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Old Aug 19, 2006, 04:13 PM
Old age is not for sissies
Azarr's Avatar
Dayton Intl, Ohio, United States
Joined Jan 2000
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Quote:
Originally Posted by Tony65x55
Sort of. The manuals on the Horsefly Hobbies website show a folded leading edge construction and while it is very similar in its construction methods, it is not the same as the K-F in cross section. See pic below.

Tony
Thanks for clarifying that Tony, From the pictures I thought it was the same as the folded leading edge. I'll have to try that on a foamy soon.

Azarr
www.ecubedrc.com
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Old Aug 19, 2006, 05:11 PM
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The video looks like a nice stable flyer!

One way to test if its really the airfoil or just this particular plane - temporarily fill in the step area, adjust the CG to exactly match, and re-fly and se what happens.

That may confirm the airfoils effectivness.

Larry

P.S. The title of the video needs a little spell checking - its Fogleman not Fogelberg
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Old Aug 20, 2006, 06:58 AM
I'm not flying backwards!
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Thanks Larry, changes made.

Tony
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Old Aug 20, 2006, 11:12 AM
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Palmdale, CA
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Quote:
Originally Posted by Larry3215
The video looks like a nice stable flyer!

One way to test if its really the airfoil or just this particular plane - temporarily fill in the step area, adjust the CG to exactly match, and re-fly and se what happens.

That may confirm the airfoils effectivness.

Larry

P.S. The title of the video needs a little spell checking - its Fogleman not Fogelberg
.
I did that.. built a K-F wing, flew it, covered the step, flew it, and then uncovered just one side, and flew it.
If the K-F idea worked, that side should have had less drag than the covered side. It didn't. Had to change the trim to compensate for the increased drag.
K-F is little more than pushing a sailboat with a fan on the sailboat.
That doesn't work either.
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Old Aug 20, 2006, 11:41 AM
Fly long and land softly
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Madison, Alabama USA
Joined Oct 2005
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Sparky Paul:

Thanks for sharing your experience, especially your photos.

The logical next question will be whether anyone has tried or will try something like this with the step on the Bottom of the wing. Top or Bottom seems to be a debatable point.

To me, drag might well be less important than the real possibility of an unstallable wing.

Thanks again to all who contribute.
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Old Aug 20, 2006, 04:34 PM
Charles, in the sandbox
Currently deployed in Iraq
Joined Aug 2006
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Kline-Fogleman Airfoil

It's a real pleasure to come across like minded folks. A good friend of mine once said, "Great minds think alike!" That said, I wish to start this reply by saying that I truly respect those fliers who have done more than I have. Tony, you are doing something that I have dreamed about doing for years since I was a kid and read the book that started my fascination with model airplanes in general The Ultimate Paper Airplane.

I've been doing a lot of research trying to find out more information on the airfoil, unfortunately not much exists on the net. What is available is mostly concerning the patent that kline-fogleman put together. The patent is the wedge shaped design. In their book, they (the inventor and author) talked about how they made a mistake in the patent process. Instead of submitting the wedge shape like they did, they felt that they should have submitted something more airfoil like. Most likely something semi-symmetrical with a 90 degree step somewhere near the cg. The book doesn't really talk about where exactly the cg should be, but I have a feeling based on the hundreds of hours I spent building the paper airplanes as a kid and even more recently several years ago. I'm reasonably certain the step should be near the cg, probably somewhat aft by 5%. I'm no expert by any means and it's only a guess.

These paper airplanes flew quite well, and the stall characteristics is almost nill. Given favorable conditions, they would fly for a couple of minutes. I remember flying one at a football field, I gave it a toss upwind, it climbed about twenty feet, made a nice gentle left hand turn and proceed to the endzone where it land neatly. Mind you, I had started from the middle of the field.

I would encourage you to get the book if you haven't done so already, and put a few paper planes together to study the design. Once you see the paper version completed, you will most likely see the possibilities that I see using depron. As for rc, I do believe that depron would be an excellent choice for building material, yet the wing design is important to getting proper results. The design should be easy to enlarge. Most of the paper planes are delta shaped somewhat i.e. like an F-16. Take note that in most of the planes the step angles to the rear some what. I do remember experimenting with the angle, and putting to much angle on the step becomes detrimental. Also, the foil itself is some what like a para foil, like on a hang glider.

