Originally Posted by Dickeroo

Most airfoils produce lift from the leading edge back to 30%-50%

im not sure i would phrase it that way. "airfoils produce MOST lift from le to 30%" might be a better description? cg/cl are typically about 1/3 the way back so while fore does contribute more there also seems to be a lot coming from the aft area.

as mentioned previously the kf didnt actually improve lift for us. it didnt affect l/d too much negatively either. its only advantage there seemed to be in improved lift at high aoa where other foils would stall. this might be mistaken for general increase in lift which we didnt observe.

Originally Posted by Dickeroo

Perhaps this also explains why the CG needs to be a little further back on the KFm2 airfoil.

i was going to mention that to the fellow who asked a few posts back but you beat me to it. for us it did seem to push things back a few percent depending on step size and position. had to move the battery a bit. maybe related to the better stall characteristics.

I really, really don't like the idea of flat plate wings but I must admit some guys get them to go very well.
Take a look at this guy's plane.
http://www.rcgroups.com/forums/showthread.php?t=1583116
Flat everywhere. Top, bottom, LE and TE, but has a good speed-range and looks vice-free.
Shakes my belief system...

You could skip the first video. It's just ground-handling.

i came across this thread in the science forum today. if kf is similar to turbulators as im guessing from similar behavior in my tests (by no means certain) then this may be interesting to check out.

something appears to be trapped there if not vortices. and the difference in onset of separation between low and high angles of attack relative to the steps may be noteworthy too.





http://www.rcgroups.com/forums/showt...r#post20828947

I built a little plane to help me find my way around our indoor venue.
It started off with a 30" wing with a KFm4 section as is labeled 'Pure' in the pic below. It flew very well but was a tad fast.
In an effort of enable it to fly a little slower I added a 4" extension to each wingtip. These are symmetrical in section with no step and taper to flat plate at the tips. It was indeed able to fly slower with this mod.
My wing-mounted landing gear gave problems and had damaged the wing, so in an effort to get something together to fly I cobbled up a horrible looking quick-fix.
A 16" balsa spar was glued and taped under the LE, and an 8" UC brace added to the center section.
The whole caboodle was covered with tape and produced the silliest looking leading edge in the known universe.
At the Hall it lifted off sweetly and flew nicely and to my surprise I found the plane was now able to fly much more slowly. All the other characteristics seemed the same. No nasty stalling or other nonsense was experienced.
So this stupid looking wing produces more lift than it did when 'pure.'
How strange. I guess it's just added under-camber, but the entry is nasty.

Very interesting. Looks like you just added another step on the bottom, albeit one very close to the lead-edge.

So, more lift, or more drag?

More of both maybe.
No doubt about more lift however, or looking at it another way; the same lift at a lower airspeed.

The fatter LE might be good for some of ,the benefit. That's one thing I noticed when I did my first KFC wing; more gentle behavior. (hey sorry I missed your call sun.)

Originally Posted by Whiskers

More of both maybe.
No doubt about more lift however, or looking at it another way; the same lift at a lower airspeed.

Just curious as I'm no expert. Would you say you were flying with the wing at a slightly higher AOA when you are flying slower?

Originally Posted by tolladay

Would you say you were flying with the wing at a slightly higher AOA when you are flying slower?

That is a good point.
I think it was at a slightly higher AOT at the slow speed.
The speed difference is quite large.
Before I added the extra wing tips it was, "Woa! I gotta keep on top of this thing."
With the extra area it was, "OK, that's not too bad but I need to concentrate."
With the Ugly LE it was, "Hey! This thing goes slow. I can relax a bit."

Originally Posted by Whiskers

That is a good point.
I think it was at a slightly higher AOT at the slow speed.
The speed difference is quite large.
Before I added the extra wing tips it was, "Woa! I gotta keep on top of this thing."
With the extra area it was, "OK, that's not too bad but I need to concentrate."
With the Ugly LE it was, "Hey! This thing goes slow. I can relax a bit."

Makes sense to me.

I'm working on a short story where a full-scale glider (actually larger than full-scale) ends up using a KF airfoil to save itself from a crash. In the process of writing this story, I'm trying to make sure I understand how a KF airfoil functions.

If I understand correctly a KF airfoil allows a wing to fly at a higher AOA without stalling, and when it does stall it is a gentle one. This comes at the cost of more parasitic drag. Drag in your case is a good thing as it slows the plane down to a more manageable speed.

Originally Posted by tolladay

Drag in your case is a good thing as it slows the plane down to a more manageable speed.

In my case it was being able to fly at about a quarter throttle instead of about a third, rather than the extra drag.
In normal flight it didn't seem 'draggy' but indoors I don't explore the high end of the speed range.
Outdoors I have the opposite reputation.

Whiskers and Tolladay...

I am sitting here in rehab having had knee replacement surgery and my wife brought me an iPad so I could see what's going on in the RC Groups.

When I read of that interesting experiment that you had done, Whiskers, I really got excited. Thanks for making my day! I am so pleased that the KF concept allows for so much experimentation cause that's where all the fun is.

Have fun...

Dick

Originally Posted by Whiskers

In my case it was being able to fly at about a quarter throttle instead of about a third, rather than the extra drag.
In normal flight it didn't seem 'draggy' but indoors I don't explore the high end of the speed range.
Outdoors I have the opposite reputation.

Curiouser and curiouser. Would you say that before the mod the slowest you could fly the plane before it stalled was 1/3 throttle, and after the mod was 1/4 throttle? I'm trying to visualize what is going on, without my head exploding.

Originally Posted by Dickeroo

Whiskers and Tolladay...

I am sitting here in rehab having had knee replacement surgery and my wife brought me an iPad so I could see what's going on in the RC Groups.

When I read of that interesting experiment that you had done, Whiskers, I really got excited. Thanks for making my day! I am so pleased that the KF concept allows for so much experimentation cause that's where all the fun is.

Have fun...

Dick

Dick, bummer on the knee. I hope your recovery is quick and relatively painless.

...and wait until you see my story. I think you're going to enjoy it greatly. I have some editing and other "housekeeping" chores to be done to it before I post a link.

Among other issues, I have VERY LARGE airplanes flying at upwards of 50k feet AGL, for very long periods of time, and I need a good reason for them to be there. What the heck is up that high that is not found at sea level? Essentially, what economic motive would I have for flying a plane up there day in and day out? I know electronic signaling has been suggested (similar to a satellite only lower, and easier to maintain), but I would prefer a more mobile (as in not stuck over the same place) answer.

Originally Posted by tolladay

Dick, bummer on the knee. I hope your recovery is quick and relatively painless.

...and wait until you see my story. I think you're going to enjoy it greatly. I have some editing and other "housekeeping" chores to be done to it before I post a link.

Among other issues, I have VERY LARGE airplanes flying at upwards of 50k feet AGL, for very long periods of time, and I need a good reason for them to be there. What the heck is up that high that is not found at sea level? Essentially, what economic motive would I have for flying a plane up there day in and day out? I know electronic signaling has been suggested (similar to a satellite only lower, and easier to maintain), but I would prefer a more mobile (as in not stuck over the same place) answer.

Cellular relay if orbiting over a fixed area.