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steveinindy
12-18-2011, 03:31 AM
Does anyone know what the "average" thickness of a Kevlar or carbon fiber skin for an aircraft weighs per square foot? I'm trying to do a preliminary weight calculation and I'm having some trouble with finding a reliable estimate for anything but solid foam core construction (which is not the method I am looking at using). Even if someone could just give me a good estimate on what the skin thickness for aircraft like the Lancair IV-P are at various points (cockpit and wings predominately), I can work from there.

Also how does one estimate the weight of the epoxy needed?

WLIU
12-19-2011, 11:54 AM
The problem that you are up against is that the numbers that you are looking for depend on the methods used for construction. It is pretty easy to look up the thickness and other physical properties of the kevlar or carbon fiber fabric, but you have to know what style weave you will use. The numbers are out there for the weight per volume of the resin systems, but the amount of epoxy used to wet out that fabric is a function of the method and quality of your work. Will you vacuum bag? Hand layup? How many plies? What kind of mold? Your skin may weight more or less than my skin based on our experience, the tooling and the tools that each of us uses.

The original Rutan book on Moldless Composite Construction, talks to starting by making some simple things and exactly what the final weight should be based on the ideal ration of fabric to resin. Good place to start.

You can figure your numbers out, but plan to do a lot of reading and learning. Start by Building something small like a box you can use as a step stool and carry in your baggage compartment.

Best of luck,

Wes
N78PS

Jeffrey Meyer
12-26-2011, 01:00 AM
As WLIU says, it's very dependant upon how you build and the best way to get a more accurate number is to make a test sample. But as a start you can use 0.17 lb/sq.ft (plus/minus 10%) for a 0.020" layer of carbon, kevlar will be about 10% less.
Glass will be about 20% more. First guess on the weight of epoxy is 40% of the total finished weight.
Hope this helps.

steveinindy
12-26-2011, 03:35 AM
Thanks guys. The biggest hurdle I have had with regards to this is figuring out the right amount of epoxy per square foot. I figure that working off of factors of 0.17 lb/sq foot (to account for areas of greater thickness) will at least allow me to ball park this thing for the initial calculations.

Tom Downey
12-26-2011, 10:29 AM
The folks that have completed this home work are CubCrafters in Yakma Wa. they are on line at cub crafters.com.

steveinindy
12-26-2011, 11:34 PM
Thanks Tom. I remember talking to some of the folks affiliated with them at Oshkosh last year. Nice folks.