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Old Oct 12, 2011, 04:20 AM
just Some Useless Geek
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Soory aboot that, eh? Edited previous post now that the steam has cleared a bit.
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Old Oct 18, 2011, 09:53 AM
RC beginner
New York
Joined Oct 2008
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Originally Posted by JetPlaneFlyer View Post
Perhaps KF should be declared a religion and Dick Kline a deity?
i thought that has already been the situation for some time now. certainly since i was a member.

jetplaneflyer is in the position of preaching necronomicon to the choir here.

the guy that got me started on rcgroups compared dozens of airfoils including many kf and recorded lift to drag etc using chainlink fence backdrop. i was there myself a few times and built a couple myself (top and bottom). he came to pretty much the same conclusion as government testing. jetplaneflyer kinda summed it up:

Quote:
Originally Posted by JetPlaneFlyer View Post
KF provides a stiff wing -- relative to a flat plate. We have proven that the KF provides a lower stall speed -- relative to a flat plate. We have proven that the KF provides better overall stability -- relative to a flat plate.
these are real advantages but its a shame overzealous enthusiasts cloud the issue with myth and magic. i can personally atest kf is huge fun and has true benefits but efficiency and lift are not among them.

im grateful to dick for introducing us to this great idea with his paper plane book.
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Old Oct 18, 2011, 10:48 AM
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There are many ways of implementing KF variant stepped discontinuities into the design of miniature aircraft wings. There are 'quick & dirty' ways of layering foam sheets which result in great fun fliers. These builders are simply enjoying flying what they build. The variety is great, and the creativity displayed is to be applauded.... the idea is that lots of flyers are having an incredible amount of fun doing it!

I've focused some of my foamie wing design & construction work on lower profile step implementations than those commonly being used- ways of designing & building foamie wings which exhibit minimal drag, good glide efficiency, precise control response and very good stability.

The slope flying report on DANCER III with the 59" MH32/KF3P wing may be of interest. Wind speeds were recorded at up to 29 MPH while I was checking before launch, and I was flying without any power / motor run in slope winds of this velocity (& gusting stronger at times) at a wing loading of only 5.7 ounces per square foot.

Here's a link to that report in the DANCER discussion thread.

http://www.rcgroups.com/forums/showp...5&postcount=35

VIKING
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Old Oct 18, 2011, 11:10 AM
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What a terrific report.

VIKING...

I read your experiences with KFm3 DANCER III and it was thrilling to hear how well she flew in those wind conditions. You've really refined the step applications to a fine art. And, you have contributed so much to the development of the KFm Family of Airfoils with your experimental approach to refining the different configurations.

Dick
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Old Oct 18, 2011, 12:43 PM
Jack
USA, ME, Ellsworth
Joined May 2008
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Quote:
Originally Posted by viking60 View Post
There are many ways of implementing KF variant stepped discontinuities into the design of miniature aircraft wings. There are 'quick & dirty' ways of layering foam sheets which result in great fun fliers. These builders are simply enjoying flying what they build. The variety is great, and the creativity displayed is to be applauded.... the idea is that lots of flyers are having an incredible amount of fun doing it!

I've focused some of my foamie wing design & construction work on lower profile step implementations than those commonly being used- ways of designing & building foamie wings which exhibit minimal drag, good glide efficiency, precise control response and very good stability.

The slope flying report on DANCER III with the 59" MH32/KF3P wing may be of interest. Wind speeds were recorded at up to 29 MPH while I was checking before launch, and I was flying without any power / motor run in slope winds of this velocity (& gusting stronger at times) at a wing loading of only 5.7 ounces per square foot.

Here's a link to that report in the DANCER discussion thread.

http://www.rcgroups.com/forums/showp...5&postcount=35

VIKING
Bruce,

If you had to guess at it, as generalization, what kind of winds would you want to fly the Dancer III as a slope glider without power on that slope?

Like if you wanted to have wind enough and lift enough off of the slope face to make reliable turns and transits across the slope face and to recover altitude?

I know it is a very variable thing with the geography and even the person flying, I'm just try to get a general idea. I'm getting more interested in gliders and am trying to get a feel for the geography and conditions for slope flying.

The Dancer III's performance in slope gliding, as a motor glider with the motor simply not used, is a beautiful thing! As a guy that is somewhat enamored by having a motor to "rescue a glider from stupidity and the evils of nature" a Dancer III will get built this winter for sure.

Jack
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Old Oct 18, 2011, 04:29 PM
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Originally Posted by jackerbes View Post
Bruce,

If you had to guess at it, as generalization, what kind of winds would you want to fly the Dancer III as a slope glider without power on that slope?

Like if you wanted to have wind enough and lift enough off of the slope face to make reliable turns and transits across the slope face and to recover altitude?

I know it is a very variable thing with the geography and even the person flying, I'm just try to get a general idea. I'm getting more interested in gliders and am trying to get a feel for the geography and conditions for slope flying.

The Dancer III's performance in slope gliding, as a motor glider with the motor simply not used, is a beautiful thing! As a guy that is somewhat enamored by having a motor to "rescue a glider from stupidity and the evils of nature" a Dancer III will get built this winter for sure.

