(1.38.193.5/16.2) id AA10703; Wed, 8 Feb 1995 00:12:48 -0500 Date: Wed, 8 Feb 1995 00:12:48 -0500 From: Ewestland@aol.com Subject: Re: Mailing List Members/personal progress 3) Question: On some of my layups, I'm noticing a small amount of air in the layup (I guess its a little dry) after cure. I don't notice the bubbles when the glass is wet. The instructions say to not use any part with more than 10% (by area) air bubbles. I don't think I'm in that range. I've been peel plying the whole layup and rolling each layer out with the 3" rollers, and as I said, the layup looks good when wet (and with the peel ply on). When I built the Q2, I would pour the epoxy on and squeegee it around with the squeegee, and the plane came out a bit overweight (maybe 30 lbs). This time, I'm painting the epoxy on with a brush and not squeegeeing at all (yet). Obviously, I'm not getting quite enough epoxy on the layups, and although its not at the danger point, I'd like to have better control of the dryness without adding too much weight. Anyone have any advice here? Marc, Using a squeegee is a must as far as I am concerned. Sometimes you just can't get one in there, but the squeegee not only removes excess epoxy (especially with a hairdryer), but it also removes the trapped air. Excess epoxy also weakens the layup. One other tip : when I first started, as long as the epoxy was wet, I tried to use it. I did not want to waste epoxy or time mixing up what seemed at the time to be needless mixing time. Now I rarely mix up more than I can use in 10 minutes. Fresh epoxy wets out the fastest and while it can still be used after 10 min., it takes longer to wet it out. Trapped air also gets harder to sqeegee out as time goes on. Thats what I know anyways, I wonder what others experience in this area as I still get the "white spots" appearing occasionally after I go to bed! By the way, great job on the mailing list! Thanks. Eric Date: Wed, 8 Feb 1995 09:13:38 -0500 From: SidLloyd@aol.com Subject: Re: Mailing List Members/pers... > I'd like to have >better control of the dryness without adding too much weight. >Anyone have any advice here? Try weighing. Use equal weights of glass and epoxy and you should be fine. I learned this in Alexander Aeroplane's course from Stan Montgomery and even if you've been building for a long time the class is worth triple what they're charging. Definately GO! Sid From: Lee Devlin Subject: Re: Updated Mailing List Date: Mon, 13 Mar 95 10:51:36 MST Hi Marc, Thanks for the updated mailing list. I started the Cozy last week so I guess that puts me on Chapter 4. I did the educational stuff a while ago. It was available as a separate chapter of the Solataire manual from Rutan and is sold through A/C Spruce as a 'composites educational kit'. I skinned the front seat back before leaving on our ski trip and last night I skinned the other side. I have a question for you. After knife trim (which should be called sharp razor trim -- since that's the only thing that works) how do you get the edges nice and straight? I can only be so accurate with the razor and it leaves the edge with wiggles in it. In your mailing list, you gave me credit for being a Mechanical Engineer. Although I do appreciate it, I don't have a degree in that field. My degrees are in Industrial (B.S & M.S.) and in Electrical (M.S.) & P.E.. My IE degrees were concentrated in the area of designing automated production equipment, so that's how I ended up doing things more closely related to what people consider Mechanical Engineering than what people think an IE _should_ be doing (i.e. pretending to be an engineer :-). Lee Date: Mon, 13 Mar 95 13:50:24 EST Subject: Re: Updated Mailing List Lee; > Thanks for the updated mailing list. I started the Cozy last week so I > guess that puts me on Chapter 4. I did the educational stuff a while > ago. It was available as a separate chapter of the Solataire manual > from Rutan and is sold through A/C Spruce as a 'composites educational > kit'. I skinned the front seat back before leaving on our ski trip and > last night I skinned the other side. Excellent. Glad you've gotten going. I've flipped the fuselage, and I'm about to start gluing up the bottom. Looks like a boat! > I have a question for you. After knife trim (which should be called > sharp razor trim -- since that's the only thing that works) how do you > get the edges nice and straight? I can only be so accurate with > the razor and it leaves the edge with wiggles in it. I've found that either a single edge razor blade or a SHARP utility knife blade work well. The utility knife is easier to handle, and you can put more force on it. What I do is wait until the epoxy has set up a LOT - so that the glass is REALLY stiff, but just tacky. Then I saw back and forth with the knife, always pushing in the direction of the underlying structure (so that I don't tend to lift the layup off). I've been able to knife trim up to 6 UNI or 3-4 BID this way, and get a close, straight edge. More than that, I let it cure and then use a hacksaw blade in a small handle to saw the excess off. If I try to trim when the epoxy is not cured enough, I tend to get ragged edges. Then I just need to sand it smooth. I use a rubber sanding block and 36 grit paper - taking long, smooth strokes gives a very straight, smooth surface. > In your mailing list, you gave me credit for being a Mechanical > Engineer. Although I do appreciate it, I don't have a degree in that > field. My degrees are in Industrial (B.S & M.S.) and in Electrical > (M.S.) & P.E.. My IE degrees were concentrated in the area of > designing automated production equipment, so that's how I ended up doing > things more closely related to what people consider Mechanical > Engineering than what people think an IE _should_ be doing (i.e. > pretending to be an engineer :-). Fixed. Lee, I'm not sure you've been in school long enough - 4 degrees is pretty piddling! :-). FYI, I've found a Internet Service Provider around here which will give me 2 hours/mo. and 5 Meg ftp/WWW space for $5/mo. I'm going to go for it, so my stuff will be available to everyone pretty soon. I'd be happy to put everyone else's info up as well, and provide templates people can edit which I can then put in place. If you're interested, let me know. 5 Meg won't be enough for EVERYTHING, but I'll check into the charges for more space. -- Marc J. Zeitlin E-Mail: marcz@an.hp.com Date: Thu, 13 Apr 1995 19:35:35 -0400 From: CozyBldr@aol.com Subject: Re: Chapter 5 In regards to glassing taking longer than expected - ALWAYS give yourself plenty of extra time to complete a section. Don't start if you have somewhere to be later on. I did that twice and both times I was late and the work had areas that were not perfect. Paul Stowitts From: Lee Devlin Subject: Knife trimming tip Date: Thu, 13 Apr 95 17:44:30 MDT I've been doing my knife trimming with an Exacto knife and had been changing the blades quite regularly until I discovered that they weren't really getting dull, just gummed up with a thin transparent layer semi-hardened epoxy. If you want to make your blades last a very long time, clean them frequently with acetone or other suitable solvent while you are knife trimming parts. Lee Devlin Date: Thu, 13 Apr 1995 21:42:31 -0400 From: Ewestland@aol.com Subject: Re: Chapter 5 When estimating time for a lay-up, read what Nat says, then figure how long it will take YOU to do it, then double it! I learned this when it took a Saturday to build the "2-hour" front seat bulkhead. I could build it in 