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#1
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Replace fabric with glass
Most of the fabric covered aiplanes I've seen didn't seem that hard.
That is, you could walk up to them and push the fabric in with your hand. The way I understand the fabric process, it is basically a composite structure. You have a nylon cloth with a paint "epoxy". Could a much stronger and lighter covering be made by wetting out some 2.5oz glass cloth on plastic, waiting till it's tacky and then wrapping it around the airframe? The epoxy would be much lighter than paint, and fiberglass cloth is MUCH stronger than nylon. I've seen some places where builders used composites in place of fabric, and it seemed that they all aimed for a multlayer, stiff panel, putting the weight far above the original. I just don't understand why? -- http://www.ernest.isa-geek.org/ "Ignorance is mankinds normal state, alleviated by information and experience." Veeduber |
#2
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"Ernest Christley" wrote in message m... Most of the fabric covered aiplanes I've seen didn't seem that hard. That is, you could walk up to them and push the fabric in with your hand. The way I understand the fabric process, it is basically a composite structure. You have a nylon cloth Most cloth like Polyfiber's and Ceconite's is polyester, trade name Dacron. Nobody uses cotton any more because it can't hold a candle to polyester. I don't know of any use for nylon on aircraft wings. with a paint "epoxy". The coatings are nitrocellulose or vinyl base, not epoxy,afaik. Paints for Polyfiber are vinyl based or polyurethane with a flexitive. much stronger and lighter covering be made by wetting out some 2.5oz glass cloth on plastic, waiting till it's tacky and then wrapping it around the airframe? The epoxy would be much lighter than paint, and fiberglass cloth is MUCH stronger than nylon. One of the covering processes uses fiberglas cloth. I remember Ray Stits badmouthing it on his videotape. It has at least one desirable quality --- resistance to deterioration from UV rays. |
#3
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On Thu, 8 Apr 2004 15:32:43 -0400, " jls"
wrote: One of the covering processes uses fiberglas cloth. I remember Ray Stits badmouthing it on his videotape. It has at least one desirable quality --- resistance to deterioration from UV rays. that is razorback. it's weakness is that it will fret away where it goes over a former or stringer. the glass vanishes over time and you are left with glass panels joined by just the finish. polyfiber is nothing to be afraid of. it is the best system going so far. if you use polytone paint it is permanently repairable. Stealth Pilot |
#4
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Stealth Pilot wrote:
polyfiber is nothing to be afraid of. it is the best system going so far. if you use polytone paint it is permanently repairable. Stealth Pilot That's one I agree with totally. Ease of use, repairability, and a nice high quality finish. Using Polyfiber with and electric HVLP is about as easy as covering an airplane can get. Richard http://home.earthlink.net/~n6228l |
#5
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On Thu, 08 Apr 2004 20:01:51 +0000, Ernest Christley wrote:
Most of the fabric covered aiplanes I've seen didn't seem that hard. That is, you could walk up to them and push the fabric in with your hand. The way I understand the fabric process, it is basically a composite structure. You have a nylon cloth with a paint "epoxy". Could a much stronger and lighter covering be made by wetting out some 2.5oz glass cloth on plastic, waiting till it's tacky and then wrapping it around the airframe? The epoxy would be much lighter than paint, and fiberglass cloth is MUCH stronger than nylon. I've seen some places where builders used composites in place of fabric, and it seemed that they all aimed for a multlayer, stiff panel, putting the weight far above the original. I just don't understand why? The fabric must be quite taut so that the external surface of the aircraft maintains the correct shape, even when subjected to the force of the airflow. How would you achieve this with fibreglas without having excessive weight? -- Kevin Horton RV-8 (finishing kit) Ottawa, Canada http://go.phpwebhosting.com/~khorton/rv8/ e-mail: khorton02(_at_)rogers(_dot_)com |
#6
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Ernest Christley wrote:
