Date: Fri, 10 Jan 1997 12:29:43 -0500 From: George Berven Subject: COZY: Deep Stall Recovery To preface this to all, I am in the pre-build stage of researching potential projects (very interested in Aerocad! & King Kozy?). I have not built an airplane an am not qualified to design one but would like to put forth an idea for critique, and if I'm nuts just say so. Please correct any misconceptions I also might have. Many thanks to Pat Young for giving such a detailed description of the accident he had in Oct. '96. Reading this letter gave me more pertinent information than all the articles I have read thus far. The chance for a deep stall, although very remote, made me come up with this design. In theory it is very similar to what Nat Puffer had done in the c.g. testing of the Mark IV. Although hopefully it could be applied to all canards which have the possibility of operation outside c.g. restrictions. I know we should all fly within c.g. restrictions but from what I have read about accidents, people aren't perfect and absentmindedness happens. What Mr. Puffer had done in testing the Cozy was to have a ballast weight that could be moved fore and aft to test c.g. boundaries. This way if deep stall did occur in testing, the ballast could be moved forward to stall the canard so the main wing could recover. My idea is to have a similar system in which the ballast compartment in the nose of the aircraft is replaced with another fuel tank. This tank could have a separate gauge in the cockpit which could be calibrated to measure weight. In this manor the existing need for ballast could be offset on each flight by pumping the appropriate amount of fuel into the ballast tank. This fuel would qualify as part of reserve needs on cross-country flights. As applied to deep stall recovery this tank should have the additional capacity to take on fuel. So that if/when a deep stall occurs, fuel can be pumped into the forward tank until the main wing recovers. This would have to be done quickly to account for rate of altitude loss during stall. I can also think of a light weight efficient system with which this can be done as the fuel pump does not have adequate capacity to get the job done fast. More on this if anyone is interested. There are problems with this design which need to be considered. 1) This system would have disastrous affects if it was used to recover from a low a.g.l. stall, such as an accelerated stall during take-off or landing. Therefore an automated system of stall detection in conjunction with altitude encoder may be needed to lock out use during low flight. The main danger is if terrain collision is not avoided, you now have a major fire hazard right in front of you on impact. 2) Effective and fast weight transfer to and from main tanks without increasing gross weight by more than say 15#. 3) Automated systems for a situation in which I would most likely panic and not have full reasoning capabilities. 4) Many other problems which I haven't foreseen. Can anyone tell me the rate of decent (vertical), the rate of forward velocity (full power & idle), and the impact angle for a typical deep stall crash? George Berven Pre-build. gberven@erols.com Date: 10 Jan 1997 16:11:32 -0400 From: "Judd Stewart" Subject: COZY: Re: COZY- Deep Stall Recove RE>>COZY: Deep Stall Recovery 1/10/97 Hello to all, How about mounting a small parachute in a lower winglet to upset the aircraft from the deep stall attitude? The big boys do this in spin testing. I think it would fit and wouldn't especially be hard to activate manually. The activation mechanism would have two position, deploy and jettison. Any ideas as to; -The reaction of aircraft - structural integrity of the wing - entanglement etc. judd Date: Fri, 10 Jan 1997 15:46:52 -0500 From: wilhelmson@scra.org Subject: Re: COZY: Deep Stall Recovery The subject of a permanent emergency stall recovery system for canard aircraft is one that I have though about for several years. The idea of a system that uses fuel or some other liquid that can be pumped rapidly from back to front was considered and rejected as to complicated and heavy. My current idea is to develop a small 40#, five second duration, electrically fired, solid fuel retrorocket system that can be mounted permanently in the nose. This system would not weight more than five lbs and could use the same solid fuel used in model rocket engines. I have no interest in marketing a system like this. but I would like to have one and I think it would make the canard design truly stall free if it could be developed. I would welcome help, and\or information about sources for fuel etc. that the members of this forum might have. My airplane has been flying for ten years with no stalls of any kind. I am aware though that the airplane could be put in a main wing stall condition by wake turbulence or