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Old Jan 09, 2011, 02:13 PM
High Altitude Flyer
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Fairplay, South Park, CO
Joined Sep 2005
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Quick Fligh Report

I flew in hazy conditions while the leading edge of the incoming snow storm hung over the 14,000 foot peaks to the west & north, gradually moving towards me. Without enough sun to produce noticeable surface air heating & with light winds out of the northwest, I flew DANCER III trimmed for minimum sink. It's quite impressive as to how well it covers a lot of sky while sinking very little! With stronger lift conditions, it would be possible to trim more for maximum glide ratio at a faster glide speed... with today's conditions on the edge of the advancing storm, flying at low speeds at the minimum sink trim setting was just right.

I had added the rounded contour to the faces of the steps by simply depressing the Bluecor foam with a rounded burnishing tool. This is not necessarily very precise, yet I was happy with how easily I could end up with the rounded 'vortex pocket' contour on these low profile steps. Could I tell any difference in flight? I'd have to say no, the very slight change was not really noticeable from my last previous flight before the re-contouring.

But the bottom line is this: This MH32/KF3P wing is the best gliding wing I've produced to date; it has less drag, and glides more efficiently at minimum sink trim than any other KF variant wing which I've built to date.

I'll post a report on the slope flying performance after I've had a chance to fly some strong slope winds in Arizona in February... (slope flying here at temperatures as cold as they are is just no fun!)

VIKING
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Old Jan 10, 2011, 12:04 PM
High Altitude Flyer
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Fairplay, South Park, CO
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How do wings really generate 'lift'?

A picture is worth a thousand words (or more?)

'Lift' has very little to do with the creation of 'low pressure areas' above the wing's upper surface... it's primarily about controlling airflows and deflecting those airflows downward.

VIKING
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Old Jan 22, 2011, 07:11 PM
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Meet the Wave II

According to this info... the step seems to work quite well regarding the low drag issue.

"This side-by-side two seat urban car was the sleeper of the competition. Built on a lightweight aluminum chassis and carrying 20.7 kWh of perhaps the best available lithium-ion batteries for BEV applications (Dow-Kokam), the vehicle still weighed in at only 2176 pounds. Paired with a permanent magnet electric motor of 38 kW continuous power and a 91.5% efficient battery charger, the Wave II demonstrated outstanding low mechanical and aerodynamic drag resulting in high efficiency."
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Old Jan 23, 2011, 10:15 AM
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The car has a small step relative to the "wing" thickness. It is much like Viking's recent tests. Since there is nothing rear of the step, the vortex can form aft of and below the step (like the Flight International drawing Dick posted).

The more we test the more variations we come up with.

I decided to replace the Slow Stick fuse and tail. I am finishing a new fuse and tail assembly to carry the test wings. It is sleeker, has lots of room for all the electronics, provides a platform to hold the cameras, and supports a much larger motor. It is a center wing design, with a hatch above the wing. The hatch and wing saddle have to be modified to accommodate KFM1 and 4 wings, but it should not be a big deal. The resulting airplane should be able to go reasonably fast as well as slow. It might even be able to hover. We'll see.

Viking's testing makes me think, that KFM3 testing needs to be done with both a "traditional" KFM3 step, and a thinner angled step. So test plans a now to do the KFM2, then add the rectangular KFM3 strip, then the angled KFM3, then KFM4 and KFM1 last. Of course if the plane flies really well with the KFM2, I may have too much fun flying it to get down to the data collection.

I'll post photos once the paint work is done.

Roger
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Old Jan 23, 2011, 10:24 AM
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Viking, People have been arguing what causes lift since planes have been flying. Three basic things are happening at once on a wing in flight: A low pressure is created above the wing and higher pressure below, air is deflected downward, and a circular airflow is created from the high pressure on the bottom, to the low pressure on top (the last is derived from the equations of lift). This is yet another over simplification, but it should provide more food for argument (discussion).

Roger
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Old Jan 23, 2011, 12:14 PM
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How about 285 mpg?

A friend of mine sent me this VW Diesel Hybrid that greatly reduces drag. Another blunted rear end.


