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Old Feb 22, 2011, 09:01 AM
internet gadfly
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That would be easy enough to test. Just cut a long thin wedge of styrofoam and wrap it around the trailer immediately upstream of where oil flow tests have shown separation to start.

--Norm
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Old Feb 22, 2011, 09:38 AM
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Originally Posted by gpw View Post
Apologies!!! Not meaning to get too off topic ... The guys at the TT and Teardrop trailer forum are on again about drag reduction ...
The problem is the shape is just too FAT to let the air smoothly roll off ... not like a long thin airfoil ...
So , I was thinking , maybe applying the KF principle to these would be of some benefit ... and may even allow better handling in tow ... Works Great on planes eh !!!
Any thoughts/opinions ??
GPW... here are two hybrids, one a VW, that use a blunt or flat rear end. The only reason they use this shape is because it is more efficient than a more rounded form. It doesn't appear to make any sense, but it works for the box fish and nature seems to know how to design things pretty well ...

– Dick
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Old Feb 22, 2011, 09:47 AM
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Forgot to include the box fish story.

Mercedes Benz applied the box fish shape to one of their hybrid vehicles.
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Old Feb 22, 2011, 10:29 AM
gpw
“There’s no place like Foam”
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That's MOST interesting Dick !!! I'll run it up the flagpole ... Thanks !!! Box fish ... whooda' thunk it ???

Norm , cool idea for testing ... foam and all ...
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Old Feb 22, 2011, 10:44 AM
Arizona Rim Country
Joined Nov 2001
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Tear Drop Trailer

Just a thought. Race cars do all they can to keep a car "stuck" to the road. These trailers are usually pretty light. I'm thinking less contact with the road might be a problem. On the front end of things . . . I've seen fellas that angled the roof downward a bit to help with wind deflection, but it ended up putting quit a bit of extra downward force on the hitch. So, they changed over to a V nose design. Just my nickels worth
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Old Feb 22, 2011, 12:00 PM
gpw
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Another nickel in the hat ... Those cars are looking like more and more the recumbent racing /speed bicycles eh ...

Pca, the trailers will likely be loaded down with camping stuff ... and airplanes
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Old Feb 24, 2011, 12:18 PM
Grumpy old git.. Who me?
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Originally Posted by Dickeroo View Post
My friend, Bob Tilden, sent me this video which shows an inflatable wing which has a series of indented ribs running the length of the wing. The wing is then placed in a smoke tunnel and compared against a conventional airfoil. You can clearly see how the ribbed configuration prevents separation of airflow whereas the conventional wing is unable to hold the airflow closer to the surface of the airfoil. Quite possibly, a similar thing is happening with the KF steps.
Dick,
As the others have said.. 'trips' or 'turbulators' are nothing new and have been used on freeflight models for decades in low Re applications. The 'humps' in the inflatable wing are not your typical turbulator design but they work on the same principal. The Re numbers that benefit most from turbulators are generally lower than most RC models would fly at.

It is possible that KF steps could work like turbulators, but only if they are very small. The typical KF step is almost certainly far too deep for flow to re-attach itself after passing over the step. Also the turbulator location is very critical. You can clearly see in the video that at Re = 50k flow separation occurs on the normal wing within about 15-20% chord width of the leading edge. To have any positive effect the step would have to be located before the separation point, and I've never seen a KF wing that was designed that way, steps are always at least 50% chord by which time the flow would be well and truly detached.

A simple way to add a turbulator is glue a length of thread along the wing surface, or perhaps a strip of tape.
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Old Feb 24, 2011, 09:44 PM
just Some Useless Geek
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Hmm. While it's hard to argue against your science on conventional trips, I take exception to your blanket statement about separation and the position of the KF step. What some of the research (such as it is) has shown is that the step is causing the turbulence to increase the effective height of the wing profile, thus lifting the air off the surface of the wing before it separates.

I'd love to see more data accumulated through the kind of smoke testing that was used in the video cap Dick pointed us to. Does anybody here have a wind tunnel and smoke trail generator?
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Old Feb 25, 2011, 12:43 AM
Grumpy old git.. Who me?
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Originally Posted by A Useless Geek View Post
......What some of the research (such as it is) has shown is that the step is causing the turbulence to increase the effective height of the wing profile, thus lifting the air off the surface of the wing before it separates.
Geek,
Even if you accept this explanation, if the step were to "lift the air off the surface before it separates" then surely the step would have to be located before the point of separation?

To be honest though your explanation has me confused because the definition of seperation is when the freestream air 'lifts off the surface of the wing' so effectivly you appear to be saying that you create separation in order to prevent separation

Steve
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Old Feb 25, 2011, 04:11 PM
just Some Useless Geek
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Yepper. Dick Kline his own bad sef might be able to explain this better (or not, the science is still very fuzzy), but my understanding from what research that has happened is that the step causes a turbulence that makes the wing look thicker/taller to the apparent wind. Thusly, the air is lifting off of the surface of the wing but riding on top of the turbulent bubble. Whatever.