a thunderstorm as well as other situations. ______________________________ Reply Separator _________________________________ Subject: COZY: Deep Stall Recovery Author: George Berven at Internet_gateway Date: 1/10/97 12:29 PM Date: Fri, 10 Jan 1997 14:06:53 -0700 (MST) From: Ron Lee Subject: Re: COZY: Deep Stall Recovery Portions snipped and I am NOT an aeronautical engineer nor do I portray one on any TV show. Avgas at about 6 pounds per gallon might require several gallons to make the CG change needed. Must verify moment change needed!!! Gas would have to be pumped very quickly. perhaps at rate of 20 gallons per hour to effect the change. Depends on altitude and rate of descent. My opinion is that it is too much work to correct something that is so close to being unstable. If going solo and throwing baggage in back puts you at aft cg, seems to me that you should placard the plane, change the design, or permanently install weights or useful equipment up front to stay away from the aft cg. As a question to the group, have some of the deep stalls been attributed to lack of lower winglets and/or vortilons? Ron Lee At 12:29 97/1/10 -0500, you wrote: > >What Mr. Puffer had done in testing the Cozy was to have a ballast >weight that could be moved fore and aft to test c.g. boundaries. This >way if deep stall did occur in testing, the ballast could be moved >forward to stall the canard so the main wing could recover. > >My idea is to have a similar system in which the ballast compartment in >the nose of the aircraft is replaced with another fuel tank. This tank >could have a separate gauge in the cockpit which could be calibrated to >measure weight. In this manor the existing need for ballast could be >offset on each flight by pumping the appropriate amount of fuel into the >ballast tank. This fuel would qualify as part of reserve needs on >cross-country flights. > >George Berven >Pre-build. >gberven@erols.com > > Date: Fri, 10 Jan 1997 16:45:13 -0500 (EST) From: DFinn7971@aol.com Subject: Re: COZY: Deep Stall Recovery In a message dated 97-01-10 12:55:46 EST, gberven@erols.com (George Berven) writes: << My idea is to have a similar system in which the ballast compartment in the nose of the aircraft is replaced with another fuel tank. This tank could have a separate gauge in the cockpit which could be calibrated to measure weight. In this manor the existing need for ballast could be offset on each flight by pumping the appropriate amount of fuel into the ballast tank. >> George, I think you have a nifty idea but there might be a problem with space. The ballast area in the nose is really pretty small. I could probably handle a gallon at best. depending on how far out of c.g. you are this may or may not be enough weight. The area from the rudder pedals froward is pretty well taken up with the brake cylinders (some people (i.e. Nat) have also installed the GPS antenna in that area. You also need to be able to access the area for work on the nose gear. I think that it would be difficult to expand the nose fuel tank back of the nose cone. Nattest rig would certainly avoid the problem but it runs through the passenger seat back and up into the nose through the passenger leg holes. This could get a bit uncomfrtable for the passengers :-) I did hear some time ago about a fellow who proposed installing a ballistic parachute on either a Long or Cozy. There was a lot of discussion about the ability of the wing spar to to handle this. Dick Finn Cozy Mark IV #46 DFINN7971@AOL.COM From: Lee Devlin Subject: Re: COZY: Deep Stall Recovery Date: Fri, 10 Jan 1997 17:50:14 MST George wrote: > As applied to deep stall recovery this tank should have the additional > capacity to take on fuel. So that if/when a deep stall occurs, fuel > can be pumped into the forward tank until the main wing recovers. This > would have to be done quickly to account for rate of altitude loss > during stall. I can also think of a light weight efficient system with > which this can be done as the fuel pump does not have adequate capacity > to get the job done fast. More on this if anyone is interested. A typical aircraft fuel pump is rated at 30 gal/hr excluding system losses. This means that your weight transfer will be in the neighborhood of 3 lbs/minute if you used off-the-shelf fuel components. A typcial descent rate of 3000-4000 ft/minute of a deep stall will afford you little time to move the weight. I'd estimate that you would need about 25-50 lb/min transfer to recover from a even a high altitude deep stall and require a capacity of between 4 to 8 gallons in the nose. That flow rate is equivalent to 4-8 gallons per _minute_ which is about capability of a kitchen faucet running with 60 psi and using 1/2" tubing. It seems like it would be a lot safer to just do the calculations and make sure you're not going to be aft c.g. before taking off. Lee Devlin | HP Greeley Division | Long EZ N36MX Piper Colt N4986Z | 700 71st Ave. | Cozy MK IV under const. 