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Old Nov 17, 2011, 09:43 AM
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Originally Posted by rdeis View Post
Mathematically, though, isn't stall is when Cl drops to zero, (which generally occurs when flow separation occurs?)
i dont think stall occurs on separation but rather happens long after separation begins. in fact maximum lift coincides with quite advanced separation as seen in the diagram below from a well respected aerodynamic text. stall occurs at critical angle of attack only after separation is virtually complete. imo it is the actual separation that is responsible for kf characteristic slow flight and friendly stall.
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Old Nov 17, 2011, 10:14 AM
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The VortexCell Project

Does anyone know whatever became of the VortexCell2050 Project?
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Old Nov 17, 2011, 10:36 AM
Jack
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Does anyone know whatever became of the VortexCell2050 Project?
I looked at that when it came up a year or so ago and while there was this site:

http://www.vortexcell2050.org/index.php

I was not a member and could not get into the "members area" so if any results are there, they require a member's login to be accessed. Like a lot of developmental sciences, it looks like a boondoggle to me. And that is much like the KF foil has appeared to be to those that are not using it in modeling.

When I look at the details of the Vortexcell2050 wing thicknesses and the size and shape of the vortex cavities (in the pdf files that Dick posted) I really lost interest in it. What they were studying would have been very impractical to build in FFF or similar sheet foam materials. It might have lent itself to molded foam wings or something like that.

The chord to thickness ratios on the VortexCell2050 wings was sort of bizarre, looked like a cartoon.

Jack
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Old Nov 17, 2011, 12:31 PM
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Originally Posted by rdeis View Post
Mathematically, though, isn't stall is when Cl drops to zero, (which generally occurs when flow separation occurs?)

The neat thing about Kf is that the Cl doesn't do that, but rather ralls off gradually.
No, technically stall is the point where Cl reaches it's maximum and begins to fall, so in fact it's as far from zero Cl as it's possible to get.

As i mentioned a few times previously, any proper testing that's been done on models shows a quite conventional stall, as shown in the tufting tests linked in my last post.
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Old Nov 17, 2011, 12:38 PM
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Originally Posted by dave1993 View Post
i dont think stall occurs on separation but rather happens long after separation begins. in fact maximum lift coincides with quite advanced separation as seen in the diagram below from a well respected aerodynamic text. stall occurs at critical angle of attack only after separation is virtually complete. imo it is the actual separation that is responsible for kf characteristic slow flight and friendly stall.
That's true, separation starts before the wing fully stalls. Stall is the point where separation extends to such an extent that the lift produced by the wing decreases with increasing AoA rather than increases, but it is separation that causes stall and separation is ALWAYS a bad thing. In addition to reducing lift separation also massively increases drag.

Planes use all sorts of devices to prevent stall, turbulators, vortex generators, leading edge slats, boundary layer suction, flap blowing; these are all methods of preventing separation and if you can prevent separation you prevent stall.
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Old Nov 17, 2011, 12:54 PM
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OK. So proper description of the benefit then, isn't that they don't stall or that they stall late, but merely that stall behavior is very benign.

In flying terms it doesn't feel so much like stall, but more like a mush. Yes?
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Old Nov 17, 2011, 02:18 PM
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Yes, i think that's the benefit most seem to report, a very gentle and benign stall.

I'll be able to make some first hand comments once i get my KF winged Elf discus launch glider in the air...

Steve
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Old Nov 17, 2011, 07:15 PM
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How close are you?????
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Old Nov 17, 2011, 07:57 PM
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Originally Posted by Cap_n_Dave View Post
Not sure what you mean by this.

If the purpose of the test is to examine properties of KFm sections/wings at "model airplane Reynolds Number(s)," then the person conducting the test must ensure the Reynolds Numbers match (i.e. the Reynolds Number of test section/wing matches "model airplane Reynolds Number(s)").
What I mean is this:
The test sections can have a cord dimension similar to that of a medium sized model.
That is, a full-sized wing section.
The air can be puffed down the tunnel at speed similar to the airspeed of foamie models.
So no 'scale effects' are involved.
Of course, if we tried to test little models of our models the situation would be very different.
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Old Nov 17, 2011, 09:33 PM
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What I mean is this:
Or, said a different way- test measurements can be made at appropriate reynolds numbers so that the data is not skewed by "scale effects" resulting from using full-scale-like reynolds numbers?

Agree.
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Old Nov 17, 2011, 09:34 PM
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Originally Posted by JetPlaneFlyer View Post
I'll be able to make some first hand comments once i get my KF winged Elf discus launch glider in the air...
Looking forward to that, I need a DLG myself and the Kf price is hard to beat...
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Old Nov 18, 2011, 12:35 AM
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How close are you?????
Very close. life has been hectic of late so not much time to do any building but all i need to do is glass the wing join. I could probably have got away without the glassing if not for the error with the bottom spar cap, but as it is the glassing is essential otherwise the wing would rip-off under DLG launch stress.

Weather permitting i should fly it this coming weekend.

Steve
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Old Nov 22, 2011, 01:26 AM
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Does anyone know whatever became of the VortexCell2050 Project?
The project wrapped up this year with inconclusive results. A passive flow control (i.e. a step alone) didn't work. Active flow control could work but only at a single angle of attack. I think they are being quiet while they try to find money to do more research.

Rick.
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Old Nov 22, 2011, 07:29 AM
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Thanks, Rick

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Originally Posted by rpage53 View Post
The project wrapped up this year with inconclusive results. A passive flow control (i.e. a step alone) didn't work. Active flow control could work but only at a single angle of attack. I think they are being quiet while they try to find money to do more research.

Rick.
Appreciate your input.

Dick
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Old Nov 24, 2011, 02:42 PM
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I should add that the Vortex team feel they are on the right track, they just need more work, and have been giving a lot of oral presentations in Europe. I haven't noticed any published papers but I haven't been searching.

Rick.
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