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Old Dec 31, 2013, 01:43 AM
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lessram's Avatar
Baar, Switzerland
Joined Oct 2006
242 Posts
Build Log
Winter project: Red Kite

Background:
All my jet projects are currently on hold, since it is too cold in my hobby room. 5 – 10° C (41 – 50° F). I made the experience, that the glue will not work and I need a hairdryer to warm up the material and the glue. So I wanted something with minimal gluing involved.
Inspired by Joel’s golden eagle, I thought why not going for a raptor and since we have a small red kite population where I live, the “model” question was decided.

Planning:
Straight forward: I just downloaded a good picture from a red kite, set it as background and traced the wings and body. That’s it. For the size, I wanted to go near the original, so it has span of 1.5 m (59 inch)

Prototyping:
To see, whether I planned something which could be attributed with the term “has flying characteristics”, I just did a quick and dirty 50% build with 3 mm depron. The second reason for the prototype was to get an idea about the location of the CG. Luckily, it worked out fine. It’s not a great glider, but OK.

Build:
I started with the body. First I wanted to do the body in layers of 6 mm depron. As soon as I saw, how much depron I would need, I changed my mind. Since I had a piece of XPS lying around (“borrowed” it form a trash container of a construction site nearby), cutting and sanding was the way to go.
As for the wings: three layers of 6 mm depron with two cf-rods between the first two layers.
The rest, I just made it up as I went along building.

Mishap:
Since I will not be able to paint the bird in a way you could recognize it as a “red kite”, I printed the bottom view of the wings on paper and glued it onto the wings. Big mistake. Though it looked good on the day I did this, the next morning a nasty surprise was waiting on me. Huge air bubbles between paper and depron and the wing distorted. So I had to rip of the paper.


Current state:
The bird is wired, motor attached. Still need to sand the head section, link the control surfaces and it’s RTF.

Since I never did a “plane” like this, anything special I need to consider for the maiden ?
Any hints are appreciated
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Old Dec 31, 2013, 03:36 AM
All can fly...Launch stronger!
ttersu's Avatar
France, Centre, Romorantin-Lanthenay
Joined Oct 2013
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Looks great
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Old Dec 31, 2013, 03:40 AM
An itch?. Scratch build.
eflightray's Avatar
South Wales U.K.
Joined Mar 2003
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Will you be adding a vertical stab, (fin), for directional stability ?

I fly an Eagle, (scratch build Depron look alike of the EPP Eagle), it uses a 'V' tail with ruddervator for control, (no ailerons), and some dihedral for lateral stability.
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Old Jan 01, 2014, 12:45 AM
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lessram's Avatar
Baar, Switzerland
Joined Oct 2006
242 Posts
Ray
I built a small fin which I will glue on the "elevator". It's an abbreviation of Tom Nelsons fin on his eagle.
I don't know whether it will give enough stability, but still better than nothing.
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Old Jan 01, 2014, 10:27 AM
treefinder
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SE MI
Joined Oct 2004
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Nice looking "bird"! I have been fascinated by how we have to add vertical surfaces for yaw stability, when the birds don't. I do recognize the occasional twisted tail flights of redwing blackbirds in close in maneuvers, but never see it in the hawks soaring above me. What do they know that we don't? (Now that was a dumb question- what thousand little things about flying do they know that we don't?) I suppose that they make constant tiny corrections we can't see.
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Old Jan 01, 2014, 12:57 PM
When pigs fly rc
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USA, NY, Chester
Joined Apr 2008
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So much for the common use of bird brain.
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Old Jan 02, 2014, 03:37 AM
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lessram's Avatar
Baar, Switzerland
Joined Oct 2006
242 Posts
Springer
I really could live without comments like yours
So I blame you for my last two hours browsing through the net, trying to find an answer.
What I found: "... it follows that the sweep in slotted wing tips provides a substantial contribution to the aerodynamic yawing moment and, thus, to yaw stability." Since birds may change the sweep, like we move our hands, I assume that's how they correct any imbalance "in flight" without moving the tail.

