Bob Tallini wrote: >>The design I would like to use is the one Roy Marsh developed for the KR2S prototype. It is a modified NACA 230012. <<
Bob, I just plain wouldn't use a 23012, no matter how modified it was. Although it was used on everything from Cherokees to Bonanzas, the stall characteristic is not something you want to intentionally build into any new aircraft. Visit http://home.hiwaay.net/~langford/23012.gif and notice how the wing stalls very abruptly. It goes from flying to stalled almost instantly (the "cliff-like" plot on the left). I believe Roy once told me he had to land at about 80 mph, and that doesn't surprise me. Why not use an airfoil that was designed specifically for the KR2S by modern methods with one of the design goals being a reasonable stall speed and gentle stall characteristic (gradual). If you haven't seen it, visit http://www.krnet.org/as504x/ for the details, and check the same curves. You'll see something a lot more gentle. Making the spar thinner will give you problems with gear mounting, wing tank capacity will be significantly reduced, and you have the strength problem (weight will go up) that you're now faced with. Yes, Roy did it, but Roy also sold his plane after a few short years. Ron Lee bought it, flew a few times, and sold it quickly. Not sure if anybody's flying it now, but I'm not convinced you really want to replicate that wing. Funny thing about that plane is that it's the "poster child" for RR's KR2S advertisements, although the wing is a completely different animal than the plans call for. If you really want to do this, I've temporarily posted some "shareware" software that will do that analysis for you at http://home.hiwaay.net/~langford/spar.zip . Plug in the dimensions and characteristics for a stock wing, then plug in the dimensions for yours, and then tweak caps and plywood dimensions until you get strength numbers the same or better than stock. This is just an approximation, as there are fine points of plywood layers and such that probably enter into it, but it's a good "ballpark" method of making sure you don't do anything stupid. Still, I wouldn't touch that airfoil with a ten foot pole. You mention this airfoil to an aerodynamicist, and he'll start shaking his head. Yes, I know Roy's son is an aero engineer, and he specified this airfoil, but he didn't have the AS504x airfoil at his disposal, and he didn't have to fly it... Mark Langford, Huntsville, AL N56ML "at" hiwaay.net see KR2S project at http://home.hiwaay.net/~langford
