Re: wing spars witc C grain at front?

From: ray_harlan <rbharlan_at_comcast.net>
Date: Sat, 07 May 2011 20:42:24 -0000

Pretty interesting discusions on spar grain, but I think everyone has missed the real point. As Mark has tested, the grain in spars doesn't matter for a bending situation. Since that is what spars do, it makes no difference which grain is on the front face or top face. The big reason for using A grain sheets is that they are much more consistent than C grain, since the whole sheet was grown over a short period of time and doesn't have effects from different seasons, as can C grain. Therefor, you get more consistent spars from A grain than C. It is much more economical.

Since ribs fail in bending or buckling, and they usually are nearly square, I don't think the grain matters for them either.

C grain is used when the sheet needs to be bent around a form, across the grain, as in hollow motorsticks and tailbooms. It resists bending in that direction much better than A grain and will hold its shape once baked. A grain tubes will collapse more easily and when they do, the resulting decrease in section modulus makes the beam (tailboom) weaker in bending and it breaks. Same thing goes for motorsticks, which buckle sooner if the crossection isn't maintained.

Ray



--- In Indoor_Construction_at_yahoogroups.com, "izgo" <izgo@...> wrote:
>
>
> Hello
>
> why all use A grain for wing spars (C grain up and down) and not in C grain in the front. In this way looks more trong, as the way it works in ribs.
>
> thanks.
> Igancio
>
Received on Sat May 07 2011 - 13:42:32 CEST