dyrbr_d

Is using a plywood (.8mm thick in this case) turtle deck lighter and stronger than using balsa? For balsa you would have to use formers, stringers and balsa sheeting. For this particular build they used a plywood turtle deck, front and rear formers and I don't know if there are any stringers or not, but I would assume no. It appears they build extremely light. Not much strength comes out of a turtle deck would this be a good idea?


http://www.geocities.com/CapeCanaveral/Cockpit/3328/

kdheath

The plywood is about 1/32 inch thick. I suspect that you could mold a 1/16th part of really light (4-5 pound) balsa and save a little bit. But I doubt that it would be worth it. The rest of the fuselage looks nicely designed and light, as is. If it was me, I would leave it be, unless the ply was extremely heavy for some reason.

allanflowers

It looks pretty strong to me but there are two issues worth considering. First, you probably don't need all this much strength in the rear fuselage. Secondly, balsa would also make a strong, simple structure too - and you probably wouldn't need additional formers and certainly no stringers even with balsa. In any case it would be good to wet the wood and preform it to shape, let it dry, then glue it in. If you try to force it into shape, it may pull a twist into the fuselage.
To compare balsa to the ACply, you would have to weigh both materials. AC ply is rather heavy, even in thin sheets. It is also more expensive.
Allan
PS, the pix show another example of such construction plus a method of handling the ply for preforming...

BMatthews

Plywood will tend to sag to a pure circular arch in the middle just like dry bent balsa. But as mentioned balsa could be soaked in hot water and bent over a form and allowed to dry and would hold its shape. Plywood cannot be bent so easily since the inner cross plies will still continue to try to equalize the tension in the arch and that will result in a caved in sort of upper keel line as the middle area tries to assume a circular rather than elllipcital, parabolic or otherwise free sketched pointy top arc.

And I believe that you'll find that 1/64 ply is about the same weight at light to medium density 1/16 balsa so for a free bent plywood deck to replace balsa it would need to be very thin and thus flexible.

allanflowers

I would have to agree with Bruce on the tendency for ply to "cave in" along the keel line. Now that I think about it, the model which I showed in my pix did have a former in the middle (mainly to support the FIN) and a centerline stringer. Plus, the fixture shown forces the curvature to concentrate along the center, rather than going 'circular'.