2 hours now(3 years later), but you are almost always doing things for the first time when working on your project. Fortunatly, it's still fun! Other suggestions include: 1) Never tell your wife you will be done in x hours. You won't. 2) Tom Snyder is now on after Letterman! Still building, Eric Date: Thu, 13 Apr 1995 21:42:40 -0400 From: Ewestland@aol.com Subject: Re: Knife trimming tip Another idea on keeping the tip clean would be to store the blade in the same acetone you keep your brushes in. I used to throw my brushes in the freezer between lay-ups, but I now store them in a glass jar with a little acetone or laquer thinner in it. Prior to using them, I shake them out good and let them air dry for 10 minutes or so and they come out better than new - better in the sense that most of the loose bristles disappear after ther first or second use. Heat it with a hair dryer if you need it quicker and wrap the handle in a little saran wrap if the wood soaks up a little acetone - I suspect this could cut through the hand cream leaving you unprotected. Eric Tue, 16 May 1995 16:36:38 +1000 Date: Tue, 16 May 1995 16:30:51 +0200 From: parkyn@citr.uq.oz.au (Nick Parkyn) Subject: Wax paper / peel ply / vacuum bagging While Saran wrap and foil are best in certain specific instances, it is useful to use thicker clear plastic on both sides for most applications. To cut the piece to the correct shape use a rotary "pizza" cutter. Remove the plastic from the one side and apply to the surface. Use a small roller to roll on top of the plastic to compact the laminate, then remove the plastic. Later queegee the whole laminate as necessary. When vacuum bagging it is fine to peel ply the entire laminate as the vacuum will prevent air entrapment, making inspection of the laminate less essential. The Vacuum is compacting the laminate and constantly "bleeding" resin through the peel ply. This resin is then absorbed into bleeder material, removing it from the laminate. The vacuum compresses the laminate for the full duration of the cure! You do not have to fit the part into a bag to vacuum bag it, you can use (sheet) bagging film and attach it to the part being bagged with "tacky tape" and vacuum laminate on parts of the structure. This is regular practice in the marine industry. I believe that it is possible to vacuum bag most laminates on the Cozy if you plan it carefully. Laminate quality (no air bubbles and good wet out) is more important than slight resin richness - you must be able inspect the laminate if you are not vacuum bagging. The blowing of hot air onto the peel ply and laminate reduces the viscosity - of the resin. While you are lowering the viscosity, you are not forcing resin out of the laminate by compacting it - the peel ply will simply "wick up" a little more. I have not seen any tests on laminates using room temperature cure resins where temperatures have been raised to arbitrary values during cure. Are the laminate properties unaltered! Elevating temperatures for post cure is acceptable, but this is after the normal cure cycle. The following process has been suggested: A new Perforated Release Film (mylar) can be applied over the layup with just a squeegee.The perforated mylar compresses the fibers,excess epoxy comes out the perforations and you end up with a glass smooth finish without drying out the layup. This process will yield resin rich laminates unless used in the vacuum bagging process. In order to have a glass smooth surface you have filled the weave with resin and this is denser (therefore heavier) than filling it with resin / filler. Where areas are large this is a significant penalty! Resin / filler used to fill the weave also helps to protect the laminate and is less "brittle" than resin only. Date: Tue, 16 May 1995 22:08:03 -0400 From: Marcnadine@aol.com Subject: Re: Wax paper / peel ply / va... >The following process has been suggested: >A new Perforated Release Film (mylar) can be applied over the layup with >just a squeegee.The perforated mylar compresses the fibers,excess epoxy >comes out the perforations and you end up with a glass smooth finish >without drying out the layup. I would like to correct some misinformation left by Nick about using Perforated Release Film. This process does not leave you with a exess epoxy layup. When you use this process you Squeege out the excess epoxy the way you always do, to get the layup just right. THEN you apply the Film over the layup and squeege again. You will notice even more resin coming out the perforations. You are at this time compressing the fibers and getting even more epoxy out of the layup, and in the end giving you a great finnish that is even lighter then the normal layup. Marc Date: Mon, 19 Jun 1995 21:42:34 -0400 From: Marcnadine@aol.com Subject: Glassing Fabric Problems About a month ago one of our members mentioned that they are using a new Biaxial fabric and loved. Well after reading the latest newsletter (that I got today) Nat said not to use triaxial fabric. So I placed a call to Nat today to see if the Biaxial was ok. He was very upset and said to use the parts called out on the manual, only. Has anyone been using the Biaxial Fabric? Marc P. Date: Tue, 19 Sep 1995 09:46:39 -0500 "Marc J. Zeitlin" From: tims@enet.net (Tim Sullivan) Subject: Vacuum bagging I Went to the Alexander Aircraft (AA) Advanced composites course this last weekend and thought I would share a few items. The course was two days and covered mostly vacuum bagging (VB) and web and flange type construction similar to kit such as the lancair and glasair. We made a small (four feet) wing section using may new material for epoxies and vacuum bagging with the web and flange type construction. The few items that may be of interest to the Cozy builder are: 1. VB, if done properly, can save a tremndous amount of finish time by eliminating a majority of the pin holes. 2. VB does not take that much time to perform. I would say maybe 15-20 per layup. Yes then can add up but item 1 above makes up for the lost time easily. 3. VB can be rather expensive in initial costs, however most of the materials can be reused with the exception of the bleedply. 4. You can layup and VB bothside of a part at the same time which can save time if your the type who works on one part at a time. If you do this you must perferate the foam so that the epoxy can make its way to the top. The holes should be 1" apart made with a board and finish nails. Just like a bed of nails. 5. It is quite possible and now is an industry practice to mix layup layers with carbon fiber or kevlar with e-glass. The elongation problem that was expected has not been a problem in testing results. 6. There are substitute materials for filling rahter than using dry micro and flox. One of these is a structural adhesive from AA. Works well, pours likes cake frosting and is very strong. The use of plastic Q cells rather than micro has may advantages. One advantage is workability in dry micro situations and weight. 