'Spirit of rec.aviation'| Greeley, CO 80634 | (Chapter 10) Date: Fri, 10 Jan 1997 18:31:33 -0800 From: berkut@loop.com Subject: Re: COZY: Re: COZY- Deep Stall Recove This goes the the heart of the disagreement between Nat and Shirl about lower winglets. Nat found that without them, aft CG, the airplane went divergent, dropping a wing sharply. Shirl thinks that's a good thing, better than a _stable_ deep stall with no control at all. Nat prefers the extra aft CG margin the lower winglets provide. The parachute isn't bad, but you'd have to be _sure_ that it would cut away. If not, I think I might prefer the deep stall. I agree with those who advocate meticulous CG calculations -- and/or wear a parachute. When we were looking at deep stall testing, we discussed plumbing high pressure hose to the nose, with a ball valve and a scuba bottle. It turned out we couldn't load aft CG no matter what we did, so we never used it, but it's a thought for a testing scenario. "Judd Stewart" wrote > RE>>COZY: Deep Stall Recovery 1/10/97 > >Hello to all, > >How about mounting a small parachute in a lower winglet to upset the aircraft >from the deep stall attitude? The big boys do this in spin testing. > >I think it would fit and wouldn't especially be hard to activate manually. The >activation mechanism would have two position, deploy and jettison. > >Any ideas as to; > >-The reaction of aircraft > >- structural integrity of the wing > >- entanglement etc. > >judd > > > > > -- Czech Sikhs! Richard Riley "The important things are always simple. The simple things are always hard." See the Berkut at http://www.berkut.com Date: Fri, 10 Jan 1997 21:31:48 -0500 From: DL Davis Subject: Re: COZY: Deep Stall Recovery At 04:45 PM 1/10/97 -0500, DFinn7971@aol.com wrote: >In a message dated 97-01-10 12:55:46 EST, gberven@erols.com (George Berven) >writes: > ><< My idea is to have a similar system in which the ballast compartment in > the nose of the aircraft is replaced with another fuel tank. This tank > could have a separate gauge in the cockpit which could be calibrated to > measure weight. In this manor the existing need for ballast could be > offset on each flight by pumping the appropriate amount of fuel into the > ballast tank. >> > >George, > I think another basic point needs to be made. It isn't necessary at all to build such an elaborate deep-stall recovery system for our airplanes. Our airplanes will recover from a deep stall just as a conventional airplane will, PROVIDED THAT THE CG IS WITHIN LIMITS! Like Jack said earlier, he has never seen a wing stall in his airplane and I suspect most EZ flyers will never see a wing stall. I have flown several years in my COZY, including some mighty slow flight on approach to Oshkosh and Sun N Fun each year, as well as some mild aerobatics (rolls, wingovers, etc), and I have never even come close to a deep stall....except once when I induced it myself by flying straight up until I had no airspeed.....The airplane quit flying, naturally, and the nose fell through gently and surely, and within 5 seconds the nose was pointed at the ground and I was flying again. No problem. I think the lesson from Pat's accident is very simple, GET THE CG RIGHT! The airplane will fly fine. So you may ask, what about all the Velocity deep stall accidents. It seems there was a rash of accidents where it was impossible to recover from deep stalls. People began to think that a "deep stall" was somehow different in a canard airplane, and must be sure death! The reason for those unrecoverable stalls was eventually ascribed to a design flaw in the fuel tank baffling that allowed all the fuel to run too far aft in a tail-down attitude. Supposedly this is fixed now. Up until Pat's accident, I had never heard of an unrecoverable stall in a COZY (and only very, very, rarely in any other EZ), which is why I was especially anxious to hear about the cause of this accident. Now that we know it was a case of a severe aft CG, we already know how to avoid that problem...balance the airplane! I also think it is important to keep in perspective that we are not going to have a deep stall and crash, even if we forget to move the ballast from the nose to accomodate a passenger (or vice versa). It happens every day, and airplanes actually fly pretty well at the aft end of the CG box. Even with the very severe out of balance condition that Pat had, he was recovering from intentional canard stalls routinely, until that last flight when the vortilons were removed. And he deliberately induced that last stall with a very unsubtle maneuver. It is amazing to me that the airplane recovered so often and so well even with the CG that far out of bounds. So rather than build another system to recover from deep stalls, why not just balance the airplane so it will recover itself. But to answer George's original question about the pump ballast system.....Vance Atkinson built that very system into his COZY. Although his motive was different. He was not trying to build a stall recovery system. He was simply trying to find a more useful ballast than lead. He figured he could pump fuel into the nose tank to maintain CG when flying solo. I asked him what happens if he runs into a situation where he actually has to burn that fuel and therefore loses his ballast? No problem, the airplane flies fine at aft CG....he would just fly that landing with a little extra speed on final....