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Has anyone tried doing this?

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Old 05-13-2007, 05:43 PM
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T.W.
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Default Has anyone tried doing this?

I'm part-way through building a Mojo .40 and am wondering whether to try gluing tri-stock onto the leading edge of the vertical and horizontal stabs. I've never seen this done previously, in fact I've never seen any leading edges anything close to being "sharp," but I'm wondering if there might be an advantage in doing so. Wouldn't they would cut through the air much better than if I just leave them "blunt." Has anyone tried doing this . . . . if so, how did it affect the flight characteristics?

Tony
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Old 05-13-2007, 06:09 PM
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matchlessaero
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Default RE: Has anyone tried doing this?

No advantage at all.. Profiles are about using drag, not reducing drag. Leave the leading and trailing edges of the tail square and bevel the hingelines only.
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Old 05-13-2007, 06:42 PM
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RC MANIAC119
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Default RE: Has anyone tried doing this?

WHAT HE SAID!!!!!
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Old 05-13-2007, 07:08 PM
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Default RE: Has anyone tried doing this?

TW, besides making your plane 1/2 oz heavier, I can't see how it would hurt. What I don't like about the idea is the mind set. What I mean is that if anything, look for ways to reduce weight while still leaving the airframe just strong enough for normal handling on the ground and those extreme manuevers in the air. With a design that has a lot of wisdom in it, it wont be easy to find ways to improve it.
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Old 05-13-2007, 08:42 PM
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Dr1Driver
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Default RE: Has anyone tried doing this?

A sharp leading edge does not necessarily equal lower drag. Also, it can cause violent stall behavior at all speeds. My advice is to leave the leading edge as is. A 3-D/Funfly plane benefits from high drag at low speeds.

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Old 05-13-2007, 11:06 PM
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Default RE: Has anyone tried doing this?

Had a fellow club member build the leading edges on a ultra sport "sharp" plane was almost unflyable. I test flew it,..... made the runway intact after lots of expected vector changes. The leading edges are round for a good reason.
I have a MOJO 60. Paul Swany has designed a great fun fly toy, build and fly it as instructed then after gaining a little time on the plane you can always tape some tri stock on and give it a go.
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Old 05-14-2007, 09:54 AM
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Default RE: Has anyone tried doing this?

I like to "soften" the edges with a foam block sander. I think it looks better and it definitly helps the covering stay on by not having a sharp edge where the covering seam is.
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Old 05-14-2007, 12:34 PM
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Default RE: Has anyone tried doing this?


ORIGINAL: T.W.

I'm part-way through building a Mojo .40 and am wondering whether to try gluing tri-stock onto the leading edge of the vertical and horizontal stabs. I've never seen this done previously, in fact I've never seen any leading edges anything close to being "sharp," but I'm wondering if there might be an advantage in doing so. Wouldn't they would cut through the air much better than if I just leave them "blunt." Has anyone tried doing this . . . . if so, how did it affect the flight characteristics?

Tony
One musn't think too much.........One must fly

No real advantage though.

You will really enjoy this bird.

J.

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Old 05-15-2007, 04:23 AM
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Default RE: Has anyone tried doing this?

Thanks for all your comments. So the consensus is that I definitely shouldn't "sharpen" the l.e. of my Mojo's tail surfaces. OK, I thought you'd say this, so we're all in agreement

I posted this question because I got to thinking about how great Shock-Fliers fly with their "sharp" leading edges . . . . but "thinking-on" I quickly realised that the whole of the Shock-Fliers flying surfaces are just as thin as their leading edges, so there's no actual "sharpness" at all (as JohnnyMojo said: I should stop thinking and go flying!)

But, just one last thought before I call it a day and get my Mojo completed: What is the best treatment od the leading edges of the v- and h-stab in a profile model? Should they be rounded-off - or is it best to leave them "squared-off?" Looking back at some of my previous models I have to admit that I can't say I've noticed any difference in performance no matter which way I finished-off the l.e.'s . . . . but have you?

Tony
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Old 05-15-2007, 09:03 AM
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Default RE: Has anyone tried doing this?

Just lightly soften the edges with a sponge sander.
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Old 05-16-2007, 10:03 AM
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Default RE: Has anyone tried doing this?

