LE of the blade. Assemble the blades together, utilizing the >square blade block ends to help keep the bottom of the blade at the correct >angle and elevation. Finally, hand shape the upper surfaces. Then I will >cut off the square ends of the blade. > >I hope this helps with your blades... > > >> Lee: I am having trouble visulizing the helix... > > >Hopefully the drawing will help explain the helix. > >Look at the end of the blade block. From the trailing corner (left bottom) >project a line to the right side (LE) for each blade angle.... or take: > >Tan(blade angle)*bottom block distance = LE height for the LE side of the >block. > >Mark each station. Draw a line (fig 2.. already done for you... :-) ) >connecting each point in a smooth curve. > >You now have a line to cut extended from the vertex (TE) to the LE side of >the block along the bottom of the blade. You have to make a small guide >for the band saw TE to keep it from moving when you cut along the LE line. > That way you only have one line to try and use for a guide, the other side >of the block is tracked by your gig. > >Then you cut the upper part of the helix which is a parallel cut to the >bottom part of the blade. (hence the can trick explained in the last >email) > >When you cut the helix the block will not be square anymore.. You have to >tape the resulting scrap back on the helix to mark the upper surface of the >block for the LE, and cut the LE curve. (you can use the .dfx file again >for a template. > >I took some foam scraps, glued them together and tested the helix cut, then >I did the same test on a wood blank. I found the 1/2" blade to be a little >tough to work with. I will probably use a 3/8" blade. > >>Size of saw? > >It depends on the size of your block. What is the diagonal of 3.5x3.5" >block? No more than 5? inches. I have a 12" craftsman. Works fine. > >>It looks like your blade block is differnt from mine.... > >The end view of the blade is just a representation of the stacked blade. I >am using 3/4" x3.5" boards also. > >The sanding drum (to shape the bottom blade) is above the side view of the >sanding guide. (3/8" rod with bearings and drum and handle at the end). > >The cradle (upper left) is the sanding guide. In this view you are looking >from the hub out to the blade tip. In this view notice the helix track on >the right side through the full rotation of the helix. The three blocks >are part of the helix track (for the necessary width) to allow for the >rotation (helix) the sanding drum has to make to sand/shape the bottom. If >you look directly below it you will see the plan and side views of the >guide and the helix track. > >The idea here is to first build the sanding guide. Much easier to shape >the helix on the guide than the bottom of the blade. Screw the band saw >cut blade into the guide. Hook the die grinder up to the sanding drum and >final sand the bottom to shape by moving the drum along the guide. This >will ensure all three blades have the same bottom profile. > >Neat eh? I wanted to ensure I had exactly the same angles on all the blades >(critical part). Once I build the sanding drum and the drill templates, I >will be set. If I build a different pitch blade, the only change will be >to build a new sanding guide helix. > >>Lee: You appear to be cutting the blades from rectangular > blocks whereas I'm cutting the laminates into planform shape and then > gluing them together. I would not have the long straight reference > surfaces on the outside of the prop to make accurate helix cuts. > >I thought about doing that also, but it make cutting the helix difficult. >You could still mark the leading edge and make the cut but I dont think it >would be as accurate. There is more waste using my method but the time >saving is worth it for me. > > > > >Attachment Converted: D:\MAIL\leprop1.dwg > From: Lee Devlin Subject: PROP-FAB: Re: COZY: Nigelprops (making your own) Date: Wed, 21 Jan 98 17:26:05 MST Hi Steve, > To fully understand how this works I really need the sketch. My fax is down so > would you > be able to mail me a copy. 1400 Robert E Lee Ln Brentwood, TN 37027 I'll bring in a copy of Nigel's sketch tomorrow and make a copy of it and send it to you. > If soft wood is used for the prop construction the torque required to keep the > prop > on is a real concern. I'm sure you know that the crush plates hold the prop > on.....not > the bolts. I will check into this with a local prop maker. Yes, I'm aware that the crush plate friction is what transmits the torque from the hub to the prop. There was a lot of discussion about this in the CP's and Central States. I feel that the encapsulation of the wood by the epoxy/fiberglass provides a constraint that compensates somewhat for the fact that the pine is softer than most traditional prop woods. If Nigel can speak to this, maybe we can better understand how 'crushable' the prop feels compared with the many other types of props he has tried. The Long EZ plans call for 180 in-lb (15 ft-lb) of torque. I'm sure you are aware that 15 ft-lb does not feel like much on 3/8" bolts. This torque is specifically limited to avoid crushing the wood. I've heard of people ruining props by mixing up in-lb with ft-lbs and trying to apply 180 ft-lb to wooden props! I think that this discussion is relevant to everyone on the list so I am going to CC: the PROP-FAB group. > I'll keep you updated on my progress. Are you a member of the prop-fab > group? >> No I am not. How do I join? Send email to marcz@an.hp.com and ask to be added to the PROP-FAB list. Marc, since I'm going to forward this to the list, maybe you can add Steve Wright to it. Lee From: Marc J. Zeitlin Subject: PROP-FAB: Carving machine info. Date: Fri, 23 Jan 98 23:24:04 EST People; A week or so ago I sent away to "Allred and Associates" asking about their propeller carving machine. J.B. Allred called me and asked if I wanted them to send an info package, and they did so. I got it today with a bunch of pictures and a price, so I figured I'd report back here. The pictures are not substantially different than the ones on their web page (at http://www.wood-carver.com), but they do show what looks like a well made, sturdy device. It's not very different from the homemade wooden job that Lee Devlin faxed me the plans for in theory, but I imagine that this one (being made of steel with linear roller bearings) is much stiffer (whether that makes a difference is unknown - the wooden one might be more than stiff enough). Anyway, to get to the point, this baby goes for $1750 + ~$250 shipping and handling. It weighs in at 150 lbs. It can carve a 84" diameter prop (42" blade) with a 8.5" chord and 6" of thickness. So, given that a single 3-blade wooden prop goes for $1500 - $1800, it would seem that this thing would pay for itself on the second prop (which seems almost a given). If a couple of people close to each other bought it together, you'd get a real nice machine for a lot less than the cost of the props you'd buy; might even be worth it for an individual. On the other hand, if the wooden carving machine works, and you've already got a router, you can save yourself $1800 at least and get the same props...... -- Marc J. Zeitlin Email: marcz@an.hp.com Date: Sat, 24 Jan 1998 09:09:15 -0500 (EST) From: "George A. Graham" Subject: Re: PROP-FAB: Carving machine info. On Fri, 23 Jan 1998, Marc J. Zeitlin wrote: > > On the other hand, if the wooden carving machine works, and you've > already got a router, you can save yourself $1800 at least and get > the same props...... Hold your horses ! A rough carved blank is a long way from a finished propellor ! I'm using the wooden carver machine on it's second prop. First off, the plans built carver is sized for three 3/4" boards prop thickness for a VW engine size prop. It is really flimsy, meaning that you have work real slow and leave plenty of extra wood for sanding smooth. That is a tremendous amount of wood to make into sawdust with a router ! It feels like trying to cut logs with a hacksaw might feel. The carving methods described in Clutton's book appear to me to be the best idea eg, sawing slots, then chiseling rough, spokeshave & sand. Also, the shock vibration of the router cutter tends to break the glue joints (and grain) which appears to me to be the killer problem. I'm still looking for anyone who is flying a prop they carved with a router. Professional carving machines use a hog like dado head to remove the excess wood, as the prop spins horizontally. Given all that, you still have pretty rough piece of scrap when you are finished carving, the burning question remains whether it can be transformed into an airplane propellor. George Graham ca266@freenet.buffalo.edu (716) 874-3277 Modified Eracer - Mazda Powered Date: Sat, 24 Jan 1998 09:49:18 -0500 (EST) From: Nigel Field Subject: Re: PROP-FAB: Carving machine info. At 09:09 AM 1/24/98 -0500, George wrote: >On Fri, 23 Jan 1998, Marc J. Zeitlin wrote: > > >> >> On the other hand, if the wooden carving machine works, and you've >> already got a router, you can save yourself $1800 at least and get >> the same props...... > >Hold your horses ! A rough carved blank is a long way from a finished >propellor ! > >I'm using the wooden carver machine on it's second prop. First off, >the plans built carver is sized for three 3/4" boards prop thickness >for a VW engine size prop. It is really flimsy, meaning that you have >work real slow and leave plenty of extra wood for sanding smooth. > >That is a tremendous amount of wood to make into sawdust with a router ! >It feels like trying to cut logs with a hacksaw might feel. > >The carving methods described in Clutton's book appear to me to be the >best idea eg, sawing slots, then chiseling rough, spokeshave & sand. > >Also, the shock vibration of the router cutter tends to break the >glue joints (and grain) which appears to me to be the killer problem. >I'm still looking for anyone who is flying a prop they carved with a >router. > >Professional carving machines use a hog like dado head to remove the >excess wood, as the prop spins horizontally. > >Given all that, you still have pretty rough piece of scrap when you >are finished carving, the burning question remains whether it can be >transformed into an airplane propellor. Thanks to Marc for the info on the sturdy model. Good report George, thanks for the first hand experience. I had pretty much come to the same conclusion by experimenting with my router by hand on some scrap lumber. I tried a variety of cutters and found the same thing, takes a lot of cutting, it burns the wood and it vibrates. On a thin blade profile out near the tip it would take many very fine cuts to get any kind of accuracy. I concluded that there was no time to be saved from the saw, chisel and mallet method. Its not as if we are mass producing these, then a prop lathe might be the way to go. I use the nose of my belt sander with a 40 grit belt which rips it down pretty quick up near the hub area where it blends to the hub diameter. A disk sander in my drill is also handy for quick shaping of the blades after the spoke shave, but the final work is best done by hand with coarse grit (I use cut up sanding belts) and a hard block. Just leave it rough as it gets skinned with glass anyway so there is no reason to sand it nice and smooth like a pure wood prop. The router would be good for making the spar grooves if someone can figure out how to make a guide that follows the helix and tapers the cut depth. The .25 inch wide chisel is time consuming and one must be especially carefull not to slip and drive it into body parts. I have a distinct memory from early boyhood when my dad stuck a chisel into his wrist and bled all over the place, he still has the scar. So be carefull in this step. Nigel From: CCady Date: Sat, 24 Jan 1998 10:38:40 EST Subject: Re: PROP-FAB: Carving machine info. In a message dated 98-01-24 09:12:33 EST, you write: << prop_fab@hpwarhw.an.hp.com (Propeller Fabrication) >> The pictures I got in the mail from Allred and Associates showed a technique where they apparently route out grooves in the prop blank. Then it shows them taking out some of the excess material between preliminary cuts with a chisel. Then they cut down to shape when the excess is removed. They still say it will take half a day to cut one which is quite a bit of time at the machine. Their machine is made from steel which I would think would help prevent excess vibration or movement of the cutter from a accurate profile? Cliff Date: Sat, 24 Jan 1998 13:07:27 -0500 (EST) From: "George A. Graham" Subject: Re: PROP-FAB: More Carving machine info. On Sat, 24 Jan 1998, CCady wrote: > The pictures I got in the mail from Allred and Associates showed a technique > where they apparently route out grooves in the prop blank. Then it shows them > taking out some of the excess material between preliminary cuts with a chisel. > Then they cut down to shape when the excess is removed. They still say it > will take half a day to cut one which is quite a bit of time at the machine. That is also the method that I used. A crosscut saw will cut groves much better than a router. The problem lies in being accurate at making the saw cuts. > > Their machine is made from steel which I would think would help prevent excess > vibration or movement of the cutter from a accurate profile? > > Cliff > Perhaps, although I should have called it chatter rather than vibration, so it is cutter dependant more than frame rigidity. That said, the people who make props for a living must know how ! But I would bet money that it ain't with a router. I didn't mention how much trouble I had getting the right boards - $ 120 worth of hard maple - plus $ 25 for one pint of Resourcenol. I didn't use epoxy because the first prop spilt at the glue lines. Now you need to warm the wood to get the glue to adhere, then you have about 10 min to get the many clamps together, only enough time for one board at a time. Starting in the middle and clamping toward the ends left the blank thicker at the ends. The right type of glue clamp is a heated press. Follow Nigels advice, it is well thought out. George Graham ca266@freenet.buffalo.edu (716) 874-3277 Modified Eracer - Mazda Powered From: CCady Date: Sat, 24 Jan 1998 14:08:35 EST Subject: Re: PROP-FAB: More Carving info. In a message dated 98-01-24 13:10:17 EST, you write: << Now you need to warm the wood to get the glue to adhere, then you have about 10 min to get the many clamps together, only enough time for one board at a time. Starting in the middle and clamping toward the ends left the blank thicker at the ends. The right type of glue clamp is a heated press. >> When I was a kid my dad built a 28' wood sailboat and he had many clamps for his many glueing operations. We used Resourcenol glue alot. For gluing prop blanks you could set up a table and use many clamps of wood and 1/4" threaded rod. Thats what we used to glue up the mast in our yard once. I heard a comment that the prop. makers get their wood blanks pre-made from some source. I don't know if that is true, but if so and that source could be located perhaps they would sell to the little guy? Cliff Date: Sun, 25 Jan 1998 08:07:03 -0500 (EST) From: "George A. Graham" Subject: Re: PROP-FAB: More Carving info. On Sat, 24 Jan 1998, CCady wrote: For gluing prop > blanks you could set up a table and use many clamps of wood and 1/4" threaded > rod. Thats what we used to glue up the mast in our yard once. > That is the type of clamp I used, and it still takes time to put together. > I heard a comment that the prop. makers get their wood blanks pre-made from > some source. I don't know if that is true, but if so and that source could be > located perhaps they would sell to the little guy? > > Cliff > Good idea Cliff ! George Graham ca266@freenet.buffalo.edu (716) 874-3277 Modified Eracer - Mazda Powered Date: Wed, 28 Jan 1998 05:36:15 -0500 (EST) From: "George A. Graham" Subject: PROP-FAB: prop Thank you Lee for the sketch of Nigels prop. Radical eh ? You included a planform cross section plot which I found interesting. The trailing edges are inline, as on my first pattern. The idea is to move the blades aft for better performance. After I fabricated that pattern, I noticed that the wood boards which carry the thrust load - which is the outer tips - were very thin and weak near the hub. For that reason, I rejected that pattern and instead, aligned the center of lift with the prop centerline. It looks much better, aligning the leading edge might also work, but that moves the prop forward. Thank you again. Still sanding, that's why they call it Hard maple ! George Graham ca266@freenet.buffalo.edu (716) 874-3277 Modified Eracer - Mazda Powered From: Lee Devlin Subject: PROP-FAB: Re:Composit prop Date: Wed, 28 Jan 98 14:43:11 MST Hi Steve, You make a good point in your message regarding the potential for softening of the epoxy/fiberlass due to elevated hub temperatures. In Nigel's installation, there is a rather long distance between the prop and the engine since he's running a speed conversion unit. I'm going to be using a regular O-235 which currently has a 3" extension. I know that there was a lot of discussion about overheating props and destroying the resoursinol glue in Central States about 1 year ago. There was speculation about the source of the heat, and whether it was the exhaust or the conduction of heat from the crankshaft to the flange/prop extension. A composite prop is a good candidate for post curing so that the Tg can be elevated to as high as practical before flying it. It would also make sense to use the temperature measuring waxes during a static test to see what kind of temperature rises one should expect prior to flight testing. Lee > Hi Lee > Thanks for the drawings. The design is similar to a prop that was developed by > an old friend of mind in Houston many years ago. I feel it has lots of > potiential. The only concern I have at this point is the crush plate effect on > the hub at the elevated temps which occur after shut down. In the summer, on a > hot ramp, after shut down, the hub can reach temps that will soften epoxy. > Has this issue been discussed? I live in "Aviation Valley" Tennessee where we > have 3 different propeller manufacturers, and 3 kit manufacturers. Eric > Clutton is an ol friend. If enough of us wanted a 3 blade prop carved out of > pine we may be able to get them quite cheap. One of the prop makers has a C&C > machine. > Steve From: SWrightFLY Date: Thu, 29 Jan 1998 10:57:18 EST Subject: Re: PROP-FAB: Re:Composit prop In a message dated 98-01-28 16:43:37 EST, ldevlin@hpgrla.gr.hp.com writes: << softening of the epoxy/fiberlass due to elevated hub temperatures. In Nigel's installation, there is a rather long distance between the prop and the engine since he's running a speed conversion unit. I'm going to be using a regular O-235 which currently has a 3" extension.