(that wouldn't be the time to test stall recovery). But after building the system, Vance decided he didn't like the risk of having all that fuel at his feet. Even a minor runway excursion could be disastrous if that tank ruptures, or even a gear up landing gets a lot riskier. So now he just keeps water in the nose tank for ballast, rather than fuel. One more point...sorry this is getting so long....but at an Oshkosh forum where Nat's test pilot was describing the hairy ride he got from the deep stalls, I believe he said that he found the way to recover is to get the airplane rocking from side-to-side until it eventually falls off one wing or the other. I have heard Dick Rutan and Mike Melville describe this as the approach to recover from a deep stall. It sounded from Pat's message that he tried the ailerons but he only got yaw. He didn't say specifically if he tried to rock in sympathy with the yaw in order to build up the oscillations so it would eventually fall over. I don't know if the technique didn't work for him, or if he didn't have time to try it, or think about it, (entirely understandable), but I believe that should be attempted if somehow you do find yourself in a stabilized deep stall. And as a last resort, you could try what one of those Velocity pilots did, climb out of the cockpit and lean on the nose!!! This was described in an AOPA article last year. If your CG is even close, you would think that's enough! Dewey Davis Date: Sat, 11 Jan 1997 10:08:56 -0500 From: Tom Teek Subject: COZY: Deep Stall---Ballistic Parachute. Tim Crawford who owns Wide body Long-ez N3R has it equipped with a ballistic parachute. It is located aft of where the rear passenger sits and would depart through the top as it is a give-away part. He has posted his e-mail address on the canard aviator page. I feel sure he would be happy (I think I'm sure) to espouse on it if contacted. He is a very interesting and pleasant person,and does some very interesting flying for NOAA. crawford@atdd.noaa.gov Tom LE--N58AT Date: Mon, 13 Jan 1997 09:45:46 -0500 From: wilhelmson@scra.org Subject: COZY: Deep Stall recovery comments. It appears that as Canard builders, test pilots, and flyers we need to consider that we have at least two completely different stable aerodynamic conditions that can occur with the canard design (depending on CG position). The normal condition is main wing unstalled and canard stalled or unstalled, The second is main wing stalled and canard unstalled or also stalled. The center of lift moves forward in the second condition especially during entry when the canard is still not stalled. As the forward airspeed decreases the canard also stops producing lift and the center of lift moves back, but not to the normal flying position. The question is: what is the CG limit where the nose will fall through during a main wing stall (no mater how it was entered), how do we calculate it, and how do we safely test for it? The realization that we do not yet have the answers to these questions could save someone's life. I do not have the answer to this question for my airplane. My testing was limited to proving that the airplane would not stall at the CG limits when entered unaccelerated. Nat answered this question by testing his airplane at considerable expense and risk. Discussion's on this subject can only help us understand the risks and therefore make good decisions. Date: 13 Jan 1997 09:23:20 -0800 From: "Judd Stewart" Subject: COZY: Re: COZY- Deep Stall Recove RE>>COZY: Deep Stall Recovery 1/13/97 Dewey, Yes that's true, but what of a airplane that has never flown? There are just to many variables that come into play that having a system or systems (that are later removed) to save the plane during these initial flights seems prudent. After all, you wear a parachute to save yourself! Judd Stewart Date: Tue, 14 Jan 1997 00:45:07 -0500 From: INFINITY Aerospace <72124.347@compuserve.com> Subject: COZY: Re: Re: Deep Stall Recovery Hi Richard, Judd and All, >Richard Riley wrote:< >This goes the the heart of the disagreement between Nat and Shirl about lower winglets. Nat found that without them, aft CG, the airplane went divergent, dropping a wing sharply. Shirl thinks that's a good thing, better than a _stable_ deep stall with no control at all. Nat prefers the extra aft CG margin the lower winglets provide.