Ray Fuenzalida wrote: >I need a clarification on the new airfoil. Are stability issues limited to >the KR and not the slightly larger KR2S? If I have the Diehl wing skins >and use those, what should I expect in the future? Slight instability? >Major instability? Please throw out some guidance.
I think a large part of the stability improvement that both Bill Clapp and Mark Jones are experiencing is due to the fact that they are flying the KR2S with longer fuselage and larger horizontal (and vertical) stabilizer (per plans). I forget how long Mark's h/s is, but Bill Clapp's is a little longer than even the stock plans call for, maybe 3" per side. If Marks's is 6" longer per side like mine, that would definitely make a difference. And the fact that the horizontal stabilizer is a "real" airfoil has to make it more effective than the thing shown in the plans, somewhat equivalent to making it larger. That horizontal stab airfoil is one that I'll take credit for, since I sized it to fit my airplane, and created the drawings that are now on the net for it. The vertical stab is definitely my creation, as it's a one-of-kind 5.5% airfoil based on a known airfoil formula, designed to fit the "stock" vertical stab spars. Another part of the stability improvement may be attributed to the improvement in decalage, lining the wings up with the fuselage so the two are not "fighting" each other for priority. That's total conjecture on my part however, and may be total hogwash, but I'm groping for an explanation. Troy does report a real improvement to his airplane though, and all that changed was his main wing and it's incidence to the fuselage. His tail size is unchanged, I think, but the tail's control surfaces were actually made smaller. Hard to say which one caused his improvement. If he did lengthen his h/s, that would certainly account for some of his improvement. Larry Flesner says his 24" longer KR2 has great stability too, and so does Jeff Scott (both have stock size tails, I think) so I still think it's safe to say that the extra length between wing and horizontal stabilizer makes a big difference. And you can't discount that most of us are far more aware of aft CG than our predecessors, so we're probably keeping it forward rather than aft, which helps there. But apparently there is also some real contribution from either the airfoils or the relationship between them that make the new wing "somewhat more stable" as Troy's experience would point out. It's hard to say for sure, but one thing that is for sure is that new airfoils have significantly less drag than the RAF48, and the AS5048/45 gives a lot more room for fuel and aileron cables in the wings, not to mention stronger spar (due to the fact that it's taller), and there are other trade offs. So I can see no reason to build a new plane using the RAF48 other than you have a set of Diehl wing skins in hand already, or don't think you can spend the time to build the wings. Bill Clapp told me the other day at SNF that he built his wings in three weeks, but your mileage will almost certainly vary. I know mine did, but I also built different ailerons, controls, and flaps into mine. I really think the old line that the new wing hasn't proven itself doesn't fly anymore though. But to answer your question Ray, there is no shame in using the Diehl wing skins, and that's a great reason to stick with the RAF48, and finish your plane quicker. I think if you are building a KR2S, you will be quite happy with the stability, whether it has the new airfoil system or not... Mark Langford, Huntsville, Alabama see KR2S project N56ML at http://home.hiwaay.net/~langford email to N56ML "at" hiwaay.net
