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Why are all the wings flat bottom?

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Why are all the wings flat bottom?

Old 01-06-2010, 04:19 PM
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Default Why are all the wings flat bottom?

I've been playing around with 4mm coro and have a good looking wing but its a symetrical shape.

Flutes are running cordwise. I scored the LE and folded it over, I glued the aileron inbetween the top and bottom TE.

I then spread the top and bottom and slid the yardstick into position. Very difficult to do. ( I had glued sections of coro inside to make a channel to hold the yardstick in position.

Looks great, a little heavy cause its all 4 mil.


So why do I SEE ALL FLAT BOTToM WINGS?

Steve
Old 01-06-2010, 04:29 PM
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Default RE: Why are all the wings flat bottom?

Hi Popriv
I would say it is an evolutionary thing. Those who made free plans available started with flat wings. Another reason is that the flat bottom fits perfectly to the flat fuselage. Makes things simple, like in Simple Plastic Airplane Design, or SPAD. My SPAD Biplane has symmetrical wings, but all of my other SPADS have had flat or semi-symmetrical wings.
Old 01-06-2010, 06:41 PM
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Default RE: Why are all the wings flat bottom?

Here is a picture of my first attempt with coro..
Just trying to see what I would get.
Its all 4mm, 36" x 12" with a 2.5" aileron...
I dont see a problem making a wing saddle for the shape?

I wish I had made it longer...

Sooo, how does it look?

After doing more reaserch I see that this wing size doesnt match up (size wise) with any of the free plans.

I'm trying to figure out a fusalage and power plant to use with it.

My power options are :

OS.15LA (should be here tomorrow!)
TTPro .36
OS.46LA

I'm afraid this smaller, somewhat heavy wing will be to much for the .15LA??

I have a Gnat ready and waiting to mount the OS.15 to see how that flys but I'm looking into a wing with an airfoil VS the Gnats wing..

The end plan is to get something our club can use for combat this summer.

One of the other guys is working on the same project only he is working on Foam with a wire cutter. Then we will see which plane works the best.

Lots of Fuselage options so we are focusing on the wing construction first.

Thanks for any help

Steve
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Old 01-06-2010, 06:46 PM
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Default RE: Why are all the wings flat bottom?

Here is the Gnat!
I put the power plant from my Easy Glider on it while I waited for my OS.15LA.

It flew but I dont think the 12" folding prop was right for this?

It flew but not that great. I'll see how it does with the >15 and an 8x3 prop?


Steve
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Old 01-06-2010, 07:21 PM
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Default RE: Why are all the wings flat bottom?

hey popriv, thats an awesome looking semetrical wing! I find its easier to do a semetrical than a flat wing, I rarely make mine all 4 mill, some RNAF and mostly 2 mil wings
Old 01-07-2010, 12:39 AM
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Default RE: Why are all the wings flat bottom?

Yeah Pop, that's a good looking wing.    Maybe you could try out the calculator here at http://www.geistware.com/rcmodeling/model_calc.htm and try to find one of the ships at STTB that your wing will fit on or just build something from scratch.  As far as your coro plane vs. your buddy's foam wing, Draftman1 has loads of experience and can tell you which one would be best.  My *ignorant* opinion is that if you're flying glow, you're going to have to cover that foam wing one way or another to keep the fuel out.  I would *think* that the coro would be an easier build.  But every time you have a mid-air or some kind of "gnawing on" with the foam you're going to have to seal it back up to keep fuel out of it and I've bashed my coro plane pretty good a couple times and I've had no repairs other than landing gear.  [:@]
Old 01-07-2010, 10:47 AM
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Default RE: Why are all the wings flat bottom?


ORIGINAL: Villa

Hi Popriv
I would say it is an evolutionary thing. Those who made free plans available started with flat wings. Another reason is that the flat bottom fits perfectly to the flat fuselage. Makes things simple, like in Simple Plastic Airplane Design, or SPAD. My SPAD Biplane has symmetrical wings, but all of my other SPADS have had flat or semi-symmetrical wings.

Also, most of the original SPADs were Combat oriented and using the heavier materials we used to have to deal with. Heavy PVC/All 4 mil. Since combat consists mostly of a lot of loops a flat bottom wing will produce more lift making a heavier plane fly better upright and loop tighter than a symmetrical wing of the same dimensions and weight. So what makes for an easy to build wing is actually optimized for our purpose. Past that though if you want to switch up to lighter materials making it symmetrical like you have done is quite the easy thing to do.
Old 01-07-2010, 12:48 PM
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Default RE: Why are all the wings flat bottom?