I've heard and done a lot of leading edge changes with tri-stock on the wings, never heard of doing it to the tail feathers? On the wings, it does change the way a plane "penetrates". I did it to a .46 U-Can-Do to see if it would harrier better, I added tristock at first to just the prop wash areas and then eventually, most of the leading edge(about 2/3 span from root to tip). It did make the plane come in a lot "hotter" than before, but no other drastic changes. It did also help with harriers a little but adding tri-stock to the wing TRAILING edges so I got the deflection needed for spoileron mix did the trick to harrier.With about 45% up spoilerons, the little Do would harrier like a champ, very HA too. Its just that these little planes seem to 3-D best when its "foamy weather"(zero wind). Doesn't happen much around here.
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Old 05-16-2007, 05:11 PM
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Default RE: Has anyone tried doing this?

Yep, I've got tri-stock on the trailing edges of my Mojo for the same reason you mention MIXMASTER - to get the absolute maximum deflection. I also used it on a home-design more than 10 years ago too, and it worked great so I completely agree with this. It was the leading edge of the stabs I was wondering about though. Think I'll just treat them the way buildflycrash suggests . . . . I suppose I'm going to need plenty of drag to slow her up, what with the Saito 72 up-front doing its best to make her progress

Tony
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Old 07-25-2007, 01:53 AM
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Default RE: Has anyone tried doing this?

check out the aerodynamics forum... you don't want sharp L/E's on any of your flying surfaces. the rounded L/E that you see on almost every wing/stab provides much better airflow over the surface. on the other hand, a sharp T/E works well.
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Old 07-25-2007, 03:27 AM
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Default RE: Has anyone tried doing this?

Thanks troposcuba. The model's finished and flies great now

Tony
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Old 01-16-2008, 07:48 PM
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Default RE: Has anyone tried doing this?

I usually just kiss the edges of the wings with 100 grit sand paper to take the corners off. This seems to help the airplane fly a little faster but other than that it makes no difference, for me that is.
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Old 02-06-2008, 10:19 PM
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Default RE: Has anyone tried doing this?

A sharp leading edge will cause abrupt and irregular stall patterns. The slower a plane flies the rounder the edges should be. In control line aerobatics we learned back in the 50's that pointy leading edges caused the planes to hunt rather than groove. The only time leading edges on anything should be pointed is for supersonic flight. Then they help form the shock wave and control its location. Trailing edges should not come to a point either. That will induce trailing edge vorticies and can induce flutter. The least drag trailing edge at subsonic speeds is actually a thin flat edge with sharp corners at the airfoil intersection. Most folks think that looks like poor workmanship though so they get rounded. Its slower cause it induced vorticies as well but they are not violent and unpredictable like the razor sharp edge (which of course will be lost to hanger and transport rash in short order anyway. Penetration of the air has nothing whatsoever to do with it. The air starts to part to top and bottom of the wing far ahead of the leading edge. Take a look at wind tunnel pics and you will see this pretty clearly illustrated.

keep the oily side evenly distributed,

bob
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Old 02-13-2008, 05:14 PM
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Default RE: Has anyone tried doing this?

Thanks for this Bob. I'm very happy with the way my MoJo flies - no, that's completely wrong . . . . I'm absolutely and utterly delighted with it!

I opted for making the tail-end leading edges ever so slightly less than square, and it worked-out just fine. All I was wondering was: what would happen if I sharpened them up. But seeing-as most think it was a bad idea, I didn't go with it. But I may do one of these days, just out of curiosity

Tony
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Old 02-13-2008, 07:20 PM
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Default RE: Has anyone tried doing this?

Well, one of the lovely things about slabs is that if you try something and it doesn't work, you just hit the power and fly out of it. Much nicer option than with most other types!.

MOJO's a great bird.

bob
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Old 02-15-2008, 09:56 AM
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Default RE: Has anyone tried doing this?

I used tri stock on my .46 Do with some positive results, I placed them slightly above the center of leading edge on the wings to make a "sharp" separation point to bring on full stall at lower angles of attack. The constant radius leading edge has a very wide area(angle of attack) before separation occurs, I believe thats why Do's rock so much until its almost standing up. Full scale aircraft use stall strips to test stall characteristics. Power on -level flight wasnt affected much, only increased landing speed was noticed and it did harrier a little better,still not very good in gusty winds though, still rocked on those days.
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Old 02-15-2008, 03:29 PM
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Default RE: Has anyone tried doing this?

The Mojo needs nothing whatsoever doing to the wing. It's by far the best-flying model I've ever flown, and I just love it. I only started this thread to check if anyone had tried sharpening-up the tail-end leading edges - and with what results. The wing I really wouldn't touch at all as I can't imagine anything being better than the stock otem (actually, I wouldn't change the tail-end either now that I come to think about it )
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