< I agree with Shirl, Richard and Dave - no bottom winglets. If I was flying aft of the aft CG for whatever reason, I would rather have a warning of the onset of main wing stall from divergent wing rock that I can recover from, before the onset of an unrecoverable flat deep wing stall with bottom winglets. Also, looks better without the bottom winglets. The primary reason for the bottom winglets is to protect all those plys wrapped around the outside of the winglet from grinding off from ground loops, etc. - kind of a major fix. I wrapped the outside with Kevlar, then finished it off with glass (also the bottom of the fuselage and the leading edge of the strakes). Another small benefit of the bottom winglets is to help out at very slow speeds in yaw stability, as Jeff has noticed a little (otherwise, they are just more drag). With longer ailerons, you may not notice the difference of no bottom winglets. When you fly the plane in primer, make them removable and test the difference in your original aircraft. Or, put a low profile/short bottom winglet like I believe Jeff did - less drag and maybe the slight increase in stability. >I agree with those who advocate meticulous CG calculations -- and/or wear a parachute.< Concur, and always wear a parachute during any flight test. >Judd Stewart wrote:< >How about mounting a small parachute in a lower winglet to upset the aircraft from the deep stall attitude? The big boys do this in spin testing. I think it would fit and wouldn't especially be hard to activate manually. The activation mechanism would have two position, deploy and jettison.< How about a cutaway drogue/spin chute to get the nose pointed down, then land a little fast? OR How about a BRS, which has been done in Vari-EZE's and Long-EZ's? Cheap insurance, and your premiums would be cheaper - like having airbags means as much as 60% less premiums for medical insurance. HTH. Infinity's Forever, EAA Member EAA Technical Counselor JD EAA Flight Advisor AOPA Member Test Pilot James D. Newman, President LCDR F-14 USNR INFINITY Aerospace Mailing Address: P. O. Box 12275 El Cajon, CA 92022 Shipping Address: 1750 Joe Crosson Drive, D-2 El Cajon, CA 92020 (619) 448-5103 PH & FAX 72124.347@compuserve.com OR INFINITY_Aerospace@compuserve.com Checkout our Stick Grips, Retractable Main Landing Gear and the Infinity 1 Home Page http://ourworld.compuserve.com/homepages/INFINITY_Aerospace Date: Tue, 14 Jan 1997 17:56:19 -0500 (EST) From: CCady@aol.com Subject: Re: COZY: Re: Deep Stall Recovery I had lower winglets on a Long-Ez and none on my E-Racer MKII. The Long-Ez had more apparent wing rock and I less yaw stability too. The only difference that might account for this might be a more aft cg for the Long-Ez and almost 200 lbs more empty weight on the E-Racer. Another difference between the two is the E-Racer winglet leading edge is forward to the leading edge of the wing. Also the winglet cant angle is 90 degrees vs the inward cant angle on the Long-Ez. The roll effect of the rudders appears to be less with the E-Racer which surprised me as I remember this alot from the Long-Ez. The absence of the lower winglets doesn't appear to have any real negatives and sure does look better. Of course I haven't done extensive stall tests at aft CG either but I have less apparent wing rocking which is nice. In a message dated 97-01-14 00:49:32 EST, you write: <> Date: Thu, 16 Jan 1997 09:51:04 -0500 From: wilhelmson@scra.org Subject: Re[2]: COZY: Deep Stall Recovery Dewey: The question is what are the CG limits for each airplane where it will recover from a deep stall? Are they the same as the limits for where it will not enter a deep stall when only unacclerated maneuvers are performed? I hope so, but I think (based on velocity and other deep stalls) that there may be a narrow CG range (for all canard airplanes) where the airplane will not stall under unaccelerated conditions, but when a deep stall is induced by accelerated manuevers the nose will not fall through and recover. Date: Thu, 16 Jan 1997 22:58:55 -0500 From: DL Davis Subject: Re: Re[2]: COZY: Deep Stall Recovery At 09:51 AM 1/16/97 -0500, wilhelmson@scra.org wrote: > Dewey: > > The question is what are the CG limits for each airplane > where it will recover from a deep stall? Are they the same > as the limits for where it will not enter a deep stall when > only unacclerated maneuvers are performed? I hope so, but I > think (based on velocity and other deep stalls) that there > may be a narrow CG range (for all canard airplanes) where > the airplane will not stall under unaccelerated conditions, > but when a deep stall is induced