>> I agree that this is not a problem with Nigel but will be for everyone else. <> Everyones best guess (as I remember) is that the massive extension (hub) was the heat transmitter. A composite prop is a good candidate for post curing so that the Tg can be elevated to as high as practical before flying it. It would also make sense to use the temperature measuring waxes during a static test to see what kind of temperature rises one should expect prior to flight testing. >> Good point......... The safest way to avoid the problem might be to use high temp prepreg glass. I attended a composit expo last week in Nashville and got some prepreg carbon samples from Thiokol TCR Composits Division that may work very well. It is room temp. storage material and will cure at 350 degrees F in 3 hours. The only downside is cost and it must be bagged. Date: Thu, 12 Feb 1998 06:27:57 -0500 (EST) From: "George A. Graham" Subject: PROP-FAB: Spinning ! While my attempt at prop making is not very high tech, the thing seems to work perfectly on the ground ! My two blade 66" dia X 80" pitch maple fan spins at 5200 rpm engine speed, through a 2.21 to 1 psru, for 2350 static prop rpm. Smooth as silk, I should add. I really love that auto engine ! George Graham ca266@freenet.buffalo.edu (716) 874-3277 Modified Eracer - Mazda Powered Date: Thu, 19 Feb 1998 16:33:42 -0500 (EST) From: "George A. Graham" Subject: PROP-FAB: Re: Urethane for leading edge I have some of this, will use it and report soon. George Graham ca266@freenet.buffalo.edu (716) 874-3277 Modified Eracer - Mazda Powered ---------- Forwarded message ---------- Date: Sun, 15 Feb 1998 11:09:07 -0500 From: Janet L Schubert To: ca266@Freenet.Buffalo.EDU Subject: Re: Making wood propellers > >OK ! Now I am getting somewhere ! My prop LE is rather curved, so I >was worried about getting the tape on. How do you apply the urethane >? >Where did you get it? How much is it ? Etc. If you are just dying to get rid of your money you can order it (Hexcel Uralite #3148 part A & part B) from Kindt-Collins Co. in Cleveland, Oh 216-252-4122. It cost me about $32+ to get a small kit a couple years ago. (1 qt resin 1 pt hardner) Date: Mon, 23 Feb 1998 07:50:38 -0500 (EST) From: Nick J Ugolini Subject: PROP-FAB: PROP I wanted to publicly say, THANK YOU to Nigel Fields. Thanks for the ideas, email, calls and support. Nigel, you were right. Once you fly a 3 bladed prop, you never go back to a two. I am spoiled already. I started my prop construction on 1/22/98. So far I have 85 hours into construction. (although the next one I build, I could do it in considerably less time. I test flew the prop this weekend 2/21/98. I went through the same apprehension test flying this prop as I did when I flew my plane the first time. Very nervous. After having a wood prop self destruct and landing on a road (I only lost the right rudder and the wheel pants), you get the idea. Runups, Closed pattern flying, ....expanding the flight envelope. And.....I LOVE IT! My initial impression is... It is MUCH quieter than the 2 blade. MUCH, MUCH smoother, take off roll is better (I have to REALLY press on the brakes to hold it back during static runup), top speed it a bit higher. These are rough numbers. I plan to do a thorough test once I have it 100% complete (I have to fill and paint). I only have 2.7 hours on it but so far. I have also built into the prop the ability to dimple it without affecting the strength of the blade (I made a recess along the top of the blade and filled the recess with micro). I can then dimple the prop without digging into the glass. If it doesn't work I will refill the holes. 2 blade 3 blade Static RPM 2330 2270 Climb 950 900 (I was about 150 lbs heavier) Take off roll Much shorter ?? maybe 500 ft (I can feel a noticable acceleration now) Top speed 156 158 RPM 2620 2850 Sound Whoop Whoop Buzz (I can now hear the engine) If you have hear a ultraLight with a rotax engine and a 3 bladed warp drive, you will know the sound. When I cut the throttle, I have a definite braking action from the 3 blade I did not have the 2 blade. I would highly recommend building your own prop. If I could do it anyone could. It is just attention to dimensions and measure, measure, measure. I am putting my thoughts into an email I plan to send out sometime. I have taken bunches of pictures I eventually will build into a web page. Ah, so much to do and so little time... From: cdenk@ix.netcom.com Date: Mon, 23 Feb 1998 20:38:16 -0600 (CST) Subject: Re: COZY: Oil on Fiberglass I don't know about the oil, but the rough surface of the glass may be giving you performance problems. Recently tested a prop where the urethane leading edge was not coated, but masked when the wood was painted. A light sanding to knock off the masking ridge resulted in 5 Knots faster at all altitudes, and 30 second less climb to 8000. Roughening the prop with 600 paper, lost maybe 1 or 2 knots, refinshed prop, improving flatness of curved side of airflow increased performance slightly. I remember the 5 knot numbers, while online now, I can't get at the actual numbers, but there is hard data - digital engine gages and clock. Climb: every 1000' - constant 100k airspeed - record time, temperature, manifold pressure, RPM Level flight - 2000RPM - 2700RPM or full trottle, 200 RPM increments, airspeed, temperature, manifold pressure, RPM, 2000' - 8000' or 10000', 2000' increments. All altitudes with Altimeter set to 29.92" Date: Tue, 24 Feb 1998 19:52:14 -0500 (EST) From: Nigel Field Subject: Re: PROP-FAB: PROP At 07:50 AM 2/23/98 -0500, Nick wrote: > >I test flew the prop this weekend 2/21/98. I went through the same >apprehension test flying this prop as I did when I flew my plane the first >time. Very nervous. After having a wood prop self destruct and landing on >a road (I only lost the right rudder and the wheel pants), you get the >idea. Runups, Closed pattern flying, ....expanding the flight envelope. >And.....I LOVE IT! Way to go Nick. Really nice to hear you got it up, your prop that is, and you like it. You are the first one to fly so we will look forward to your follow on reports and data. >My initial impression is... It is MUCH quieter than the 2 blade. MUCH, >MUCH smoother, take off roll is better (I have to REALLY press on the >brakes to hold it back during static runup), top speed it a bit higher. Yes the 3 blades are much queiter and way smoother as you have confirmed. > >These are rough numbers. I plan to do a thorough test once I have it 100% >complete (I have to fill and paint). I only have 2.7 hours on it but so >far. > >I have also built into the prop the ability to dimple it without affecting >the strength of the blade (I made a recess along the top of the blade and >filled the recess with micro). I can then dimple the prop without digging >into the glass. If it doesn't work I will refill the holes. I like that idea of making the dimple provision, very clever. I guess I am still a bit sceptical about that process actually improving performance so again await your results. I plan a similar test this spring to see if I can duplicate some of the reports I've heard. Your early data looks good, but you can expect a noticeable improvement when you get it filled and painted. Props are quite sensitive to roughness on the leading edge so a nice smooth coat of paint will help. I use hardware store spray can grey with silver fleck and rub it out with 600 then 1200 and polish it with brasso metal polish then wax it. It comes up to a beautiful smooth finish which lasts the season easily. I always re-paint mine every year and fill up any small nicks that are hard to prevent on a pusher so no point in using expensive paint. > >When I cut the throttle, I have a definite braking action from the 3 blade >I did not have the 2 blade. Yes I found that also and now can do a steeper approach. The first time I landed it with the 3 blade I pulled off power as I flaired and it dropped much quicker than I expected, almost bounced it. > >I would highly recommend building your own prop. If I could do it anyone >could. It is just attention to dimensions and measure, measure, measure. >I am putting my thoughts into an email I plan to send out sometime. I have >taken bunches of pictures I eventually will build into a web page. Now you have done your first one you will want a different one with a little more pitch or more sweep back or whatever. Told ya it wasn't that hard. Thanks for the report, Nigel Date: Wed, 25 Feb 98 7:38:01 EST From: "Nick J Ugolini" Subject: PROP-FAB: prop Thanks for your email and your help. I amazed my friends at the club when I showed up with the prop. Most of them thought I had really gone off the deep end. If they only knew the strength of the prop! I think the overall strength has got to be much higher than the 2 bladed wood prop I was flying. I am in the process of filling and finishing. It should only take about a week to complete it... The first time I landed I landed hard too. I am used to the sound of the engine when I come down. Same sound...lower speed. Until I get used to it I am watching my rpm and airspeed very closely ...I can definitely overspeed the engine now when descending (easily gets up to 185 knots). I a just a bit concerned about my top end rpm. Right now it is 2850. Do you feel that is ok for a 0235. Recommended max rpm is 2800 although I hear you get the most horsepower at 2900.... How would I lower the rpm maybe 100 rpm? Thanks Date: Sat, 28 Feb 1998 10:49:19 -0500 (EST) From: Nigel Field Subject: Re: PROP-FAB: prop At 07:38 AM 2/25/98 EST, Nick wrote: >Thanks for your email and your help. > >I am just a bit concerned about my top end rpm. Right now it is 2850. Do >you feel that is ok for a 0235. Recommended max rpm is 2800 although I >hear you get the most horsepower at 2900.... > >How would I lower the rpm maybe 100 rpm? > Yea those thin tips really lower the drag and therefore torque requirement so it will turn up a bit faster flat out. Mine came out the same, I have to watch for overspeed when beating up the field flat out and a little nose down. Could be also that your drag profile or power curve are a little different than what we used for the calcs. Its hard to get it exactly right until you get some really accurate data. It may overspeed even more once you get it painted with nice smooth airfoil leading edges, but it will climb better too. I don't think 2850 will hurt your engine but I would not run it there continously as it will wear out much faster. I am assuming this is flat out level RPM here. The prop stresses are for 3200 RPM for a safety factor of 5 so I would not worry about the prop itself. If you reduce power for cruise to about 2600 or so you should not loose more than 4 or 5 kts in speed, thats where you want to cruise it. The reduction in torque should allow some blade flex to a slightly steeper pitch but this will vary with blade stiffness and sweep back. Perhaps you could try that and pass on your data. You have the same dilema we all get into searching for the ideal, perfect prop. I have concluded that it does not exist so one has to get the best compromise for your airplane and flight style. You have some options here. You could scarf on an extra .5 inch of carbon on the tips. This will lower your static RPM and therefore shaft HP but with an extra 1 inch diameter will increase disk area yet not lower your TO thrust significantly. This is the easiest change. But what I recommend and plan to do myself, is make a second prop with a little more blade area and another .5 to 1.0 degree pitch. This would be my cruising prop for long trips where a fast climb is not important. Indeed this is what I did do with my 2nd prop, only a 2 blade design. It has a lower cruise RPM but lower climb than my 3 blade. But it runs like a typical 2 blade and since I like the 3 blade so much more, I just hung it up as an easily shipped spare. I plan to make another 3 blade soon so I will have 2 for this season. Then I can fly my existing one most of the time and change over when I go to Osh or somewhere far and enjoy a slightly lower RPM cruise. Just a tip here, put a drop of oil on your bolt threads as they gall up after a few installations. I got a set of perfectly good prop bolts with galled threads that are now just lathe metal stock. Its really great to get your results Nick. You have confirmed that prop making is not rocket science and once you have done one, then the skills are there to make other props more easily. These don't cost much once you have the tools so I think this adds a lot of versatility for homenuilders since the prop is such a critical and otherwise expensive item. Cheers, Nigel Date: Mon, 2 Mar 98 7:50:24 EST From: "Nick J Ugolini" Subject: PROP-FAB: Prop I now have 5 hours on the prop and am really enjoying it. This past week, I filled, sanded, primed and painted. Against my own inclination, I took Nigels suggestion and painted it with a can of spray paint (I was going to use Imron). Nigel knows best! I used silver metal flake with red metal flake tips (paint from Home Depot). After wet sanding with 1200 grit and buffing the prop looks like a Aluminum prop with clear coat. On the ramp, all the old timers were wondering where I found an Al prop for the plane! Here is some thoughts I have. After you build your prop, check the prop torque after each flight until it stabilizes. I noticed a vibration after about an hour, and it seem to be the torque had changed (due to wood crush). After 3 retorques, it is starting to settle down. After I retighten the prop, my vibrations stopped. When it finally settles down, I will recheck my tracking. You might want to consider making a flox rod (in addition to the flox pad) for the prop bolt holes especially if you use fir like I did. Lee, After running my prop for a while (we both have the same prop calcs) I would recommend the following changes (these are based on my prop). Increase the blade angle in the cruise area (nearer the hub) to reduce cruise RPM, and decrease the blade angle near the tips (increase static RPM). My top rpm (4500'@156kts true) is 2750. My static is 2230. I think those numbers could be improved. Nigel I need your help on this one.... I think we could benefit from a change the layup schedule of the glass. You recommends the glass layups with one parallel to the trailing edge and one parallel to the leading edge (top and bottom). I have been thinking of the blade twist. Instead of the glass being in the same orientation (top and bottom... this has a tendency to KEEP the blade from twisting) you orient the torsional fibers (the glass at an angle to the trailing edge) in opposite directions (top in one directon and the bottom in the other direction). This would allow the blade to have more freedom to twist in one direction but not the other. The question is do you want the tip to twist to increase or decrease blade angle. This will tell you which direction to orient your tension fibers. Also, my blade tips are very flexible. I can move them 4"+ axially (to the Center Line of the plane). I think maybe a thinner blade cross section (near stations 5&6) and extend layup 3 closer to the tip and reduce layup 4, so it does not extend as far might help improve efficiency (thinner) and stiffness (extending the #3 layup). Also, maybe lengthening the carbon tips a bit further up the blade (from 6 to 10")....????? Thoughts..... Nick BTW, If I had time (too may other projects) I would be starting a new prop, and sell the one I just built. Building props is really fun! From: Lee Devlin Subject: Re: PROP-FAB: Prop Date: Mon, 2 Mar 98 9:04:44 MST Nick wrote: > After you build your prop, check the prop torque after each flight until it > stabilizes. I noticed a vibration after about an hour, and it seem to be > the torque had changed (due to wood crush). After 3 retorques, it is > starting to settle down. After I retighten the prop, my vibrations > stopped. When it finally settles down, I will recheck my tracking. You > might want to consider making a flox rod (in addition to the flox pad) for > the prop bolt holes especially if you use fir like I did. I was concerned about this as the pine/fir is rather soft. I hoped that there would be a limit to the amount it crushed and that the fiberglass/epoxy encapsulating it would help. What torque are you using? In the LongEZ manual it states to use 180 in-lb (15 ft-lb). This is what I use on my B&T and it occassionally needs to be retorqued. I'm not sure about using flox rods as I'd be concerned about not getting uniform friction across the surface of the prop hub. I had thought about pressing in metal inserts at one time, to alleviate wood crush, but arrived at the same conclusion. > Lee, > After running my prop for a while (we both have the same prop calcs) I > would recommend the following changes (these are based on my prop). > Increase the blade angle in the cruise area (nearer the hub) to reduce > cruise RPM, and decrease the blade angle near the tips (increase static > RPM). My top rpm (4500'@156kts true) is 2750. My static is 2230. I think > those numbers could be improved. Well, I can tweak it a little, I suppose, but how do you know which angles will produce what effect? My expectation is that the all of the stations of blade work to some degree in static and cruise. In fact, I felt that the inside of the blade, which has a much smaller pitch advance was more critical for static thrust and that the tips were more critical for cruise since they have a higher pitch advance. > Nigel I need your help on this one.... > I think we could benefit from a change the layup schedule of the glass. You > recommends the glass layups with one parallel to the trailing edge and one > parallel to the leading edge (top and bottom). I have been thinking of the > blade twist. Instead of the glass being in the same orientation (top and > bottom... this has a tendency to KEEP the blade from twisting) you orient > the torsional fibers (the glass at an angle to the trailing edge) in > opposite directions (top in one directon and the bottom in the other > direction). This would allow the blade to have more freedom to twist in > one direction but not the other. The question is do you want the tip to > twist to increase or decrease blade angle. This will tell you which > direction to orient your tension fibers. My understanding is that the layup schedule intentionally omitted any torsional (i.e. not parallel to blade length) layups to _allow_ the blade to twist. This is what is needed for a quasi-constant speed prop. Adding a layup in any orientation other than parallel to the blade will make it stiffer in twist which will prevent it from increasing pitch with higher rpm. Since the trailing edge is straight, it's easy for me to determine how to make a layup parallel to it. The leading edge is curved so that is not so obvious what I need to use to set the fiber orientation parallel to it. My assumption was that a small angle between plies is necessary to transmit loads more uniformly and minimize the torsional rigidity of the blade. > Also, my blade tips are very flexible. I can move them 4"+ axially (to the > Center Line of the plane). I think maybe a thinner blade cross section > (near stations 5&6) and extend layup 3 closer to the tip and reduce layup 4, > so it does not extend as far might help improve efficiency (thinner) and > stiffness (extending the #3 layup). Also, maybe lengthening the carbon > tips a bit further up the blade (from 6 to 10")....????? Are you saying that the tips are more flexible than the rest of the blade? Do you think the prop should be changed so that it will have a more gradual bend sort of like a constant stress beam? Decreasing thickness is likely to result in a blade that is not as stiff. I'd like to thank Nigel and Nick for all the trailblazing they are doing in this prop making adventure. Lee Devlin Date: Mon, 2 Mar 1998 21:50:17 -0500 (EST) From: Nigel Field Subject: PROP-FAB: Re Prop At 07:50 AM 3/2/98 EST, Nick wrote: > > Here is some thoughts I have. > >After you build your prop, check the prop torque after each flight until it >stabilizes. I noticed a vibration after about an hour, and it seem to be >the torque had changed (due to wood crush). After 3 retorques, it is >starting to settle down. After I retighten the prop, my vibrations >stopped. When it finally settles down, I will recheck my tracking. You >might want to consider making a flox rod (in addition to the flox pad) for >the prop bolt holes especially if you use fir like I did. I am surprised to hear that. Mine has not crushed at all and my torque stays put. Perhaps the Lyc hub is hotter than mine which is causing the problem, but my gear box runs around 210 F ( it has a temp probe in it) and the shaft is short but I don't actually know the hub temp. Just keep a real close watch on that Nick it has me concerned. Not sure of a cure but will give it some serious thought. It may well settle down though and become a non-problem (I hope). > >Lee, >After running my prop for a while (we both have the same prop calcs) I >would recommend the following changes (these are based on my prop). >Increase the blade angle in the cruise area (nearer the hub) to reduce >cruise RPM, and decrease the blade angle near the tips (increase static >RPM). My top rpm (4500'@156kts true) is 2750. My static is 2230. I think >those numbers could be improved. Actually 2750 is not too far off for flat out. It won't change much with altitude as the HP and prop load drop together dead linear. The only constant is engine friction which takes up a larger share of developed HP as you go up so the RPM will drop just a little when you get up high. I thought from your previous post that you were getting 2850 at level which is a bit high. But I agree your prop could be better (whats new), but I don't agree with your analysis here Nick. The helix is purely a geometric function of the vector sums of rotation and forward speed to establish the correct blade angle of attack at the designed speed. As with any calculation, the input data accuracy is critical. Without data, its an educated guess so you need a reference prop and some good data. You (we) now have that and if you can get some more data we can further refine the design. But Lee's LE will be a bit different so we get into this endless loop. Still your data is valuable and should allow Lee to adjust his parameters if he is not too far along. I think by eyeballing the data that you need about 1 to 1.5 degrees more pitch and possibly some more blade area. I will work the numbers again but would like to wait till you got some more data with the paint on it. The larger diameter is a very good thing but it tends to make the prop higher Q, or lets say more tuned for one condition with a lesser performance when off from the design parameters. A short stubby prop tends to have lower Q, (more bandwidth), or a wider operating range but with lower "on design" performance. Its all one big compromise. > >Nigel I need your help on this one.... >I think we could benefit from a change the layup schedule of the glass. You >recommends the glass layups with one parallel to the trailing edge and one >parallel to the leading edge (top and bottom). I have been thinking of the >blade twist. Instead of the glass being in the same orientation (top and >bottom... this has a tendency to KEEP the blade from twisting) you orient >the torsional fibers (the glass at an angle to the trailing edge) in >opposite directions (top in one directon and the bottom in the other >direction). This would allow the blade to have more freedom to twist in >one direction but not the other. The question is do you want the tip to >twist to increase or decrease blade angle. This will tell you which >direction to orient your tension fibers. No I don't agree here. Any bias to the plies will increase the blade torsional stiffness. There is about 5 or 6 degrees of bias already which is plenty. If you want more CS effect you need to sweep the blade back a little more from the radial line. But that will only lower your cruise RPM when you reduce torque and it will still overspeed at full throttle on the deck. > >Also, my blade tips are very flexible. I can move them 4"+ axially (to the >Center Line of the plane). I think maybe a thinner blade cross section >(near stations 5&6) and extend layup 3 closer to the tip and reduce layup 4, > so it does not extend as far might help improve efficiency (thinner) and >stiffness (extending the #3 layup). Also, maybe lengthening the carbon >tips a bit further up the blade (from 6 to 10")....????? > >Thoughts..... The thin blades will flex when not loaded up with centrifugal loads. This is OK, like helicopter blades that flap all over the place when stopped. If you want them stiffer then make them thicker (double the thickness give 8 times the stifness) but then you got a thick draggy prop. No thats not the problem here, you just need more area and pitch. Your engine is putting out more than we designed for. Be great if Lee could try yours before he sets his in stone, or is that glass :-). How far apart are you two?? Its a bummer being first, you make all the stuff, get the data and others reap the rewards. Your next one will be perfect, for a few weeks anyway, this I do know. Let me think on this some more and play with numbers for a few days. Keep us informed on that crush problem please. Nigel Date: Tue, 03 Mar 1998 06:32:41 +0200 From: Rego Burger Subject: PROP-FAB: Carving props Hello, As one of the newest members to this list I need some serious guidance on this subject. I wish to carve my own props 2 blade to start with, now the thing is this we have a few varieties of wood in RSA but how do I choose the right one? We have Oaks ( Saligna ) as a local one and Oregon Pine as imported. These are the most common available, are they any good for props at the HP range of 150 + . Or is glass a better option? Rego Burger, web site: http://home.intekom.com/glen/rnb.htm (home e-mail) mailto:rnb@intekom.co.za RSA Date: Tue, 3 Mar 98 7:32:06 EST From: "Nick J Ugolini" Subject: PROP-FAB: Prop Torque >After you build your prop, check the prop torque after each flight until it >stabilizes. I noticed a vibration after about an hour, and it seem to be >the torque had changed (due to wood crush). >I am surprised to hear that. Mine has not crushed at all and my torque stays put. Perhaps the Lyc hub is hotter than mine which is causing the problem,.... I dont think heat is the problem. I post cured @155 deg f, and after flight the prop extention is hot BUT much less hot than post cure, I would guess 130 deg. (I could easily put my hand on it for 20 sec). I was thinking about soft wood (fir) and crush. I think my design (fir) and lack of flox rods may be the problem. I also thought about the effects of bolt torque and power transfer. Here they are... With a wood prop you have an infinite number of planes to transfer power from the engine to the prop. Bolt torque is necessary to compress all the planes so power is transferred through shear throughout the prop and to keep the prop from moving around. With the glass prop, you only have two planes in shear to transfer the power (negating the wood). The upper and lower skin. The shear is resisted by all the points where the upper and lower skin attached and the BID around the prop hub. With a foam prop (I actually think it is do-able) ALL the power would be transferred through the shin. If you had a foam core all the engine power would be absorbed by the skin on the prop flange side and transferred to the other skin in shear. The bolt would be used just to hold the prop on, not to help transfer power through the compression of the material. In my case most of the engine power is transferred through the skin (glass) and a bit through the wood. The softer fir is crushing which ends up deforming the glass to some extent. The question is DO we really need to CRUSH our glass prop for power transfer? Lets say I built a foam prop, and put in flox rods in the bolt hole area. I could torque the prop down for friction and attachment purposes, and the power transfer would be through the skin. I really doubt I could ever elongate the 5/8" holes of the threaded prop bolt studs in the flange. Maybe the prop could be built with more layups of BID in the hub area for the shear transfer.... Nigel, THANKS for your thoughts on the last email. I have to ponder it a while. I will take some more data on my prop now that it is painted... I now get more ooohhh and aaaahhh about the prop than the plane. I guess prop building is even more mysterious than plane building. Nick From: SWrightFLY Date: Tue, 3 Mar 1998 08:42:52 EST Subject: Re: PROP-FAB: Prop Torque In a message dated 98-03-03 08:30:07 EST, njugolini@efdsouth.navfac.navy.mil writes: << The question is DO we really need to CRUSH our glass prop for power transfer? Lets say I built a foam prop, and put in flox rods in the bolt hole area. I could torque the prop down for friction and attachment purposes, and the power transfer would be through the skin. I really doubt I could ever elongate the 5/8" holes of the threaded prop bolt studs in the flange. Maybe the prop could be built with more layups of BID in the hub area for the shear transfer.... >> Without 240 to 300 inch pounds on an 0-320 or 0-360 the power pulses will allow the prop to slip and over time the bolts will fail in shear. How about makeing the hub of the prop out of hard maple and the baldes out of soft pine or fir? Steve Wright From: Ken Reiter Date: Tue, 3 Mar 98 08:48:44 CST Subject: Re: PROP-FAB: Prop Torque Hi Guys, Ron Gowan (rotary powered RG-Long) is building the his prop as below; with hard maple at hub and pine on blades. He is ready to cover the blades with glass. As his prop develops, I will keep you all posted. Ken > > Without 240 to 300 inch pounds on an 0-320 or 0-360 the power pulses will > allow the prop to slip and over time the bolts will fail in shear. How about > makeing the hub of the prop out of hard maple and the baldes out of soft pine > or fir? > Steve Wright > From: lschuler@cellular.uscc.com Date: Tue, 03 Mar 98 08:59:41 -0600 Subject: Re: PROP-FAB: Re Prop Nigel wrote: >snip >Let me think on this some more and play with numbers for a few days. Keep >us informed on that crush problem please. Just wondering if the 'crush' problem is really due to the notoriously nasty Lycoming torsional impulses which Nigel's smoother Subaru doesn't have? If bolts keep needing tightening, could be an endless loop where the impulses loosen the grip, they get re-torqued, loosen again; ad-nausium. Softer pine could exacerbate the problem. Larry Schuler lschuler@cellular.uscc.com Date: Tue, 3 Mar 98 10:15:50 EST From: "Nick J Ugolini" Subject: PROP-FAB: Re: torque > > Without 240 to 300 inch pounds on an 0-320 or 0-360 the power pulses will > allow the prop to slip and over time the bolts will fail in shear. How about > making the hub of the prop out of hard maple and the blades out of soft pine > or fir? I would agree friction would play an important part of power transfer in a material like hard maple than it plays in 20+ layers of glass, flox pads and post cured epoxy with a softer core. I dont see how bolts could shear on a wood prop unless the wood sheared near the prop hub due to low bolt torque. The wood would shear just above the threaded nut inserts twisting the bolt and thus shearing. The wood transmits torque throughout its internal structure. I think the glass props transmits much of the torque on the Outer structure. It took me 3+ hours to get the prop to fit into my extention. I used a drill guide for the pattern (VERY accurate) and I was a few TEN thousands off. I tried everything I could to elongate the hole to force the extention to fit with no results. It would have been much easily forced the extention onto a wood prop. The glass is totally unforgiving to "miss" drilling and is EXTREMELY tough. I ended using a 1/2" end mill to slightly adjust the holes for an almost press fit. I postulate that the engine torque _in_ this_ case_ may be largely transferred via the 5/8" threaded inserts on the prop flange than by a combination of friction and the threaded inserts. ??In a glass prop will the friction transfer play a roll if much or all the power transfer is handled by the shear of the threaded inserts at the glass surface?? For flaming sake.... Lets look at this in another way. Maple (hard), Fir (soft), foam (nothing). When you torque a bolt, the force is transferred to the head and back down through the material underneight with the purpose of creating pressure (friction) against the flange. With maple you spread that pressure more equally than with fir (localized crushing). If you built a flox tube in the bolt areas in a foam prop you could still obtain the same torque as a maple prop, no crushing. A higher pressure would be developed in a localized area BUT the over all pressure would be the same. The pressure is right over the points at which torque is transferred.... Thoughts.... Go ahead, make my day! Nick Date: Tue, 3 Mar 98 13:31:22 EST Subject: PROP-FAB: Re: torque Nick wrote: > Steve Wright wrote: >> Without 240 to 300 inch pounds on an 0-320 or 0-360 the power pulses will >> allow the prop to slip and over time the bolts will fail in shear. How about >> making the hub of the prop out of hard maple and the blades out of soft >pine or fir? >I postulate that the engine torque _in_ this_ case_ may be largely >transferred via the 5/8" threaded inserts on the prop flange than by a >combination of friction and the threaded inserts. ??In a glass prop will >the friction transfer play a roll if much or all the power transfer is >handled by the shear of the threaded inserts at the glass surface?? >... When you torque a bolt, the force is transferred to the head >and back down through the material underneight with the purpose of creating >pressure (friction) against the flange. With maple you spread