What altitude did you use for the test? 12 degrees C is 3000 feet for the standard atmosphere. The predicted best glide numbers in the table were computed for zero sink using the AoA for estimated best L/D for the new airfoil without accounting for wing washout.
This page is a good discussion of glide performance: http://142.26.194.131/aerodynamics1/Performance/Page3.html Right now I'm having even more fun with numbers My drag numbers are not looking good. From the graph it looks like Cd = 0.008. Using the equation for induced drag, Cdi = CL^2 /(pi AR e) where e is an efficiency constant (the Oswald efficiency factor) typically between 0.7 and 0.9 (it is a perfect 1.0 for an eliptical wing with no fuselage)and the aspect ratio for the KR2 of 5.5, I calculate Cdi = 0.038 using e = 0.8. A 1075 lb plane descending at 566 ft/min is generating 18.44 HP. For the standard atmosphere at 2000 feet, using the graph Cd at 75mph the wing would be generating 1.7 HP of drag. Using Cdi it would be generating 8.0 HP of drag. The max L/D occurs when the induced drag = the parasitic drag. Which means total drag should be 16 HP if this is the best glide speed which translates to a descent rate of 489 fpm. If you use 0.7 for e (lower values are associated with boxy square wings and large fuselages), Cdi = 0.043, induced drag is 9.1 HP and descent rate is 559 fpm. Your numbers for 70 mph, 566 fpm sink give a L/D ratio of 10.9. All three combinations below give an L/D of 10.9 (for AR = 5.5). e | 0.7 | 0.8 | 0.91 Cdp | 0.02545 | 0.02909 | 0.03303 CL | 0.555 | 0.634 | 0.72 Having stared at equations for hours now I think I have an idea on how to predict the best glide speed based on measuring the sink rate at two combinations of weight and velocity. I'll try to describe it after getting some sleep. -- wesley scott k...@spottedowl.biz ----- Original Message ----- From: "larry flesner" <fles...@midwest.net> To: "KRnet" <kr...@mylist.net> Sent: Tuesday, July 06, 2004 6:30 PM Subject: KR> CL eqns available ?? Stall speeds > > > >It wasn't readable so this time I pasted into notepad to convert it to plain > >text and then still had to add formatting. It should be in straight ascii > >now. > ++++++++++++++++++++++++++++++++++++++++++++++++++++ > > > Wes, > > I'm still having trouble making sense of the numbers. My KR at > approx 1075 pounds appears to have a best glide speed, from > test flown, of about 75 mph indicated. If I read my notes > correctly it was 12 degrees C and pressure of 29.99 inches. > Does that sound about right. I figured a decent rate of > 535 fpm. Not bad for an airplane with a 20 foot wingspan. > 70 mph indicated was very close with 566 fpm or > a 3 second difference in 500 feet of altitude. I'm not sure > my flying was that percise and either of these figures would > have a + or - error. > > My best rate of climb appears to be between 80 and 90 mph > but it was hard to duplicate the numbers from one test > to the next so I'm not sure how accurate they are. > > Larry Flesner > > > > > _______________________________________ > to UNsubscribe from KRnet, send a message to krnet-le...@mylist.net > please see other KRnet info at http://www.krnet.org/info.html > > >
