** Kline-Fogleman (KFm) Airfoils - Advanced Theory/Science ** - Page 124 - RC Groups
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This thread is privately moderated by maguro, who may elect to delete unwanted replies.
Jun 11, 2018, 08:03 AM
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A lot of people seem to want to discuss things not related to the forum subject, which is KFM airfoils theory and science. Going forward I will delete irrelevant posts.
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Jun 11, 2018, 11:34 AM
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OK, back to science then.

Does the KFm offer any advantage over a traditional airfoil in swept-back, swept-forward, or delta configurations?
Jun 11, 2018, 12:04 PM
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Quote:
Originally Posted by SirRexAlot
OK, back to science then.

Does the KFm offer any advantage over a traditional airfoil in swept-back, swept-forward, or delta configurations?
No studies that I know of. Certainly not any that would be of use to us. IIRC high subsonic and supersonic were done by NASA long ago.

That being said, a number of swept/delta designs have been successfully flown with KFM wings. Lots of the designs are in another KFM forum.
Jun 11, 2018, 04:17 PM
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Michael V's Avatar
Quote:
Originally Posted by SirRexAlot
OK, back to science then.

Does the KFm offer any advantage over a traditional airfoil in swept-back, swept-forward, or delta configurations?
I have a swept forward Kfm wing (slope). Nothing surprising about it: stall resistance, higher drag.
I have a significantly swept back Kfm plane, which never flew satisfactorily, but I cannot conclude that the Kfm is the culprit. Behavior is strange. I only tested on the slope and I have plans to turn it into electric at some point, which may solve the issue if it is what I think it is. So far speculation is that the issue is the general design which is not adapted for sloping, not an airfoil issue. The short of it is I think the design calls for an adaptive neutral point, which of course we cannot have simply (moving CG if you will, function of AOA and other parameters). Real aircrafts of similar design always have some kind of system doing that. By using a pusher motor, I expect to push through (literally) the problem. We'll see. On a sloping glider I just can't because it is purely subject to gliding behavior.

I have long suspected (but without proof or studies, other than some basic visuals clues) that a big difference in Kfm behavior is due to its influence on spanwise flow. It just changes it, which may be the source of certain characteristics compared to traditional airfoils. Furthermore typical aero studies do not look too much at the spanwise flow
If that is the case (spanwise flow is an important factor), then sweep and delta, may exhibit a further difference in behavior too (aside from the typical differences). I haven't seen it studied or mentioned anywhere so far though.


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