that >pressure more equally than with fir (localized crushing). Lets look at this analytically. The simple (and not completely correct, but close enough for our purposes) relationship between torque and force on a bolt is: T = K x d x F pt Where: T = Torque K = Fudge factor (about 0.25 for cadmium plated bolts) d = bolt diameter F = Bolt Force pt So, with 5/8" diameter bolts and 300 inch-lb of torque, we get a force/bolt of: T 300 in-lb F = ------- = ---------------- = 1920 lbs. pt K x d 0.25 x .625 in. With 6 bolts, we've got about 11,520 lb. of force squeezing the prop crush plate (which I assume is thick enough to evenly spread out the force created by the bolts - at least it was on my Q2). A 100 HP engine puts out about 200 ft-lb of torque at 2700 RPM. Now, I'm going to make some assumptions just to get a ballpark figure here, but this will tell us if we're in the right range. If the crush plate/prop extension is 6" in diameter, we can say that the torque reaction due to friction will be reacted about 2" from the center. With 200 ft-lb of torque, we'll need 1200 lb. of reaction force at a 2" radius to prevent relative motion. Now, if the friction coefficient between the prop extension and the prop is more than 1200/11,520 = 0.11, there will be no slippage between the prop and the extension, and all the torque will be transmitted via friction and not the bolts. Yes, I know that there's a lot of hand waving here, and that the #'s are just rough estimates, but I think it shows that it's more than likely that all the torque is transmitted via friction (even in this case). A friction coefficient of 0.1 would be difficult to achieve even if we were trying to - my guess is that we're closer to 0.4 or 0.5, unless Nick's been polishing his prop hub and prop extension. This also shows us that for O-360 engines with almost twice the torque (and large torque pulsations) this issue is more critical - a higher bolt torque and/or stiffer crush plates and/or higher friction coefficient materials may be necessary. Now, if there's no crush plate, or if the crush plate is wimpy and allows local force concentrations, then Nick's theorizations may have validity. -- Marc J. Zeitlin Email: marcz@an.hp.com Date: Tue, 3 Mar 98 13:24:27 EST From: "Nick J Ugolini" Subject: PROP-FAB: Torque Had a thought: If you had a perfect glue and could glue your prop on the hub (perfect friction) I contend you would still need the bolts in a wood prop. They would then only be used then to keep the shear in the wood (infinite working planes) to an acceptable level. Bolts would not be necessary in a glass prop because the shear would be taken up in the BID between the two working planes. From: Marc J. Zeitlin Subject: PROP-FAB: Re: torque Date: Tue, 3 Mar 98 13:31:22 EST Nick wrote: > Steve Wright wrote: >> Without 240 to 300 inch pounds on an 0-320 or 0-360 the power pulses will >> allow the prop to slip and over time the bolts will fail in shear. How about >> making the hub of the prop out of hard maple and the blades out of soft >pine or fir? >I postulate that the engine torque _in_ this_ case_ may be largely >transferred via the 5/8" threaded inserts on the prop flange than by a >combination of friction and the threaded inserts. ??In a glass prop will >the friction transfer play a roll if much or all the power transfer is >handled by the shear of the threaded inserts at the glass surface?? >... When you torque a bolt, the force is transferred to the head >and back down through the material underneight with the purpose of creating >pressure (friction) against the flange. With maple you spread that >pressure more equally than with fir (localized crushing). Lets look at this analytically. The simple (and not completely correct, but close enough for our purposes) relationship between torque and force on a bolt is: T = K x d x F pt Where: T = Torque K = Fudge factor (about 0.25 for cadmium plated bolts) d = bolt diameter F = Bolt Force pt So, with 5/8" diameter bolts and 300 inch-lb of torque, we get a force/bolt of: T 300 in-lb F = ------- = ---------------- = 1920 lbs. pt K x d 0.25 x .625 in. With 6 bolts, we've got about 11,520 lb. of force squeezing the prop crush plate (which I assume is thick enough to evenly spread out the force created by the bolts - at least it was on my Q2). A 100 HP engine puts out about 200 ft-lb of torque at 2700 RPM. Now, I'm going to make some assumptions just to get a ballpark figure here, but this will tell us if we're in the right range. If the crush plate/prop extension is 6" in diameter, we can say that the torque reaction due to friction will be reacted about 2" from the center. With 200 ft-lb of torque, we'll need 1200 lb. of reaction force at a 2" radius to prevent relative motion. Now, if the friction coefficient between the prop extension and the prop is more than 1200/11,520 = 0.11, there will be no slippage between the prop and the extension, and all the torque will be transmitted via friction and not the bolts. Yes, I know that there's a lot of hand waving here, and that the #'s are just rough estimates, but I think it shows that it's more than likely that all the torque is transmitted via friction (even in this case). A friction coefficient of 0.1 would be difficult to achieve even if we were trying to - my guess is that we're closer to 0.4 or 0.5, unless Nick's been polishing his prop hub and prop extension. This also shows us that for O-360 engines with almost twice the torque (and large torque pulsations) this issue is more critical - a higher bolt torque and/or stiffer crush plates and/or higher friction coefficient materials may be necessary. Now, if there's no crush plate, or if the crush plate is wimpy and allows local force concentrations, then Nick's theorizations may have validity. -- Marc J. Zeitlin Email: marcz@an.hp.com From: Marc J. Zeitlin Subject: PROP-FAB: Torque Date: Tue, 3 Mar 98 15:28:55 EST Nick Ugolini wrote: >Had a thought: That happens to me on occasion. I generally get over it :-). >If you had a perfect glue and could glue your prop on the hub (perfect >friction) I contend you would still need the bolts in a wood prop. They >would then only be used then to keep the shear in the wood (infinite >working planes) to an acceptable level. I believe that this is incorrect. Remember, we're talking about a couple of thousand pounds of force distributed over the ~30 square inche prop hub face - that's less than 100 psi of shear stress - substantially less, on the average. Not an issue, no matter what the wood, really. The bolts are purely and simply there to ensure an adequate frictional level between the face of the prop and the prop extension face. _If_ you could create a perfect joint between the face of the prop and the face of the extension, you wouldn't need the bolts (don't try this at home, kids). >......... Bolts would not be necessary in a >glass prop because the shear would be taken up in the BID between the two >working planes. Not at all sure what you're referencing when you say "working planes" for either the wood or the glass. In a wood core glass prop, the shear stress would be absorbed for the most part by the glass skin (being much stiffer than the wood), but other than that there would be no difference between the characteristics of the glass/wood prop and the all wood prop with respect to frictional interaction and need for bolts. -- Marc J. Zeitlin Email: marcz@an.hp.com Date: Tue, 3 Mar 98 13:45:33 EST From: "Nick J Ugolini" Subject: PROP-FAB: RE: Marc Nice analysis Marc. I hadnt quite thought about it in that way.... My thoughts were along the line: the slippage would not be at the face of the prop and the extention. Most prop fit very tightly onto the prop flange studs. You would have to shear the 5/8" (??) threaded studs which stick 3/4" into the prop. I believe that would be impossible. I was thinking of the wood just above the insert where there is a 5/8"X 1/8+" void before the hole reduces to 3/8" for the prop bolt. I believe this would be the "worst case" stress point on the prop and the area where slippage (ie, wood shear on a flat plane) would occur. Q. Exactly where did the failure of the prop which sheared the bolts occur? Nick From: Marc J. Zeitlin Subject: PROP-FAB: torque Date: Tue, 3 Mar 98 16:17:31 EST Nick Ugolini wrote: >My thoughts were along the line: the slippage would not be at the face of >the prop and the extention. Most prop fit very tightly onto the prop flange >studs. You would have to shear the 5/8" (??) threaded studs which stick >3/4" into the prop. I believe that would be impossible. Yup, it would be, and it's not what happens. >I was thinking of the wood just above the insert where there is a 5/8"X >1/8+" void before the hole reduces to 3/8" for the prop bolt. I believe >this would be the "worst case" stress point on the prop and the area where >slippage (ie, wood shear on a flat plane) would occur. Maybe, but that's not what happens. What would happen if the bolts weren't tight enough is that the prop would slip a bit (probably in both directions as the torque pulses pushed it back and forth) and the holes would elongate slightly due to LOCAL crushing of the wood right at the insert/bolt. Once this starts occurring, the prop would slip back and forth an increasing amount over time, as the wood crushed locally more and more. As this happens, there's excessive heat buildup and degradation of the wood in the hub area, eventually leading to failure either of the prop or the extension. Once it starts slipping, you're pumping a LOT of heat/energy into a small area. >Q. Exactly where did the failure of the prop which sheared the bolts occur? Are you referring to this statement? >>(which I assume is thick enough to evenly spread out the >>force created by the bolts - at least it was on my Q2) If I gave the impression that I sheared some bolts, I'm sorry - that's not the case. What I meant was that the crush plate used on the Q2 for the revmaster engine was thick enough so that there was no measureable deformation under the recommended bolt torque, and therefore the force was evenly distributed over the face of the crush plate and hence the prop extension/crankshaft. -- Marc J. Zeitlin Email: marcz@an.hp.com Date: Thu, 5 Mar 1998 21:27:22 -0500 (EST) From: Nigel Field Subject: PROP-FAB: Prop Design --=====================_889204727==_ Content-Type: text/plain; charset="us-ascii" Folks, FW an Email with Cozy builder Steve Sharp with his blessing that contains some good engine data and a prop design FYI. Nice to see another smooth engine soon to fly. Nigel > ---------- >From: Steven D. Sharp >To: FieldNigel >Subject: Prop-fab >Date: Tuesday, March 03, 1998 9:56AM > >Nigel, > I finally was able to interpolate the horsepower and torque >graphs for >my EJ-22 set-up. > > Engine RPM Prop RPM HP Torque > 2100 1135 58 130 > 2400 1297 62 137 > 2800 1514 72 135 > 3200 1730 84 135 > 3600 1946 92 134 > 4000 2162 103 134 > 4400 2378 114 136 > 4800 2595 125 137 > 5200 2811 130 130 > >Max HP is 130HP @ 5200 RPM >Max torque is 138lb-ft @ 4600 RPM > >The set-up is a stock EJ-22 with a Holley 2300 350cfm carb and a >McNeilly mixture control system. The data is information obtained by Ron >Steber on a dyno. I have duplicated his set-up and do have the engine >running. The PSRU is a Ross 1.85:1 The torque curve appears to be pretty >"flat" based on the above data. > >The airframe is a stock Cozy 3 place w/ Roncz canard and the stock >cowlings on it. I anticipate the finish weight to be about 1000# > >For the Prop-Opt do you need any additional info? > >Would you recommend the Prop-Opt program (I checked their web site - >$125) > >Anyway, I deeply appreciate all the help. I am really looking forward to >building a prop - especially after the reports I have read from you, >George Graham, and Nick. > >Again, Thanks > >Steve Sharp >cozyiii@eathlink.net > > Hi Steve, Sorry for the delay got busy at work. Attached is a design file for your Cozy III and EJ-22 engine. Its a DOS ASCI file so read it with Wordpad or any good WP application. Assumed you wanted 3 blades. The 1.85 ratio results in a stubby prop but still pretty good performance. I like the power curve you sent, looks to be honest real numbers so the prediction should be pretty close. Set payload at 250 lbs as this is more what you would fly most of the time so the gross weight calc is lower than what the airplane would take but is what is used for the prop calcs. The propopt application is valuable if you do a lot of this stuff as I do, but not worth it if you just want to make a prop or 2. There are several of us who can run the numbers for you. Its user hostile and takes a while to get used to it, but it is powerfull. Would you mind if I post this to the prop list also as others may find the discussion and design calcs interesting. Regards, Nigel --=====================_889204727==_ Content-Type: text/plain; charset="us-ascii" Content-Disposition: attachment; filename="COZ3185.O" COZY-3 1.85 RATIO Prop Design 3 Blade CONTROL NPAYOFF=2 AIRFOIL=2 @ 1 is clark Y, 2 is RAF 6 IOPT=1,2,3,4,5,6,7 BLDOP=1 pdes=1 END DESLIM AFLIM=60,120 abmin=2.0 @ cldes=.4 DMAX= 68 RCLM=1 END DESVAR @ afdes=80 REDFAC=1.85 DIAM=66 PITCH=75 NB=3 RPMCRS=5200 ALTCRS=3000 DREF=66 WT0=1000 WPAYLD=250 SPAN=26 OSWALD=.851 SFCLM=1 sfcrs=.1 pctpwr=100 VCRS=190 RPMCLM=5000 VCLM=100 ALTCLM=300 KS=1.00 ADRAG=2.1 END TABLES STA=.2,.3,.4,.5,.6,.7,.8,.9,1. CHORD=5.217 5.138 5.090 5.023 4.852 4.527 4.080 3.424 2.651 TCTAB=.4064 .2937 .2436 .2007 .1684 .1440 .1355 .1151 .0902 RPMTAB=3600 4000 4400 4800 5200 HPTAB= 92 103 114 125 130 SFCTAB= .43 .43 .42 .41 .40 END EOF COZY-3 1.85 RATIO Prop Design 3 Blade @ 03/06/98 05:34:27.19 >>>> OPTIMIZED DESIGN: VARIABLE INITIALLY OPTIMIZED LOWER LIMIT UPPER LIMIT AFDES 90.4682 60.0000 60.0000 120.000 DIAM 66.0000 59.7487 13.6000 68.0000 PITCH 75.0000 68.8543 37.5000 150.000 RPMCRS 5200.00 5200.00 3600.00 5200.00 VCRS 190.000 188.269 142.500 237.500 RPMCLM 5000.00 4565.25 3600.00 5200.00 VCLM 100.000 105.393 75.0000 125.000 PROPELLER DESIGN CRUISE PERFORMANCE, ALT= 3000.00 FT NUMBER OF BLADES = 3 VELOCITY, MPH = 188.27 BLADE ACTIVITY FACTOR= 60.00 THRUST, POUNDS = 192.75 DIAMETER, INCHES = 59.75 DRAG, POUNDS = 192.75 GEOMETRIC PITCH, IN = 68.85 EFFECTIVE PITCH, IN = 70.73 ABSOLUTE PITCH, IN = 85.59 THRUST HP = 96.77 BLADE ANGLE DEG @75%R= 31.30 SHAFT HP = 116.91 ALPHA @ 0LL DEG @75%R= 4.62 HP AVAILABLE = 116.91 DESIGN LIFT COEF, CL = 0.5587 PROPELLER RPM = 2810.81 THRUST COEF, CT = 0.0657 ENGINE RPM = 5200.00 POWER COEF, CP = 0.0939 REDUCT FACTOR = 1.85 ADVANCE RATIO, J = 1.1838 PARASITE DRAG,LB = 174.16 EFFICIENCY, ETA = 0.8278 INDUCED DRAG, LB = 10.42 ETA COMPRESS CORRECT.= 0.00% SLIPSTREAM DRAG = 8.16 ETA PROFILE DRAG CORR= 0.35% SFC, LB/HP/HR = 0.40 ETA DIAMETER CORRECT.= -1.47% MILES/GALLON = 24.16 FUEL FLOW, GPH = 7.79 SLIPSTREAM COEF, KS = 1.0000 SOUND SPEED,FPS = 1104.88 ADRAG, SQ FT = 2.100 TIP SPEED, FPS = 783.09 GROSS WEIGHT, LB = 1250.0 TIP MACH NUMBER = 0.71 WPAYLD, LB = 250.0 CAFE CHALLENGE = 601184. CLIMB PERFORMANCE AT V= 105.39 MPH, ALTITUDE= 300.00 NUMBER OF BLADES = 3 CLIMB RATE, FPM = 1443.77 BLADE ACTIVITY FACTOR= 60.00 THRUST, POUNDS = 296.99 DIAMETER, INCHES = 59.75 DRAG, POUNDS = 102.41 EFFECTIVE PITCH, IN = 45.10 THRUST HP = 83.47 BLADE ALPHA DEG @75%R= 13.54 SHAFT HP = 117.65 BLADE LIFT COEF, CL = 1.3322 HP AVAILABLE = 117.65 PROPELLER RPM = 2467.70 THRUST COEF, CT = 0.1212 ENGINE RPM = 4565.25 POWER COEF, CP = 0.1290 PARASITE DRAG,LB = 59.12 ADVANCE RATIO, J = 0.7548 INDUCED DRAG, LB = 30.71 EFFICIENCY, ETA = 0.7095 SLIPSTREAM DRAG = 12.58 ETA COMPRESS CORRECT.= 0.00% GROSS WEIGHT, LB = 1250.00 ETA PROFILE DRAG CORR= 0.07% SOUND SPEED,FPS = 1115.30 ETA DIAMETER CORRECT.