While I am currently deployed overseas, limiting my rc'ing to non-existing, I plan on setting up a foam cutter when I get home to do some experiments myself. Using some of the money I've saved(kinda nice not to have to pay taxes legally while deployed lol) should allow for a decent setup so I can study the airfoil myself. Might even setup a wind tunnel. I'd be interested in knowing if a regular wing similiar to a trainer with the airfoil built in would work better than the delta wing of the paper planes.

Just about everyone in this forum has more experience with building, flying, and crashing than I have. I sincerely respect that, and hope that I, the noob haven't stepped on any toes as if I knew more than anyone else on this subject. I joined this group to learn and expand my knowledge of rc airplanes. Before you can lead, you must learn to follow.

Tony, awesome plane, I hope that you keep experimenting, perhaps we can share ideas. I do believe that the Kline-Fogleman airfoil has a future. Too bad it was mismanaged. Fly on!
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Old Aug 20, 2006, 06:59 PM
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My nephew did some research on the K-F wing for his senior project at San Jose State in '98.
I built a plane to his first sketch, which turned out to be impossible to fly.
I then built the wing photo'ed here, based on an NACA 23015 profile, and flew it as a K-F wing.. nothing of any interest showed up.
It sat for a few years, then I dusted it off and flew with the K-F notch and the changes noted.
The effects observed were contrary to the theory, as I mentioned.
In reading the book, I noticed a few weasel words about the actual performance when tested on r/c models... "feels", "appears".. these aren't quantifiable engineering terms.. they're words used because someone expects something different, but hasn't really achieved a real difference.
And later in the book, the safety aspecte are touted, instead of the performance. This is a cop-out.
A plane which requires more engineering and more material to fly slower and with less range is not competitive. Safety is good up to a point... but that point vanishes when comparing cost per mile between takeoff and landing.
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Old Aug 20, 2006, 11:48 PM
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Quote:
Originally Posted by Sparky Paul
My nephew did some research on the K-F wing for his senior project at San Jose State in '98.
I built a plane to his first sketch, which turned out to be impossible to fly.
I then built the wing photo'ed here, based on an NACA 23015 profile, and flew it as a K-F wing.. nothing of any interest showed up.
It sat for a few years, then I dusted it off and flew with the K-F notch and the changes noted.
The effects observed were contrary to the theory, as I mentioned.
In reading the book, I noticed a few weasel words about the actual performance when tested on r/c models... "feels", "appears".. these aren't quantifiable engineering terms.. they're words used because someone expects something different, but hasn't really achieved a real difference.
And later in the book, the safety aspecte are touted, instead of the performance. This is a cop-out.
A plane which requires more engineering and more material to fly slower and with less range is not competitive. Safety is good up to a point... but that point vanishes when comparing cost per mile between takeoff and landing.
I noticed that it looks like the step on your test wing is quite a ways back behind the CG. I wonder if that could have contributed to the lack of K-F performance?

Im also curious if you remember what the wing loading was on the test plane? I have a feeling that hi wing loadings may show less benifit.

I do know that the paper airplanes did perform unusually well. The other person experimenting with a K-F like airfoil (linked above by arx_n_sparx) also shows some interesting flying qualities. I have seen it fly.

The other thing I am sure about - if you get three RC'ers to do the same exact thing - you will get three different results

Larry
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Old Aug 21, 2006, 12:13 AM
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Quote:
Originally Posted by Sparky Paul
In reading the book, I noticed a few weasel words about the actual performance when tested on r/c models... "feels", "appears".. these aren't quantifiable engineering terms.. they're words used because someone expects something different, but hasn't really achieved a real difference.
And later in the book, the safety aspects are touted, instead of the performance. This is a cop-out.
A plane which requires more engineering and more material to fly slower and with less range is not competitive. Safety is good up to a point... but that point vanishes when comparing cost per mile between takeoff and landing.
Yes and no. As Larry pointed out, different folks will have different opinions.

I can see this 'foil being a boon in the new LSA category. You're limited to 1 passenger, 1200 lbs or so, and a top speed of 120 kts (138 mph). Considering that many crashes occur because of pilot error, having a 'foil that is difficult to stall would be a real boon. If the trade-off is the fact that you can't go like stink, so be it. I'd be willing to trade speed for safety.

Brad
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Old Aug 21, 2006, 01:45 AM
Charles, in the sandbox
Currently deployed in Iraq
Joined Aug 2006
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Kline-Fogleman Airfoil

Quote:
Originally Posted by Larry3215
I noticed that it looks like the step on your test wing is quite a ways back behind the CG. I wonder if that could have contributed to the lack of K-F performance?

