weskel

When scratch building and designing an aircraft where do you recommend using 5 ply plywood and also where would you use light ply?

The plane I am working on is not a 3D bird, just a low wing symetrical airfoil simar to a large GP easy sport.

I know you would use plywood for the firewall and wing attach points, where else in your experience would you use plywood?

I am assuming you would use light ply for the fuselage formers, wing saddle area. etc.

Thanks

Chad Veich

My Feedback: (60)

The 5-ply Birch is very heavy and needs to be used sparingly. As you say, firewalls, possibly wing attach points, landing gear mounts. I often use light plywood with a Birch plywood doubler for those wing ribs that have retract rails attached to them, etc. I like light plywood for fuselage formers, fuel tank boxes, and wing ribs although I will often use balsa for the formers aft of the CG and for the wing ribs in the outer most portion of the wing panels. Really depends on the size of the model being built as the larger models can handle the additional weight of the light plywood better than smaller models.

Lnewqban

http://www.airfieldmodels.com/inform...ircraft/03.htm

BMatthews

I always found light ply to be so brittle that I feel it's pretty much useless and I don't even buy it at all.    Just being exposed to it in a couple of kits years ago put me off the stuff.  Mind you while it may be brittle at least it's heavy.....

Chad Veich

My Feedback: (60)

Was it the good 3-ply Italian Poplar light plywood? This is the stuff I use and I love it. The only real drawback I have found is that it likes to warp and needs to be stored flat and often weighted. Just my .02 cents of course.

BMatthews

Likely not. I've handled poplar "bending plywood" and it was a far cry from the brittle, heavy and sad stuff I saw in the kits that used "liteply". And the liteply I've seen in the hobby shops seemed to be the same sort of brittle wood that came in the kits. So I avoided it like the plague.

As you say the poplar bending plywood is so warp'y that I never thought of using it. But I suppose for smaller bits or if there's a way to flatten and KEEP it flatit then it would be suitable for a number of uses. At least it wouldn't shatter like cheap stemware at the first rough landing like the stuff I had in those kits did.

Frankly for stability and weight if I'm looking for a cheap building material I'd rather use luan doorskin plywood. It comes flat and stays flat and is surprisingly strong as well as flexible. It's heavier than poplar bending plywood but I suspect that it could be cut to smaller cross sections to match the weight and still be stronger and more dimensionallystable. The reason that the poplar bending ply is so curvy and potato chip like is that the wood is not very dimensionally stable under changing humidity levels. But that means that the plywood will also alter dimensions when built in to a model. Most wood does in fact, including balsa. So maybe it's just a case of allowing for this or using it in smaller pieces.

Anyhow, it's pretty obvious from all this that I'm not taken with the stuff for model use. Other folks love the stuff and more power to 'em.

WhiteRook

My Feedback: (38)

i wouldnt mount the engine on a lite ply firewall, use birch aircraft ply

allanflowers

I like to use liteply but it is a material with demanding engineering properties. It falls in between regular ply and balsa in strength and weight. Because it is a three layer laminate, it is much stiffer and stronger (not the same thing, by the way) in one axis than the other. These properties represent major limitations and should be addressed in the actual design configuration.
Generally, on a ladder type fuselage side, the vertical elements must be broader because of the weakness in that direction. Tab/slot elements can also weaken the parts, at least before they are glued up. The grain should run vertically on formers so their vertical sides compensate for the weak verticals on the sides.
Balsa and basswood sticks can be combined with the liteply, working together to make a stronger unit.
I have also laminated liteply to balsa sheet (running in opposite directions) for dual layer formers which take advantage of both materials’ properties (see pix).
The major advantage of this material is allowing for easier construction using elaborately precut parts with tab-slot attachments – greatly speeding a build as well as making accuracy much easier to insure.
I think, if properly engineered, a liteply structure can nearly equal the low weight and strength of a conventional built-up assembly – and improve accuracy and reduce build time.

weskel

Those are some very interesting structure you posted, what are they for?

allanflowers

Those are formers on my 1/6th scale Siemens Schuckert D.III.
The bottom parts get trimmed off after the side and top skins have been added.