= -1.47% TIP SPEED, FPS = 661.65 ADRAG, SQ FT = 2.100 TIP MACH NUMBER = 0.59 FIXED PITCH STATIC PERFORMANCE AT SURFACE ALTITUDE= 0. FT STATIC PROPELLER RPM = 2366.90 STATIC THRUST LB = 305.69 STATIC ENGINE RPM = 4378.76 SHAFT HP = 113.33 THRUST COEF, CT = 0.1345 IDEAL THRUST @75%HP= 303.58 PROPELLER BLADE SHAPE _____STATION_____ CHORD ___THICKNESS___ CHORD ANGLE ___LOCAL___ R/R(TIP) INCHES INCHES RATIO INCHES DEGREES MACH REYN 0.2000 5.97 3.13 0.4064 1.27 51.40 0.142 2.4E+05 0.3000 8.96 3.08 0.2937 0.91 45.07 0.213 3.6E+05 0.4000 11.95 3.06 0.2436 0.74 38.77 0.284 4.7E+05 0.5000 14.94 3.02 0.2007 0.61 34.09 0.354 5.8E+05 0.6000 17.92 2.91 0.1684 0.49 30.43 0.425 6.8E+05 0.7000 20.91 2.72 0.1440 0.39 27.51 0.496 7.4E+05 0.8000 23.90 2.45 0.1355 0.33 24.76 0.567 7.6E+05 0.9000 26.89 2.06 0.1151 0.24 23.02 0.638 7.2E+05 1.0000 29.87 1.59 0.0902 0.14 21.88 0.709 6.2E+05 BLADE AIRFOIL COORDINATES R.A.F. 6 BLADE STATION= 5.975 BLADE ANGLE= 51.403 DEG X YU YL 0.000 0.127 0.127 0.078 0.522 0.010 0.157 0.751 0.000 0.313 1.006 0.000 0.626 1.209 0.000 0.940 1.273 0.000 1.253 1.260 0.000 1.566 1.209 0.000 1.879 1.107 0.000 2.193 0.942 0.000 2.506 0.713 0.000 2.819 0.446 0.000 3.132 0.178 0.000 SECTION BLOCK WIDTH, INCHES = 2.042 HEIGHT= 2.878 LEADING EDGE RADIUS = 0.127 L.E. CHORD LINE ELEVATION = 2.448 L.E. TANGENT ELEVATION = 2.428 T.E. UPPER CHORD ELEVATION = 0.111 T.E. LOWER CHORD INDENTATION= 0.139 BLADE AIRFOIL COORDINATES R.A.F. 6 BLADE STATION= 8.962 BLADE ANGLE= 45.069 DEG X YU YL 0.000 0.091 0.091 0.077 0.371 0.001 0.154 0.535 0.000 0.308 0.716 0.000 0.617 0.861 0.000 0.925 0.906 0.000 1.234 0.897 0.000 1.542 0.861 0.000 1.851 0.788 0.000 2.159 0.670 0.000 2.468 0.507 0.000 2.776 0.317 0.000 3.085 0.127 0.000 SECTION BLOCK WIDTH, INCHES = 2.231 HEIGHT= 2.509 LEADING EDGE RADIUS = 0.091 L.E. CHORD LINE ELEVATION = 2.184 L.E. TANGENT ELEVATION = 2.184 T.E. UPPER CHORD ELEVATION = 0.090 T.E. LOWER CHORD INDENTATION= 0.090 BLADE AIRFOIL COORDINATES R.A.F. 6 BLADE STATION= 11.950 BLADE ANGLE= 38.766 DEG X YU YL 0.000 0.074 0.074 0.076 0.305 0.000 0.153 0.439 0.000 0.306 0.588 0.000 0.611 0.707 0.000 0.917 0.744 0.000 1.222 0.737 0.000 1.528 0.707 0.000 1.834 0.648 0.000 2.139 0.551 0.000 2.445 0.417 0.000 2.750 0.261 0.000 3.056 0.104 0.000 SECTION BLOCK WIDTH, INCHES = 2.418 HEIGHT= 2.215 LEADING EDGE RADIUS = 0.074 L.E. CHORD LINE ELEVATION = 1.913 L.E. TANGENT ELEVATION = 1.925 T.E. UPPER CHORD ELEVATION = 0.081 T.E. LOWER CHORD INDENTATION= 0.065 BLADE AIRFOIL COORDINATES R.A.F. 6 BLADE STATION= 14.937 BLADE ANGLE= 34.089 DEG X YU YL 0.000 0.061 0.061 0.075 0.248 0.000 0.151 0.357 0.000 0.302 0.478 0.000 0.603 0.575 0.000 0.905 0.605 0.000 1.206 0.599 0.000 1.508 0.575 0.000 1.809 0.527 0.000 2.111 0.448 0.000 2.413 0.339 0.000 2.714 0.212 0.000 3.016 0.085 0.000 SECTION BLOCK WIDTH, INCHES = 2.522 HEIGHT= 1.947 LEADING EDGE RADIUS = 0.061 L.E. CHORD LINE ELEVATION = 1.690 L.E. TANGENT ELEVATION = 1.707 T.E. UPPER CHORD ELEVATION = 0.070 T.E. LOWER CHORD INDENTATION= 0.047 BLADE AIRFOIL COORDINATES R.A.F. 6 BLADE STATION= 17.925 BLADE ANGLE= 30.429 DEG X YU YL 0.000 0.049 0.049 0.073 0.201 0.000 0.146 0.289 0.000 0.291 0.388 0.000 0.583 0.466 0.000 0.874 0.491 0.000 1.165 0.486 0.000 1.457 0.466 0.000 1.748 0.427 0.000 2.039 0.363 0.000 2.331 0.275 0.000 2.622 0.172 0.000 2.913 0.069 0.000 SECTION BLOCK WIDTH, INCHES = 2.529 HEIGHT= 1.687 LEADING EDGE RADIUS = 0.049 L.E. CHORD LINE ELEVATION = 1.475 L.E. TANGENT ELEVATION = 1.493 T.E. UPPER CHORD ELEVATION = 0.059 T.E. LOWER CHORD INDENTATION= 0.035 BLADE AIRFOIL COORDINATES R.A.F. 6 BLADE STATION= 20.912 BLADE ANGLE= 27.509 DEG X YU YL 0.000 0.039 0.039 0.068 0.160 0.000 0.136 0.231 0.000 0.272 0.309 0.000 0.544 0.372 0.000 0.815 0.391 0.000 1.087 0.387 0.000 1.359 0.372 0.000 1.631 0.341 0.000 1.903 0.290 0.000 2.174 0.219 0.000 2.446 0.137 0.000 2.718 0.055 0.000 SECTION BLOCK WIDTH, INCHES = 2.422 HEIGHT= 1.425 LEADING EDGE RADIUS = 0.039 L.E. CHORD LINE ELEVATION = 1.255 L.E. TANGENT ELEVATION = 1.272 T.E. UPPER CHORD ELEVATION = 0.049 T.E. LOWER CHORD INDENTATION= 0.025 BLADE AIRFOIL COORDINATES R.A.F. 6 BLADE STATION= 23.899 BLADE ANGLE= 24.756 DEG X YU YL 0.000 0.033 0.033 0.061 0.136 0.000 0.122 0.196 0.000 0.245 0.262 0.000 0.490 0.315 0.000 0.735 0.332 0.000 0.980 0.329 0.000 1.225 0.315 0.000 1.470 0.289 0.000 1.715 0.246 0.000 1.960 0.186 0.000 2.205 0.116 0.000 2.450 0.046 0.000 SECTION BLOCK WIDTH, INCHES = 2.233 HEIGHT= 1.179 LEADING EDGE RADIUS = 0.033 L.E. CHORD LINE ELEVATION = 1.026 L.E. TANGENT ELEVATION = 1.042 T.E. UPPER CHORD ELEVATION = 0.042 T.E. LOWER CHORD INDENTATION= 0.019 BLADE AIRFOIL COORDINATES R.A.F. 6 BLADE STATION= 26.887 BLADE ANGLE= 23.019 DEG X YU YL 0.000 0.024 0.024 0.051 0.097 0.000 0.103 0.140 0.000 0.206 0.187 0.000 0.411 0.225 0.000 0.617 0.237 0.000 0.822 0.234 0.000 1.028 0.225 0.000 1.233 0.206 0.000 1.439 0.175 0.000 1.645 0.133 0.000 1.850 0.083 0.000 2.056 0.033 0.000 SECTION BLOCK WIDTH, INCHES = 1.898 HEIGHT= 0.908 LEADING EDGE RADIUS = 0.024 L.E. CHORD LINE ELEVATION = 0.804 L.E. TANGENT ELEVATION = 0.816 T.E. UPPER CHORD ELEVATION = 0.030 T.E. LOWER CHORD INDENTATION= 0.013 BLADE AIRFOIL COORDINATES R.A.F. 6 BLADE STATION= 29.874 BLADE ANGLE= 21.883 DEG X YU YL 0.000 0.014 0.014 0.040 0.059 0.000 0.080 0.085 0.000 0.159 0.113 0.000 0.318 0.136 0.000 0.477 0.144 0.000 0.637 0.142 0.000 0.796 0.136 0.000 0.955 0.125 0.000 1.114 0.106 0.000 1.273 0.080 0.000 1.432 0.050 0.000 1.592 0.020 0.000 SECTION BLOCK WIDTH, INCHES = 1.480 HEIGHT= 0.648 LEADING EDGE RADIUS = 0.014 L.E. CHORD LINE ELEVATION = 0.593 L.E. TANGENT ELEVATION = 0.601 T.E. UPPER CHORD ELEVATION = 0.019 T.E. LOWER CHORD INDENTATION= 0.007 BLADE SECTION BLOCK DIMENSIONAL SUMMARY IN INCHES STA WIDTH HEIGHT LE RAD LE ELV CHRD ELV TE ELV TE INDT BTM ELV 5.97 2.042 2.878 0.127 2.448 2.428 0.111 0.139 0.000 8.96 2.231 2.509 0.091 2.184 2.184 0.090 0.090 0.184 11.95 2.418 2.215 0.074 1.913 1.925 0.081 0.065 0.331 14.94 2.522 1.947 0.061 1.690 1.707 0.070 0.047 0.465 17.92 2.529 1.687 0.049 1.475 1.493 0.059 0.035 0.595 20.91 2.422 1.425 0.039 1.255 1.272 0.049 0.025 0.726 23.90 2.233 1.179 0.033 1.026 1.042 0.042 0.019 0.849 26.89 1.898 0.908 0.024 0.804 0.816 0.030 0.013 0.985 29.87 1.480 0.648 0.014 0.593 0.601 0.019 0.007 1.115 OVERALL MAXIMUM SECTION BLOCK WIDTH= 2.529 HEIGHT= 2.878 NOTE: BTM ELV is the centered block, bottom elevation mark of each section referenced to the bottom of the tallest section block. All other elevations are referenced to their own section block bottom. TE INDT is the trailing edge mark on the bottom of each section block inward from the trailing edge vertical side. These marks should only be used as a rough starting guide. Blade airfoil sections should be completed using angle templates to get blade angle correct and airfoil templates to get leading edge radius and surface curvature correct for each section. NOTE: Blade chord angle is measured from the plane of rotation. The chord line is along the flat bottom of the airfoil. Airfoil coordinates are measured along the chord line from the leading edge (X) and perpendicular to the chord line (YL = lower surface and YU = upper surface positive up). Section block dimensions are given without margin. Add whatever working margin you may need. The primary concern is accurate blade angles. The block for each blade station can be shifted in any consistent manner for alignment. If shifted forward or aft circumferentially it will effect a slight sweep. Any sweep will tend to increase torsional deflection under load and reduce performance. Each block could be centered on a line through the center of the hub. A possibly simpler and better method would be to align the bottom of each block flat with the back of the hub and centered on a plane through the propeller shaft. This will tend to compensate for any forward axial coning under load. Finally, shape the leading edge radius accurately and keep the trailing edge squared off, not rounded. CONSTRAINT VALUES MEASURE THE SUCCESS OF THE OPTIMIZATION. EQUALITY CONSTRAINTS ARE SATISFIED WHEN = 0 INEQUALITY CONSTRAINTS ARE SATISFIED WHEN >= 0 TYPE: EQUALITY = 0, UPPER BOUND = 1, LOWER BOUND = -1 SYSTEM CONSTRAINT VALUES: NAME TYPE ACTIVE INACTIVE REQUIREMENT THRUST=DRAG 0 -0.6813E-08 SATISFIED CRUISE SHP=HPA 0 -0.7697E-08 SATISFIED CLIMB SHP=HPA 0 -0.5582E-08 SATISFIED ALPHA>=ABMIN -1 2623. SATISFIED CLIMB RATE>=RCLM -1 0.1443E+07 SATISFIED PAYOFF= 393.897 (-VCRS) TRIAL RUNS = 906 PROP OPTIMIZER (tm) v1.95 Copyright 1994 Donald R Bates - All Rights Reserved BATES ENGINEERING, 2742 Swansboro Road, Placerville, CA 95667 Phone/FAX 916-622-1886 Registered Owner: Nigel Field Copy Date 12/27/94 --=====================_889204727==_ Content-Type: text/plain; charset="us-ascii" --=====================_889204727==_-- Date: Mon, 9 Mar 98 7:56:27 EST From: "Nick J Ugolini" Subject: PROP-FAB: Re: Lee Lee wrote: I was wondering how your prop is doing. Do you think it's a big improvement over the one you had on there? I have been busy lately with some other things and haven't gotten back to carving mine yet but I hope to get the blades roughed out this week. How did you handle the prop extension? Did you cut off the centering boss? --------- Hi Lee, I machined the prop extention boss off. It only took me about 20 min. The "crush" seems to have stabilized and torque remained the same after a few more flights (prop TT 8 hrs). One thing I noticed on inspections is some deformation where the prop and the extention meet (a ring recessed a little more on one side than the other). I want to check the tracking again, and remove the paint to see what is going on. I THINK it may just be that I put to many coats of paint on the face and the heat and pressure caused the ring, but I will let you know. I plan to put two more layers of glass on the face. When you adjust your tracking you have to build up the face with some Flox and then mill and sand most of it off. That may be part of the problem, I dont know but I will after tonight... I will let you know. >Do you think it's a big improvement over the one you had on there? I changed the 3 blade prop out last week and put the AD back on for a trip to Florida. One thing I noticed with my old 2 blade prop is it is a cruise prop. It needs to get up to 35-40 knots before it really starts to bite and even then it is not much, BUT the top speed is 160 knots. I am now taking very accurate measurements at various altitudes at different manifold pres (.5 in) and measuring my speed, fuel burn, rpm etc... Our 3 bladed design is definitely a climb prop. It kicks major ass on take off roll and climb and yet still gets me up to 154 knots. It is MUCH quieter am smoother. Since it spins at a higher rpm my fuel burn is up (almost .75 gal/hr). When I put it back on the plane, I will take the same manifold/speed/rpm readings, and send them to you. I would highly recommend changing your prop design calcs to optimize the cruise aspect of the prop. Take off is a little too good, and I would prefer better cruise speed and decreased rpm. With Nigel's help, we could change a few assumptions in the programs and get a better prop fit to our planes. I am planning to buy the wood tonight for my "cruise prop". I have a totally different idea on how I will build my next prop. Hopefully, it will take much less time to build... Nigel, What information can I give to you to help optimize Lee's and my next prop for cruise given we now have a starting point to work with? Thanks... Take care everyone...... Date: Mon, 9 Mar 98 9:04:52 EST From: "Nick J Ugolini" Subject: PROP-FAB: Blade sweep Nigel could you further explain > If you want more CS effect you need to sweep the blade back a little more from the radial line. But that will only lower your cruise RPM when you reduce torque and it will still over speed at full throttle on the deck. Do you mean: keeping the radial line and the trailing edge parallel, increase the distance between the radial line and the trailing edge. Or rotate the blade at some point (lets say sta 16) on the radial. How did you do your? Nick From: Lee Devlin Subject: PROP-FAB: Blade sweep Date: Mon, 9 Mar 98 12:49:06 MST Nick wrote: > Nigel could you further explain > > If you want more CS effect you need to sweep the blade back a > little more from the radial line. But that will only lower your cruise RPM > when you reduce torque and it will still over speed at full throttle on the > deck. > > Do you mean: keeping the radial line and the trailing edge parallel, > increase the distance between the radial line and the trailing edge. Or > rotate the blade at some point (lets say sta 16) on the radial. To get sweep, I first aligned a radial from the centerline of the hub to meet with the midpoint of the end station's chord and made the trailing edge parallel to this radial. This would be 0 sweep. Then I rotated the blade (with respect to the center of the hub) back about 2 degrees to allow radial to intersect the end station at the leading edge. If you want more sweep, you can rotate it even further back, although too much is likely to set up some significant stresses at the hub/blade intersections which tend to move the blade's cg back toward a radial on the axis of rotation, especially at high RPM. In taking a closer look at Nick's CAD drawings, it appears that he aligned the radial with the leading edge of the end section by shifting the whole blade laterally on a radial line about 1 inch. This may have achieved a similar effect as rotating it, but it's hard to know. It's not clear to me how the sweep enhances the constant speed properties of the prop, but I'll trust Nigel's experience that it does. I am making a some further progress on my prop. You can see some of it at the URL below. I made 3 'practice' blades before making my latest prop, although that wasn't my intention. Seems that the prop made with my original blades would have worked if my engine was on the front, or if I was running an auto conversion spinning clockwise :-). Oh well, if I decide to finish it, I can always install it if I want to do a lot of backward taxiing. My wife thought it would make a good wall clock. My latest goal is to carve the cambered part of the blades with a CNC machine. This proved to be the a time-consuming, iterative process on the practice blades. I'll still do the bottoms and the hub blending by hand. I'll keep the list posted on how this works out. Lee Devlin http://members.aol.com/lee810 From: Lee Devlin Subject: PROP-FAB: CNC blade carving Date: Mon, 9 Mar 98 18:19:07 MST We cut my blades today on the CNC machine and it worked out extremley well. The CNC machine does a beautiful job and it took about 1.5 hrs per blade. This would obviously be expensive, but we did it as a 'learning' project so there was no cost. It sure got a lot of enthusiastic interest from our MEs. We only carved the cambered section up to station 3 and I will blend the rest into the hub by hand. I also intend to carve the flat side of the blade by hand. When I get some pictures of the carving process, I'll put them up on my Web page. Lee Devlin http://members.aol.com/lee810 From: Lee Devlin Subject: PROP-FAB: Enhancing Crush Resistance Date: Mon, 9 Mar 98 18:38:09 MST I was thinking of some possible ways to add 'crush resistance' to the hub of my prop. One possibility, suggested by Nick, was to extend the flox pads that are called out around the bolts right through the hub. I was also considering drilling a number of .25" holes through the hub and filling them with flox. This would have the effect of producing pillars which would be a lot harder than the soft pine and would get anti-buckling support from the wood. The goal is to avoid point loads so that the the force can be spread out as smoothly as possible. I also considered aluminum dowels floxed into the hub but was worried that they would be so much more rigid than the wood that they would essentially end up taking all the crush load. Any other suggestions? Lee Devlin http://members.aol.com/lee810 From: SWrightFLY Date: Tue, 10 Mar 1998 08:00:47 EST Subject: Re: PROP-FAB: Enhancing Crush Resistance In a message dated 98-03-09 20:39:57 EST, ldevlin@hpgrla.gr.hp.com writes: << Any other suggestions? >> Why not make the hub from hard maple....or anything that is similar in density.........? I feel this would be easier that all the flox pillars which I do not think will work as the surface area that takes the crush loads would be to small. Steve Wright Date: Tue, 10 Mar 1998 21:28:02 -0500 (EST) From: Nigel Field Subject: Re: PROP-FAB: Re: Lee At 07:56 AM 3/9/98 EST, Nick wrote: ....... > > When you adjust your tracking you have to build up the >face with some Flox and then mill and sand most of it off. That may be >part of the problem, I dont know but I will after tonight... I will let >you know. I think the flox may be the problem, mine has no flox on the hub, made of softer pine and has not crushed at all with 30 ft lbs bolt torque. > > >Our 3 bladed design is definitely a climb prop. It kicks major ass on take >off roll and climb and yet still gets me up to 154 knots. It is MUCH >quieter am smoother. Since it spins at a higher rpm my fuel burn is up >(almost .75 gal/hr). When I put it back on the plane, I will take the >same manifold/speed/rpm readings, and send them to you. Yea it sure sounds like a climb prop. It needs some more pitch. Wish I could see, touch, feel it and compare it to mine, its a bit hard to evaluate just what it needs by Email. > >I would highly recommend changing your prop design calcs to optimize the >cruise aspect of the prop. Take off is a little too good, and I would >prefer better cruise speed and decreased rpm. With Nigel's help, we >could change a few assumptions in the programs and get a better prop fit to >our planes. I am planning to buy the wood tonight for my "cruise prop". > I have a totally different idea on how I will build my next prop. >Hopefully, it will take much less time to build... > >Nigel, >What information can I give to you to help optimize Lee's and my next prop >for cruise given we now have a starting point to work with? Thanks... Just post your best flight data for both your props and we can review and discuss it, then run some new numbers. I think the thinner tips are skewing the blade drag data a little so it is running faster. Mine came out a little high also but only slightly. Lee if you have not yet joined your blades, based on Nicks results you may want to angle the root flox joints to increase your blade angles by 2 degrees. This will give a slightly uneven hub face but just mill it flat in a drill press with a mill cutter or router bit at high RPM, slide the hub around on the table then do the other side to get them flat and parallel. ...... and Lee wrote: >We cut my blades today on the CNC machine and it worked out extremley well. The CNC machine does a beautiful job and it took about 1.5 hrs per blade. > Green with envy, wish I had access to one of those. Thats the way to make blades. >I was thinking of some possible ways to add 'crush resistance' to the hub of my prop. One possibility, suggested by Nick, was to extend the flox pads that are called out around the bolts right through the hub. I was also considering drilling a number of .25" holes through the hub and filling them with flox. This would have the effect of producing pillars which would be a lot harder than the soft pine and would get anti-buckling support from the wood.