Im also curious if you remember what the wing loading was on the test plane? I have a feeling that hi wing loadings may show less benifit.


Larry
Good point Larry, in fact in the paper airplane models, the step is near the cg, if you take a pair of scissors, tweezers etc and figure out it's balance when built as described in the instructions, the cg and step are very close to each other. Also make note of the delta design of the plane as well, similiar to an F-16 etc. The airfoil is also similiar in design to an f-16 as well, somewhat sharp edge, NOT razor sharp as the patent would suggest, nor is it flat, it has a curve to it like an airfoil. I've ordered the book myself and having it sent here, when it comes, I'll post pictures of it and models produced using the instructions for further clarification. Be about a week before I get it, takes time to get things sent over here.

Sparky, I agree with you, that words like feels and appears are not words that scientists should use to confirm that the airfoil works. In no way shape or form does it prove anything. The whole book is based on a hypothesis. Nothing was actually confirmed. It's unfortunate too, based on my personal experiences flying the paper models and other designs as well(I was an avid paper airplane maker lol), nothing flew as well as the paper models being discussed. I am glad that you made the attempt to prove/disprove the hypothesis. I also think you did an excellent test as well. Covering the wing and then removing it was a really good idea. Would you be willing to try a different dimension of a Kline-Fogleman Airfoil? I'm also curious if you have constructed any of the paper planes?

For now, I'm interested in a response from Tony, the originator of this thread. I'm curious to see what he has to say about all this. Fly on!

Charles
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Old Aug 21, 2006, 02:52 AM
Oops get the hot glue gun
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Lansing, Michigan, USA
Joined Sep 2004
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This is a very timely thread as I just built my first wing with a folded leading edge last week. The bottom surface ends at 25% of the chord with the spar located against the TE of the bottom surface. I had considered putting the spar between the upper and lower surfaces, which would have resulted in a form of the K-F I guess. Wish that I had tried that.

After reading the patent application and all of the comments here, it might be interesting to build a wing with a folded leading edge but not glue the bottom surface, leaving it flexible and hook the TE of the bottom surface to a servo arm so that the thickness of the step could be changed in-flight and see what happens going from minimal thickness, like the folded/glued style to a thicker gap between the top & bottom like the K-F.

Interesting stuff!

BTW - cesnyderces welcome to the forum!

Gary D.
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Old Aug 21, 2006, 06:30 AM
I'm not flying backwards!
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Oshawa, Canada
Joined Sep 2004
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Folks, thanks for all the great input. Based upon the very limited experience so far with the KF foil I would have to agree that it's applications may be somewhat limited. So far, it does not look like a foil one would want on a plane designed for speed.

However, the wing flies very well, although slowly, and is rock stable. The Kid, who is flying in the vid, is 13 years old, hyperactive and never listens to anything. My flying partner has declared he's never seen a plane the Kid couldn't crash and he can fly this wing through hand launch, 30 degree climb out, continuous loops, rolls, inverted flight, and spot landings. OK, maybe it is not perfect for all applications, but as a trainer type, I'm impressed so far.

I have way too much control throw on it and have not adjusted that yet. This wing, with one of the conventional foils, would be a tip stalling, death spiraling, snap rolling S.O.B. It has all the ingredients, it is fairly big, underpowered, with 200% control throws. Yet not only does it fly well, when loaded with 4 1/2 ozs of dead weight payload, it retained the benign characteristics.

I placed the step at the 40% mark on the wing. The thought was similar to that mentioned above regarding floats and flying boats. Both air and water are fluids and while I acknowledge they are very different fluids, it seemed a logical starting place to put the step a hair behind the CG. The depth of the step (1/2") was a TLAR guess. There is definately a step, yet it is not too pronounced. I think, again a guess, that the drag of this section will increase dramatically in proportion to the size of the step. Too small a step, no positive effect, too large and the drag overwhelms any possible benefits. There has got to be a sweet spot and we need to do a lot of experimentation to find it. When I get access to the wind tunnel at the National Research Labratory I'll find it (LOL, yeah right)

I admit to being puzzled over two things. 1) the lack of elevon reflex required to maintain rock table flight. The airfoil does not seem to possess a pitching moment. But even a neutral moment does not explain this. For the aircraft to fly forward the CG must be forward of the CP and this would automatically induce a nose down pitch, but it doesn't. Can't get my head around this. Is it planing on the step like a boat hull?