Most of the fabric covered aiplanes I've seen didn't seem that hard. That is, you could walk up to them and push the fabric in with your hand. The way I understand the fabric process, it is basically a composite structure. You have a nylon cloth with a paint "epoxy". You have a cloth material coated with a doping silver compound to reinforce the material and make it taut, on top of which paint is applied. The former does not penatrate the material but is on one side. Could a much stronger and lighter covering be made by wetting out some 2.5oz glass cloth on plastic, waiting till it's tacky and then wrapping it around the airframe? The epoxy would be much lighter than paint, and fiberglass cloth is MUCH stronger than nylon. Keep in mind that fabric covered structures are not Load-bearing in the structural sense of the term. The fabric is there to keep the aerodynamic shape and provide an area for the pressure to act on. It is not a stressed skin structure in that the fabric takes pressure loading, especially on the wings, but does not contribute to the strength of the underlying framework as in metal skined designs. As such, the extra strength is not really required on existing fabric covered structures. You could maybe argue for a weight saving factor in the days of lead based paints, but now... There is the advantage of better UV resistance and not cracking or pealing over the lifetime. I've seen some places where builders used composites in place of fabric, and it seemed that they all aimed for a multlayer, stiff panel, putting the weight far above the original. I just don't understand why? This is where there is some skin loading required. Stressed skin designs can make the use of very thin aerofoil sections possible by taking some of the load off the spars and ribs making for lighter and stronger structures. |
#7
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Cotton (rare these days) is not worth a hoot. Probably no better lasting than
say....15 years. Linen is only good for maybe.... 20. GA |
#8
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In article ,
Ernest Christley wrote: Most of the fabric covered aiplanes I've seen didn't seem that hard. That is, you could walk up to them and push the fabric in with your hand. The way I understand the fabric process, it is basically a composite structure. You have a nylon cloth with a paint "epoxy". Could a much stronger and lighter covering be made by wetting out some 2.5oz glass cloth on plastic, waiting till it's tacky and then wrapping it around the airframe? The epoxy would be much lighter than paint, and fiberglass cloth is MUCH stronger than nylon. I've seen some places where builders used composites in place of fabric, and it seemed that they all aimed for a multlayer, stiff panel, putting the weight far above the original. I just don't understand why? There have been some fibreglass/dope coverings around for at least 45 years. I remember a couple of Stearmans that the University of Illinois had that were covered in glass/acetate dope. They looked like wrinkled shirts whenever theweather was coll & humid. I understand that CAB dope works bettere here. The shrinkage of the butyrate dope provides the taughtness that the fabric needs. Another disadvantage of this process is weight -- glass weighs more than Dacron. The glass process is also more susceptable to "ringworm" -- little ring-shaped cracks in the finish. As others have posted, fabric provides very little in the way of structural loads -- all it really does is help to provide aerodynamic shape. |
#9
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Orval Fairbairn wrote:
In article , Ernest Christley wrote: Most of the fabric covered aiplanes I've seen didn't seem that hard. That is, you could walk up to them and push the fabric in with your hand. The way I understand the fabric process, it is basically a composite structure. You have a nylon cloth with a paint "epoxy". Could a much stronger and lighter covering be made by wetting out some 2.5oz glass cloth on plastic, waiting till it's tacky and then wrapping it around the airframe? The epoxy would be much lighter than paint, and fiberglass cloth is MUCH stronger than nylon. I've seen some places where builders used composites in place of fabric, and it seemed that they all aimed for a multlayer, stiff panel, putting the weight far above the original. I just don't understand why? There have been some fibreglass/dope coverings around for at least 45 years. I remember a couple of Stearmans that the University of Illinois had that were covered in glass/acetate dope. They looked like wrinkled shirts whenever theweather was coll & humid. I understand that CAB dope works bettere here. The shrinkage of the butyrate dope provides the taughtness that the fabric needs. Another disadvantage of this process is weight -- glass weighs more than Dacron. The glass process is also more susceptable to "ringworm" -- little ring-shaped cracks in the finish. As others have posted, fabric provides very little in the way of structural loads -- all it really does is help to provide aerodynamic shape. There have been a lot of very informative responses in this thread, but they don't seem to address the question I have; therefore, my conclusion is that I didn't ask the question very clearly. Razorback has been mentioned several times. Everyone seems to agree that it's heavy, the glass will last forever...IF it is supported properly, and that the dope which makes it taught needs some care. Corky and several others make the point that the fabric doesn't need