> I agree this may help if there is still a problem. I am at a loss to suggest anything better. I think the input data could be adjusted to better match the LE. The flat plate drag could be lowered about .2 ft sq and the HP curve increased about 5 HP. You may want to try those numbers in propopt and see if it gives a bit more pitch and possibly wider blades. Once we get one right on then the data will be there. Lee wrote: >Seems that the prop made with my original blades would have worked if my engine was on the front, or if I was running an auto conversion spinning clockwise :-). Ya know I did the same on my first blade, I cut it backwards, it would work on your engine though. Perhaps the diagram was confusing as I think I drew it for reverse rotation as in my application. Great to hear the progress and problems. Not sure there is much more that I can add from here, have passed on what I learned and you guys are up to speed. From here it is just pass around data and new ideas and move forward. My next will start soon as I get my engine back in this WE and plan a few improvements based on the group discussions. Lee please keep up the reports. Now if I can just get one of the Contractors that I deal with in my day job to let me into his CNC shop -:) . Cheers, Nigel From: Lee Devlin Subject: PROP-FAB: Climb vs. Cruise Date: Wed, 11 Mar 98 8:36:16 MST I looked at Nick's numbers and feel that the prop would still be much better than what I have on at the moment. I'll try this from memory, my numbers on my current prop (a B&T 66x62) are: 2250 RPM Static 2650 132 Kts TAS 2750 137 " " 2850 142 " " 2950 147 " " (full throttle) This is at around 7000' Density Altitude. I like to cruise at around 2650 to keep the noise down and the RPM below redline so my prop is really not so good. My prop seems to be neither a cruise nor a climb prop since it doesn't get off the runway much faster than my friend's Great American 62x62 and he is at least 10 kts faster at 2650 than I am at 2950. His static is 2350. The GA (no longer available) is made of hard rock maple and its airfoil is much thinner than mine, especially at the tips. I may attempt to add a little more twist in mine, but may instead elect to do a separate cruise prop. Climb performance can be a matter of life and death, whereas additional 5 kts. of top end speed is purely for vanity :-). Lee Devlin From: Lee Devlin Subject: PROP-FAB: Foam blades Date: Wed, 11 Mar 98 9:07:55 MST Nick wrote in an earlier posting about making foam blades. It may be possible to hot wire the cores using a miniature hot wire saw and cutting the blade in small (~3.2") sections. Then they can all be microed together. The twist can be set on a helical surface (made using Nick's band saw technique) by laying up the bottom and weighing it down on the helix while it cures. Then the top can be blended into shape, laid up, and cured in the same fixture. Lee Devlin Date: Thu, 12 Mar 1998 10:41:10 +0200 From: Rego Burger Subject: PROP-FAB: PITCH Can someone please explain to me or send me a sketch ( via scanned image ) on how to determine or calculate the angle that makes up the pitch on a prop blade. It is normally indicated in inches eg. 58" pitch... this will have different angles at various stations from hub to tip? How do I do this? Regards Rego Burger, web site: http://home.intekom.com/glen/rnb.htm (home e-mail) mailto:rnb@intekom.co.za RSA Date: Thu, 12 Mar 1998 14:00:34 +0200 From: Rego Burger Subject: Re: PROP-FAB: PITCH -Reply OK! I've got the base and the height now!? 1.)The stations do I take them from the "centre" of the base ( circum.) to work out the angles at stations for half a blade? or 2.) Do I use the whole baseline div. 10 and transpose those angles to 10 stations on half a blade? Be patient..I'm learning here... :-) Rego >>> "George A. Graham" 12/March/1998 01:43pm >>> On Thu, 12 Mar 1998, Rego Burger wrote: >>>snip>>>>There is a really simple method in the Clutton book. From my memory, you calculate your pitch desired - how many inches forward per revolution. Then use that number as the height of a triangle. The circumference of your prop is the base of the triangle. You can calculate or measure the angles of the hypotenous (sp?) on the base at each station - usually tenths on the base line up to the top of the verticle pitch line. Just divide the base (circumference) line into tenths, then draw a line from each tenth up to the top of the pitch line. I have the book here somewhere. George Graham ca266@freenet.buffalo.edu (716) 874-3277 Modified Eracer - Mazda Powered Date: Thu, 12 Mar 98 7:12:03 EST From: "Nick J Ugolini" Subject: re: PROP-FAB: Foam blades >foam blades The distance is so short (I had thought about hot wire..band saw...) and felt that sanding foam would be the easiest... I will have some good numbers on Friday (flying to ATL) and plan to rerun prop op. My prop results came out almost EXACTLY by the predicted number. Yesterday, I was climbing at 12-1300 ft/min 85 mph and my top speed was 154kts. I was very careful in my construction and my prop is built exactly according to the model... The crush problem turned out to not be a problem. The paint crushed under the heat and pressure and is now not changing. 8.5 hrs on the prop and it is fine..... ------------- Original Text From: "Lee Devlin" , on 3/11/98 11:07 AM: Nick wrote in an earlier posting about making foam blades. It may be possible to hot wire the cores using a miniature hot wire saw and cutting the blade in small (~3.2") sections. Then they can all be microed together. The twist can be set on a helical surface (made using Nick's band saw technique) by laying up the bottom and weighing it down on the helix while it cures. Then the top can be blended into shape, laid up, and cured in the same fixture. Lee Devlin Date: Thu, 12 Mar 1998 08:41:07 -0500 (EST) From: "George A. Graham" Subject: Re: PROP-FAB: PITCH -Reply On Thu, 12 Mar 1998, Rego Burger wrote: > OK! I've got the base and the height now!? > 1.)The stations do I take them from the "centre" of the base ( circum.) > to work out the angles at stations for half a blade? > or > 2.) Do I use the whole baseline div. 10 and transpose those angles to 10 > stations on half a blade? Yes, use the entire base, the tip (100 percent radius) will be at the end of the base (cir) line. Then divide up the whole line into tenths for the stations. Station zero, will be straight down the right triangle, and the pitch angle will be ninety degrees. I am painting the plane now. Am about to cover my maple prop blades with BID and install a JB Weld leading edge. Sorry, no scanner ( no windows,mouse,or graphics either, 1983 technology) George Graham ca266@freenet.buffalo.edu (716) 874-3277 Modified Eracer - Mazda Powered Date: Fri, 13 Mar 1998 07:42:12 +0200 From: Rego Burger Subject: PROP-FAB: PITCH -3 I'm a slow learner, that's a nice term for thick! George wrote: >>>Almost, full prop dia times pi (the circumference). The most distant point will be station 100. and the angle will be somewhere around twenty degrees.<<< Ah! I messed up again....not reading too well, see why the readback...Circumference is much larger than Dia. I was sitting with sum mean angles here, they would make good oars for a row-boat. Q.)Now station 100 , is that the tip of ONE blade the other being a mirror image? Thanks for the education George! Rego Burger, web site: http://home.intekom.com/glen/rnb.htm (home e-mail) mailto:rnb@intekom.co.za RSA Date: Tue, 17 Mar 1998 12:51:32 -0500 (EST) From: "George A. Graham" Subject: PROP-FAB: balance There was a thread on prop balance in RAH, but I'd rather stay off it However, I do have a balance problem. I used a 3/4 inch tube through the prop hub which would roll on a couple of straight edges, to get my prop in balance. This setup was very accurate as the smallest amount of paint would throw it off ( it is a two blade). I ran the prop which seemed ok, but I noticed that the 3/4 inch hole had a wobble ! I stuck the tube into the hole, then held a marker up to the tube as it was spinning. The hole is accurate between the tips, but is about .030 off to one side of the prop. I then made a PSRU that does not have the gears in, but does have the prop hub and good bearings. Sure enough, the prop balances good when the blades are horizontal, but it will not stand up straight. It leans over to 11 and 5 oclock position, maybe 10 and 4 sometimes. So now, maybe that is ok, maybe the hole being off goofed it up, I don't know. I've tried sanding on the hub but that does not seem to alter it. If there was a bolt exactly centered between the blades, then I could add an extra washer, perhaps I should drill a hole and add weight ? I did recheck that the blades are 180 degrees apart, looks good. George Graham ca266@freenet.buffalo.edu (716) 874-3277 Modified Eracer - Mazda Powered From: "Hunter GA (Gary) at MSXSCC" Subject: RE: PROP-FAB: balance Date: Tue, 17 Mar 1998 15:44:53 -0600 Hi George - it's me again. This is a fairly common form of defect in propellers that won't balance. If in fact, the 3/4D hole is off-center, AND it was used to align the drilling guide for the prop bolts and/or the counter bore for the shaft flange bosses you may never get it balanced. It is possible to static balance it, but dynamically, it may not be acceptable. It all depends on how bad it is off. Your's doesn't sound that bad. But, if the actual center of the prop bolt holes and the counter bore are correct, then you can definitely balance the prop hub as follows. As you have already experienced, you can static balance it with trial weights in the bolt holes. After you have balanced it and established where and how much weight needs to go, total up the weights on a scale. If it is more than say 50 grams, it is getting pretty excessive and you may want to resort to plant "B" for fixing the off-center situation proper. Plan "A" -If the weight necessary it is not excessive, you can drill a 1/4D hole in the hub near the bolt hole or between the bolt holes as deep as is necessary. Gather up out some old fishing weights or wheel weights from you car tires and melt them down until you have a little more weight than is needed to balance the prop. Clean off the slag and pour the molten lead directly into the hole you drilled in the hub. Check the balance and see how far you missed it. If it came out too heavy - you can drill out some lead. Too, light - add some more. When all done - take a drift and give the lead a good shot with a hammer and squash it into the hole a little bit. It tends to shrink away from the wood and squashing it this way expands a portion of it to keep it from rattling around in the hole. I have done this to many props with success. Plan ''B" - recentering the prop. - pretty obvious what needs to be done here. And, there are all kinds of ways to do it. The most important hole to center is the 3" or so counter bore that fits over the boss on the prop flange or extension if you have one. This 3" counter bore is what really centers the propeller. I have a few ideas on how to do this. The simplest to me is to put back everything that was bored out. Glue wooden plugs back in the 3/4D and the 3D counter bore and start over. You can elongate the counter bores for the prop lugs with a dremel drum sander or so. The bolt holes can be simply opened up to a larger diameter. Gary Hunter - Crew Chief - Pushy Galore EAA Technical Counselor Vari-Eze - N235GH gahunter@shellus.com > ---------- > From: George A. Graham[SMTP:ca266@freenet.buffalo.edu] > Sent: Tuesday, March 17, 1998 11:51 AM > To: prop group > Subject: PROP-FAB: balance > > > There was a thread on prop balance in RAH, but I'd rather stay off it > > However, I do have a balance problem. I used a 3/4 inch tube through > the prop hub which would roll on a couple of straight edges, to get my > prop in balance. This setup was very accurate as the smallest amount of > paint would throw it off ( it is a two blade). > > I ran the prop which seemed ok, but I noticed that the 3/4 inch hole had > a wobble ! I stuck the tube into the hole, then held a marker up to > the tube as it was spinning. The hole is accurate between the tips, > but is about .030 off to one side of the prop. I then made a PSRU > that does not have the gears in, but does have the prop hub and good > bearings. Sure enough, the prop balances good when the blades are > horizontal, but it will not stand up straight. > > It leans over to 11 and 5 oclock position, maybe 10 and 4 sometimes. > So now, maybe that is ok, maybe the hole being off goofed it up, I > don't know. > > I've tried sanding on the hub but that does not seem to alter it. > If there was a bolt exactly centered between the blades, then I could > add an extra washer, perhaps I should drill a hole and add weight ? > > I did recheck that the blades are 180 degrees apart, looks good. > > > George Graham > ca266@freenet.buffalo.edu > (716) 874-3277 > Modified Eracer - Mazda Powered > Date: Tue, 24 Mar 98 16:39:58 EST From: "Nick J Ugolini" Subject: PROP-FAB: Gen questions I have been thinking about the prop 2 I have started starting biulding and have a few general questions. How do you determine the center of lift for an airfoil (RAF)? Does the COL change with airspeed? When trying to establish baseline performance, Will it be consistant when you use Density Altitude? As temp and pres changes would I think it would be the only way to relate prop performance. I plan to build my next prop a bit differently. Using a hard wood prop hub and foam blade cores. Update: The first prop's crush has stablilized. Now at 25 hrsTT working very well. Date: Tue, 24 Mar 1998 22:36:24 -0500 (EST) From: Nigel Field Subject: Re: PROP-FAB: Gen questions At 04:39 PM 3/24/98 EST, Nick wrote: >I have been thinking about the prop 2 I have started starting biulding and >have a few general questions. > >How do you determine the center of lift for an airfoil (RAF)? >Does the COL change with airspeed? > >When trying to establish baseline performance, Will it be consistant when >you use Density Altitude? As temp and pres changes would I think it would >be the only way to relate prop performance. Nick these are good questions which are right on the edge of my limited knowledge. I believe the centre of lift for an RAF 6 or similar airfoil is at the 25% chord point from the LE. As for changes with density altitude I dont think it will move but I'm not really sure. I rely on Propopt to do all the calcs as the theory is out of my range. Marc Z may know this, or perhaps Bill Kleb from the Cozy list, I think he works in that field at NASA. > >I plan to build my next prop a bit differently. Using a hard wood prop hub >and foam blade cores. Nick you need to think real hard about this. I don't like the idea of foam blade cores very much as I don't think it will stand up to the torsional and longitudinal blade flexing. Now it may work, I believe Hartzel (sp) make a carbon one with dense foam cores and I have an application note around somewhere which describes it, if I find it will fax it to you. Nick please research this carefully and get some engineering advise first, Marc can you give us some words here. The question is why, what are you attempting to achieve by using foam? You understand of course the seriousness of a blade failure in flight, my friend had one last summer in a Lancair and barely got away with his butt in one piece, his airplane is in many pieces and will never fly again. This was a NSI controllable pitch 3 blade BTW which threw a blade at 2.5 hrs TT. > >Update: The first prop's crush has stablilized. Now at 25 hrsTT working >very well. > Good to hear Nick, been thinking about your data a bit, seems its doing exactly what was planned, in giving improved low speed thrust for TO and climb. The cruise should be a little better though so a bit more pitch or area on you next one. Nigel From: SWrightFLY Date: Wed, 25 Mar 1998 08:49:15 EST Subject: Re: PROP-FAB: Gen questions In a message dated 98-03-24 22:40:19 EST, nfield@magma.ca writes: << I don't like the idea of foam blade cores very much as I don't think it will stand up to the torsional and longitudinal blade flexing. Now it may work, I believe Hartzel (sp) make a >> With this design........It was my understanding the material in the blades only takes compression loads so even balsa wood would work well but soft pine is plentiful and cheap and works well so why not use it? Steve Wright From: Marc J. Zeitlin Subject: Re: PROP-FAB: Gen questions Date: Wed, 25 Mar 98 9:14:36 EST Nigel wrote; >.... I believe the centre of lift for an RAF 6 or similar airfoil is >at the 25% chord point from the LE....... For Clark Y and other airfoils of it's ilk, 25% is a reasonable estimate. The COL position can be calculated from an integration of the lift distribution over the airfoil top and bottom surfaces, or else it can be measured experimentally in a wind tunnel. I believe that the airfoil books list the COL position for each airfoil described, although I might be mistaken. I seem to remember seeing that # with the L/D vs alpha curves as well as the moment curves, but it's been 20 years since I did that research ...... >..... Marc Z may know this...... Or he may not, and just make up something that sounds good :-). >>I plan to build my next prop a bit differently. Using a hard wood prop hub >>and foam blade cores. > >Nick you need to think real hard about this......... Marc can you >give us some words here. This is completely from the seat of my pants, but I wouldn't see anything wrong with it in PRINCIPAL, but it would take a lot of experimentation to get it right. You'd want some 45 degree BID wraps to take the torsional stress (how much? who knows). One other thing the wood does is act as a damper