Mark- After thinking about your post, I'm compelled to comment further. Understand going in that I'm as amateur as one can be, so I don't know what I'm talking about:
It was mentioned that Roy Marsh's son is an aero engineer and chose 23012 for Roy's PURPOSE-BUILT KR2S speedster. The magazine article that so featured that airplane several years ago, stated clearly that Roy built it to win a specific race. If that's true, let's consider what things his son might have done vs stock, toward winning the race. 1. Clip the wing span to reduce wing area and increase wing loading...clip the exact amount that will result in the lowest total drag at low altitude at design speed. The article said Roy clipped his wings from those of a stock KR2S. 2.Choose a different airfoil from the stock one. My copy of THEORY OF WING SECTIONS is back home and I'm not, but I believe I remember that 23012 has a very small twisting moment, such that when Roy flew full tilt, his horizontal tail would have to lift downward very minimally. 23012 is also thinner. 23012, like the RAF family is turbulent, so good results were had from wood-and-composite constuction. Result of all this is lower total drag at design speed. 3. Retain the KR2 planform, or the KR2S planform. Again, I don't have the URL for the site, but the U of Ill sight showing posted data by Selig has a spot where Ashok's airfoil is discussed. Somewhere in a thread from that, I found Ashok discussing the stock planform. Planform can do much to reduce drag. Turns out the stock KR2 planform is about as near-perfect as a rectangular-with-tapered-tips can come vs optimal. Lower drag at design speed. 4. DON'T BUILD IN AS MUCH GEOMETRIC TWIST...aka washout...as you would for a plane you intended to fly regularly for enjoyable (aka "safe") sport. The safest amount of twists reduces the efficiency of the wing, because the roots are working harder than the tips...this is why the roots stall first, and because the tips stall later, you retain aileron control during stalls. Take twist out to the point the entire wing stalls all-at-once and you have a wing working equally tip-to-tip. Net result is lower total drag at design speed. 5. Turbocharge the thing so you can pull more-than-stock power yet remain within the rules?@#$%? More power is as good as less drag. Now, if all that was accomplished and the airframe were built very light, we'd expect an unusually fast machine at low altitudes that would stall the entire wing at once on every landing. And of course, once we'd set the record or won the race, we'd sell it. Or simply build another wing tailored for sport flying...like the stock KR2S using one or two of Ashok's new airfoils. I remind you, this is just conjecture on my part...I don't know what I'm talking about. -Lloyd Mark Langford wrote: > 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 > > _______________________________________________ > see KRnet list details at http://www.krnet.org/instructions.html
