** Kline-Fogleman (KFm) Airfoils - Advanced Theory/Science ** - Page 120 - RC Groups
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Aug 14, 2017, 09:38 PM
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Dickeroo's Avatar
Just stumbled across this.... the second paragraph refers to the KFm2.


http://www.ijetae.com/files/Volume7I...AE_0217_29.pdf

International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 7, Issue 2, February 2017)

The increased DU 06-W-200 overall aerodynamic performance (up to nearly 2% with respect to NACA 0021) is due to an increased blade performance during downwind operation: even though the maximum torque values are generated during the upwind revolution of the turbine, downwind blade operation has proved to be determining in improving DU 06-W-200 rotor aerodynamic behavior. Finally, it has been proved that the maximum torque values generated during the operation of a vertical axis wind turbine blade correspond to mutual position where rotor blades are experiencing very high relative angles of attack, even beyond the stall limit.[14]

Karunakaran C.S et al. (2013): Authors has made an attempt to investigate and compare the flow over a typical scaled down models of NACA 23015 airfoil and Kline-Fogleman (KFm2) airfoils at different angles of attack in subsonic wind tunnel. Both were tested in wind tunnel for pressure tapping and the e lift and drag forces were calculated. The analysis were done at a free stream velocity of about 25m/s in subsonic wind tunnel. Magnitudets of static pressure admitted the quality of flow field experienced .It was then found out through comparison that the Kline-Fogleman variant with a step at 50% chord length acquired better lift characteristics. The KFm2 did not stall till angles of α=450after that it leveled off with a good L/D ratio .This can be of very useful as leveling off prohibits the risk of accidents happened by free fall at critical angles.[18]
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Aug 14, 2017, 10:23 PM
Build straight - Fly twisty
Whiskers's Avatar
I lost interest when I read, "There is, unfortunately, also a retarding force on the blade, the drag. This is the force parallel to the windflow, and also improves with angle of attack. If the aerofoil shape is good, the lift force heaps than the drag, but at very high angles of attack, especially when the blade stalls."
This seems to be written by a random word generator.
Aug 14, 2017, 11:28 PM
Must not buy more planes!
mclarkson's Avatar
"If the aerofoil shape is good, the lift force heaps than the drag, but at very high angles of attack, especially when the blade stalls."

WUT???
Aug 15, 2017, 01:56 PM
Registered User
Non-native English speakers.

I think the paragraph basically says KFm has good stall tendencies.. which anyone in this thread already knows.
Aug 15, 2017, 05:35 PM
Build straight - Fly twisty
Whiskers's Avatar
Yes, it's well known that an upper surface vortex generator will delay a stall.
Way back in the Dark Ages, before RC was a practical thing, I was into freeflight tow launched sailplanes.
I built an A2 class model with a crazy high aspect ratio wing which resulted in a cord of just 3 inches.
It was impossible to trim. It stalled at every slight disturbance and was totally noncompetitive.
However, when I glued a piece of thread along the 1/4 cord line it became transformed into a quite good performer.


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