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Old Oct 03, 2009, 12:05 PM
fix-it-up chappie
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Valley Village, CA
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Quote:
Originally Posted by jp.electrik
Well said! I wonder if my smaller steps are more conducive for the extra steps I have had success with?
jp
I have a pet theory, which I have been unable to work on, in which I believe that eventually the best wing for parkflyer types of planes will have multiple, smaller (as in less high) KF steps, running both parallel, and perpendicular to the wingspan.

I say this only because so far the most efficient KF wing I have seen is already in production, albeit in limited production runs, and looks something like this:


Note the top and bottom KF steps. (top KF steps not visible in this photo) Also note the long perpendicular running KF steps near the back of the wing which slowly rotate to (near) parallel at the wingtip.

Also note that the KF step is significantly larger (as a percentage of the wing chord) near the root than it is at the tip. It looks to be non-existent after about 75% of the span. There's even a little dip in the KF step which must do something, although my limited knowledge cannot even guess its value at the point.

If you're going to design something, I say you steal from the best.
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Old Oct 03, 2009, 12:47 PM
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Quote:
Originally Posted by tolladay
I have a pet theory, which I have been unable to work on, in which I believe that eventually the best wing for parkflyer types of planes will have multiple, smaller (as in less high) KF steps, running both parallel, and perpendicular to the wingspan.

I say this only because so far the most efficient KF wing I have seen is already in production, albeit in limited production runs, and looks something like this:


Note the top and bottom KF steps. (top KF steps not visible in this photo) Also note the long perpendicular running KF steps near the back of the wing which slowly rotate to (near) parallel at the wingtip.

Also note that the KF step is significantly larger (as a percentage of the wing chord) near the root than it is at the tip. It looks to be non-existent after about 75% of the span. There's even a little dip in the KF step which must do something, although my limited knowledge cannot even guess its value at the point.

If you're going to design something, I say you steal from the best.
Tolladay... the designs that nature comes up with are unbeatable. The picture of that bird is a great illustration of the use of steps.
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Old Oct 03, 2009, 01:09 PM
fix-it-up chappie
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Quote:
Originally Posted by Dickeroo
Tolladay... the designs that nature comes up with are unbeatable. The picture of that bird is a great illustration of the use of steps.
I agree. The only problem I see is reproducing this kind of design out of the materials we have, and at a price point which is accessible to us guys putting things together in our garages.

That's the genius of engineering.
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Old Oct 03, 2009, 05:15 PM
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[QUOTE=jackerbes]"..I dont think anyone has tried to quantify the depth vs the glide..."

This one confuses me though:

"..Ive also tried 12mm steps on a constant 380mm chord. only two steps at 3%..."

Should that be "two steps at 30%"? In a KFm4 top and bottom configuration?


Sorry to confuse you... the steps on the KFm4 top and bottom were both at the 50% location, each step was 12mm deep..3%..
total wing thickness was 30mm..7.9% of the chord at 380mm

Tolladay
Here is my friend Richards birdie design based on other Eagles that are on the forum..It is a KFm2 and flys very slow. The balsa spar is overlaped by the shaped depron, so there is a small recess just under the feathered edges on the top step..It flies a treat..

Thats another possible avenue for exploration, we always use a square back on our steps, which works well, but richards birdie has a small ovehang..and in winds of just a few MPH will float up out of your hands...Is it the overhang or the feathered shape that is giving the float
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Old Oct 03, 2009, 08:52 PM
Jack
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"..Sorry to confuse you...''

Not a problem, that is my normal state a good part of the time. But I get it now.

That is interesting about the overhang. Another thing to be explored.

Jack
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Old Oct 03, 2009, 08:57 PM
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Thats another possible avenue for exploration, we always use a square back on our steps, which works well, but richards birdie has a small ovehang..and in winds of just a few MPH will float up out of your hands...Is it the overhang or the feathered shape that is giving the float[/QUOTE]


Dave... you've just reminded me of something. When I started out with my paper airplanes, which had terrific float, the step was completely open. It was not squared off at all. It would be interesting to see what the difference in glide would be between a squared-off step and a curvature d step. It would perhaps mimic the rotation of the vortex attachment. It would also make for a more difficult built as well. But it is interesting to think about none the less.
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Old Oct 04, 2009, 12:22 AM
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Quick question, does the chord include the ailerons? In other words do I make a KF2 at 50% to include ailerons?

The reason I ask is at 50%, including ailerons seems to inhibit airflow to the ailerons?
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Old Oct 04, 2009, 12:24 AM
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Also. Is dirty on the bottom clean on the top the best way to go? IE. servos on bottom?
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Old Oct 04, 2009, 04:45 AM
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Chords include the ailerons in the measurement... but if you havnt done that dont worry the step will still work and you will be hard pushed to notice the difference.. work the step %ages with ailerons and without..

Ive only had problems with airflow over the ailerons when the step is almost on the hinge line. This was a KFm3 design where the second top step lined up almost on the hinge line...With no input the wing was flying well, but as soon as you moved the ailerons it did not like it at all..
With more than 1.5" clearance I have always been ok

Putting gear on top or bottom... it looks better out of sight..
BUT underneath unless the gear is protected you will damage your bits on a landing.
Hook up a control horn in the grass snap it and strip the servo gears..etc..

