That is the one thing I don't like about the mahogany ply. It has three plies with the outside plies in the same direction, but they are thinner than the poplar center. All the birch plywood I have seen has plies about the same thickness and I would buy the birch if I did it again.
I have no doubts that the mahogany is fine, but I do believe that the birch would be better, not to mention that it costs less. Brian Kraut Engineering Alternatives, Inc. www.engalt.com -----Original Message----- From: krnet-boun...@mylist.net [mailto:krnet-boun...@mylist.net]On Behalf Of Wood, Sidney M. Sent: Thursday, July 01, 2004 9:21 AM To: KRnet Subject: RE: KR> spar skins Plywood has an odd number of plies with outside plies in the same grain orientation. That is the strongest dimension orientation. Sid Wood, Tri-gear KR-2 N6242 Mechanicsville, MD USA sidney.w...@titan.com ---------------------------------------------------------------------------- ------------------------------------------------ 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 _______________________________________ to UNsubscribe from KRnet, send a message to krnet-le...@mylist.net please see other KRnet info at http://www.krnet.org/info.html