7. It has been found that when finishing a compisite plane, that if you use an epoxy primer mixed with micro w/o micro fillling this work very well and eliminates the micro finishing step and weight. All in all the class was pretty good. One of the attendees was Terry Shubert from Central State. Terry's a real canard plane encylopedia. The class also lightly covered how to use and make molds but we just don't have to deal with those (thank goodness). Tim Sullivan (tims@enet.net) Phoenix, AZ | * | Cozy MK IV Builder #470 |-----(/)-----| The journey begins 8/10/95 / \ o o Date: Wed, 20 Sep 1995 00:52:42 -0400 From: JHocut@aol.com Subject: Vacuum bagging Tim Sullivan made some very good points about vac. bagging. One question on # 4. >4. You can layup and VB bothside of a part at the same time which can >save time if your the type who works on one part at a time. If you do this >you must perferate the foam so that the epoxy can make its way to the top. >The holes should be 1" apart made with a board and finish nails. Just like a >bed of nails. Is this saying that I would need to poke holes all the way through my canard, for instance? Is the epoxy going to make it's way all the way through the canard's foam core? Am I misunderstanding? Also, on the subject of vac bagging, does anyone know of data concerning weight reduction and increased physical properties w/ vac bagging. I've heard lots of opinions on the subject, but so far haven't seen any facts backed up by experiments. If I were to make a few test layups, is there someone out there I could send them to for testing? (We're talking free services here, I'm building an airplane and am BROKE) Thanks Jim Hocut (Cozy IV # 448) Thu, 21 Sep 1995 10:19:50 +1000 Date: Thu, 21 Sep 1995 10:12:02 +0200 From: parkyn@citr.uq.oz.au (Nick Parkyn) Subject: Vacuum bagging I refer to mail from Tim Sullivan (>>) and Jim Hocut (>): >Also, on the subject of vac bagging, does anyone know of data concerning >weight reduction and increased physical properties w/ vac bagging. The weight saving of vacuum bagging over conventional construction reported on the Cozy Classic molded by MAP in France is 15kg. This construction is vacuum bagged in a female mold. By vacuum bagging separate layups while using the conventional construction technique would give lower weight savings since not all layups would be vacuum bagged only the major structural ones. Laminate physical properties are up to 10% better - based on glass to resin ratios - you would not require testing as number of plys etc. would remain as per plans, and laminate properties would always be better than those assumed by the laminate designer. >4.You can layup and VB bothside of a part at the same time which can >>save time if your the type who works on one part at a time. If you do this >>you must perferate the foam so that the epoxy can make its way to the top. >The holes should be 1" apart made with a board and finish nails. Just like a >>bed of nails. >Is this saying that I would need to poke holes all the way through my canard, >for instance? Is the epoxy going to make it's way all the way through the >canard's foam core? Am I misunderstanding? This depends upon the exact situation if you can "bleed" the a foam cored part on both sides you do not need bleed holes through the foam. A canard would be vacuum bagged to allow "bleed" on both sides so holes would not be required. Bleeding through the foam is not optimal as the resin in the holes adds weight. Vacuum bagging requires a lot of practice and experience with different type of parts which require different types of techniques,as with most things it is not as easy as it looks especially on large parts! >>5.It is quite possible and now is an industry practice to mix layup >>layers with carbon fiber or kevlar with e-glass. The elongation problem >>that was expected has not been a problem in testing results. Be careful - this statement is not strictly true! Using layers of different materials in a laminate is called hybridisation. There are two types: o Inter-lamina hybridisation - different materials as different plies. o Intra-lamina Hybridisation - different fibres woven into a fabric which is used as a ply. In inter-lamina hybridisation the different properties of the materials in the different plies must be considered because of load paths (how the loads are shared by different plies). The design of these laminates is not trivial and the position of the different materials in the ply stack is important. If anyone is interested in more details regarding vacuum bagging, hybrids and KEVLAR, Carbon fibre etc. - an excellent book "Composite Concepts and Techniques" is available from: Design and Multimedia Systems P.O. Box 1609 Milton Business Centre Milton Queensland 4064 Australia. Price is US $19-95 plus US$6-50 postage. Nick Parkyn #0008 Date: Tue, 26 Sep 1995 09:42:29 -0500 "Marc J. Zeitlin" From: tims@enet.net (Tim Sullivan) Subject: Fiberglassing Wood Just a quick question.... When fiberglassing over wood is it necessary to use micro between the wood and glass? Seems to me that since the voids in wood are not a problem (read almost nonexistant) that micro would not be required or is there a bonding issue that I'm not seeing. Thanks Tim Sullivan (tims@enet.net) Phoenix, AZ | * | Cozy MK IV Builder #470 |-----(/)-----| The journey begins 8/10/95 / \ o o From: Marc J. Zeitlin Subject: Fiberglassing Wood (fwd) Date: Tue, 26 Sep 95 13:04:51 EDT Tim S. asks: > When fiberglassing over wood is it necessary to use micro between >the wood and glass? Seems to me that since the voids in wood are not a >problem (read almost nonexistant) that micro would not be required or is >there a bonding issue that I'm not seeing. The answer from all the directions I've ever seen is "no". You don't need (or want) anything between the wood and the glass. Believe me, you won't be able to peel the glass off the firewall or the longerons :-). -- Marc J. Zeitlin Email: marcz@an.hp.com Wed, 27 Sep 1995 09:05:41 +1000 Date: Wed, 27 Sep 1995 08:57:48 +0200 From: parkyn@citr.uq.oz.au (Nick Parkyn) Subject: Fiberglassing Wood If you layup a glass laminate directly onto raw wood the side of the laminate touching the wood can become resin starved as the wood grain absorbs a large amount of resin. It is best to saturate the timber with resin only, let this soak in, cure and seal the grain. The surface is then lightly sanded to remove the surface roughness and provide a "key". The glass layup is then laminated onto this surface. If micro is used between the glass laminate and the timber it would tend to prevent resin starvation of that side of the laminate. Nick Parkyn #0009 Date: Wed, 27 Sep 1995 11:51:24 -0500 "Marc J. Zeitlin" From: tims@enet.net (Tim Sullivan) Subject: Re: Fiberglassing Wood >If you layup a glass laminate directly onto raw wood the side of the >laminate touching the wood can become resin starved as the wood grain >absorbs a large amount of resin. It is best to saturate the timber with >resin only, let this soak in, cure and seal the grain. The surface is then >lightly sanded to remove the surface roughness and provide a "key". The >glass layup is then laminated onto this surface. I have glassed one side of the firewall and (yep) I had to use alot more resin than expected. The wood got a good dose. The glass came out just fine but I tend to really pour on the resin since wetting up at 100+F here in PHX is tough. Thanks Tim Sullivan (tims@enet.net) Date: Thu, 28 Sep 1995 10:50:53 -0400 From: TMKPIDA@aol.com Subject: Re: Fiberglassing Wood (fwd) GADD NO!! No micro between wood and glass!! Experience level: I am at glassing the outside of the fuselage. My advice: Re-Read the beginning of the manual. i.e.: Just use a thicker coat of epoxy. Remember, the wood should be roughed up a bit (36 grit paper). TMK (#0248 MKIV) Date: Thu, 28 Sep 95 13:18:23 EDT From: "Nick J Ugolini" Subject: Vacuum bagging Hi YOUALL (as they say here in the south) I have been reading with some interest the discusions about vacuum bagging, and have some thoughts of my own. Using