Sorry about the cedar comment. I had a picture of mahogony in what little brain I have left, and it came out as cedar instead. They kind of look alike, from about a hundred yards or so.
I don't have a manual in front of me right now, but I believe the manual says that either mahogany or birch is fine for skinning the fuselage, but when it comes to spars, birch is required. I may be wrong, but that's what I remember. I'll try to find an exact reference tonight. Somebody else is welcome to check for us... Mark Langford, Huntsville, AL N56ML at hiwaay.net see KR2S project N56ML at http://home.hiwaay.net/~langford