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Old Sep 26, 2009, 01:30 PM
Jack
USA, ME, Ellsworth
Joined May 2008
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The starting point for the steps is easy to define expressed as a percentage of the root chord. And extending it to the same percentage of the tip chord has certainly proven to work.

As wings go from rectangular to swept it changes some things and variables start to arise. As it is now you almost have to have one person build it both ways to see the difference. And those are still going to be one person's perceptions.

We need a rule here. No one is to build any plane except exactly as it is show on the plans. With that maidened and flying, then and only then can they proceed to modifying the design. How does that sound

The A-12 looks like something that needs to be built for sure.

gpw,

How did the fixed mounted, full time, drag tips come about? And did they add some quality or change some characteristic?

If you guys have not seen those they can be seen here:

http://static.rcgroups.com/forums/at...468-1-a12b.jpg

Jack
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Old Sep 26, 2009, 02:52 PM
PunchDrunk ex-Pug try'n fly'n
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Quote:
Originally Posted by jackerbes
We need a rule here. No one is to build any plane except exactly as it is show on the plans.
Jack
I hope that was tongue in cheek. I suspect so.

As far as Clark Y vs. KF....
I put a KF step on a Clark Y airfoil which I had previously flown. Just maidened it today. It flew well!
I must admit I had my doubts, initial glide tests were not as promising as I had hoped.
If I remember how she flew before correctly: She seems to have lost a little speed. This would be expected since I "added" the step thus increasing the thickness of the wing and therefore the drag also.
However, the glide ratio was noticeably improved, this would give evidence to the notion that the KF mod would add lift.
If this was a truly scientific test I would now remove the step and get a more accurate conclusion. The problem with that is I like the soaring characteristics of the mod! Since this is my plane I will opt to keep the step at least for now.
Science can wait I'm having to much fun right now!

jp
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Old Sep 26, 2009, 03:00 PM
gpw
“There’s no place like Foam”
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JB, the split flaps came about after seeing Boxhead's Drag Tips ... I just applied a more scale look using the same principle .. as Box would say "It works a treat" !!!! Great yaw stability ... with none of those non-scale looking vertical "cheater" fins ... and I went with the full canopy to see how it would be different from a profile canopy that far ahead of the CG ... Works fine as the air flows over it smoothly unlike the profile which just adds forward vertical area and de stabilizes the yaw... No canopy would be just as good and a whole lot easier ..
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Old Sep 26, 2009, 03:38 PM
Jack
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jp wrote:

"..I hope that was tongue in cheek. I suspect so..."

Of course it was tongue in cheek. My point was that when people ask the question "which one is better" the answer is best found by one person building both, making a comparison, and deciding it. And we have to have a common starting point, right?

Jack
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Old Sep 26, 2009, 03:59 PM
Jack
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Joined May 2008
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gpw wrote:

"..the split flaps came about after seeing Boxhead's Drag Tips..."

OK, I thought at first they were actually articulated or (from looking at the side view in the drawings) maybe a combined action in flight of mixing down elevon and a small upward deflected flap on the end of the wing. But then, no other servos or linkages were evident. I finally figured out they were fixed. Interesting concept.

The use of tip plates on KFm wings has been common and recommended. It is to fence off the air flow near the tips from spilling off as it flows across the KFm steps. The stated benefits of tip plates was a milder stall and better slow flying. On the A-12 Delta with diminishing wing surface out near the tips, maybe the drag tips accomplish something similar.

Jack
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Old Sep 26, 2009, 04:00 PM
PunchDrunk ex-Pug try'n fly'n
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Quote:
Originally Posted by jackerbes
Of course it was tongue in cheek. My point was that when people ask the question "which one is better" the answer is best found by one person building both, making a comparison, and deciding it. And we have to have a common starting point, right? Jack
Roger that!
I just lack the discipline to pursue the scientific method. I'm afraid I'm a bit selfish when it comes to my hobby. I just want to fly the "Best" airfoil I can build. And part of the fun is to have a one of a kind design.

So no thoughts/opinions on steps running perpendicular to chord on a swept wing? I will build it into my next KF and report back.
I love this thread..... "No Limits".
jp

BTW: "Boxhead's Drag Tips" ... got link?
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Old Sep 26, 2009, 05:19 PM
gpw
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Delkan link (Boxhead) http://www.rcgroups.com/forums/showt...ghlight=Delkan Once you read this , you can see how easy it was to put the A-12 together ...
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Old Sep 26, 2009, 07:32 PM
Geaux Saints
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Quote:
Originally Posted by jp.electrik
So no thoughts/opinions on steps running perpendicular to chord on a swept wing? I will build it into my next KF and report back.
I love this thread..... "No Limits".
jp
It works on Deltas which are flying wings of sorts.

Using the KF steps more or less parallel to wing span gives you more step length on the Vee shape.

Running them perpindicular on a Vee wing I haven't seen so it should be interesting to see how yours works out.

