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Composites and Kevlar


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I was talking to my brother last night and he mentioned that the techniques used for building with fiberglass and composites are similar. He also suggested that this may be true for Kevlar. My understanding is that Kevlar is lighter, stronger, but more expensive.


Does anyone know anything about this? Does anyone know anything about this? Would there be any advantage/disadvantage to building something like a Cozy IV with Kevlar?



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Would there be any advantage/disadvantage to building something like a Cozy IV with Kevlar?


You could definately make a stronger and lighter airplane using kelvar, but it would be a very different airplane in terms of structure. The stresses in the wings, spar caps and fuselage are carefully calculated. When you introduce a new material you change everything, and you have to do new engineering. Nat [the designer] would be quick to tell you that you're airplane is not a Cozy.


Ever notice how the wings on a commercial jet bend on take-off as they assume the load. They're supposed to do that. Imagine that these wings were remade in a more rigid material - where would the stresses go?


It's certainly possible to use Kelvar for non-structural components such as the cowlings, but the cost of the stuff prevents many from doing even that. My spinner is made of Kelvar.


A Cozy airframe weighing about 700lb - 800lb can be built for about $15k using the recommended materials. Presuming you can do the engineering, I wonder what it would cost to build the whole thing in carbon fiber, and how much weight you'd save. How would the weight and balance be affected when you put a 300lb engine on the back?


Lots of questions - not enough answers.


The "easy" way is to do it like the plans say.

I can be reached on the "other" forum http://canardaviationforum.dmt.net

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Kevlar also has another problem, it is strong in either tension or compression,( I forget which) but not both, these planes need strength in both directions.


It is VERY hard to work with, it doesn't sand, it balls up.

maker wood dust and shavings - foam and fiberglass dust and one day a cozy will pop out, enjoying the build


i can be reached at



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  • 4 weeks later...

When I bought the plans for the COZY Nat also supplied an aircraft performance report from CAFE ,wherein test pilot C.J.Stephens comment on turbolence quote:"the flexibility of the nongraphite fiberglass/foam structure also helps soften the turbolence"


Plane will be called `Hugin`

After Odins raven

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