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Old Sep 20, 2012, 07:54 AM
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My Pace got a rudder, so far it hasn't fluttered. But then I was only going 162. I sent the Austrian manufacturer an email to find out why it fishtails at times. His answer was that the CG is too far forward.Hope we still get some weather here that I can try out the changes I have made improve that problem.
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Old Sep 20, 2012, 03:47 PM
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Hey Knut, Im pretty sure some tip weight will help that too. If the rudder ever fluttered you could always tape it up
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Old Sep 20, 2012, 04:04 PM
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Thats what I have in mind to do if it happens Josh.
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Old Sep 20, 2012, 05:46 PM
AvB
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No way Knut. The fishtailing won't be due to CG forward ... more likely the converse.

Rudder fluttering varies from plane to plane and must be affected by complex airflows.

The Stratos rudder is big and hasn't fluttered to 180mph, which is stupidly fast for a big 3+m F3F/B style plane.

But the Vector rudder will flutter at 120 every time and has to be taped.

The light Scratcho that Jarred got to 150 at Weldon has a lightly hinged rudder and it never flutters.
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Old Sep 20, 2012, 06:57 PM
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Quote:
Originally Posted by josh18 View Post
Hey Knut, Im pretty sure some tip weight will help that too. If the rudder ever fluttered you could always tape it up
Actually Josh, this is a double edged sword.

The tip weight will dampen the yaw, but will also increase the time to recover from it should it still occur. Hence the preference towards the T-tail on the Opus as opposed to the V-tail for the same reason. I tend to agree with AvB, I doubt the cog being forward would be the cause.

More likely it is the differential setting on the ailerons.

An easy way to sus this out is to turn left and right continuously (wing waggle) while pointed into the wind. You will see the tail push out side to side while doing this if the differential is wrong. Just adjust it til there is minimal tail waggle.

Hope this helps.


Waz
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Old Sep 20, 2012, 10:15 PM
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Thanks Waz.
Do you mean banking ( using ailerons ), or turn ( using rudder ).
Are we talking about the adverse yaw, created by the down going aileron?
You could be right if thats what you mean, because I got very little differential. I thought I read somewhere it is better not to have differential when DSing.

regards
Knut
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Old Sep 20, 2012, 11:03 PM
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I agree with Andrew and waz..
Deferential will be you culprit.
Every plane likes different setting so , there is no right setting.
Some like a little more down and up OR the opposite.
Yaw , will be seen when in horizontal flight and when pushing L, R ,L , R aileron you will see if the nose goes up and down and left to right. Small movement at the nose , ends up being a lot at the tail. Get it rolling AXIAL... Perfectly and it will solve your hawing problem.

My NYX has a massive tail , and did exactly what your describing , now it rolls perfect , it's rock solid at 180+.
FYI....my rudder is taped.. and servo removed.. It ain't no thermal plane
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Old Sep 20, 2012, 11:26 PM
AvB
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Knut when you say fishtail do you mean like a waggle or shimmy, as it goes down thru the shear?? If so that's nothing to do with ail diff. Some planes just do it more than others, and V-tails usually much worse.

Some of these things are not set in stone. People differ in their opinions. Take this: Daboz told me repeatedly "I've never met a plane that didn't need some aileron differential fiddling to get it to handle right". I took that seriously and have been learning to fine tune it. Then the other day, I talked to Bruce Tebo and was mildly blown away to learn that he sets all his planes with absolutely no aileron differential. It doesn't matter if it's his D60, K100, K130, D130, Destiny or whatever, he sets exactly equal up and down, and never changes it!!! And he's one of the fastest guys on the planet, and certainly the most amazing 300mph acro pilot around. Seeing his plane coming straight up the backside at 300mph rolling axially and smoothly ... it's obviously working for him.

Currently how I set ail diff for DS speed is to give the plane a sharpish bit of inward roll coming out of the bottom turn, and watch whether the plane tends to a) nose down towards the backside or b) nose up and exit a bit high. If it's a) it means the up aileron is dragging so you need to reduce up throw, and vice versa.

Also Bruce doesn't use low rates or expo. When he sets the plane up he programs a likely rate and then programs one higher and one lower. He flies it and picks which rate he likes, and he uses that one all the time, from launch to warp speed to landing!
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Old Sep 21, 2012, 12:07 AM
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Sorry mate, don't know what "shimmy" is, haven't lived long enough in Oz for that one.
I am talking, when I come up through the shear it waggles its tail. So far have done only left turns, and it seems to take the nose to the right first when I come up. I am thinking probably not enough differential.

BTW thanks for all your comments guys.
You might be able to make a proper DSer out of me.
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Old Sep 21, 2012, 12:57 AM
AvB
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Shimmy = waggle I think! Rearward CG doesn't necessarily induce waggling - I know this because all 3 of my fast planes were almost un-DS able when I first flew them in strong conditions at Weldon, due to rearward CG, and they didn't waggle ... they tucked frighteningly as the speed built, and tracked badly and vaguely. Amazing how much better they felt moving the CG well forward. Like putting it on rails.

You gotta remember that if it yaws but you're not actually feeding in any aileron stick, then it's not aileron diff. In the ideal scenario, with a perfectly tracking plane and a nice circuit, there's very little aileron input. The plane can be flying knife edge, but if the turn is being done by elevator and the aileron surfaces are neutral, then by definition it can't be adverse yaw.
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Old Sep 21, 2012, 02:06 AM
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By the sound of it, I got to get a lot more DSing under my belt, to get that perfect line not having to use the ailerons.
That's why that trip will be so invaluable for me, to see the top notch flyers do it. Cant wait.
Cheers
Knut
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Old Sep 21, 2012, 02:38 AM
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Well back on topic, went up to Wainui with Andrew Palmer today for his first proper DS attempts. Wind was about 20mph, just enough to get into the 120s if you pushed hard. Perfect learning conditions.

We flew the two Scratchos, the Tracer, RT42, Mini Ellispe, and the two Jazzs. Just good fun conditions for acro and playing around.

Andrew has DS sorted now and got 108mph with the Scratcho. I could only manage 113 with mine in slightly better air. Got to finish his JW now for him.

He was carving up doing DS acro with his mini ellipse like a seasoned DSer! Great to watch!

Hopefully heading up again on Monday afternoon.
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Old Sep 21, 2012, 03:21 AM
AvB
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Brilliant. Congratulations to Andrew. Looks like Monday is gonna be pretty big up there?
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Old Sep 21, 2012, 03:24 AM
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Forecast has dropped. Will keep an eye on it over the weekend
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Old Sep 21, 2012, 04:39 AM
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Hey knut, I thought you were talking about fish tailing or waggleing through the shear. I think what causes it is when one wing tip crosses the shear before the other. I reckon tip weight settles it down heaps (some will say it does the opposite), It works to dampen out roll, so I reckon it dampens out yawing from turbulence too.
Like Waz said, it makes it more likely to tip stall and takes longer to recover, but they go Sooo much better at DS that way!
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