conventional glass layups (as discussed in the plans) a builder is lucky to achieve a 55-65% (or more) resin-to-glass layup, which varies from layup to layup. Vacuum bagging reduces the resin to glass ratio to 35-40% or less. Vacuum bagging ONLY reduces the amount of resin and air bubbles (non lamination) in your part. More strength NO, less weight YES. Why? You must keep in mind that resin only holds (entraps) the glass fibers and spreads the tensile loading to ajacent fibers through SHEAR strength. Exact resin/hardner combination is needed to develope maximum shear strength. Additional resin means larger distances between glass fibers, thus increasing the shear forces in the resin. Resin also provides the majority of COMPRESSION and IMPACT strength in a layup, BUT very little tensile strength. Tensile strength is critical, and is mainly what you are after with the layups. Compression and impact strength is not as critical. Our plane is mainly designed for tension loading. All this means is.. .... the higher the resin ratio in your plane, the more useless weight you are carrying with little increase in the essential strength your are looking for in your plane. Ideally, you should be shooting to reduce the amount of resin in your plane. A 50/50 resin to glass ratio for hand layups is considered very good. I routinely get 45% or less, which is getting close to vacuum bagging without the expense. Sometime, try weighing all your materials in a layup to see what kind of ratio you are achieving. There is a very easy way to reduce the resin ratio, AND get very consistent layups. I use this method, and, when comparing my layups to another Cozy builder in my area (part per part), I ALWAYS weigh in less than his layups, and the thickness of my layups is thinner (ie. the hardpoints) than his (less resin). This is my procedure. You need an electronic scale (about $65.00), and plenty of plastic bags. I bought a roll of small CLEAR trash bags. 1. Cut your cloth pieces to whatever size required for the layup. Cut a little oversized (appox 1/2") because the cloth edges will sometimes unravels a little bit. 2. Weigh each piece with the scale and record the weight (I weigh all the pieces I need for the layup and record the weight and layup order number on little yellow stickies I place on the cloth). 3. Calculate the amount of resin and hardner for the epoxy you need. I used a spread sheet, and made a 3 column table which compares Cloth weight, Hardner weight, and Resin weight for a series of cloth weights for the type of resin I am using. Remember: *** THE WEIGHT OF THE CLOTH MUST EQUAL THE WEIGHT OF THE RESIN/HARDNER. **** Your layup's starting point will be EXACTLY 50/50 cloth-resin ratio. Consistantly. You're already ahead of the game! I don't recommend a epoxy pump because they are not always as accurate (clogging, bad seals, etc) as a electronic scale. You need exactly the right amount of hardner to resin in order to form the proper molecular bonds (maximizes shear strength). 4. Record the required resin/hardner amount on each sticky. ** For small layups pieces, I combine the pieces (weights) together, (ie hardpoints) and mix resin for 5 or more pieces at the same time and do them all at once. When doing larger pieces of cloth, you may only want to do one at a time. I have found that about 150 grams of cloth is the maximum weight which is comfortable for me. 5. Put your mixing cup on the scale (zero the cup's weight out - the Tara weight) pour the resin in the cup, and add hardner. The weight of resin and hardner in the cup must equal the cloth weight. Mix competely. 6. Put the cloth and mixed resin into a plastic bag and knead the bag until the resin COMPLETELY saturates the cloth. The cloth will become clear. 7. Pull the saturated cloth out of the bag and place on your foam. Don't forget to micro, flock, as necessary. Use a squeegie to work out any air bubbles. As alway, take time to MAKE SURE your cloth fibers are correctly oriented and very straight. Any waviness in the fiber threads, will mean the threads will not be proper loaded when placed in tension. (Try pulling a wavey rope. You must pull it straight before it will take a load). 8. You can reuse the plastic bag and cup for additional layups until the resin starts setting up, then use a new one. 9. Go back to step 5 for next layup. 10. When the layups are completed, peel ply and use a rubber squeegie to smooth the surface (which removes additional resin). 11. Let the part harden then remove the peel ply. You will have the best looking layup you have ever seen. The resin that remains in the bag, cup, mixing sticks and peel ply will reduce the original 50/50 ratio to something much less depending on the number of layups, bag and cup changes. I feel my plane's weight will be very close to what could be achieved by vacuum bagging all parts. This may sound like a bit of work, but... once you are set up and rolling, it is very quick. The most time is spent kneading the cloth, is balanced by the time you would have spent working the resin into the cloth with a brush. Try getting a helper or two to knead while you are laying the cloth out thus speeding the whole process up. The reduced weight, complete saturation of cloth and consistent layups are worth it. Hey, if you are in a hurry, buy a Velocity. Good Luck. Nick Ugolini #002 Fri, 29 Sep 1995 10:25:42 +1000 Date: Fri, 29 Sep 1995 10:17:39 +0200 From: parkyn@citr.uq.oz.au (Nick Parkyn) Subject: Re: Nick J Ugolini - Vacuum bagging I with to comment on his email as follows: > Vacuum bagging ONLY reduces the amount of resin and air bubbles (non >lamination) in your part. Air bubbles constitute voids and voids affect the strength of laminates. Vacuum bagging also provides pressure to the laminate to core bond in sandwich structures which improves this bond. > More strength NO, less weight YES. This is not correct - MORE STRENGTH - YES AND LESS WEIGHT - YES! This can be physically proven by test samples. >Tensile strength is critical, and is mainly what you are after with >the layups. Compression and impact strength is not as critical. Our plane is >mainly designed for tension loading. This is not correct, both tensile and compressive strength is critical. If we consider one of the main structural members - the wing spars - if one spar cap is in tension, the other cap is in compression, both tension and compression caps are just as critical and failure of one will result in structural failure. The shear web is in shear but shear loads are low when compared with tension and compression loads. I would suggest that Nick consult a book on aircraft structures! Composite fibres are always better in tension than in compression and composite designers allow for this. Using only the correct amount of resin to achieve the desired glass to resin ratio and pre - wetting out on plastic is an accepted method in the composite industry for hand / wet layup structures. Any mixing methods including both pumps and weighing can be error prone and accurate mixing is essential. To ensure the quality of the laminates you can either test the actual laminates for Barcol hardness or save cured resin samples from all layups and test these for Barcol hardness. Barcol hardness will indicate that the resin has cured properly (mixing ratio was correct). Vacuum bagging will save more weight and will create laminates with better physical properties - this has been proven in the composites industry for many years. Care should be taken when vacuum bagging low density cores like