Jack
Jack,

As you mentioned, the variability of the geography / topography of a given slope really is a major factor. Dave Thornburg, in his "Old Buzzard's Soaring Book" devotes chapters 7 & 8 to this topic. (The book is one of the best I know of about flying gliders; Dave was the creator of the fine "Bird Of Time" glider, & a top competitor in his time.) At one time this book was available through the AMA book store. The book should be available from the publisher:

Pony X Press, 5 Monticello Drive, Albuquerque, NM 87123 505-299-8749

At a wing loading of 5.7 Oz, the DANCER III will glide well in light lift. Maybe 5 to 6 MPH will be adequate to stay up on a nicely shaped slope and have fun flying without having to work at it much at all. (It'll cruise across Antelope Flats at 20 feet off the ground for a couple of hundred yards in calm warm air and barely loose any altitude when it's trimmed out right, so it doesn't need a lot of 'up' component to the air to keep flying.)

The fact that it will continue to penetrate, handle cleanly and smoothly, and can stay out in front of the slope in winds up to & over 30 MPH without adding any additional ballast is what is really significant. That says to me in no uncertain terms that the wing and fuselage design are aerodynamically clean enough, that the drag from all of the various design aspects has been minimized fairly effectively.


Flying cycling lifting / sinking air on a slope before the big winds come up


I also definitely agree that having the motor with the folding prop as a backup adds a lot of options when heading out to the slope. On many mostly sunny to partly cloudy days of inland slope flying, earlier in the day before the strong slope winds build to consistent strength, you'll see waves of 'lift' - cycles of warm air move into the slope face. Each lift cycle may only last for 30 to 45 seconds earlier on a given day, with warm rising air coming across into the slope, rising, and sometimes separating as major bubbles of lifting air. But for every rising warm air mass, there has to also be a following mass of cooler sinking air that's being drawn in to replace that bubble of rising warm air. So you may have 30 to 45 seconds of 'up' air followed by two to four minutes or more of cooler sinking air (depending upon the rate of the prevailing breezes cycling these air masses into the face of your slope.)

When you're up & flying a lifting air cycle, and the lift dies & you feel the air going a bit cooler as you watch your glider start to struggle to hold altitude, you can power up and punch out well in front of the slope into the next mass of warmer flyable air. Once you detect the 'bump' from flying into that next cyclic mass of warmer rising air, you can chop the power and explore the extent of the warm air mass, and follow it back to the face of your slope. When the cycle of cool air which follows it moves in and the lift dies out, you can simply power up & punch way out upwind again to find the next mass of warm air. (The pure slope gliders are busily watching your lead, launching & landing, waiting for the next cycle of lift to reach the slope, & trying to land again before the air goes too cool & they have to end up landing down slope.)

Flying this type of cycling lift / sink air is a bit of magic once you understand what's happening. Once the prevailing winds build to a stronger speed for slope flying, you'll still feel the warmer / cooler masses of air as they move through, and you can watch your aircraft and see the affects which these air temperature variation cycles have upon the handling of your slope ship.

VIKING
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Old Oct 18, 2011, 04:56 PM
Jack
USA, ME, Ellsworth
Joined May 2008
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Bruce,

Wow! What a wonderful reply! A complete slop flying lesson for a new sloper...

I just found that book for sale at Carsten's and ordered it. I needed something like that...

There is so much to learn and so little time and I do love books.

Thanks again,

Jack
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Old Nov 15, 2011, 08:07 PM
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The Netherlands, ZH, Delft
Joined Nov 2010
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Wind Tunnel Testing

Hello, people of the internet...
I've been following this thread for a while now, and it is quite apparent that there has been absolutely no wind tunnel testing on the KFm family. Hopefully this is to change soon, as I have proposed a to do just that as part of my graduation thesis. This means that I can test a wide range of configurations in one of the university 400x400mm low speed wind tunnels, perhaps even verify some results with PIV...
I'll keep you posted on any further developments, but i should be carrying out the first tests by the beginning of next year.

greetings,
thefamoushat
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Old Nov 15, 2011, 09:18 PM
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Australia, QLD, Little Mountain
Joined Feb 2010
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Woo Hoo!
Excellent news.
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Old Nov 16, 2011, 01:54 AM
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Aberdeen
Joined Mar 2006
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Quote:
Originally Posted by thefamoushat View Post
Hello, people of the internet...
I've been following this thread for a while now, and it is quite apparent that there has been absolutely no wind tunnel testing on the KFm family.
Actually there was some wind tunnel testing done of the original bottom step KF airfoil by NASA and others back in the 70's. Results were very disappointing in terms of lift/drag (similar to a flat plate) and that largely explains why the airfoil design was never used in full size aviation. I beleive a top step KF airfoil was also tested about the same time with slightly better results but still poor compared to a 'regular' airfoil. I think these were in higher speed tunnels simulating full scale conditions rather than model airplane Re numbers.