by accelerated manuevers > the nose will not fall through and recover. > I don't know what happens under all conditions, I don't suppose there is a lot of testing in this area. But I think of the problem this way. It doesn't really matter so much what causes the main wing stall. When the airplane stops flying it might as well be a rock. Assume it was accelerated into the stall or not, assume it tumbles into any orientation you choose. Sooner or later it will act like a rock and fall toward terra firma. As it falls toward the ground, aerodynamic forces will begin to act on the surfaces of the airplane and cause it to change attitude. With the wings swept back as they are, and the drag on the wings being greater than that on the nose, the nose will fall through. I understand that this tendency is actually quite pronounced in the EZs and the nose can actually seem to snap down rather quickly. The most recent CSA newsletter has an article about Long EZ tail slides where this phenomenom is described in some detail. This all assumes that the airplane is balanced correctly of course. If it is so heavy in the ass that the nose can't fall through despite the aerodynamic forces trying to right the airplane, then all bets are off. The point of my original post was simply that the airplane will behave just fine if it is balanced right from the beginning. I won't argue with anyone that wants to build more safety devices into the airplane, wear parachutes, hire test pilots, whatever. But in my opinion, the most important thing to do to avoid a stabilized deep stall is to balance the airplane correctly before you fly it. Dewey Date: Fri, 17 Jan 1997 05:04:48 -0500 (EST) From: KSPREUER@aol.com Subject: Re: COZY: Deep Stall recovery comments. In a message dated 97-01-13 09:56:16 EST, you write: << It appears that as Canard builders, test pilots, and flyers we need to consider that we have at least two completely different stable aerodynamic conditions that can occur with the canard design (depending on CG position). The normal condition is main wing unstalled and canard stalled or unstalled, The second is main wing stalled and canard unstalled or also stalled. The center of lift moves forward in the second condition especially during entry when the canard is still not stalled. As the forward airspeed decreases the canard also stops producing lift and the center of lift moves back, but not to the normal flying position. The question is: what is the CG limit where the nose will fall through during a main wing stall (no mater how it was entered), how do we calculate it, and how do we safely test for it? The realization that we do not yet have the answers to these questions could save someone's life. I do not have the answer to this question for my airplane. My testing was limited to proving that the airplane would not stall at the CG limits when entered unaccelerated. Nat answered this question by testing his airplane at considerable expense and risk. Discussion's on this subject can only help us understand the risks and therefore make good decisions. >> Implied in this discussion is a very important point that has not been said in so many words. That is, that it is very likely that it will require more of a C.G. shift to recover from a fully developed deep stall than merly to move the C.G. back to within the standard envelope. As far as I know there is not any data on how much that might take. I have thought of putting a 40# weight in the back seat on a rope during minimum speed test flights. In case of stall I would pull the weight into the front seat and place it as far forward as possible. Would It be enough? I don't know. Date: Wed, 22 Jan 1997 11:40:48 -0400 From: Carlos Vicente Leon Organization: Maquinaria Diekmann Subject: Re: COZY: Winglets John Meernik wrote: > Some changes will have more effect that others, but all changes > will have some effect. (some changes might even improve stall behavior, but > not many of the ones that I have seen discussed) > Has anyone had any experience with installing vortex generators on top of the wing. Can this improve the stall behaviour of a canard aircraft ? Carlos Leon Varieze YV-11X Cozy Mk IV (twin) YV-22X Date: Tue, 22 Apr 1997 09:35:13 -0400 From: wilhelmson@scra.org Subject: Re: COZY: Re: Canopy & Aerocanard Parts The subject of modification of the Canard design continues by many builders. My opinion on this is that all builders benefit from this process. The Velocity deep stall saga is a good example of this. Until this happened most builders and flyers of Canard airplanes were blissfully unaware that Canard airplanes would deep stall in a unrecoverable manner. It is recognized by most Canard flyers (I pray all) that all Canard airplanes will deep stall at some CG position not too far removed from where we fly them. What is not commonly