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Old Mar 11, 2012, 05:18 PM
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Quote:
Originally Posted by tolladay View Post
Would you say that before the mod the slowest you could fly the plane before it stalled was 1/3 throttle...
I would say that before the mod the slowest I could fly the plane before it started to lose height was 1/3 throttle.
I may have accidentally reinvented a fixed Krueger flap.
This, Wicki informs me is a, "Hinged flap which folds out from under the wing's leading edge while not forming a part of the leading edge of the wing when retracted. This increases the camber and thickness of the wing, which in turn increases lift and drag.
Invented by Werner Krüger in 1943 and evaluated in Goettingen, Krueger flaps are found on many modern swept wing airliners."
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Old Mar 11, 2012, 05:41 PM
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Originally Posted by Dickeroo View Post

When I read of that interesting experiment that you had done, Whiskers, I really got excited. Thanks for making my day!

Dick
Dick, first and foremost I send you every good wish for a speedy and brilliant rehab.
I am so happy that you found the Ugly LE to be interesting.
Personally I would not dignify this as an 'experiment.'
It's more of an observation of a result I had not anticipated. It could of course lead to experimentation, but as I have mentioned above the work may have already been done.

Warm vibes from the other end of the globe...
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Old Mar 11, 2012, 06:31 PM
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Quote:
Originally Posted by Whiskers View Post
I would say that before the mod the slowest I could fly the plane before it started to lose height was 1/3 throttle.
I may have accidentally reinvented a fixed Krueger flap.
This, Wicki informs me is a, "Hinged flap which folds out from under the wing's leading edge while not forming a part of the leading edge of the wing when retracted. This increases the camber and thickness of the wing, which in turn increases lift and drag.
Invented by Werner Krüger in 1943 and evaluated in Goettingen, Krueger flaps are found on many modern swept wing airliners."
Good guess on the Kruger flap. I never would have thought of that.

My backyard mechanic definition of a stall is when the wing produces less lift then what the plane weighs. Like every time a plane lands.
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Old Mar 11, 2012, 06:41 PM
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A wing often produces less lift than the weight of the plane and most often a stall is not involved.
Every time the plane loses height it's because weight is more than lift.
A stall occurs when the air-flow separates and causes a sudden and large loss of lift.
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Old Mar 12, 2012, 02:10 PM
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doesnt necessarily involve overcoming weight or losing height either.

http://en.wikipedia.org/wiki/Lift_(force)

Quote:
lift in its technical sense can be in any direction since it is defined with respect to the direction of flow rather than to the direction of gravity.
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Old Mar 12, 2012, 04:39 PM
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That link does not work for me.
My post was in reply to the statement, "My backyard mechanic definition of a stall is when the wing produces less lift then what the plane weighs. Like every time a plane lands."
It took me back to my youth at the Aero Club when I offered a similar definition of a stall. An instructor very firmly pointed out my error.
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Old Mar 12, 2012, 05:16 PM
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from a backyard definition all the above statements are acceptable, but you know me...

i am fascinated by the 1/4 vs 1/3 throttle part and also the slow speed. im obsessed with slow flight and its the main feature of kf i enjoy. im trying to figure a way to work that "ugly flap" into my single surface wings. it looks like much more than just increasing parasitic drag from your description.

dick, hope your up and about again soon.
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Old Mar 12, 2012, 06:02 PM
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Here is an illustration of the Krueger flap ripped from Wiki.
You may want to try a strip of foam glued under the LE. If you give it a go please report back on your results.
A KF on a KF, how very cute...
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Old Mar 12, 2012, 07:42 PM
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Quote:
Originally Posted by dave1993 View Post
from a backyard definition all the above statements are acceptable, but you know me...

i am fascinated by the 1/4 vs 1/3 throttle part and also the slow speed. im obsessed with slow flight and its the main feature of kf i enjoy. im trying to figure a way to work that "ugly flap" into my single surface wings. it looks like much more than just increasing parasitic drag from your description.

dick, hope your up and about again soon.
Dave... I'm now in rehab but I can't find Lindsey Lohan here.
I've come through the operation without any real pain. Just swollen and sore and tight muscles. There are many people here who have been this route. I never knew that getting old could be this much fun!

Thanks for your good wishes.
Dick
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Old Mar 12, 2012, 08:07 PM
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lol! good to see the drugs havent dulled your sense of humor.

after looking at all those diagrams im thinking it might be time to re-visit steps on the lower surface again. previous tests showed more benefit on the top but a short thin adjustable step on the bottom hinged at le might be interesting. reports say weather is warming up this week and wind dying down so maybe ill put something together in the next few days.

i just finished up experiments with chisel shaped airfoils this weekend to settle discussions in the bernoulli/newton thread. after i get a chance to download those photos to the forum ill start playing with wings again. this is fun stuff.
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Old Mar 12, 2012, 09:21 PM
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Hello,

I would like to make a couple of observations upon stepped airfoils based upon research accessible on internet (without having to pay), and comments from people who have personal experience with them.