But you are right in that the 'KFm family' of airfoils hasn't (to the best of my knowledge) been tunnel tested. Definitive testing will be a bit a challenge not least because there are no accepted coordinates for any of the KFm (or original KF) airfoils, just general shapes and approximate step positions. So before you do any testing first you have to define precisely what the coordinates for each of the KFm airfoils actually is

Steve
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Old Nov 16, 2011, 07:38 AM
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I would like the test sections to be similar to those actually used on scratch built foamies.
The Micks, for their KF testing, used an Aquila type section with a step. This was not representative of the usual 'foamie KF."
Sections similar to those used on the popular designs listed in this forum would be a good starting point, and they could be compared to a thinned Clark Y and a conventional symmetrical airfoil.
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Old Nov 16, 2011, 08:55 AM
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Quote:
Originally Posted by JetPlaneFlyer View Post
Actually there was some wind tunnel testing done of the original bottom step KF airfoil by NASA and others back in the 70's. Results were very disappointing in terms of lift/drag (similar to a flat plate) and that largely explains why the airfoil design was never used in full size aviation. I beleive a top step KF airfoil was also tested about the same time with slightly better results but still poor compared to a 'regular' airfoil. I think these were in higher speed tunnels simulating full scale conditions rather than model airplane Re numbers.

But you are right in that the 'KFm family' of airfoils hasn't (to the best of my knowledge) been tunnel tested. Definitive testing will be a bit a challenge not least because there are no accepted coordinates for any of the KFm (or original KF) airfoils, just general shapes and approximate step positions. So before you do any testing first you have to define precisely what the coordinates for each of the KFm airfoils actually is

Steve
I would like to point out that the wind tunnel testing that was done many years ago was totally incorrect. When we filed for a patent, it was for introducing a step on an airfoil. Our patent drawing showed a flat upper surface with a step or discontinuity 50% back on the underside. It also had a sharp leading edge. We did not try to define an entire airfoil profile. To my knowledge the patent drawing is what was tested, not an entire airfoil configuration. Naturally, everyone got poor results. The reason we showed the step on the bottom was because supersonically it would pick up the higher L/D because the characteristics tend to reverse themselves going from subsonic to supersonic. We learned this from the test results at Notre Dame. We also knew that the step worked in various ways and we couldn't patent them all.
In Frank White's book, Fluid Mechanics, he shows the test results of our patent drawing along with several other airfoils. Even with the disadvantage of a sharp leading edge and flat upper surface, the KF airfoil still resisted stalling out beyond 50 angle of attack. Yet no one seemed to want to know how this could be.
If the KF airfoil produces too much drag, it doesn't seem to bear out with the KFm4 airfoil which is faster than all the other KFm airfoils. With a step on top and on the bottom one would expect it to be twice as draggy, but it is the opposite. Can someone explain where the drag went?
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Old Nov 16, 2011, 09:02 AM
just Some Useless Geek
Chicagoland
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The drag disappeared down the rabbit hole of bad science, Dick. It's unfortunate that there hasn't been enough good science to counteract the effect of all the bad press the KF has received over the years, this despite the wealth of empirical data supporting the KF's effectiveness. Amazing that nobody with any cash on hand wants to put traditional aerospace science to the test and find out if these stepped discontinuities have something to them or not. Perhaps thefamoushat's school can provide the raw data needed to finally shut up some of the naysayers.
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Old Nov 16, 2011, 09:16 AM
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Originally Posted by A Useless Geek View Post
The drag disappeared down the rabbit hole of bad science, Dick. It's unfortunate that there hasn't been enough good science to counteract the effect of all the bad press the KF has received over the years, this despite the wealth of empirical data supporting the KF's effectiveness. Amazing that nobody with any cash on hand wants to put traditional aerospace science to the test and find out if these stepped discontinuities have something to them or not. Perhaps thefamoushat's school can provide the raw data needed to finally shut up some of the naysayers.
Usefull Geek...

It is also interesting that Richard Whitcomb really bashed and trashed the KF airfoil concept, yet he uses a coke bottle or wasp waist fuselage to reduce sonic boom. The depression in the fuselage allows some of the displaced air to fill in the body of the fuselage thus relieving some of the pressure build-up. He also has a slight cusp on the trailing edge of his super-critical wing. He claimed that the KF airfoil was the worst airfoil he ever tested. The worst? Hmmmmmmmmm.......
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Old Nov 16, 2011, 09:31 AM
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New York
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there are few actual naysayers. in fact ive never heard a single contradiction to the true advantages. it is also untrue that rigorous studies are lacking. numerous government and academic evaluations were done although it does take time to dig the data out.

as i mentioned before the fellow who got me started in this hobby built dozens of kf wings, top and botton, of varied percentages with careful measurments of lift-to-drag/glide-ratio. i was there. in ALL tests kf exhibited increased drag over flate plate and other common airfoils and no major improvement in lift. on the other hand kf improved stall characteristcs big time. similar to vortex generators.

i built a few myself and found the plane much more fun to fly. my kf wings were significantly stronger too. however getting to altitude on a given mah were slightly inferior to flat plate and markedy less efficient than the famous 4-40 uc.

its unfortunate that religious zeal often overshadows real world benefits of this wonderful wing configuration.
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