I spoke to Ed Sterba about that a few years ago and he told me that low drag planes like the KR and the Midget Mustang can go faster than the theoretical pitch will allow.
I am not a prop expert, but if I had to take a wild guess as to a theory which may or may not be correct I would look at this. Prop pitch is not as simple as the angle of incidence of the airfoil. A propeller is not a screw that exactly moves so many inches forward for each revolution. For one thing, it is an airfoil, not just a flat surface. It is not "screwing" its way through the air, it is creating lift 90 degrees to the axis it is spinning. And if it were a screw you need to remember that the root is a much higher pitch than the tips so the prop would "screw" its way further at the root than the tip. The effective distance it would "screw" forward is somewhere between the pitch of the root and the pitch of the tip and depends on the drag of the plane. Or to sum it all up, it is PFM and black magic and the formula, as Mark says, does not always fit, it is a rule of thumb to get an approximation only. -------- Original Message -------- Subject: Re: KR> [CorvAircraft] Prop From: Mark Langford via KRnet <krnet at list.krnet.org> List-Post: [email protected] Date: Sun, June 12, 2016 7:32 pm To: CorvAircraft <corvaircraft at list.corvaircraft.org>, 'KRnet' <krnet at list.krnet.org> Cc: Mark Langford <ml at n56ml.com> That equation has never worked for me either. If it makes anybody feel any better, Joe Horton reminded me today that he can reproduce 180 mph TAS on a regular basis, and his ASI system is well calibrated. He also has a nosewheel out front. Temperature and altitude are factors, and of course RPM and weight of the plane. I flew the KR2 (old wing) with a 54x50 prop today at WOT at 168 mph TAS at about 2500 ft, so I'm getting over 100% efficiency. Bottom line is this equation doesn't fit KRs. Properly built, they are simply more efficient than most airplanes out there, especially at the time that equation was probably hatched...I'm guessing the early 1940's. Mark Langford ML at N56ML.com http://www.n56ml.com _______________________________________________ Search the KRnet Archives at http://tugantek.com/archmailv2-kr/search. To UNsubscribe from KRnet, send a message to KRnet-leave at list.krnet.org please see other KRnet info at http://www.krnet.org/info.html see http://list.krnet.org/mailman/listinfo/krnet_list.krnet.org to change options