to absorb vibration - I doubt the foam will do that. I don't remember what you've got for an engine - maybe on an O-235 it wouldn't be an issue. On an O-360, I'd be more concerned. >...... The question is why, what are you attempting to >achieve by using foam? This is a good question. Unless there's some LARGE gain from it (weight maybe? ease of construction wouldn't register for me on a safety issue), I'm not sure I'd experiment in this manner. However, if you do, I'd spin the thing at 3500 RPM or more for a long time before taking it into the air, and then stay close to the airport for a while. -- Marc J. Zeitlin Email: marcz@an.hp.com From: Lee Devlin Subject: PROP-FAB: Ground testing to 3500 rpm? Date: Thu, 26 Mar 98 10:13:55 MST Marc wrote: > This is a good question. Unless there's some LARGE gain from it (weight > maybe? ease of construction wouldn't register for me on a safety issue), > I'm not sure I'd experiment in this manner. However, if you do, I'd spin > the thing at 3500 RPM or more for a long time before taking it into the > air, and then stay close to the airport for a while. How can you spin it at 3500 RPM *without* taking to the air? The static RPM on these props is around 2300 RPM and the HP required to spin it faster just isn't available. I don't have any spare engines laying with 2.5 times the HP of the one I'll have on the plane, which is what I believe is needed to get 3500 RPM static. Anyone have any clever ideas? Lee Devlin LongEZ 36MX http://members.aol.com/lee810 Date: Thu, 26 Mar 1998 15:07:37 -0500 (EST) From: "George A. Graham" Subject: Re: PROP-FAB: Ground testing to 3500 rpm? On Thu, 26 Mar 1998, Lee Devlin wrote: I don't have any spare engines laying with > 2.5 times the HP of the one I'll have on the plane, which is what I > believe is needed to get 3500 RPM static. Anyone have any clever ideas? Just try it Lee. I tried to make a pattern blade from blue foam. Gave it up aand went to pine. I found the foam too flimsy to hold its form while shaping. You'd need to carve one flat side and glass it, then carve the other side, it seemed more work than it was worth, and not likely repeatable. But Hey, it's an experiment right ? George Graham ca266@freenet.buffalo.edu (716) 874-3277 Modified Eracer - Mazda Powered Date: Fri, 27 Mar 1998 06:46:01 -0500 (EST) From: "George A. Graham" Subject: PROP-FAB: pine blade To clarify: I made a pine blade for use as a pattern. With the router driven prop carving machine, you need one blade only to duplicate. That is what I tried to make from foam. My thanks to Gary Hunter for his advice on fiberglassing the blade tips on my maple prop. It is finished now and awaiting ground testing. BTW, I did get it to balance. George Graham ca266@freenet.buffalo.edu (716) 874-3277 Modified Eracer - Mazda Powered Date: Mon, 30 Mar 98 7:43:27 EST From: "Nick J Ugolini" Subject: PROP-FAB: Re: questions << I don't like the idea of foam blade cores very much as I don't think it will stand up to the torsional and longitudinal blade flexing. Now it may work, I believe Hartzel (sp) make a >> With this design........It was my understanding the material in the blades only takes compression loads so even balsa wood would work well but soft pine is plentiful and cheap and works well so why not use it? Steve Wright ---------- I built the first prop out of fir (easier to work nicer grain than pine). It worked (shaped) well, but after competing the prop, I have elected to make a few construction changes in my next prop. The hub will be partially hollow (weight) where there is no requirement for strength. I plan to cut the bottom of the blades with a mini hot wire saw using templates (aka wings), full length wing spars........ Wood shaped ok, but wouldn't it be nice to cut the bottom of the blade to shape in one pass, or the spar grove with a hotwire? Will it work? Heck, I asked myself that question the first time I put the throttle down at the end of the runway and attempted to fly my homemade plane, and again when I took off with my homemade prop. If someone told me in Jan I could build a 3 bladed fiberglass prop using FIR, I would have said they were crazy. Perpective changes with experience. You can bet my life I'll be careful with my foam prop. BTW: for those of you using the Prop Op program, the flat plate area of a LongEZ is 1.85 sq ft. I worked it out a couple of times an kept arriving at the same answer... Nick Date: Mon, 30 Mar 98 10:57:42 EST From: "Nick J Ugolini" Subject: PROP-FAB: Prop Hi Lee, > > I see you're back on line! You must have replaced your home computer? I made my own a 233mhz P2, 64 meg ram, APG video, 64gig, sound card, Recordable CD rom drive for $1450. I love it. Check out the site www.pricewatch.com It is a great resource for pc parts. Funny that both of us are still justifiying our respective decisions made at Oshkosh > last year. When I am rich, I'll get the Bose, for now I'll just make do with > the Lightspeed. I am not rich, just single living a a dump. If I got married, I would have to buy a nice home, upkeep my wife and then I would be poor....... > Did you see my posting on the Minidisc? Yes sound interesting. I use a AM/FM car radio with a cassette. I may have to look into your system.... Although I would like a automotive type radio. I like listening to NPR in the mornings on my trips. > I made the center spindle on a lathe at work per your drawing on Friday. I > forgot to ask you how well it worked for you. Was the balancing of the prop > made easy with the adjustable screw? DESIGN CHANGE: The original idea worked VERY well, although I have modified my design for the balance to increase sensitivity, alignment and ease of construction. It came from another design (the BUZZ Ballancer). Much easier to do, and probably more accurate (less friction). This is the way..... Wait until your prop is built prior to drilling the final hole in the spindle (if you have drilled an alinment hole for the drill templates youre good to go). After the prop is built AND THE TRACKING OF THE BLADES has be set, put your small bit in the drill press, align the center hole again, clamp the blade down, and over drill it for a 1/2" threaded bolt size. (the process will insure the hole is now alined perpendicular to the mounting flange (tracking)... sometime the center hole will change during the building process ESPECIALLY if you predrilled the rod before completing the tracking). NOW , tap the bottom of the prop (spinner end) for a 1/2" bolt. Take a 1/2" bolt (about 2-3" long) drill a 1/16" hole on the end (threaded end) about 1/4" deep. Turn it around and drill the head end 3/8" until it intersects with the small hole. Now you have a hollow bolt with a small hole in the end. Thread some fine line (I used fine nylon braded line) in the small hole and tie a knot. DONE Now when you want to balance the prop, thread the line thru the bottom of the prop, thread the bolt in the bottom, and adjust the height until you obtain the sensitivity you want. Hanging the prop instead of supporting it on a point reduces the friction..... I like this method over my original idea because, it aligns the spindle with the tracking, It reduces the friction even more (the stiffness of the line determines the fiction) and is just as adjustable for the location of the CG as my original idea. To check the balancing, I took 3 little (home depot.. $2.00 for two) plastic bubble tubes (removed from plastic line levels), formed them into a triangle and put a drop of RTV on the ends to hold them together. I just put them in the center of the flange with the points toward each blade. It is VERY sensitive. (a 1"sq piece of paper at the blade tip will tip it over). Drill a hole in the flange (between the mounting holes and drop in lead fishing weights, pound down with a punch, and fill the holes back up with epoxy. You are finished. > When are you going to scan some pictures of the prop project and put them on a > web page? Pictures are developed, I will try and get some scaned this week...... Take care. > Date: Mon, 30 Mar 1998 22:44:25 -0500 (EST) From: Nigel Field Subject: Re: fwd: Re: PROP-FAB: Gen questions At 07:37 AM 3/30/98 EST, Nick wrote: >Hi, > >I am finally back home after two weeks.... > >Did you send a message (see below) out about my questions? If so, I never >recieved it. > >The main purpose of my email was does the COL change with airspeed, and >where is the COL on our airfoil shape. Hi Nick, Yes I took a stab at answering it and Marc Z added some comments in another post. I think the concensus was that its at the 25% chord point from the LE and we don't know if it moves with DA but probably not, your out of my range of knowledge here. > >The second on is how do I get consistant data point for my prop/performance >measurements? Does using Density alt mean that my prop/speed and engine >output should be same, so I should get repeatable results? Yes you need a reference DA, pick one you can achieve at any time and in still air, any chop will spoil the data. Then get your first data point at WOT as that is as stable a power reference you can get. Let it settle down for about 3 to 5 minutes before you log any readings, it takes that long to slowly stop accelerating, at least mine does. You need manifold pressure to get other data points as that is directly proportional to engine torque. You cant use RPM as an input as it is a result of speed and loading. For example if you set on say 2500 RPM and measure speed then fiddle with the pitch (major work) and try it again at 2500 RPM you will get a different speed which will be faster if you increased the pitch, but you will be using a higher MAP to get the RPM therefore HP is higher, and only MAP (or a torque meter) will tell you that. So use various MAP setting at the given DA and log RPM and IAS and temp then correct for TAS. Graph that in a SS and see your curves. For climb a stop watch is best, establish your stable climb at a reference IAS and start timing 500 ft below your reference DA that you have calculated prior to flight and stop timing when 500 ft above, from that data calculate ft/min. Try different speeds to get best climb speed and best climb angle. You need to have a reference weight for all of this too if it is to be accurate so try and fuel it to the same weight for each flight. Lots of work getting and making sense of flight data but I find it the best part, I love doing it. If you dont have MAP installed try and borrow or buy one and set it on your lap. I have a 2.25" Mitchel MAP in the panel and set all my power with it, I would give up the tach before the MAP if I had to choose but you really need both. > >I have a spread sheet now with some interesting data if you are >interested.... Would love to have that data if you can FW, can read Lotus and Excel, thanks. Really like your string suspension balancer idea, simpler than mine and probably more sensitive, got to try that. Nigel From: Marc J. Zeitlin Subject: PROP-FAB: Airfoil software - Cp calcs, etc. Date: Wed, 1 Apr 98 13:16:33 EST People; Nick was recently asking about calculating the Cp for airfoils - there's a web site with some relatively cheap (or free, even) software that can do this sort of stuff. Check out: http://www.hanleyinnovations.com/ The guy's got an M.S. and PhD. from MIT, so he must know what he's doing, right? :-). -- Marc J. Zeitlin Email: marcz@an.hp.com Date: Wed, 01 Apr 1998 15:12:05 -0500 From: Nick Ugolini Subject: PROP-FAB: RE: Lee In the first prop after construction I found the centerline of the shaft to be a bit off. This in addition to the tracking adjustment (and reading others prop owners with centerhole misalignment) caused me to rethink my original construction methology. Originally, I drilled the rod, inserted it into the hub after floxing the blades together. Glassed all the blades, drilled the mouning hub holes painted and balanced. My new thoughts are to: build the hub, drill the rod with an alignment hole for the drill guide, drill all the holes for the mounting flange (including the bolt holes). Cut the bottom of the blades (the flat side), attach them to the hub and glass the bottom of the prop ***Be sure to add a 1/8" layer of flox to the hub prop to covering with peel ply. When hard, remove peel ply turn the prop over (unglassed part on the drill press) and machine (I used a fly cutter) the floxed hub until you just begin cutting into the BID. This will insure the upper and lower surfaces are parellel. Shape the top of the blades, and glass, add 1/8" flox and machine as you did the bottom of the blade. Check the tracking. You will find it necessary to sand the hub a bit to correct the tracking. Mine is +/- .020". Will your center rod be perpendicular with the flange? If you drill after construction it will be. Using the pivot point type of balance worked well for me, but I think hanging the prop is better. I think your rod will still work, all you need to do is to find a bolt that will tread into the hole you will have when you overdrill your rod after you complete the prop. Thread the rod and drill the bolt and youll be set..... I hope this explains it a little better for you... Nick Nick LongEZ N29TM Cozy III (under construction) Date: Wed, 01 Apr 1998 21:37:13 -0500 From: Nick Ugolini Subject: PROP-FAB: Re: Lee Lee, I spent a little time thinking about your prop balancing (since you have already drilled the rod). Your problem has lead me to an easier answer to the balance issue. Instead of threading the center rod, I will just drill it to 1/2", (yours is already done) build the balancing bolt, and place a adjusting nut on the balancing bolt. This way you won't have to thread the rod, and you can still adjust the pivot point. Actually I like this way better, because once you get the balance sensitivity point set, the whole bolt and adjusting nut can be slid in or out of the prop as a unit.... If you will send my your fax number, I can hand draw you the bolt assembly.... Take care, Nick LongEZ N29TM Cozy III (under construction) Date: Tue, 7 Apr 98 8:33:38 EDT From: "Nick J Ugolini" Subject: PROP-FAB: Balance I had a few questions about my post on balancing the prop. Here is my latest update. I made another balancer for my prop last night in about 10 min that works much better than my first one. Went to home depot, and purchased a 1/2 X 2" nylon bolt (they now stock them) for $1.05. The end had a dimple on it (perfect for a center drill). I drilled a hole 1/8 x 1/2" deep in the end then cross drilled a 3/16" hole to intersect the 1/8" hole (about 3/8" from the end). I then inserted a 1/8" nylon string into the end and out the cross hole and tied a knot on the end and pulled the knot back into the cross hole..... It ends up looking like a bolt that is hanging by a string by the threaded end... I also purchased a nut to adjust the pivot point, but found washers did a better job. My prop has a 1/2" center hole in the Al rod that the filaments wind around. I just threaded the string through the hole and hung the prop up. Adjusting the balance point (the point of balance in relation to the centroid of the prop) was achieved by slipping washer onto the bolt prior to threading the string through the hole. Use AN washers because you can buy VERY thin ones..... As little as a 1/32" can make a difference. You will know when you have added too many washers, when you can tilt the prop over (in any direction), let it stabilize and it will stay there. Back off on the washers until it will just fall toward the heavy side. The balance is so sensitive a 1"sq of newspaper will cause a noticeable change. To indicate level, I took 3 bubble levels from home depot (cheap line levels, cut away the plastic case to remove the bubble vial, arranged them in a triangle, and RTV'd the ends. I place the level with one point toward each blade. Very Accurate. I tested my original balancing idea (pivot point on a machined cup) and the string balance. The string is much more sensitive. Good luck with your props.... Date: Fri, 24 Apr 98 8:48:03 EDT From: "Nick J Ugolini" Subject: PROP-FAB: Prop Hi, Just got back from SNF, and I wanted to give you a few thoughts.... Prop has 40hrs working great.... Refinished it (again 2x so far) because the paint wasn't holding up. This time I used PPG DCC (2 part poly), metallic with white tips and 3 coats of clear. Looks just like a metal prop. I found that the Al tape leading edge did not hold up in heavy rain. On the newly refinished prop I tired using the 3M leading edge wing tape (16" long, 1"w tapering to .5" wide) When placed on the prop and stretched about .5" it naturally folded itself around the prop with NO wrinkles in it. I was amazed.. It become completely invisible! VERY sticky and will remain flexible forever. I then took some clear coat to seal the edges and tapered the clear back about .25 in. Sand/buff and the seam of the tape disappeared. Worked very well.... When you all build your props I would recommend the possibility of building into your prop a leading edge of the JB weld.. I couldn't do that because my prop is completed. Doing it again I would flatten the leading edge slightly from the tip to about 16-17" in, glass everything, then build up with JB. Reshape. I believe it would be better than the Al tape.. Less expensive than the 3M tape (unless you already have it like I did..) Looked at that prop carving machine.. Worked very well. I was amazed to hear the designer saying that it took him 6 full time weeks to carve 1/2 prop (master blade) to use in the duplicator. It took 4 weeks to get my prop flying...?? Looked at the IVO props. Talked with him and asked so many questions he looked at me and said "you aren't a prop builder are you?" Of course I said "Geezz, I could never do that!" He builds his cores out of micro, poured into a mold. The steel rod for adjusting the pitch is coated with teflon prior to placement in the mold. The thickness ratio is constant (as well as the width) for the length of the blade, also there is very little helix twist along the length of the prop. Since his leading edge is straight, he used soft SS foil with adhesive on it for his leading edge protection. UOO UUOO, I would also recommend making our blades a bit thinner...