to be strong, it's just there to catch the wind. So let's take an example. I have an aileron that was designed for a medium weight fabric (which is 4oz/sq yard?). A 2oz FG woven finish fabric would still be much stronger by far, but it will be much thinner. Being thinner, it won't need as much "filler" (whether that be epoxy, dope, or paint). The process would go like this. I cut a piece of fabric the dimension of my aileron with an inch or so overlap. I wet out the glass on a sheet of 6mil plastic, set the aileron on top of it and bring the fabric/plastic up around the aileron sides...just wrap it over. The fabric is bonded to the ribs and around all the edges. No shrinkage necessary, since it will be the exact size. Once that cures, I repeat the process for the other side. The FG will add no more to the structrual integrity than the fabric did. It's bonded to the ribs, so no more attachment work or possibility of fretting. It has the smooth FG look, and even with an exterior coat of paint will be thinner and hopefully lighter than the medium weight fabric. Concerning Corky's excellent point about the aerodynamics, a suitably flexible epoxy will allow the fabric to have just a slight amount of give just like a fabric covering. This seems like a way to make a stronger, lighter skin without as much work. But on the other hand, I'm dreadfully afraid of falling out of the sky. How could this technique be safely tested? -- http://www.ernest.isa-geek.org/ "Ignorance is mankinds normal state, alleviated by information and experience." Veeduber |
#10
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On Fri, 09 Apr 2004 14:59:24 GMT, Ernest Christley
wrote: So let's take an example. I have an aileron that was designed for a medium weight fabric (which is 4oz/sq yard?). A 2oz FG woven finish fabric would still be much stronger by far, but it will be much thinner. Being thinner, it won't need as much "filler" (whether that be epoxy, dope, or paint). The process would go like this. I cut a piece of fabric the dimension of my aileron with an inch or so overlap. I wet out the glass on a sheet of 6mil plastic, set the aileron on top of it and bring the fabric/plastic up around the aileron sides...just wrap it over. The fabric is bonded to the ribs and around all the edges. No shrinkage necessary, since it will be the exact size. Once that cures, I repeat the process for the other side. The FG will add no more to the structrual integrity than the fabric did. It's bonded to the ribs, so no more attachment work or possibility of fretting. It has the smooth FG look, and even with an exterior coat of paint will be thinner and hopefully lighter than the medium weight fabric. Concerning Corky's excellent point about the aerodynamics, a suitably flexible epoxy will allow the fabric to have just a slight amount of give just like a fabric covering. This seems like a way to make a stronger, lighter skin without as much work. But on the other hand, I'm dreadfully afraid of falling out of the sky. How could this technique be safely tested? Ernest, from what I've read and seen in the world of fabric covered airplanes, it's really hard to substitute something for the fabric itself and do any better in the weight saving department. I've heard of people laying up fiberglass as a sheet and applying it to fuselages, but the airplane ended up being heavier than when it was covered with just fabric. Fabric works fine by the way, it was used right through WWII on a number of airplanes including bombers and fighters. The Corsair, one of the most powerful fighters to fly originally had a portion of the wing covered with fabric and even during the Korean War still flew off carriers with a fabric covered rudder. The P-51 Mustang, one of the fastest fighters of the war had a fabric covered rudder. Are you trying to save money or weight, or both? When you wet out the fiberglass fabric, it sometimes takes a lot of primer to fill the weave, depending on the weight of the cloth. That could make for a looonnnnggggg time of finishing to make it look good. So what's the thought process you're going through? Why are you interested in making the substitution? If you are looking for additional strength, you don't really have to. Here's why: When a friend of mine was covering his biplane, he thought it would be interesting to test the fabric for strength, just for fun. He had a metal stool with two loops on either side so he glued fabric across the loops and taughtened it with the iron just like he did with the wing. He then reached into his toolcabinet and pulled out a 16oz ballpeen hammer. He made a half hearted swipe at the fabric and the hammer bounced off without a mark. He swung harder and got bounced off harder. So he stepped back and lunging forward, put every ounce of his strength behind the swing. He hit the fabrice right in the middle and was rebounded so hard he almost hurt himself. The fabric was undamaged. Try that with an aluminum wing. ;-) Corky Scott |
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