Remeber the newsletters? Used to come in the mail, printed on paper? Back in March 1977, issue #21, page 2 had a short article on a builder using douglas fir on his KR, and how he tested and documented the substitution. The recommendation was to use 19/32" instead of the full 5/8". This gave parts slightly stronger than sitka spruce, and only slightly heavier.
A very large (for dialup, anyway) FAA document talks about wood specifications for airplane use. Reading and understanding this can help you make more informed choices regarding wood substitution. http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/0/99c827db9baac81b86256b4500596c4e/$FILE/Chapter%2001.pdf or http://tinyurl.com/6m3aj One main specification is grain slope (no greater than 15:1). Most lumberyard wood is flat sawn (cross grain more or less parallel to flat side of board). Not a problem for us with stringers, as we can rip the strips and then turn them 90 degrees. 1x6 fir in the lumberyard is about 1.5x the price of 5/8x5/8 spruce at Aircraft Spruce. If you can get two out of a board you'll come out ahead ;-) More work, less money. Your choice. But please, make an informed decision. Regards, RonB
