And having said that, here's one from Don Reid where he advocates running the grain horizontal, rather than vertical. I'd trust just about anything Don says as gospel. ---------------------------------------------- List-Post: krnet@list.krnet.org Date: Jul 20, 1999 8:27 AM
From: Donald Reid <donr...@erols.com> Subject: Re: Grain direction.....who cares it's plywood...my turn at a 'STUPID' Question Tim wrote: > Like Aircraft Plywood is either 90 or 45 degrees, I assume this is how > the ply's (3-7) are layered. So grain direction of the top sheet is of > interest, but I wouldn't think the orintation is as critical in dealing > with the Spar web as perhaps Aluminium ..... OK, here are some numbers. Anyone who is interested can make up their own mind. All data are for birch plywood and taken from ANC-18, Design of Wooden Aircraft Structures. (The thick pieces are included just to show the effect with more plys) thickness # plys parallel perpendicular 0.125" 3 15.17 5.544 0.160" 5 21.46 11.47 0.410" 7 131.1 80.91 All plys are equal thickness. The numbers are moment for fiber stress at the proportional limit in units of inch-pounds per inch of width. As to why the KR plans specify a vertical orientation, it is because Ken Rand and Stu Robinson got it wrong. ----------------------------------- Mark Langford, Huntsville, AL N56ML at hiwaay.net see KR2S project N56ML at http://home.hiwaay.net/~langford
