Lite Ply for spar shear webs or ribs?


Help Support HomeBuiltAirplanes.com:


Well-Known Member
Nov 13, 2007
Please don't kick me too hard for asking this...
What are the possible dangers of using lite ply (poplar plywood) for spar/rib shear webs? Assuming that it is strong enough for my design, and I can confirm that the strength is adequate by some rudimentary testing, why not use it for shear webs of spars or ribs?
The reason for asking is 1) for the same weight lite ply will be a lot thicker (I am guessing 1.5-2 times?) than birch plywood, but probably only a little thicker than mahogany plywood? 2) the price is 3-4 times lower than the "real" stuff (see http://aircraftspruce.com/catalog/wppages/liteply.php ); 3) it is very easy to work with. The thickness will help to resist buckling in the shear webs. Instead of 1-1.6mm birch plywood I can use 3mm lite plywood and not worry about the shear web getting "wavy" at extreme loads.
If I use proper protection measures (epoxy varnish) will lite plywood have similar longevity as birch or mahogany plywood? This is my major concern. I suppose lite ply does not conform to any standards and is not designed to withstand humidity and temperature variations.
Thanks in advance for any advice.


Well-Known Member
Sep 20, 2003
Corona CA
Sounds like an ideal material for the webs for ply ribs to me. I admit I never heard of it.
Ribs are such lightly loaded parts that a thicker, lighter material than the usual birch ply seems perfect. At that price, I'd simply make a few trial pieces and see how it performs.