Chris, Concur with Mark.
I don't think there is going to be any value in doing the calculation. As I recall from my engineering courses on aerodynamics, the equations are just predictors - you must test the airfoil to get the results. It is a circular loop; calc - test - revise your original data to conform to results, do all over again. That is why wing tunnel testing is still required. There are plenty of KRs flying. The stall speeds are pretty close to the published data. Keep it light and it will stall at 50-55 mph. Thanks, Rob Schmitt N1852Z Kansas City, MO -----Original Message----- From: KRnet [mailto:krnet-bounces at list.krnet.org] On Behalf Of Mark Langford via KRnet Sent: Tuesday, November 29, 2016 6:51 AM To: KRnet <krnet at list.krnet.org> Cc: ml at n56ml.com Subject: Re: KR> Useful Load Kayak Chris wrote: > Can i assume that no one has used the formula to determine stall > speed? Not sure how to with the RAF48, no idea what the Coefficiant of > Lift is, although the "new" airfoil probably has it someplace, or what > to input with the density of air number. Anyone care to take a stab at > it with the KR1 or 2? See the diagram next to the bottom of http://www.n56ml.com/kraf48.html for the max lift coefficient, which is the Eppler code diagram, and was done fairly recently, calculated from the coordinates of the RAF48. I don't claim to be an aerodynamicist, but I would choose use the solid Re (Reynolds number) line (1x106) curve to be conservative (based on 50 mph stall at 15 degrees AOA, standard air density, and 42" average wing chord (anal extraction). This gives a ~Re of 1.7M or so (and the solid plotted line represents 1.0M). I'd work the details and give all my assumptions, but as soon as I do, some real aero engineer will pick it apart to make me look stupid, so I'll let him make the assumptions and provide results, and take the glory. I did this calc 20 years ago, and the units were the PITA, but using an online converter, it makes it easy. If nobody's done it by this weekend, I'll do it again. I haven't volunteered because I've (almost) learned to quit volunteering to do stuff that other people can do...I couldn't get everything done that I plan to do before I die, even if I lived another 50 years! [I'm getting selfish with my time]. The table at the very bottom of the page is for the RAF40, which is something like 1.33 at 16 degree AOA "un-flapped", which is what almost all of the KRs are. And the KRs that have flaps are not full span, for sure. It's provided as it probably came from real wind tunnel data, but was likely generated in the 1930's or 40's, although the thinner chord would likely have a little less lift anyway. Density of air is "standard air density", which you are probably familiar with, standard pressure and temperature. Either find a density that's in the proper units, or put conversion factors in the equation. I'm supposed to be working right now... Mark Langford, Harvest, AL ML "at" N56ML.com www.N56ML.com _______________________________________________ Search the KRnet Archives at http://tugantek.com/archmailv2-kr/search. Please see LIST RULES and KRnet info at http://www.krnet.org/info.html. see http://list.krnet.org/mailman/listinfo/krnet_list.krnet.org to change options To UNsubscribe from KRnet, send a message to KRnet-leave at list.krnet.org