recognized (from my personnel conversations with my fellow flyers) is that some canards will fall through after a full deep stall and recover and others will not even though the CG is the same. The aerodynamics of a falling (as opposed to flying) object explains this. The center of lift of a falling object versus the center of gravity of the object determines weather it falls nose first or tail first. While this seems evident and quite a simple principal it is not that simple when the canard airplane is considered. However, to make my point: widening the front of the airplane, extending the nose, longer canard, high drag areas under the nose (such as open landing gear areas) can have a negative result in this unknown balance equation because all these modifications (and others you may think of) move the centroid of the flat plate area forward. I have actually calculated the change in the flat plate area centroid of my airplane (COZY plans no.1) caused by the addition of 3" of canard length on each side. It moved the centroid .75 inches forward. Date: Tue, 22 Apr 1997 19:51:06 +0200 From: Rego Burger Subject: COZY: Canard CG Quote by unsigned writer above. Thanks for the inspiration: Living in a little of a dreamland between layups etc. I allow my mind some freedom of thought, often ideas come up which when shared could hopefully be beneficial to others. Here goes! Imagine doing your ( cozy's) CG balancing with the nose wheel retracted, yes it will be a little difficult but with some thought not impossible. Most, if not all canard flyers I've heard of have not given it a thought or at least been brave enough to voice it publicly! Once you have established a CG in limits of max safe aft CG with the nose gear up ( in flight mode ) you will inevitably have about 20" distance forward weight when the gear comes DOWN for landing, an extra margin of safety in this configuration. So we do have a little movable weight on board! I am NOT saying this will get you out of a deep stall but instead HOPE it will help keep one a little away from it. The "normal" way of doing CG causes a slight aft CG effect when retracting the nosegear.( yes a Fraction ) Just remember I would rather have every fraction on my side. By lowering the nose gear that little weight goes forward plus the drag from the nosewheel tends to pull the nose down a bit. Someone might take this a step further and mount lead on the nose strut but that's pushing it a little :-) Also remember if you really do wish to install any other gagets to place them upfront first. This will reduce the need to carry "dead" weight in the nose. Happy Building Rego Burger Port Elizabeth RSA ( Rep. South Africa ) cozy Mk 4 # 139 Date: Tue, 22 Apr 1997 19:53:55 -0400 From: DL Davis Subject: COZY: center-of-lift while falling Jack, Your comments about deep stall performance (center-of-lift vs CG) make a lot of sense to me. That big canard on the front of the Velocity must make a significant difference in center-of-lift in the deep stall regime, versus a Long EZ or COZY 3 or 4. I think I understood you to say that a first approximation of the center-of-lift is based on integrating the moments of the flat plate area of the airplane in plan view? Any idea what that is for a Velocity as compared to the EZs? Dewey Davis Date: Wed, 23 Apr 1997 10:09:39 -0400 From: wilhelmson@scra.org Subject: Re: COZY: center-of-lift while falling Dewey: In response to your question, I have not calculated the Velocity flat plat area and centroid because I do not have good layout data for it. I found that to be accurate I had use the actual dimensions from the full size drawings to generate the plan profile. I have however, calculated this for the Original Cozy and MKIV for both long and shortened canards. The numbers are not important except as a comparison from one to the other. The Cozy came out 109.99 The MKIV came out 108.88. Both with short canards. As something more to think about, the CG moves back as the airplane pitches up and rotates around the center of lift. If the main wing stalls and the airplane goes into free fall, the center of lift moves down (where to is another complicated problem). It is clear that at some pitch up angle the CG would coincide with the free fall center of lift and the airplane would not fall through. As a example, if the aircraft CG is at 100" and the center of free fall lift is at 109" horizontally, and vertically the CG is 18" above the center of lift (this guess comes from the fact that the engine and some other heavy items like people are located at least 18" above the bottom surface of the airplane). The pitch up angle where they cross is 26 degrees. This is all guess work, but it does illustrate the danger of changing things from a experimentally proven design. Incidentally, one observation from this is that raising the landing