ORIGINAL: Clean


ORIGINAL: Villa

Hi Popriv
I would say it is an evolutionary thing. Those who made free plans available started with flat wings. Another reason is that the flat bottom fits perfectly to the flat fuselage. Makes things simple, like in Simple Plastic Airplane Design, or SPAD. My SPAD Biplane has symmetrical wings, but all of my other SPADS have had flat or semi-symmetrical wings.

Also, most of the original SPADs were Combat oriented and using the heavier materials we used to have to deal with. Heavy PVC/All 4 mil. Since combat consists mostly of a lot of loops a flat bottom wing will produce more lift making a heavier plane fly better upright and loop tighter than a symmetrical wing of the same dimensions and weight. So what makes for an easy to build wing is actually optimized for our purpose. Past that though if you want to switch up to lighter materials making it symmetrical like you have done is quite the easy thing to do.

Good point about the lift and looping during combat. also the fact that the foam needs to be covered.

Now to get a flat bottom is it just a matter of how you line up the material at the TE? Even like I did gives a symmetrical wing. for a flat bottom I need more material on the top when I line up the TE? Seems harder that way? ( But not much)

I'm trying to find some local 2 mm coro and I'll redo the wing in that.. Less wieght.

Do you think the current wing would work? at the current dimensions?


Steve
Old 01-08-2010, 09:57 AM
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Default RE: Why are all the wings flat bottom?


ORIGINAL: Popriv
Now to get a flat bottom is it just a matter of how you line up the material at the TE? Even like I did gives a symmetrical wing. for a flat bottom I need more material on the top when I line up the TE? Seems harder that way? ( But not much)
I think that's why the top is wider than the bottom on all the STTB plans and you fold it over after your spar is glued in place, then mark it and cut it off flush. That's a lot easier than trying to calculate the distance with the spar height and the curve and all. To get the flat bottom, I have a piece of 1x4 that I cut a 45 deg bevel on one side. I fold over my wing and get the TE even with the edge of my wooden bench. I jam the 1x4 up tight against the LE and screw it down to my bench. Then I glue her up, jam the LE up under the 1x4, put a 2x2 over the TE of the wing and clamp it down tight. When I pull it out it's pretty flat except for a little bit of reflex on the bottom near the TE where the pressure of the top is pulling up on it. Seems to work pretty good. An angled 2x4 might be even better because then you've got more height so you can not jam the wing under all the way and let the LE come up a bit and you can get a symmetrical wing or a semi-symmetrical if you'd like. <br type="_moz" />
Old 01-08-2010, 11:38 AM
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Default RE: Why are all the wings flat bottom?


ORIGINAL: PatrickCurry


ORIGINAL: Popriv
Now to get a flat bottom is it just a matter of how you line up the material at the TE? Even like I did gives a symmetrical wing. for a flat bottom I need more material on the top when I line up the TE? Seems harder that way? ( But not much)
I think that's why the top is wider than the bottom on all the STTB plans and you fold it over after your spar is glued in place, then mark it and cut it off flush. That's a lot easier than trying to calculate the distance with the spar height and the curve and all. To get the flat bottom, I have a piece of 1x4 that I cut a 45 deg bevel on one side. I fold over my wing and get the TE even with the edge of my wooden bench. I jam the 1x4 up tight against the LE and screw it down to my bench. Then I glue her up, jam the LE up under the 1x4, put a 2x2 over the TE of the wing and clamp it down tight. When I pull it out it's pretty flat except for a little bit of reflex on the bottom near the TE where the pressure of the top is pulling up on it. Seems to work pretty good. An angled 2x4 might be even better because then you've got more height so you can not jam the wing under all the way and let the LE come up a bit and you can get a symmetrical wing or a semi-symmetrical if you'd like. <br type=''_moz'' />

Very good, I'll try that on my next attempt.

Right now I'm leaning towards the gnats shaped wing and I'll see how I progress with that.

( just got my .15LA to put on my gnat )

Thanks

Steve
Old 01-08-2010, 09:43 PM
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Default RE: Why are all the wings flat bottom?

I hope to get my Gnat finished to maiden on Sunday.  Just a couple things left.  I've got an old OS 20FP on it.  Good luck with yours!

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