Bruce's work shows that the leading edge shape has a lot of impact on the effectiveness of the KF for certain Reynolds/speed/AoA values. There is a lot more science to be discovered here, and generalizations based on conventional wing shapes aren't helping us collect the data we need to sort out the science. At this point the KF is still too new to dismiss anything as being "impossible" or -- heaven help us -- "obvious." There is nothing at all obvious about turbulators in general and the KF in particular. We can't afford to ignore anything.
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Old Feb 26, 2011, 02:00 AM
Grumpy old git.. Who me?
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Quote:
Originally Posted by A Useless Geek View Post
Yepper. Dick Kline his own bad sef might be able to explain this better (or not, the science is still very fuzzy), but my understanding from what research that has happened is that the step causes a turbulence that makes the wing look thicker/taller to the apparent wind. Thusly, the air is lifting off of the surface of the wing but riding on top of the turbulent bubble. Whatever.
That sounds like what's known as a 'laminar separation bubble' (google it).. It's something that you want to avoid because it increases drag. The separation of the flow in the inflatable wing video is because of a laminar separation bubble. In fact turbulators/trips are used precisely to avoid the formation of laminar separation bubbles.

PS.. KF airfoils are far from 'new' and they are also not untested. Dick's patent was filed over 40 years ago and they have been tested in wind tunnels by the likes of NASA.
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Old Feb 26, 2011, 02:37 AM
Just call me crash for short
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Ok, I'm new here, and new to the KF wing design. That being said, with my deep desire to understand what is going on with this KF design the one thing that has brought me some clarity (murkiness?) is I try to think of the vortex trapped at the step as ENERGY, not as drag / lift / shaping. Energy and it's interactions between the static surface of the wing and the moving air. Don't think I can put this into words tonight having indulged in some tasty beverages of the adult genre, but it might be something to think about. A Useless Geek and JetPlaneFlyer have valid points, although JetPlaneFlyer is thinking in the conventional text book airfoil arena and that does not seem to apply very well to the KF.

Please, no one take this wrong, it is only a discussion for the purpose of learning and I mean no insult or any such thing towards anyone.

If I may leave you all with something I had said long ago, and Dick, you have reminded of this.... It is not those that follow the text books that are remembered, it is those that the text books are written about. - Mark
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Old Feb 26, 2011, 06:41 AM
Grumpy old git.. Who me?
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Originally Posted by Quick61 View Post
If I may leave you all with something I had said long ago, and Dick, you have reminded of this.... It is not those that follow the text books that are remembered, it is those that the text books are written about. - Mark
While this might be true it would be sensible to thoroughly understand the content of those textbooks before coming to the conclusion they are incorrect. It also does not mean that it's a good idea to throw all the textbooks out of the window and 'just make stuff up' without any supporting evidence. That is not how science works, it is much more like religious faith. The title of this thread does after all have the word 'science' in it so IMHO it's best we stick to a scientific, rather than a faith based, approach to the issue.

There appears among some to be a huge 'confirmation bias' issue going on. Accepted scientific theory supported by expert peer review, years of testing, and countless real world applications are summarily dismissed as 'not applicable'. These same people are only too willing to unquestioningly accept half baked speculation which is unsupported by any factual data whatsoever. A case in point:- The 'vortex trapped behind the step'....I see this quoted often as if it were a 'cast in stone' factual statement, yet there is absolutely zero evidence that a KF step is capable of trapping a vortex. Quite the opposite is true in fact; the testing that has been done on 'trapped vortex' airfoils indicates that to maintain a stable vortex requires active vortex control ('suction' and 'blowing' of the vortex cavity): http://ltces.dem.ist.utl.pt/lxlaser/...ers/11.3_4.pdf
Quote:
Passive TVC (Trapped Vortex Cavity) flow control is not able to control the flow separation. The vortex is not confined in the cavity and vortex shedding is present decreasing the aerodynamic characteristics of the original airfoil.
Please understand I'm not trying to 'do down' the KF airfoil.. For foamy models the KF has much going for it.. But this thread is supposed to be about science

Steve
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Old Feb 26, 2011, 08:58 AM
gpw
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Anybody got a nice low speed wind tunnel and the instrumentation to gather the FACTS ??? Just for the Science guys ... I'm already a KF "believer" due to many positive flight experiences
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Old Feb 26, 2011, 12:08 PM
just Some Useless Geek
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Steve is quite correct in that we both can't simply dismiss decades of well-funded science with gobs of research data behind it and rely on seat-of-the-pants "data" as a foundation for our "science." Nonetheless, the current science simply can't explain the empirical results that have been collected by thousands -- thousands -- of R/C flyboys who have built KF wings and achieved real, validated, positive results. (So much for confirmation bias.) Therefore, there needs to be some radically new thinking to stimulate the research that will then produce new science. (Actually, "discover," since you can't create science; it's already there, waiting to be found.)

So, let's not limit ourselves to what we already know about how wings work. The KF is a departure from conventional wing design that has proven itself to be beneficial, but why? Since conventional wing science can't answer that question, how about new thinking that can lead to answers?

-- Marty, mulling it over Yet Again --
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