Perhaps because of the somewhat extravagant claims claims made for the KF airfoil when it was introduced, it seems to be subject to both positive and negative bias. In the 1974 paper by E. Lumsdaine et al it was observed that: "If an airfoil must operate continuously at an angle of attack higher than 20 degrees, the upside-down (step on the top) Kline-Fogleman airfoil with a fairly thick step (approximately 0.25 chord) appears to have an advantage with a higher CL and a higher Cl/Cd than a flat plate or the NACA airfoil" However, the opening statement in the conclusions is: "From the scope of this test program it can be concluded that the stepped airfoil offers little or no advantages over the conventional airfoil or flat plate, and in most configurations is decidedly inferior in terms of both lift and lift/drag ratio" Since the tests were done at Re = 60,000 and 135,000, this conclusion could not apply to full scale aircraft.

Mr. Stackhouse's commented that "The KF airfoils have been studied by numerous people in numerous places, and the STRONG consensus is that they have a poor L/D. And we're not talking a minor deficit, some of the studies indicate a loss on the order of 30% compared to more conventional sections. A major part of the problem is that the "steps" in the airfoil do not retain the vortex that is supposed to maintain a smooth flow path above it." I have only been able to find evidence of two studies focusing on stepped airfoils for Re < 200,000. In light of this I responded by saying "Unfortunately there has been very little wind tunnel testing of stepped airfoils in the range of Re numbers for which a laminar separation bubble could be considered a normal phenomena. A study in 1974 tested 14 sections, of which only 9 were stepped airfoils, 60,000 < Re < 135,000 - and the stated conclusions diverged significantly from the discussion of results and the data??? Of the stepped profiles tested, half had the step on the top, half on the bottom, and the only other variable tested was the position of the step - all profiles shared a sharp wedge shape back to the step. A stepped airfoil might be useful for controlling a laminar separation bubble, but until all parameters are tested we simply do not know.  I received a predictably condescending reply from Mr. Stackhouse - but that could be because he seems to take it as a personal affront if an amateur should be so presumptuous as to have an opinion, or formulate an hypothesis, in the arcane area of aerodynamics. A common reaction among experts for whom the need to be RIGHT has surpassed the desire to understand.

In lieu of wind tunnel testing that examines all parameters relevant to model airplanes, what we have are the observations of numerous modellers who have used stepped airfoils on their models. I don't think that these observations should be dismissed because they are subjective. Science does not start with rigorous testing; it starts with a casual observation which gives rise to a hypothesis. It is very likely that stepped airfoils have some utility for smaller model airplanes flying at low speeds - otherwise modellers would not continue to use them. It would be nice to know the why's - anybody want to build a wind tunnel?

Mitch
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Old Mar 12, 2012, 10:20 PM
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Quote:
Originally Posted by Whiskers View Post
That link does not work for me.
My post was in reply to the statement, "My backyard mechanic definition of a stall is when the wing produces less lift then what the plane weighs. Like every time a plane lands."
It took me back to my youth at the Aero Club when I offered a similar definition of a stall. An instructor very firmly pointed out my error.
And rightly so. Its an important distinction, and one that should be pointed out. Thanks for noticing my flaw.
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Old Mar 12, 2012, 10:21 PM
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Mitch,
There are probably a lot of us who want to build a wind tunnel.
Not many do, so feel free to get started.
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Old Mar 12, 2012, 10:35 PM
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Actually, I am attempting to build a wind tunnel right now. However, I must say that this is going to take time, effort and some money. Moreover, I do not have all resources, including time, to do vigorous testing. I hope I will be done by May .
Also I am planning to use simple basic equipment to measure lift and drag. However the problem is finding a way to do that. The wind tunnel will be 7x7in. I am open to suggestions as I have no ideas.

Also in comment to the NASA test, I feel that they do have rather good data in order to prove some concept i.e. the top step is usually more beneficial than the bottom. I also believe that the KF airfoil most likely cannot continuously maintain a stable vortex behind its step as doing to is extremely hard, in my opinion and thinking (of course my reasoning could be flawed). but hopefully we will see with this windtunnel.

Does anyone want to volunteer to make autocad plans for me for my test models? (probably will need it by May, when I am hopefully done)

Another note: I am only planning to test the KFm2 and the Clark Y
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Old Mar 13, 2012, 12:17 PM
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Originally Posted by teflyer View Post
Actually, I am attempting to build a wind tunnel right now. However, I must say that this is going to take time, effort and some money. Moreover, I do not have all resources, including time, to do vigorous testing. I hope I will be done by May .
Also I am planning to use simple basic equipment to measure lift and drag. However the problem is finding a way to do that. The wind tunnel will be 7x7in. I am open to suggestions as I have no ideas.

Also in comment to the NASA test, I feel that they do have rather good data in order to prove some concept i.e. the top step is usually more beneficial than the bottom. I also believe that the KF airfoil most likely cannot continuously maintain a stable vortex behind its step as doing to is extremely hard, in my opinion and thinking (of course my reasoning could be flawed). but hopefully we will see with this windtunnel.

Does anyone want to volunteer to make autocad plans for me for my test models? (probably will need it by May, when I am hopefully done)

Another note: I am only planning to test the KFm2 and the Clark Y
Il don't know if this is possible, but I suspect that the step delivers a small amount of forward push to the airfoil. The reason I say this is that the KFm4 is faster than the other KF airfoils. If the step enduces drag, why would two steps allow the airfoil to go even faster? There are a number of very successful KFm4 planes flying now. The KFm4 Zepher flies extremely well and can even do a vertical takeoff.
I hope that you will be able to accomplish this task you are trying to set up.
Thanks for getting involved in this project.
Dick
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