Aside from that:
I'm finished with the build. Weight wise, I'm up to 420 gr (14.8 oz).
I think I will do some glide test first, to nail down the correct CG, but flying condition are not good right now (light rain), so I have to wait ....
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Old Jan 02, 2014, 07:33 AM
treefinder
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Awww, shucks, sorry-i'll try to be better....

From your research then we should add another couple of servos in the wings to fiddle with the "feather" tips? Hmmmmm..... Oops! Hope i didn't do it again!

Your kite continues to look better and better. A bit of color and it'll be spooking all the little birds!
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Old Jan 03, 2014, 02:57 AM
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lessram's Avatar
Baar, Switzerland
Joined Oct 2006
242 Posts
Springer
So much for your „sorry-i'll try to be better....” tsssss….

I refuse to … hmm … rotatable wingtips using as rudder … NO, I just ignore your comment … using a central servo to control the sweep of wingtips … Maybe thinking a little about it … sure I would need more “slots”, so a new wing … could actually work … OK, you did it again !

I have no clue, whether the idea works or not, but I think it’s worth a try. What’s your opinion as a pro ?

But first I have to bring the red kite into the air.

Actually, I did yesterday a small gliding test (about 30 feet). Result: Nose-heavy and the ailerons have been almost ineffective. Unfortunately, I did not have the time for a second test. So everything on hold until the weekend.
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Old Jan 03, 2014, 04:22 AM
Parkjet collector
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Schweiz, AG, Merenschwand
Joined Oct 2011
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Olli,
that is a nice idea. But why don't you build a V-Tail?

Another thought: You move a weight with a central servo inside of the body from left to right to assist the ailerons.
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Old Jan 03, 2014, 08:31 AM
treefinder
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SE MI
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I have no clue either, but it would be fun to try! (Gotta build my own bird first, though)

Wobisch: "why don't you build a V-tail?" ... Why build a bird in the first place? Or Why build a bird then make it look like a plane?

Just to go deeper in the morass of copying God's creation. (Like Newton: thinking his thoughts after him) i also wonder about what it would take to do an orthinhopter bird that only has to flap it's wings as slow as real raptors do versus the frenzied flapping of most all models i have seen. Oh no! Did i do it a third time?e
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Old Jan 03, 2014, 11:09 AM
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lessram's Avatar
Baar, Switzerland
Joined Oct 2006
242 Posts
Wobisch and Springer
Both of you guys drive me just crazy !

I just wanted to document an easy build, and you two spoiled everything !

Wobisch, your suggestion to use movable weight to support roll control:
Why not using the same principle for pitch ? (Tinkering with the CG in flight)

So it ends up with the following:
Instead of having ailerons and elevator: Use movable weights for the corresponding control. The only visible part remaining would be the wingtips for yaw control.

VERY interesting concept.

I don't know if it is feasible, but I guess I have to try eventually.

But please: Let me complete the current build first

PS @Springer: Definitely NO, not a third time, twice was enough !!
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Last edited by lessram; Jan 03, 2014 at 11:29 AM.
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Old Jan 03, 2014, 11:58 AM
treefinder
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Ok, i'm done. Got enough ideas it keep the old subconscious working for a while. I have a couple builds to finish too, so i'll just watch your bird come together! Thanks for putting up with an old geezer!
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Old Jan 03, 2014, 12:10 PM
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lessram's Avatar
Baar, Switzerland
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Wrong thread
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Last edited by lessram; Jan 03, 2014 at 12:22 PM. Reason: Deleted, wrong thread
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Old Jan 03, 2014, 12:53 PM
An itch?. Scratch build.
eflightray's Avatar
South Wales U.K.
Joined Mar 2003
12,787 Posts
The 'V' tail isn't really noticeable when flying, just like the prop. The tail plus some tip dihedral, (and some birds show that with the tip feathers flexing up), make for a very stable bird that can turn tight on rudder, (ruddervators).
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