Styrofoam,to avoid deforming the core only low vaccum "pressures" should be used. For higher density PVC foam cores this is not a problem. Nick Parkyn #0009 From: Marc J. Zeitlin Subject: Layup non-adhesion Date: Mon, 30 Oct 95 11:39:34 EST People; A cautionary tale: While (or after) glassing the second 4 UNI layers of the Main Spar Shear Web in chapter 14, I had a delamination occur. I had finished the 4 UNI layup, and took a break for a couple of hours. I then returned to the basement and continued on with the LWA2 and LWA3 ( 1/8" aluminum plates over the wing attach hard points) floxing. I then glassed the 3 UNI and 1 BID strips over the LWA's, and then peel-plyed the four LWA areas and reinforcements. The next evening, I pulled off the peel-ply, and on ALL FOUR LWA areas the reinforcing layup began to come off with it. I was able to peel the four ply layups almost completely off with my hands. They had not adhered at all to the UNI shear web layup that I had done only a couple of hours before. I'm using 2427 epoxy, and the basement was at ~75 deg Farenheit. It was a very humid day on Saturday, but I had two space heaters going in the basements, so I don't think the room was particularly humid - I wasn't dripping in sweat at all. Why did this happen? I'm not sure. I think I got caught in a time period in which the previous layup was just gelled enough to be smooth, but not enough so that I could sand it and get a "bite" to the surface. I wouldn't have thought that a couple of hours would have been too late, but apparently it was. I will make sure in the future that when I put on a layer of glass and epoxy that the previous layer has NOT gelled, and that if it has, I will wait for it to cure completely and then sand it. -- Marc J. Zeitlin Email: marcz@an.hp.com Date: Mon, 30 Oct 1995 12:40:02 -0600 From: Scott Mandel Subject: Re: Layup non-adhesion X-Sun-Charset: US-ASCII Marc, >A cautionary tale This really worries me. On Saturday I put the bottom of my fuselage on the fuselage. I waited about 3 hours before I flipped the bottom onto the floxed longerons (per the instructions). Everything seemed pretty tight Sunday afternoon. Do think I might have problems later? From: Marc J. Zeitlin Subject: Re: Layup non-adhesion (fwd) Date: Mon, 30 Oct 95 13:57:24 EST In response to my story about layup non-adhesion, Scott Mandel writes: > This really worries me. On Saturday I put the bottom of my fuselage on the >fuselage. I waited about 3 hours before I flipped the bottom onto the floxed >longerons (per the instructions). Everything seemed pretty tight Sunday >afternoon. Do think I might have problems later? One thing I forgot to mention in the original message was that I also tried to pry up one of the LWA's which had been FLOXED in place as described in the plans. I was able to get it off by pounding a screwdriver under it with a hammer. It (in retrospect) was on VERY tight. I delaminated the previous day's 4 UNI layup in that area when I pried the LWA off, and will have to sand it down and redo the 4 UNI locally, as well as reflox the LWA and the reinforcing layups. So, I left the other 3 LWA's alone, assuming that the pressed in place flox bonds were good, as witnessed by the delamination. I'd assume that you're fine; you've still got the taping to do on the inside (if you've done it already, see if it peels off easily) and the whole outside glassing in Chapter 7. The flox is a structural filler, not the structural tension member holding the sides to the bottom. Not to worry. -- Marc J. Zeitlin Email: marcz@an.hp.com Date: Mon, 30 Oct 1995 16:38:01 -0600 From: Scott Mandel Subject: Air Bubbles X-Sun-Charset: US-ASCII Does everyone end up with tiny air bubble a quarter inch to half an inch long on the compound corners like the bottom of the fuselage where the contoured foam meets the bottom? Are these worth fixing? Does anyone use the syringe method? Where do you get syringes? I've been sanding off all my air bubble that don't meet acceptability is this too much work? Date: Mon, 30 Oct 1995 14:56:47 -0800 (PST) From: DALRYMPLE@TEST00.MDC.COM Subject: 2427 CURING CHARACTERISTICS HI MARK, I READ ABOUT YOUR EXPERIENCE WITH YOUR DELAIMINATION. I AM CURIOUS IF THE PROBLEM MIGHT BE THE 2427 EPOXY BY HECEL. I FIRST BUILD MY BULKHEAD IN CHAPTER 4 WITH AN EPOXY THAT WAS DARK BROWN IN COLOR (I DONT KNOW IT'S NAME) OUTSIDE TEMPERATURE IN LONG BEACH WERE ABOVE 75 DEGREES AND NO PROBLEMS. THEN I CHANGE MY EPOXY TO 2427 BECAUSE I WAS TOLD IT WAS MORE SAFE TO USE. HOWEVER, I FOUND THAT FOR THE REST OF PROJECT BUILDING TIME WITH THIS EPOXY, THAT UNDER THE SAME TEMPERATURE CONDITIONS OR HIGHER (90 DEGREES - I GUESS) I HAD PROBLEMS WITH LARGE AND MULTI LAYER LAY-UPS. FOR EXAMPLE, FOR MY MAIN LANDING GEAR LAY-UPS, AFTER 2 OR 3 LAYER OF UNI I FOUND IT MOST DIFFICULT TO WET OUT THE NEXT LAYER. I HAD TO STIPLE VERY HARD AND WORK VERY FAST TO GET THE LAY-UP TO ADHERE TO THE LAY-UP BELOW. ADDITIONAL EPOXY BRUSHED ON THE CURING LAY-UP HELP WET OUT THE NEW LAY-UP. ALSO, NOTE I WAS USING A HAIR DRYER TO THIN OUT THE VISICOSITY (SP? NO SPELL-CHECK WITH USER ABUSER VAX MAIL SYSTEM) OF THE EPOXY DURING NEW LAYER LAY-UPS. THIS PROBLEM ALSO OCCURRED DURING FUSELAGE SIDE AND BOTTOM LAY-UPS. ONCE AGAIN, I DID NOT EXPERIENCE THESE CHARACTERISTICSWITH THE OTHER EPOXY. BE CAREFUL WITH YOUR WINGS BECAUSE THIS IS NO FUN:( A FEW SQUEEGES AND FEW EXPERIENCED AND FAST WORKING PEOPLE COULD HELP TURN THIS PROBLEM AROUND OR A CHANGE TO A DIFFERENT EPOXY. GOOD LUCK!! MARK DALRYPLE PLANS #361 "THE ITCHING CONTINUES! ;)" Date: Mon, 30 Oct 1995 20:58:44 -0800 From: stetson@speed.net Subject: Re: Air Bubbles On Mon, 30 Oct 1995, Scott Mandel wrote: >Does everyone end up with tiny air bubble a quarter inch to half an inch >long on the compound corners like the bottom of the fuselage where the >contoured foam meets the bottom? Are these worth fixing? Does anyone >use the syringe method? Where do you get syringes? I've been sanding off >all my air bubble that don't meet acceptability is this too much work? Depending on where you live (and the paranoria about drugs in your region), you may be able to get syringes from a drug store or medical supply house. You just won't be able to get needles. Call them first before you make a trip You can pick up hobby type styringes at (you guessed it) a hobby store, particularly one who caters to the radio control airplane crowd. These styringes have a curved plastic nipple that comes to a point. They're about a buck apiece though. Stet Elliott stetson@aol.com Perpetual Long-EZ builder Date: Thu, 9 Nov 1995 00:05:40 -0500 From: JHocut@aol.com Subject: Vac Bag - Physical Properties I have vac. bagged my forward bulkheads, seat back, and instrument panel, with a pretty significant weight reduction from the weights I've seen from two or three other builders. To get a more quantitative comparison, I glassed two identical test pieces of 0.2" "Last-A-Foam" (approx 3" X 6") w/ 2 plies bid @ 45 and 1 ply uni (top and bottom identical), set one aside to cure, and vac. bagged the other (10" Hg dP). Well, the raw pieces were both 20 grams, the vac. bagged part was 54 gm, and the "plain" part was 66 gm - that's a weight savings of 18%, pretty substantial for airplane parts. I dragged a Velocity builder buddy of mine into this (he has more toys in his shop than I do), and we ran strength tests on both parts. They were supported along the entire width at both ends, and a force applied through a bar placed across the middle of the part (we were careful to have identical