(like IVO). Klaus said for a prop the ratio should be 10% (thickness of the blade in ratio to the cord). Our blade design program is based on a wood prop strength. It would be a simple matter to thin the blade past the hub. (station 9). Of course when Klaus Savor? (Lightspeed) looked at my prop at SNF...well "it is too flexible, too thin, will cause too much drag (reduced glide ratio if the engine quits), less efficient," yada yada yada...and his 2 blade will run just as smooth as my 3 blade????!!! I guess it is just Klaus's way. Next time I am flying at 155 kts I will have to tell my prop it is not supposed to working so well.... From: lschuler@cellular.uscc.com Date: Fri, 24 Apr 98 11:41:10 -0600 Subject: Re: PROP-FAB: Prop Nick J Ugolini wrote: >snip >Looked at the IVO props. Talked with him and asked so many questions he >looked at me and said "you aren't a prop builder are you?" Of course I >said "Geezz, I could never do that!" He builds his cores out of micro, >poured into a mold. The steel rod for adjusting the pitch is coated with >teflon prior to placement in the mold.... >snip I'm still toying with the idea that the core of Nigel's glass prop doesn't enter in the stress analysis. As an alternative to wood or foam, IVO's micro is interesting. Seems to me though, that micro is a lot more brittle that either wood or say an 18 Lb PVC foam. Just thinking out loud... Thanks for the nice report. Very informative. Larry Schuler lschuler@cellular.uscc.com Date: Fri, 24 Apr 1998 18:38:47 -0400 (EDT) From: Nigel Field Subject: Re: PROP-FAB: Prop At 08:48 AM 4/24/98 EDT, Nick wrote: >Hi, >Just got back from SNF, and I wanted to give you a few thoughts.... > >Prop has 40hrs working great.... Refinished it (again 2x so far) because >the paint wasn't holding up. This time I used PPG DCC (2 part poly), >metallic with white tips and 3 coats of clear. Looks just like a metal >prop. I found that the Al tape leading edge did not hold up in heavy rain. > > Great to hear Nick, the group has been pretty quiet lately. About the tape LE, there seems to be different properties of the stuff out there and I havent been able to tell the difference in the store. My buddy put some on his prop last year and it all came off within a few hours. The adhesive did not bond well and the strips actually slid up the blade a bit from the centifugal load, yet in contrast the stuff I have used holds up very well and is a bear to get off, you have to slice it off with a sharp knife the clean up the blade with varsol to get the adhesive off. I still have nearly a full roll of it so I gave him some and it stayed on also. But I think the JB weld idea is good, I'm addicted to the stuff anyway, use it for lots of things so will try that on my new one for sure. BTW it bonds aluminum better than anything else I have seen so might work to bond on a thin stainless steel strip, just a thought. I think George raised that idea so thanks George looks like a winner. > >Looked at the IVO props. Talked with him and asked so many questions he >looked at me and said "you aren't a prop builder are you?" Of course I >said "Geezz, I could never do that!" He builds his cores out of micro, >poured into a mold. The steel rod for adjusting the pitch is coated with >teflon prior to placement in the mold. The thickness ratio is constant (as >well as the width) for the length of the blade, also there is very little >helix twist along the length of the prop. Since his leading edge is >straight, he used soft SS foil with adhesive on it for his leading edge >protection. Thanks for the info here Nick but between us in the group I have seen so many IVO failures I have lost count, including one I tried about 4 years ago, Phil Johnson saw the result of that experiment after 3 minutes in the air. I would not be inclined to use that prop as the "standard of excellence". > >UOO UUOO, I would also recommend making our blades a bit thinner...(like >IVO). Klaus said for a prop the ratio should be 10% (thickness of the >blade in ratio to the cord). Our blade design program is based on a wood >prop strength. It would be a simple matter to thin the blade past the hub. >(station 9). Yes for sure thinner is better, we have kicked this around a bit before, so thats why I recommend thinning out the tips to about 10% section and use carbon to keep them stiff as thats where it really counts. It makes a big difference as I have discovered in past experiments thinning out the tips on wood props using carbon. > >Of course when Klaus Savor? (Lightspeed) looked at my prop at SNF...well >"it is too flexible, too thin, will cause too much drag (reduced glide >ratio if the engine quits), less efficient," yada yada yada...and his 2 >blade will run just as smooth as my 3 blade????!!! I guess it is just >Klaus's way. Next time I am flying at 155 kts I will have to tell my prop >it is not supposed to working so well.... > Yea he is like that, he told me at Osh 96 my engine would never work, guess he thought I trucked it in?? Obviously he has never flown a 3 blade, or a Subaru :-). Nick thanks for the data back a few weeks ago, I owe you an Email, accept I cant read it for some reason, using Excel but possibly too old a release. Didn't want to bug you about it though. Would really like to have that data if perhaps you could save it as a Lotus file or older version of Excel if you have some time. Anyone else have trouble?? Well I have some non airplane news, well its related I guess. Been pretty busy lately training 2 folks at work to take over my clients and files so I can finally retire. The big day is 1 May, 1 week away so I will be taking the entire summer off to fly and then possibly do some part time stuff under contract in the winter, perhaps, but only if I get bored. I have lots of things to do including getting my Cozy, ah I mean Suze II finished and flying, but right after I make a new prop for my VE and new rear deck on my house, and......, Oh yea, my airplane comes out this WE so be back in the saddle again with a bunch of minor changes and some trials to do, can't wait for that either. Cheers all. Nigel Date: Tue, 28 Apr 98 13:29:27 EDT From: "Nick J Ugolini" Subject: PROP-FAB: Re: prop > snip Nick > I am beginning to believe my next prop will be a ground adjustable stiff 3 > blade. I think it very do-able. >>Snip Lee D. How do you intend to do it? Warp Drive has a rather expensive machined hub with collars that hold the blades. I think you adjust each blade independently with a protractor. Sounds like a pain. The IVO actually twists the blades as I'm sure you saw at SnF. What are you thinking of doing? ------------ Nick I intend to take 3 steel rods, bend one end ~90deg, (blade end) put a bushing on it, and weld a cam on the other end. The cam will go in the hub. I will wrap the rods with teflon tape. Then I will build a hub first with the bushing in the hub with the cam's in the center. I will then build a adjustment bolt ~1" dia that threads in a hole and pushes on the cams. I will build the blades over the rods and glass as per plans with the top and bottom spars terminating over the end of the rods. This way it will have the advantage of a solid hub with blade adjustablity. Another way is to build in the cams, but use 3 bolts to push each rod. Then you can set each blade. More trouble to set, but easier to build. Building a fixed prop is a lot of trouble with an uncertain outcome. The biggest fear I had when I built mine was that I had gone though a lot of work and it wouldn't function properly (especally when you look at how small the blades are). I think I was lucky that everything came out exactly as planned (I was very careful on my measurements). Having some adjustablity (even a tiny bit) could make all the diffence in the world. I really want to get to the point that I can build an in flight adjustable prop. My first step is building another prop with a different core, then a ground adjustable then..... In all cases, I want a solid hub/blade assembly. I am convinced under worst case senerio, the blades may weaken but they will never just fly off, and I think they will give some warning before a major problem. Take care Nick From: Marc J. Zeitlin Subject: PROP-FAB: Three vs two blades Date: Tue, 28 Apr 98 20:34:48 EDT George Graham writes; >I've been thinking about Klaus's statements about three blade props. Whatever that was, other than he thinks two is better than three. >If aspect ratio means anything, then the two blade should have it all >over the three. It has an extra end ! Huh? If aspect ratio was the only criterion, than you'd want an infinite number of infinitely small-chord blades. It's not, and you don't. >Then look at the leading edge drag. Again it has half again as much >leading edge, assuming that the diameter is equal. With our pusher types >limitied in max diameter I would guess that they compare. There's no such thing as "leading edge drag". Not sure what you meant here. >Does anyone have any ideas how the logic works ? Not sure what "logic" you're referring to here. Propeller theory states that the fewer blades, the better, so a single bladed prop (don't laugh, they've been done) is the most efficient. However, there are so many assumptions in this that in the real world it doesn't apply, otherwise all airplanes would have single bladed props. What you want is enough blade area to absorb the power output of the engine, with a diameter small enough to let the landing gear fit on the aircraft (and not have a ridiculous ground angle of attack for taildraggers), while minimizing weight, etc., etc. When all of these factors are accounted for, then a different propeller configuration will become optimal depending upon the aircraft that it will be used on. Very high power aircraft tend to have many blades so that they can absorb all the power and still have reasonable aspect ratio blades. For our canard aircraft, it's clear that both 2 and three blade props can work fine, without a substantial difference in efficiency. Canards tend to use 3 blade props for a _slight_ theoretical efficiency increase (at least according to the "Prop Opt" program, IIRC), but also for the decreased vibration and noise caused by the interaction of the wing wake with the prop blades. Hope this helps understand props - they're just rotating wings, and obey the same rules. -- Marc J. Zeitlin Email: marcz@an.hp.com Date: Tue, 28 Apr 1998 11:02:20 -0400 (EDT) From: "George A. Graham" Subject: PROP-FAB: Three vs two blades I've been thinking about Klaus's statements about three blade props. >From a logical point of view, he seems to be right. If aspect ratio means anything, then the two blade should have it all over the three. It has an extra end ! Then look at the leading edge drag. Again it has half again as much leading edge, assuming that the diameter is equal. With our pusher types limitied in max diameter I would guess that they compare. Looking at the props at Sun-N-Fun, the chord was very wide on Klauses prop, but it was very thin. The three bladed props all had a narrow chord (is short a better word?). I do a twist test on the blade tips, as I noticed a real significant change in mine after adding the fiberglass layup to the tips. Only the Clark Lydec "Performance" props were easy to twist with your fingers. Even Alex Strongs' Wanrake "Constant Speed" prop has stiff tips, as did Carl Denks' new Sensinich (which also had square ends and a thick chord and a camber on the "flat" side). Carl is very happy with it and reported in CSA about the performance. Does anyone have any ideas how the logic works ? George Graham ca266@freenet.buffalo.edu (716) 874-3277 Modified Eracer - Mazda Powered From: lschuler@cellular.uscc.com Date: Wed, 29 Apr 98 09:34:19 -0600 Subject: Re[2]: PROP-FAB: Three vs two blades Gary Hunter wrote: >snip >...The Warp Drive is not a suitable for racing without modification - >however, we are working on one. Gary, You caught my curiosity. Without giving away the store, so to speak, can you help with some info on what the difference needs to be in a racing scenario vs climb for the Warp Drive? Width? Pitch? Taper? Strength? BTW, thanks for the excellent application description of 2 vs 3 blade on a pusher. Larry Schuler MK-IV plans #500 lschuler@cellular.uscc.com From: "Hunter GA (Gary) at MSXSCC" Subject: RE: Re[2]: PROP-FAB: Three vs two blades Date: Wed, 29 Apr 1998 15:28:04 -0500 Hey Larry, you must think I don't work at all..... > You caught my curiosity. Without giving away the store, so to speak, can > you help with some info on what the difference needs to be in a racing > scenario vs climb for the Warp Drive? Width? Pitch? Taper? Strength? > > Larry Schuler MK-IV plans #500 > lschuler@cellular.uscc.com > Climb requires low twist - racing high twist. The Warp Drive has too much twist for climb, and too little for racing. Climb likes fat chords, Racing requires thin chords. The warp is too fat at the tip for both scenarios, and not fat enough at the root. Width and Taper is used to to distribute the load most effectively across the span. The Warp Drive blades we use are standard width without taper - paddle blades. Strength - Well, the Warp Drive is nearly indistructable. A lead pipe might hurt it. Gary Hunter EAA Technical Counselor Vari-Eze - N235GH gahunter@shellus.com From: "Hunter GA (Gary) at MSXSCC" Subject: RE: PROP-FAB: Three vs two blades Date: Wed, 29 Apr 1998 08:21:23 -0500 Some food for thought, No Formula 1 racer has ever won RENO with a three bladed prop. BUT, Rare Bear has won the unlimited category several times with just 3 Big Wide Thin Short blades turning only 1100 RPM as opposed to everyone else running long 4 and 5 bladed props. Get the gist ? Fewer is better. The breaking point on efficiency is above 3 blades. As we all know, a one bladed prop is most efficient. Our prop manufacturer says a two blade is about 2% less efficient than the 1 blade, and a three blade is (believe it or not) less than 1% less efficient than a two blade - ON A TRACTOR AIRCRAFT. On a PUSHER, it CAN be different story depending on how far back the prop is from the flying surfaces. The Cirrus VK30 engineers discovered that the prop arc needs to be at least 1/4th of the wing chord behind the wing in order to minimize wing wake interference. The tail plane on the Cirrus was mounted on a boom, and the chord was only 2-3 feet. They could essentially put the prop any distance from the tail planes they wanted to but lengthening the drive shaft. With our EZ type aircraft, we are limited on how far back we can move the prop arc by the shaft extension. Similarly, with "Pushy Galore", we run a 12" extension an still run into this problem. The faster we go, the less efficient the propeller becomes. This is because the crap that comes off what most would say is a very clean back end of an airplane compared to a EZ type. It is compounded by the fact, we have a 4 stroke - 4 cylinder engine, 4 exhaust pulses, 2 wing wakes, a ventral fin / vertical stabilizer (2 more wakes), and 2 propellor blades. Everything is divisible by 2 and it does cause some weird vibrations. Because the engine shaft is aligned with the waterline of the wing and verticle surfaces, each propeller blade hits a wing wake at the same time every 1/4 of a revolution. Basically, this stalls the propeller blade for about 1/8 of a revolution. Just about the time it is about to get a good bite of clean air, it runs into another wake. The faster you go the bigger this becomes a factor. For Pushy - it happens at about 260 mph. A 3 bladed propellor works better in this situation. We use a 3 blade WARP DRIVE for our time to climb records and drag racing and have discovered a couple things. First and foremost, it climbs faster, and secondly - the weird vibrations are gone. We attribute this to the fact that with a three bladed prop, two blades are always in clean air making thrust while the 3rd one is getting trashed in a wing wake. This we believe is more efficient than having both blades of a two bladed prop getting trashed at the same time. We would probably race a three blade if we could find somebody good at making 3 bladed racing props - cheap. The Warp Drive is not a suitable for racing without modification - however, we are working on one. In my opinion, a three blade prop is a damn good idea on EZ type aircraft. Gary Hunter - Crew Chief - Pushy Galore EAA Technical Counselor Vari-Eze - N235GH gahunter@shellus.com From: "james leturgey" Subject: COZY: propfab Date: Fri, 18 Dec 1998 08:59:36 PST Propfab Group: I would like to build one of the 3-blade props like Nigel designed and several cozy_builders have done. I have carved my own 2-Blade from maple that I am now flying on my Longeze. Would someone from the propfab group please help me with the numbers such as those from the Bates prop program. My longeze weights in at 912 lbs and I have a O235 Lycoming powerplant. Any help would be greatly appreciated. Jim Leturgey Flying Longeze N537JL ______________________________________________________ Get Your Private, Free Email at http://www.hotmail.com