Adding Kevlar to cockpit floor or seatpan?

So if one layer of that was glassed on to the floor...would
it perform as well as an inside ply? Or does it gain
strength inside the sandwich...ie plywood?




At 17:01 19 January 2005, Brad wrote:
carb.com has some visual samples of a carbon/kevlar
hybrid cloth. The
kevlar part can be yellow, blue or red and looks quite
appealing. I
plan on using as the inside ply one layer of this material
when I build
my HP-24.

Cheers,
Brad

Earlier, Stewart Kissel wrote:

So if one layer of that was glassed on to the floor...would
it perform as well as an inside ply? Or does it gain
strength inside the sandwich...ie plywood?

Dunno how relevant this is, but in no particular order:

Kevlar can be nasty stuff to work with. The fibers are very tough, and
you need special scissors to cut it effectively. It's not so bad to lay
up and laminate. But once it's laminated and cured, it is troublesome
to drill or sand - what you get is a fuzzy hole or a fuzzy edge. And
then you have to deal with that fuzz. If you just throw resin at it,
it's easy to end up with tough little Kevlar-cored resin spikes that
stick out and poke you.

I'd guess that one layer of Kevlar inside a cockpit tub won't do you
much good in terms of raw impact protection. However, I think it will
help keep all the rest of the bits of the cockpit stuck together, and
that can help in a crash. It also might hurt. Crash sequences are very
hard to predict, so beyond general guidelines it's pretty much a roll
of the dice. But of course, kudos to Gerhard Waibel for his work in
evaluating and implementing meaningful crashworthiness improvements
backed up by actual test results.

If you do consider adding a layer of Kevlar, I'd suggest you add a
layer of glass on top of it to encapsulate it.

Also, consider carefully the weight you're adding, and that it would be
very difficult to remove. You're probably looking at about 2 square
yards of coverage; with 5 oz kevlar and 8 oz glass and then doubling
the fiber weight to account for the resin you're looking at the
ballpark of 3 lbs. That might not sound like a lot, but you'll
definitely be thinking of it on your next carry-out retrieve.

One more thing, in my experience stuff like this tends to look easier
than it is. Add two layers of stuff to an established concavity? No
problem - right? That is, until you consider that the surface has all
sorts of detail contours you'd have to work around. There are mounting
provisions for the seat and seat pan and control stick, there are
rudder cable tunnels and fixtures, the list goes on. I mean, it's
doable, but it can get to be a lot harder than you might expect.
Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com