placements of everything for both parts). We measured displacement (bend) vs. force for each piece, and they were darned near identical up to the limit of the scale we were using (240 lbs). We then got a different scale so that higher forces could be measured, and repeated the test. The geometries differ from the first run to the second due to constraints of the physical size of the scales, but in each case the placement of everything was identical between part A and B. Again, a plot of displacement vs. force is virtually identical for the two parts, with the exception that the vac. bagged part had a catastrophic failure (top skin cracked suddenly) at 280 lbs of force, (268 thousandths displacement) whereas the non-vac. bagged part failed much more slowly, and at a force of 315 lbs. (302 thousandths displacement). (I might note here that the vac. bagged piece looked slightly "dry", but not terribly so. I'm planning on repeating this test on pieces vac. bagged at a couple of different vac. settings.) I'd be real interested in any studies someone like, oh, maybe Hexcel may have done on this (Gordon, are you listening?). Is the approx 10% difference in ultimate strength significant enough that one should be concerned about vac. bagging the more important (structurally speaking) parts? One theory we had was that the difference in strength was due to the difference in thickness of the parts (vac. bagged 0.260, non-vac. bagged 0.290). Any input would be greatly appreciated. If anyone is really interested I can post the actual test results, or would even fax someone my graphs. Thanks, Jim Hocut jhocut@aol.com Date: Mon, 27 Nov 1995 22:38:49 -0500 From: Marcnadine@aol.com Subject: Re: Peel Ply In a message dated 95-11-27 19:05:44 EST, parkyn@citr.uq.oz.au (Nick Parkyn) writes: > >Many composite fabricators suggest light sanding of peel plied surfaces >before secondary bonding - I believe Roy Bailets also does. > > > Roy also uses Acetone as the first choice and Alcohol as the second, as a prep before second bonding. Marc N425CZ From: Lee Devlin Subject: Pizza cutter and corner tapes Date: Tue, 28 Nov 95 9:07:50 MST Randy wrote: > One thing that caught my eye was a cutting wheel and the large thick > plastic mat that was graduated with all sorts of measurements and angles > that were used to cut the fabric. The wheel resembles a pizza cutter and > is VERY sharp. Does anyone have any experience using these tools to cut, > oh say,...fiberglass? I understand that you can buy different style > wheels to make wiggle cuts, or pinking cuts. Not having ever cut any > fiberglass, I was wondering if I should get my wife one for Christmas. :-) Yes, I have one and find it useful for cutting corner tapes. The method I'm about to describe is a variation of the one Nat describes except it uses polyethylene (not wax paper) on _both_ sides and a pizza cutter. A similar technique was described here some time ago using wax paper on both sides and created a huge discussion about the evils of wax paper. Cut some clear 3 or 4 mil polyethylene big enough to lay under and fold over the amount of fiberglass cloth that you need for tapes. Pour out epoxy on the polyethylene, lay the 2 plies of BID down in it and then fold the polyethylene over the top as well. This creates a sandwich of fiberglass and epoxy inside the polyethylene. Use a squeeqy to distribute the epoxy. Even vigorous squeeging will not disrupt the fibers and you can get excess epoxy out of the tapes by squeegying it away from the cloth if needed. Using a magic marker, draw parallel lines on top of the polyethylene with the correct spacing and slice it into strips with the pizza cutter. The strips now have a protective cover on both sides which makes them easier to handle for final fitting and trimming. Then peel one side of the poly off, put the tape in place, and peel the other poly tape off of the back. Lee Devlin Date: Tue, 28 Nov 95 15:47:43 EST From: MISTER@neesnet.com Subject: Re: Pizza cutter and corner tapes My own personal preference for tapes is to use aluminum foil instead of waxed paper or poly or saran wrap for encasing the wet out glass tapes. The foil seems to smooth out easily and forms up nicely and is easy to peel off. Bob M. N342RM From: Sid Lloyd "'Lee Devlin'" Subject: RE: Pizza cutter and corner tapes Date: Tue, 28 Nov 1995 15:11:25 -0600 OR, just buy 45 degree bias tapes and cloth from Alexander. It will save you lots of leftover triangles. Sid From: Lee Devlin Subject: RE: Pizza cutter and corner tapes Date: Tue, 28 Nov 95 16:55:39 MST Sid wrote: > OR, just buy 45 degree bias tapes and cloth from Alexander. I've considered buying the bias cut tapes but did not for the following reasons: 1. These tapes cost almost 8 times as much (per sq. yard) as cutting your own. 2. The minimum tape width available is 3" which is 50% more glass and epoxy than is needed for most of the corners joints. 3. The leftover triangles are not much of a problem for corner tapes since the cut aspect ratio is high and thus the triangles are small. Lee Devlin Date: Wed, 29 Nov 1995 17:59:46 -0500 From: JHocut@aol.com Subject: Vac. Bagging Bill Schertz wrote: >Can you elaborate on what bleeder ply is, I am new to this game. Also, is >vac. bagging an option that is discussed in the Cozy plans, or an add on to >get a more lightweight part. "Bleeder Ply" is the material that soaks up the excess resin that is squeezed out in the process of vacuum bagging fiberglass parts. It's used once and thrown away, therefore the cheaper you can find a suitable material the better. I've heard of people using paper towel, old bed sheets, scrap fiberglass cloth, etc., although I really do like the material that Alexander sells (or something similar to it). Vacuum bagging is not discussed at all in the plans, it was purely my own decision to vac. bag. The advantage of vac. bagging is, of course, weight savings. I ran a couple of test pieces a little while ago to determine the approx. weight savings and saw a difference of 18%. I'm seeing, on avareage, about that same weight savings on the real live parts that I'm building. (I just finished ch. 4 and will post my build time and part weights when I can get out of this stupid motel room and return home so progress can continue on my plane). I received e-mail from another builder suggesting that the results obtained by vac. bagging depend upon the resin being used (i.e. viscosity), among other things (I tend to believe that's correct). There are really a lot of variables involved here, I'd love to hear about a book or paper that discusses this subject. I'm using Hexcel 2427 resin, and about 8" of vacuum seems to work pretty well (when I get a chance I intend to vac. bag test pieces at several different vac. levels to see how much difference there is). There's a good descriptive drawing of what's involved in vac. bagging in Alexander's catalog in the fiberglass section (don't have it with me so I can't quote tha page number). Note that they show a brass connector for getting the vacuum into the "bag", it's somewhat expensive and not really needed. I just bring my vac. tube under the edge of the plastic sheet and seal it with extra sealant matl., being sure to extend the porous bleeder ply over to the end of the tube so that the vacuum can reach everything (I think I picked this up at one of the workshops at OSH a couple of years ago). One of the arguments I've heard against vac. bagging is all the extra time it takes. I don't really think that's correct, my ch. 4 time is right about