Mike
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Old Sep 26, 2009, 08:05 PM
Lee
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If you want to test airfoils against airfoils you should probably have a longer boxy wing.

Sweeps and tapers get into the plane design characteristics not the airfoil performance.
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Old Sep 26, 2009, 08:21 PM
gpw
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Try a Foamie Hots with a CC wing ... different airfoils... that's easy !!!
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Old Sep 26, 2009, 09:31 PM
Onward through the fog.
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Quote:
Originally Posted by Lee
If you want to test airfoils against airfoils you should probably have a longer boxy wing.

Sweeps and tapers get into the plane design characteristics not the airfoil performance.
Lee,
As long as the fuselages, chords, span, sweep and thickness of the comparison wings are the same the results should be valid.

Problem for me is the KF stuff works so well I can't see justification for building anything else. Just make-work projects IMO, at least for me. I can imagine the work that went into the EEP wing core design of your Assassin. In one video you commented that: "...this one works better than last year's..." Must have been a long development process. I have 3 Assassins now #2 flies great. #3 needs throws adjusted and Paper/Foam, #4 needs to be maidened. I can't imagine "not" using a KFm4 on an aerobatic flying wing. That's just me...

Jack, Mike & Dick
Nice job on the new thread, I think it's off to a good start. Keep up the good work.

Steve.
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Old Sep 26, 2009, 10:03 PM
Geaux Saints
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Steve

We got it started now you can take over.

Have fun!

Mike
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Old Sep 27, 2009, 12:02 AM
just Some Useless Geek
Chicagoland
Joined Oct 2008
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My latest Dart is a Smart Dart XS modded with a rear-biased sweep and a KFm2 on the top. I screwed it up, though, and went 40% across the width of the wing instead of 50% as the rule states. Also, since I am a completely lazy cuss and only wanted to make something really simple and easy I just laminated one sheet of O-C pink on top of another to make the step. Results can be found here.

You'll notice that I also added the winglets (tip plates) that seem to be all the rage. Actually, I was just interested in protecting the wingtips from landing rash without adding a bunch of tape out there. The winglets are EPP and hang below as well as stick above the wing.

From a casual examination of the results I can see that the (buggered up) KFm2 creates a bunch more lift than the flat plate wings on my other SDXSs. In fact, the only other planes in my hanger that fly anything like my Smarty Pants are the ones with hollow airfoils like the Slow Stick, Pico Tiger Moth, Minium, etc. Way cool.

To my way of thinking the KFm2 is the airfoil of choice for simple and quick builds. It is far less demanding of time, material, expertise, and craftsmanship than any hollow airfoil or scale airfoil wing build. As per my experience, it is also far more forgiving than any "proper" airfoil design; my Smarty Pants was off by 20% and it still gave a significant improvement in generated lift! Try that with a scale wing. Heh.
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Old Sep 27, 2009, 12:55 AM
PunchDrunk ex-Pug try'n fly'n
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Quote:
Originally Posted by A Useless Geek
.....You'll notice that I also added the winglets (tip plates) that seem to be all the rage.....
You know my last KFm flew quite well without winglets, or LEE's tip-mod. I still added some small tip plates for vortex containment. I have begun to use smaller tips lately with good results.

I built a KF airframe with straight steps today as mentioned earlier. In hindsight I should have used more sweep, this one has very slight rear sweep; just 14 degrees, so it won't really prove much if it is a success. Oh well It is the first of this FFF bundle. Hindsight!
It is a four steps over zero experiment however.
jp
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Old Sep 27, 2009, 01:09 AM
Registered User
Gary, IN, USA
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In the mid '80s, my son had a 3 year science fair project studying a terraced airfoil which is very similar to the top KF airfoil. It began with glider pilots claiming it gave "more" lift. The study used wind tunnel, computer, RC gliders, video flight recording and comparison of a standard Ace foam rectangular wing and the Ace rectangular wing with several triangular slivers removed from the length of the top of the wing.
The lift/AoA plots showed a 10% less CoL with the terraced airfoil. That shot down the hypothesis that it made more lift......and about ended the project because who wants to show what's wrong? In a moment of serindipity, we noticed that instead of stalling at a normal 12 degrees, the terraced airfoil was good until 20 degrees.
The gliders were kiting up at a steeper angle which everyone assumed was evidence of "more" lift. Our videos of a glider with a standard wing on 1 side and the same wing terraced on the other side verified the expected stalls at different times.
Nature is smarter...it made bird feathers lift up at high AoA as in landing to stop the sudden stall. Air begins flowing along the top of the wing from the trailing edge to the leading edge at near stall AoA but the lifted feathers ...and the terraces... create blockages that slow the flow break-away at stall.
Einstien's work on relativity roughly says that what we see depends on our relative position to what we are looking at. The final year earned the boy top regional standing and the trip to the national finals. He learned scientific study and how to fly RC.
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