I always put mine on top open and dirty, radio held on velcro with extra securing velcro straps, servos hot glued to the top of the wing or recessed and glued but its your choice..

Dick ...a small recess (small gap under the back of the step) is an easy trial, I can try it on one of my builds, just stick a strip on. It will alter the step %age a bit but it should still be ok.. It might be hard to notice any change cause they all fly well enough in any case, but I will give it a go on my KFm4 wing..
A full gap step will need a different construction ..possibly ribs .. a lot more work there, but maybee worth it for anyone doing a new wing. The rear edge of the step can always be filled in later
That might be a whole lot of new stuff to evaluate, with all the KF variations available

heres what ive done added a 3/4 wide 1/16" strip along all the steps on the KFm4 making a 3/8 recess, then Ive taped over the strip to hide the sharp edge on the front of the strip..only a rough job
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Old Oct 04, 2009, 06:57 AM
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Quote:
Originally Posted by davereap
I always put mine on top open and dirty, radio held on velcro with extra securing velcro straps, servos hot glued to the top of the wing or recessed and glued but its your choice..
I do the same thing specially on a first build of a new model. Once it's been proven you can clean up the looks on later builds. I like to bury my gear in the foam and keep the servos on top for easy maintainability with the battery held in an open slot with Velcro. Exception would be a scale build but that takes too much time. I like the quick and dirty fun-fliers.

Anyone flying a Clancy Lazy Bee? Just curious.

Steve.
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Old Oct 04, 2009, 07:20 AM
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Ive tried out the recessed steps using a straight edged balsa strip to give a recess 3/8" deep on top of a 9mm step..When the strips were applied and tape covered the step locations were measured and the edge of the strips was at the 50% chord location..
The wing used for this trial is my KFm4 zagnutz that has the tip mods like Lees assasin.Before the addition it was flying excellent, the modification has not made a noticable difference to the flight, it is still excellent..
I wont bother reverting the mod, it flies great as it is
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Old Oct 04, 2009, 08:44 AM
Jack
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"..Quick question, does the chord include the ailerons? In other words do I make a KF2 at 50% to include ailerons?..."

Ah, now we are getting in to some serious KFm theology questions! When I was getting started on the Zagnutz, the anal retentive ex-machinist in me started coming to the surface as I started working with dimensions and locations.

I noticed that the Zagnutz had the step at 4.5" and that the distance from the nose to the edge of the prop slot was 11". That works out to 40.9%, the KFm1 figure says it should be at 40%, so it was close enough. I figured that the measurements for the step must be taken from the nose to the back edge of the wing on the center line regardless of the purpose or nature of the back edge (wing, prop slot, or whatever).

And I also assumed that the other surrounds or potential points to measure to (wing trailing edge, aileron trailing edge, etc.) do not enter into the equation. And that has seemed to be fairly consistent. At any rate, it is how I measure for step distances.

I even went so far as to extend the wing trailing edge and the aileron trailing edg to the center line (those points would fall in space, not on an edge) and neither of those was any closer to the 40% number so that sort of affirmed the method of locating the step for me. To just take 40% of the center line distance, nose to whatever edge is found. And for making plans, it is OK to round the number off to simplify things, so the 4.4" (40% of 11") was rounded up 1/10th of an inch to 4.5".

"..Also. Is dirty on the bottom clean on the top the best way to go? IE. servos on bottom?..."

I chose to locate the servos and linkage where they were least vulnerable being damaged or snagged on something in landings or crashes. So I put them on top of the wing. I usually put them in just in front of the KFm step if there is one on top and make the servo pocket one foam layer deep. I've used both double sided tape and hot glue but generally prefer the latter as sturdier and less like to come loose.

Jack
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Old Oct 04, 2009, 08:56 AM
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Thanks for all the info.

My question in regards to equipment on top or bottom was more directed at airflow. I try to keep all my components safe when I build however I try to take in consideration the affect it will have on airflow.
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Old Oct 04, 2009, 09:15 AM
gpw
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We had a Navy pilot tell us that they found that the top of the wing should be Clean ... For what that's worth ... they do hang the hardware on the bottom ... anything that sticks out is DRAG !!!
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Old Oct 04, 2009, 09:26 AM
Jack
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I know what you mean. I wonder about it too. When the servo leads are taped to the wing a little in front of the steps I wonder if that creates a little turbulence on the air. I just generally try to keep the servo leads taped flat with the package sealing tape and take what I get for turbulence. I certainly have never had what I thought was less lift or degraded performance from mounting the hardware in the air flow.

I have used the DuBro Micro push rods on a couple of the Divinities to get a long, curved, linkage that let me have the servos near the wing center. That required taping the push rod sheaths down with nylon filament tape. I did have trouble keeping the sheaths from moving as the servos worked so I gone away from that.

I generally like to mount the servo directly in front of the horn and use a short, lighter gauge (.047"/1mm) music wire push rod. Then I have to extend the servo leads as necessary to get them back to the receiver. The photo is of the Divinity 32, that is a typical servo mounting for me.

Jack
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