in the middle of all the times I've seen posted so far. True, other builders don't have to take the time cutting peel ply, perf. sheet, bleeder ply, plastic, laying down sealing tape, etc., but I don't spend any time squeegeeing out excess resin every step along the way. I think it comes out pretty close to a wash. The other "downside" to vac. bagging is a little added cost, plus the up front cost of obtaining a vac. pump (got mine used for $100). I think, on average, I spend about an extra $2 to $3 per layup, which is not really that bad. Sorry this got kind of long, hope it helps. Jim Hocut jhocut@aol.com Date: Fri, 1 Dec 1995 12:28:42 From: miken@csn.net Reply-To: miken@csn.net Subject: How to trim in a vacuum bag ? I'm about to start building and am intrigued with the thought of saving a few pounds by vacuum bagging. It appears that from the numbers I've heard that vacuum bagging all parts possible could save a noticable amount of weight in a complete airframe. (50-70 lbs?) I've been vacuum bagging model airplane wings for years and know it's not that difficult. However, with the way the Mark IV's layups are supposed to be done, how do you trim a partially cured part ? 1: The part is sealed inside a bag. 2: The edge(s) to be trimmed is now pressed against the side of the part. 3: If you break the seal and enter the bag before the layup is fully cured, the glass that was being compressed rebounds and draws air into the layup, NOT GOOD. I would like to build all my parts this way , but it appears that you need to look a little farther ahead and plan the layup to work with bagging. Any one with more knowledge of this ? Mike Nelson #136 miken@csn.net From: Lee Devlin Subject: Re: How to trim in a vacuum bag ? Date: Fri, 1 Dec 95 13:40:21 MST Mike wrote: > I'm about to start building and am intrigued with the thought of saving > a few pounds by vacuum bagging. It appears that from the numbers I've > heard that vacuum bagging all parts possible could save a noticable > amount of weight in a complete airframe. (50-70 lbs?) I've been vacuum > bagging model airplane wings for years and know it's not that difficult. > However, with the way the Mark IV's layups are supposed to be done, how > do you trim a partially cured part ? You could wait until after the part is fully cured to trim it. I haven't been able to knife trim since Chapter 4 since I'm usually sleeping at the optimum time for knife trimming. Therefore, I let it cure competely and then trim it with a hack saw blade followed up with a few passes with a 36 grit sanding block. It's not as easy as knife trimming before full cure, but it doesn't take very long. It's important to allow the epoxy to go into the portion of glass you want to trim off for at least 1/4 inch, otherwise it makes it difficult to cut with a hacksaw. Lee Devlin Date: Fri, 1 Dec 1995 16:24:55 -0500 From: JHocut@aol.com Subject: Re: How to trim in a vacuum bag ? Mike Nelson asked about trimming parts that are vac. bagged. OK, here's my 2 cents worth. I just leave the vacuum pump on (actually I have a pressure switch so that the pump only has to run intermitantly) until the glass is at the "knife cure" stage as described in the plans. You'll get a pretty good feel for how long that is with a little experience. I'm using 2427 resin, and approx 10 hrs. is usually about right. On the other hand, a couple of my parts I wound up leaving them until the glass had more fully cured and wasn't able to knife trim. It really wasn't that big of a deal just trimming very carefully with a sabre saw. Also, I don't know if I'd go so far as to guess a weight savings in the range of 50 to 70 lbs, I'm thinking more like 30 - 40 lbs. There a quite a few parts that no matter how iminaginative you are you just won't be able to vac. bag them (like maybe the wings and the outside fuse skin - I just don't know yet). If anyone figures out how to bag these bigger parts, please let us all know, and I'll do the same. Jim jhocut@aol.com Date: Sat, 2 Dec 1995 11:14:25 -0500 From: JHocut@aol.com Subject: re: vac. bagging Dick Finn and Scott Mandell had some questions about the vac. bagging I've done so far. I'll try to answer them all at once. >Off the top of your head to you have any idea as to the per yard cost >of the bagging material. I haven't been keeping real close tabs on my added costs related to vac. bagging, but I'd guess that I averaged about $3 per layup for the bulkheads (ch. 4). I'm guessing maybe $5 or $6 per fuse side for ch. 5. Beyond that I haven't really thought about yet. I may sit down and look at the costs in more detail when I have some time (yeah right). >What kind of vacumn pump do you use? My vac. pump was bought third hand for $100 from someone I know. It's the type used to purge air conditioning systems, and is really overkill for vac. bagging, but the price was right. I built a pressure control to start and stop the pump at preset vac. settings (others use a needle valve to bleed air in and attempt to hold a const. vacuum that way). I've got about a 1 gal. vacuum reservoir (sealed up a pickle jar real good), and the pump ends up running about 1-2 seconds out of 45 seconds. About a 5 gallon reservoir would work better. I saw a post on the homebuilding newsgroup a while ago about making a vac. pump from an old refridgerator compressor. I don't remember the details off the top of my head, but if someone is really interested let me know and I can dig through my filing cabinet until I find the right piece of paper. >What kind of sealant (would plain old caulking work)? There's no question that the sealing tape (or a hardware store equivalent) works best. However, I'm cheap and have been using rope caulk, augmented with latex caulk from a caulking gun. Wherever you hear air leaking you seal with a dab of latex caulk. Lately I've just been putting down the rope caulk and laying down a bead of latex caulk around it, works just fine. (Realize that I'm talking about the flat and semi-flat parts - bulkheads and fuse sides that are bagged one side only over a non porous surface.) >do you plan to do the large layups, using vacuum bagging? >I'm not sure how you would do it on a real large layup. Neither am I, I'll figure it out when I get there (or maybe if I'm lucky someone else will have figured it out for me by then). I'm going to try to figur out how to vac. bag everything possible. >Does vacuum bagging mean no stippling? I'd give anything to not stipple. When parts are being vac. bagged, they are uniformly pressed on over the entire surface, at 8" of vac. the pressure is approx. 