You are incorrect by you saying it is hanging on by the foam. I am making it
to where the wood and fiberglass are having full contact the entire fuselage
which it will be doing the same work as the plywood.
A few ways of doing the load is either put the glass on at a 45 or put
one going along with the longerons and the other vertical. I will still have
to do my design and annalists on this with it compared to plywood (AS&S).
Justin
----- Original Message -----
From: <ksto...@juno.com>
To: <kr...@mylist.net>
Sent: Sunday, July 13, 2003 10:45 AM
Subject: KR>Plywood vs composite skins
>
> Re: > I dont feel that plywood is a good choice.
>
> Hi everyone... from Mattoon, IL. I am a newbee to the KRNet as of a
couple of days ago. This will be my first post.
>
> I would really be afraid to use sandwiched foam for plywood. If you think
about it, when you hang 150+ lbs on the firewall, the fuselage sides between
the engine and the landing gear take a lot of stress. The top longerons are
being stretched (tension), and the bottom ones are trying to buckle
(compression). The plywood is crucial in sharing this load. It serves as
a shear web for the trussed fuselage and insures that the sides maintain
their shape in load. The outer skin of a sandwich would do very little in
sharing that shear load because it is only attached to the fuselage by the
core foam. Sandwiched structure is great for other types of loads, but I
think that the outer skin of the sandwich in that application would only
keep the wind out like Mark said.
>
> I agree with Mark in that you cannot beat plywood. I've been filling and
sanding my wings for a few weeks now and will finally just give up and take
defeat from some of the inperfections.
>
> That all said, I think it IS neat to brainstorm ideas and the 'what ifs'.
I'm not hanging my life on a plywood structure substitute, but IF I were on
a desert island that had plenty of spruce, foam, glass and epoxy. but no
plywood, I think I would sandwich the spruce members between fiberglass
layers on the fuselage. In other words, I would put foam between the spruce
members. sand it to the thickness of the side frames, and then glass both
sides (inside and out & biased to the longerons) with a couple of layers of
glass, being sure to bond the glass to the spruce everywhere. I think that
would make a much better structure than gluing sandwiched foam to the
outside of the fuselage. You would need to glass AFTER the fuselage is
assembled because I doubt that you could bend the sides after the glass was
applied to both sides of the side frames. Even if you could, the inside
skin would go into compression and do less good. You would also have lots
of fun trying to sand !
> the foam on the inside surfaces. and would need to sand perpendicular to
the longerons on the outside to maintain the fuselage curvature. After the
boat stage were finished, I think I would probably get homesick and try
using the structure to float home rather than spending 20 more years on the
island building something airworthy! (I've been building mine since '81).
>
> Good luck in whatever you decide, but just remember that neat ideas may
get you into some real trouble some day if you aren't careful! I'm sure I
will get a flashback of every deviation from plans that I have made when I
get that dude up to 500 feet for the first time!
>
> Take care,
>
> Kerwyn Stoll
> Mattoon, IL
> KR2 N40102 (60%)
>
>
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