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Jun 11, 2018, 09:03 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, 12:34 PM
Registered User
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, 01:04 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, 05:17 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.
Jul 01, 2018, 10:16 AM
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Dickeroo's Avatar
Apparently, there is a place for airfoils with stall-resistance that make it more benificial to use. And, this all came about because of the RC Experimentors. Without their contribution, this KF concept would not have been applied.

This paper gives more details on the improvements for a vertical wind turbine using a KF step. Apparently the KF stall resistance makes the device more efficient at lower wind speeds. The interesting thing is that a reverse step was applied at the trailing edge to capture and hold the vortex bubble.

LINK BELOW HAS BEEN CORRECTED.

blob:https://zapdf.com/630b836f-acf6-4006-a61f-62074b629679
Last edited by Dickeroo; Jul 01, 2018 at 01:57 PM. Reason: Correcting the link
Jul 01, 2018, 01:23 PM
Jack
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Part of your link is missing Dick, and it does not work.

If you want to copy a hyperlink to a URL you need to right click it and choose "Copy Link Location". The blue hyperlink is shortened for display purposes and if you do a drag and click copy on that it only contains what you see...

Jack
Jul 01, 2018, 02:02 PM
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Dickeroo's Avatar
Quote:
Originally Posted by jackerbes
Part of your link is missing Dick, and it does not work.

If you want to copy a hyperlink to a URL you need to right click it and choose "Copy Link Location". The blue hyperlink is shortened for display purposes and if you do a drag and click copy on that it only contains what you see...

Jack
Thanks, Jack.
I use only an iPad these days so there is no right click. Hope this works...

blob:https://zapdf.com/630b836f-acf6-4006-a61f-62074b629679

Then do a search for this document: Experimental Investigation of the Performance of Darrieus Wind Turbine with Trapped Vortex Airfoil

~ Dick
All of the KF stuff started with the RC Experimentors and Tony Bernardo getting it started in 2006. It’s an amazing story that began with folding a piece of paper. Thanks to all of you who are a part of this amazing adventure.
Last edited by Dickeroo; Jul 01, 2018 at 02:11 PM.
Jul 01, 2018, 03:30 PM
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Here is another way to skin a document....
Jul 01, 2018, 03:59 PM
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Found another document about KF Turbine Vortex Trapping....
Jul 01, 2018, 04:30 PM
OpenTX University Staff
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Dick,

Is the Kumar in the document the same person who did earlier testing of KF airfoils?
Jul 01, 2018, 05:32 PM
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Quote:
Originally Posted by maguro
Dick,

Is the Kumar in the document the same person who did earlier testing of KF airfoils?
I have no idea. Sorry, Roger.
Jul 07, 2018, 04:52 PM
Registered User
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Here is a document on testing flying wing design and applying a KF airfoil.
Last edited by Dickeroo; Jul 07, 2018 at 05:00 PM.
Jul 07, 2018, 06:25 PM
Jack
jackerbes's Avatar
That is a good one, Dick.

I'm going to add it to the KF building thread and will call the file the "Sri Lankan KF Implemented Flying Wing Study.pdf" file.

Jack
Jul 09, 2018, 03:27 PM
Registered User
Does having a curved undercut step like that help more than a 90 degree step? I thought the step was to induce a turbulent low-pressure vortex to generate lift. The back-curved step looks like it would create a smooth laminar vortex. I don't know what's best.
Jul 09, 2018, 03:43 PM
Jack
jackerbes's Avatar
We really don't know because we don't build that way and the various studies don't test foils that are made the way we make ours.

We use flat plates in layers in various combinations, they are nothing like the wing in the figure that Dick posted.

And I don't think I have ever seen a wing in one of the studies that looked like ours in cross section.

Jack


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