gear will cause the CG position to rise and thereby lower the pitch angle where recovery may not occur. I welcome constructive comments (positive or negative) on this subject. Understanding our airplanes performance in all situations so that we can fly safely is my only goal. Date: Thu, 24 Apr 1997 15:04:48 -0400 From: wilhelmson@scra.org Subject: Re: COZY: Canard CG Rego: Your comments about the nose wheel are correct, and in addition the weight of the wheel and strut go downward, which lowers the vertical CG, thereby, increasing the critical pitch up angle where recovery is theoretically not possible. As you mentioned these changes are very small. Sorry about not signing my name to my earlier comments. What is needed is a low cost light weight emergency deep stall correction device. Especially for the testing phase of experimental airplane building. Nat and the Velocity designer used a movable weight, but the installation was not easy and required considerable butchering of the aircraft. Jack Wilhelmson (Cozy plans #1). Date: Thu, 24 Apr 1997 20:50:49 -0700 From: Judd Stewart Subject: Re: COZY: Canard CG wilhelmson@scra.org wrote: > What is needed is a low cost light weight emergency deep > stall correction device. Jack I think a spin recovery chute packed in the shape of one of our lower winglets would be a effective method of upsetting the plane from this mode. I have know idea as to how big this would have to be, perhaps 3 feet in diameter, with a spreader ring to control the rate of inflation. You wouldn't want to yank off a wing and anything like that. Activation would be similar to our rudders, a cable that is pulled with a fail safe mechanism with three positive positions. Arm, Deploy and Jettison. Food for thought Judd Stewart judd@access1.net Date: Fri, 25 Apr 1997 01:33:13 -0400 (EDT) From: "'Rick - Tech Support'" Subject: Re: COZY: Canard CG Guys, This is what I am working on. I will have access to the windtunnel this summer , and I am trying to adapt F-18 technology to the Cozy and Long for the express purpose of forcing the Nose over using vectored vortices to control it. Downside seen so far: once back in level flight the device MUST be RETRACTED. Otherwise the stick forces on back stick get severe above 130 mph. Upside, the cost is approx $40 to build and install. Beyond that, don't ask until I am finished with the wind tunnel data. The computer sim shows it effective to 3 inches aft of the aft cg limit for a Cozy 3. But again, until the windtunnel and flight testing are done on the models , it is just pie in the sky. After that point , I will be hopefully flight testing the device on my Cozy. We shall see. If we don't crash the model, I might be brave enough to risk the stable stall point of the " deep stall". BTW, we are not the only ones with this problem. Mitchell wings and 2 other non-canard designs suffer from the same fate at aft of the aft cg limit. Rick On Thu, 24 Apr 1997 wilhelmson@scra.org wrote: > Rego: > > Your comments about the nose wheel are correct, and in > addition the weight of the wheel and strut go downward, > which lowers the vertical CG, thereby, increasing the > critical pitch up angle where recovery is theoretically not > possible. As you mentioned these changes are very small. > Sorry about not signing my name to my earlier comments. > > What is needed is a low cost light weight emergency deep > stall correction device. Especially for the testing phase > of experimental airplane building. Nat and the Velocity > designer used a movable weight, but the installation > was not easy and required considerable butchering of the > aircraft. > > > Jack Wilhelmson (Cozy plans #1). > Date: Sat, 26 Apr 1997 11:26:50 -0700 From: Rego and Noleen Burger Organization: R.N.B. Enterprises Subject: COZY: DEEP STALL RECOVERY AID Hello all canard pusher pilots, builders and designers. "I have on paper designed, and simply by means of a model demonstrated and will soon on a Radio Control Model Flight test a Deep Stall Recovery Aid (DSRA model GB-1) Plans will be available for you to install it on your aircraft if you wish. This device will not compensate for a WRONG CG configuration however will certainly give you a controlled advantage to get the plane flying again. This device does NOT mean you must not shorten your MANDATORY 3" cut-off's off the canard on the Cozy Mk4 Aircraft Designed by Nat Puffer. ALL other designers of similar aircraft are welcome to contact me for more information." Any Desingers or Pilots wishing to modify their flying aircraft and test it in FLIGHT at their OWN RISK are free to contact me aswell. I will not want to discuss price of plans etc. on this forum and will gladly do it via private e-mail or snail mail at: R.N.B Enterprises P.O.Box 28686 Sunridge Park 6008 Port Elizabeth RSA. Rego Burger Port Elizabeth RSA CZ4 #139