4 psi. So over a 1 square foot surface you've got the equivalent of 576 pounds. That's pretty effective at pressing the glass into place (and holding it down on corners and irregular surfaces) and squeezing out any air bubbles. Hope this is informative. I definitely don't have all the answers yet, I'm still formulating my battle plan for the wings, exterior fuse skins, etc. Maybe someone can figure it out for me before I get there. Jim Hocut jhocut@aol.com Date: Fri, 8 Dec 1995 03:27:54 -0500 From: Fritzx2@aol.com Subject: Chapter 6 Fuselage Interior Bottom Layup Hi Gang, The following is my description of the events prior, during, and after the glassing of the fuselage interior bottom at the end of Chapter 6 for my MK IV. The Saturday following Thanksgiving I glassed the inside of the fuselage bottom as described in the plans at the end of Chapter 6. The layup, including all the 2 ply BID tapes, was completed in exactly 12 hours as permitted in the plans in the last section of Chapter 6. The room temperature during the layup was maintained at 73 degrees F. Hexcel 2427 epoxy was used. At the end of 2 ply taping the interior fuselage bottom to mating surfaces, there were doubts in my mind that I had not completed the taping soon enough to make a good bond between the newly glassed bottom and the 2 ply BID tapes even though I finished in 12 hours. To have some nondestructive means of determining if my doubts were substantiated, I "taped" a leftover piece of 2 ply BID tape to the interior of the fuselage bottom adjacent to where the front wheel well will be. Not that this place was any better than anywhere else, but rather it was accessible out from under the inverted fuselage (and after a loooooong day, that was a good thing). In a 16 oz mixing cup I had some very thick leftover epoxy from the glassing of the fuselage bottom to which I also taped an extra piece of 2 ply BID tape. After 3 days of waiting ( the hardest part), I attempted to remove the test tapes. As I suspected, the test tape released from the bottom of the fuselage easier than peel ply placed on the layup. The tape connected to the epoxy in the mixing cup seemed harder to delaminate but easier than I thought it should be for a good bond. I knew at that point that it was time to remove some of the permanent tapes on the interior of the fuselage and try to determine how well they had bonded with the fuselage bottom. Without damaging the underlying skins, I removed the 2 ply BID tapes (located between both sides of the fuselage and from between the instrument panel and the front of the front seat) that joined the bottom of the fuselage to the sides, bulkheads, and air duct 4 days after the marathon layup. I estimate that the bond strength between the tapes and the newly glassed interior fuselage bottom when compared to the same tapes attached to the sides locally sanded with 36 grit sandpaper to be approximately 50 % to 70 %. Interior fuselage bottom to 2 ply BID tape interlaminate strength ------------------------------------------------ ~= 50 to 70 % Fuselage side to same 2 ply BID tape interlaminate strength This ratio is meaningful only if the layup of the 2 ply BID tape to the fuselage side was done properly and consistently which I'm pretty sure it was. In order to PREVENT DAMAGING the underlying structure, I could not apply a pure shear stress to the tapes as I think they will be stressed in service, but rather I was forced to apply a normal force to get the tapes to release. When enough normal force was applied between the tape and the bottom to initiate a delamination, the propagation of the delamination can be best described as a popping loose. The delamination between the fuselage sides and the 2 ply BID tape was as I expected it to be for a good bond to a previous layup that was prep sanded with 36 grid sandpaper and epoxy painted before attaching a subsequent layup. It is difficult to describe, but, if you have ever removed a layup, hard point, or anything else that should have bonded to a partially cured prior layup, you will know what I am trying to say and if you haven't, hopefully you will know what to look out for. To be honest, these observations are down right qualitative NOT quantitative. I am by no means an expert in the area of fiberglass reinforced composite structures. In fact, this is my first attempt at building a plane. From some engineering courses I have taken, though, I do know that interlaminate strength is a very important factor in determining ultimate structural strength. As far as I can tell, in the case of taping the interior sides or bulkheads to the bottom, the interlaminate bond is the only means of transferring the stress from tapes to bottom, sides, or bulkheads. Do NOT misconstrue this information as reason to start ripping your plane apart. Just keep it in mind when making future layups. I would welcome any comments or experiences anyone else has had regarding subsequent layups applied to a partially cured previous layup. Please note that my email address has changed to AOL listed below. My original inquiry to Marc was made while I was test driving Prodigy. I tried both AOL and then Prodigy and decided that I liked AOL better. John Fritz email: fritzx2@aol.com From: Marc J. Zeitlin Subject: Peelply/dry area (was Bulkheads/Peelply) Date: Wed, 13 Dec 95 18:15:21 EST Dick Finn wrote: >Eventually you will cover these areas with an thick micro mixture >during the finishing process so that they will not show. Usually, but not always. You probably won't micro your bulkheads or fuselage inside, since you will either upholster it or zolatone it or both. You may have to micro some areas, if they're very rough. >Dry areas are apparent from the whitish appearance. If you have a dry >area you will recognize it immediately. The peel plyed areas should >look like they are ready for finishing. This was certainly true for the safety poxy, and I'm told for the RAE stuff. The 2427 (and William didn't state which epoxy he was using) is a lot clearer than the others, and it can be very difficult to see dry areas - I find I have to view the surface at an oblique angle in strong light, and move around a lot looking for contrast and reflection changes. So, if you're using 2427, it's a little harder, but the dry areas are definitely different than fully wetted areas. >......... Nat is real good about specifying glass directions. The >plans are so detailed that it is easy to miss one detail among many. In >many cases I've found that rereading a couple of times often allows me >to find the specific thing I'm looking for. Seconded. William, if you still can't figure it out, feel free to give me a call at home one evening after 10 PM EST and I'll be happy to look at my parts and in the plans to help. -- Marc J. Zeitlin Email: marcz@an.hp.com Date: Thu, 28 Dec 1995 15:45:00 -0500 From: Dick.Finn@FNB.sprint.com Subject: Re: Latex gloves Unfortunetly I have had opportunity to become familiar with Laytex problems. My daughter has Spina Bifida and requires intermitant catheterization. The more flexible catheters are made of Laytex. Over the past few years when Erin went in the hospital (sadly she's in again over Christmas) her room and bed are labled with a sign that reads in large letters "LAYTEX PRECAUTIONS". Basically they do not use Laytex based IV tubing, gloves, etc. for fear that she will develop an allergy over time. All of us who use epoxy know how allergies can sneak up on you over time. I have had some discussion with her doctors and nurses about laytex allergies. Basically they try to use vinyl gloves. One surgeon indicates that he use vinyl for everything but surgery. He feels that Laytex provides better sensitivity. One of the nurses feels that her skin has become sensitized to the powder in either type of glove. She was real interested when I told her about Ply-9 but was concerned that it was water soluable. She washes her hands a lot. Bottom line is that thosae of us who are building plastic planes probably don't need something else to become allergic to. I suggest double vinyl gloves (some I have tried seem to have small pin holes) with Ply-9 barrier creme. Dick Finn ______________________________ Reply Separator _________________________________ Subject: Latex gloves Author: marcz@hpwarhw.an.hp.com at INTERNET Date: 12/28/95 11:03 AM People; While watching Nova on PBS the other night, I discovered what it is in latex gloves that causes allergies. -- Marc J. Zeitlin Email: marcz@an.hp.com