2) The stall characteristics are severely benign. With the exaggerated control throws, entering a whip stall from full power level flight causes the aircraft to stick its nose up about 80 degrees (you can almost see the airflow stripping off the upper surface) lower the nose gently and keep flying with very little altitude loss. Obviously it does stall and full back stick (About 40 degrees of elevon deflection) with full throttle reveals a gently porpoising with no altitude loss. You can fly it around like this as there is also no loss of elevon controls either. Do this with power off and it sticks its nose up around 30 degrees and comes down like a parachute. Simply lowering the nose or adding power restores normal flight.

Build one folks and see if your observations agree with mine. When you fly the plane it does 'feel' a little different. I know that isn't scientific and for that I apologize, but it is true. I wish I had the facilities to quantify the difference. Perhaps others do. Even with the insane control throws this is probably the most stable aircraft I've ever flown. Maybe that's where it's potential lies? Trainers, AP planes, UAVs, Park Flyers?

Tony

PS: cesnyderces (Charles), thanks for doing the work you are doing. Come home safely friend.
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Old Aug 21, 2006, 07:45 AM
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Munich, Bavaria
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Hey Tony! that is a very interesting applied aerodynamics-project!!! great thread!
Hell! to bad I`m currently on vacations (sitting in an internet-caffee on the beatyful island of Rhodes/Greece) and can not participate in practical experiments .

I found a german article about the KF-profile. it stated that the KF profile had very limited advatages w.r.t. a normal profile in term of lift to drag and only in a very narrow AoA band (around 0 degrees). normally a step means vortex generation and that is equal to additional drag...
I believe the true advantages for us Foamy-builders are only compared to a dead flat wing:
- simplicity of build
- structural strength
- thicker nose-section/airfoil-like shape and airfoillike characteristics

My gut feeling says that a true airfaoil should outperform the KF-foil.
Sparky had the correct engeneering approach! build a plane with one KF wing and one conventional one (should be identical in all other aspects like weight, span, chord etc.).The reaction oft he plane should tell which side is `better`.


greetings
chara
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Old Aug 21, 2006, 08:43 AM
I'm not flying backwards!
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Oshawa, Canada
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Hi Chara, sounds like a great place for a vacation. Have fun.

I have only seen a few articles regarding the K-F airfoil and they seem to weigh it's advantages and detriments against full scale aircraft. Our aircraft operate in a different environment and sometimes we require different things from them.

I think we might be better put to weigh our efforts into a plane with two sets of wings as one aircraft with two different wings may prove so difficult to fly that any plusses or minuses may be hidden in the control issues. Example: If one wing has higher drag the yaw induced will make it impossible to fly unless significant rudder is applied. While we can see the added rudder, it only explores one aspect of the wing. If that same wing also produces signficant lift as a trade off, then down aileron will need to applied, introducing a sideslip, thereby radically increasing the drag of the whole airframe. Then more power will need to be applied. And with all this monkey motion what did we really learn? Not much is relation to the flight characteristics of each respective wing.

I can tell you right now the wing is better than a flat plate as it exhibits none of the pitch hunting issues realted to this planform. I can also tell you it has great stall characteristics. As well, it seem to perform on minimal power and gives decent penetration relative to the other aircraft we had flying that last day. It seems to be able to operate at a higher wingloading without adversly affecting it's very forgiving stall characteristics. I can also state that it is very easy to build, well triangulated and pretty strong. I can also tell you on THIS PLANE it flies very nicely.

Do I have any numbers to back up my statements? NO Do I have some empirical experience with the K-F airfoil? Yes, a little bit. Have I flown other airfoils to have something to relate it to. Yes, lots of them.

I see what my eyes see and report it on these pages. I leave it to the scientists amongst us to explain "why". I do intend to try the K-F on other aircraft to see if the characteristics are the same with different layouts.

Please don't misunderstand me. I haven't bought into the K-F concept completely and I remain somewhat skeptical until I try it on different layouts. I think we have all had a certain plane that flew like magic and I'm not betting the farm on one experience.

But it does look promising.

Tony
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Old Aug 21, 2006, 09:12 AM
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I've gotten "better" performance from flat plate wings by bending the leading edge down at the 25% chord point. Just a 1/4" in 2-3' or so. The plane would outclimb a similar plane in the same air...
The large wing was built from the same 1/4" foam board as the delta, with the same amount of droop, and was a very decent flier.
The two without droop were miserable failures, but for other reasons.
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