"Proper aerodynamics were key to the low fuel consumption. VW engineers knew they needed a small frontal area. This led to its unusually narrow, bullet-shaped body where the passenger sits behind the driver. As well, the car features an aircraft-like canopy, enclosed rear wheels, special flat carbon-fibre front wheel covers, and an aerodynamic underpan. Even the side cooling air inlets only open when the engine needs cooling, and otherwise stay closed. . .the 1-Litre-Car has an amazingly low coefficient of drag of 0.16 (a typical car has a drag coefficient of approximately 0.30 )."
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Old Jan 31, 2011, 04:27 PM
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I've been reading this thread and had a thought. Has there been any research done with the effects of changing the step. I'll try to explain better....Rather than running the step the entire length of the wing. what effect would there be if you had the step at say 50% the cord and also 50% the span? I am still learning about KFm airfoils so if this is a crazy idea, please understand.
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Old Jan 31, 2011, 04:43 PM
From trucks to planes
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Quote:
Originally Posted by Jason Kutter View Post
I've been reading this thread and had a thought. Has there been any research done with the effects of changing the step. I'll try to explain better....Rather than running the step the entire length of the wing. what effect would there be if you had the step at say 50% the cord and also 50% the span? I am still learning about KFm airfoils so if this is a crazy idea, please understand.
I think I understand what you're saying. So fro example, the step on top would only run for example, in the center 20" left to right, of a 40" wing span? Well then what is the rest of the airfoil going to be on the remaining 10" on each side? A Flat plate (so you basically don't make as good lift from that part I would imagine)? A usual curved airfoil (Clark Y etc., so you still get good lift from those parts?)

I would think you'd want the airfoil to run full spanwise, to have a proper effect. Now I would think it would be more interesting to see how you could combine the different airfoils across the wing span. For example I made a 50" wing with 30" in the middle being KFm3, and the outer 10" are Kfm4. Without another 50" full Kfm3 or Kfm4 to compare to, all I can say is it flies fast, or slow, and pretty much just floats around and no tip stalling from what I can tell, just mushes down. Will even fly upside down (only tried it once for few seconds) with a healthy dose of up elevator. Handles winds pretty good too, though that may be due to it lacking any dihedral.
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Old Jan 31, 2011, 08:41 PM
Jack
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I think leaving half of the KFm step off would cost you half of the vortex. And that would be half of the reason for having the step there to begin with. Or something like that.

It is what it is, and it works great. I'd encourage anyone that is new to it to try any one of the variants that seems appropriate and then start changing it to see what happens. If you don't know how it works you can't really tell if you are gaining or losing with changes.

We've had a few guys that spent a lot of time finding ways to change the things they did not like about it. And some of those ended up bad mouthing the KF airfoil when their mangled up pertubations didn't do what they had hoped it would do.

Good luck with it.

Jack
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Old Jan 31, 2011, 10:36 PM
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So Jack what if you put half a KFm2 on top say inner half and Half a KFm1 on the bottom outer half , kind of a modified KFm4 . Are the AOA the same for those to airfoils ?
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Old Feb 01, 2011, 09:46 AM
Jack
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Quote:
Originally Posted by Wilfor View Post
So Jack what if you put half a KFm2 on top say inner half and Half a KFm1 on the bottom outer half , kind of a modified KFm4 . Are the AOA the same for those to airfoils ?
Wow, that's pretty complex question to think about. I have never noticed either the KFm1 or KFm2 to have any noticeable amount of AOA when flying under power and a little above the stalling speed. I'd have to say that the center panels on the those KFm wings fly level or very close to it.

Flat plate wings (like just the center panel by itself) on the other hand always seem to show some AOA at similar speeds. I think as the speed picks up the flat plate will level out but I think of them as needing enough of an angle to create that "cushion of air" on the bottom of the wing that lets them fly.

I really believe that the KFm airfoil changes a wing from "riding on a cushion of air" to "generating lift." And it is that change or transition that really got me interested in it and hooked on using it.

Many want to discuss or even argue about my take on it but to me the bottom line was that by using a KFm wing I could build a plane that flies well quickly, cheaper, and with readily available materials. To build the same plane with a Clark Y or some other "true" airfoil would involved stick building or foam core cutting or other much more complicated processes.

So to get back to the question, I'd have to say the wing you describe in the question would fly fine. A KFm1 was a bottom step at 40%, the KFm2 had the step at 50% and on the top, but the bottom line is that both of the steps are creating vortexes and making the KFm thing happen. And I think cutting the steps in half and redistributing the halves top and bottom would still work.

The only questions in my mind are like, how well?, is it better? is it worse? and in the end, is it worth all the extra work? Like all of the "seat of the pants" science here, it needs to be done to prove or disprove it.

The guy that got most of this all started here, Tony65x55, explained why and how he thinks the Kline-Fogelman airfoil works back in the Zagnutz thread about 5 and a half years ago. And I have never read a better or easier to understand explanation of it. You can read the words of the master himself here:

http://www.rcgroups.com/forums/showp...58&postcount=4

Jack
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Old Feb 01, 2011, 11:01 AM
High Altitude Flyer
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Fairplay, South Park, CO
Joined Sep 2005
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Quote:
Originally Posted by Jason Kutter View Post
I've been reading this thread and had a thought. Has there been any research done with the effects of changing the step. I'll try to explain better....Rather than running the step the entire length of the wing. what effect would there be if you had the step at say 50% the cord and also 50% the span? I am still learning about KFm airfoils so if this is a crazy idea, please understand.
Jason,

the chord line & camber line of any shape of wing have an affect on how air moves over & is deflected by a wing; those affects on the airflow, when combined with the thrust of a motor, result in flight... When we hand a motor on it, we can get a wide array of unusual shapes to move through the sky.... but that doesn't necessarily prove much.

So to really see what's going on with various shapes of wings you might throw together, turn off the motor & watch how each variation you have built GLIDES and handles in the non-powered mode. That's where you'll learn the most about how the various wing shapes perform.

That's the neat thing about building with foam... you can build a lot of different variations on a very modest budget, & compare them to each other... But in the process, please remember Jack's point about people building poor wing shapes which happen to have stepped discontinuities, then mean-mouthing the KF concept based on a 'less than ideal' implementation of the steps....

Many of us already know how superbly well some implementations really do perform, as far as glide efficiency and wind penetration capability in the power off flying mode, and these are not deep dark secrets- we've posted the information in these various discussion threads, so that everyone can read these postings & put those observations to use.

We wish you the best of success in your own experiments!

VIKING
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Old Feb 05, 2011, 12:48 PM
Lee
PERFECT LANDING !!!
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I must admit that I have been impressed with some of the KF planes out there. As someone who has designed a few planes of my own I respect the work and the theory and the performance. The debater in me however makes me question everything and want to see data to prove what appears to be happening.

I requested they plot the air flow over basic KF airfoils on the Airfoil Investigation Database. You can see the two they did here.

http://www.worldofkrauss.com/foils/l...mebeg&letter=K

There are many factors that have an effect on how an airfoil flies. The shape of the leading edge and the taper at the trailing edge are as critical as the step. If you look in the data base I listed above they have hundreds of airfoils that they have plotted and run through computer simulations so you can see how the KF compares. You can also see how a little change makes a big difference in some of the other airfoils. That is also true with the KF designs.

This is a great video of a KF airfoil at work.

http://www.youtube.com/user/wjsflywing
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Old Feb 05, 2011, 01:46 PM
just Some Useless Geek
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Oops! <aside, to self> This is the science thread, dummkopf!

Useless comment removed on account of extreme dumbness.
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Old Feb 05, 2011, 02:04 PM
Lee
PERFECT LANDING !!!
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I've been following the KF airfoils for years. Dick and I have sent many E-mails back and forth. I've even designed some planes with them and do follow the threads most of the time. Don't get me wrong I like the KF airfoils. They do create lift if done correctly but some of the planes I have seen......

Are KF airfoils better than conventional airfoils? I have lately been questioning what is a KF airfoil. The threads have created a lot of different designs that all have been put under this category. Few of them even resemble the original KF design. If I take a Clark Y airfoil and cut a notch in the top does that make it a KF airfoil? If I take a SD7032 and cut a notch out is it also a KF airfoil? If I take flat plate and layer it in the now traditional KF manner, where do I put the steps? I think it was Michael Seilig who added a strip of clear plastic tape along a fiberglass wing to act as a trip and it decreased drag in a wind tunnel significantly. If something the thickness of a piece of plastic tape can have that much effect how precise do we need to be to get the KF designs right?

We have to question everything. A lot of the information in this and other threads is subjective speculation but that is the base for scientific research. I want wind tunnel data that can be compared directly to other airfoil designs.

When someone makes a paper airplane or a light foamy that flies better that doesn't mean we should start putting it on Boeing 747s but I'll bet that if it improved the flight characteristics it would already be there becasue I have heard Nasa and Boeing have tested about everything.

If you go back and look notched and tripped airfoils have been used since airplanes were invented. The KF airfoils have brought them up in the RC hobby and there is a place for them. They are great for the home builder which I think is what makes them so valuable but they also have their limits.

Lee
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