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decoupling surfaces - mixing, or what?

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Old 10-27-2006, 10:50 PM
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fadi
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Default decoupling surfaces - mixing, or what?

Hi All
I am trying to figure out how to decouple my sig fourstar 40 in order for it to just yaw when I input rudder, just roll when I input ailerons, and just pitch when I input elevator.
AS WELL AS just change speed when I input throttle.

The major problem is with my rudder, whenever I try it by itself the nose drops considerably and at a fast rate!! On other posts members told me that it was normal for the fourstar, so I figured I just need to input elevator to compensate. The other major problem is whenever I accelerate the nose drops a little, and whenever I ease back the throttle the nose pitches up. My plane is now fully trimmed to accomodate level flight at 2/3 to full throttle.

Shall I achieve my goal with mixing on the radio, or what? Is there any other way to figure out the percentage compensations instead of trial and error?
Do I make sense being concerned about the fact that if I pefectly decouple my model, I will have to input more down elevator in rolls for instance? I am sure however, that this decoupling will help my knife edges...

I hope this is not too much asked from a plane, I just need a "PERFECT" model
Am I going to the extremes or is that how most pilots fly their models (i.e. decoupled)?
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Old 10-27-2006, 10:59 PM
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Default RE: decoupling surfaces - mixing, or what?

Mixing will help, but it will not fix design characteristics. You can begin by 'estimating' the amount you need. If it pitches A LOT start with like 6% or less. Put the mix on a switch so you can turn it off. Some planes become un-flyable with bad mixing. From there it's trial and error.

No amount of mixing will make a plane 'PERFECT'. Your plane will never be completely 'un-coupled'. The closest are pattern planes and a few scale aerobats.
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Old 10-27-2006, 11:03 PM
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Default RE: decoupling surfaces - mixing, or what?

Oh oups... that's sad to hear
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Old 10-27-2006, 11:07 PM
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Default RE: decoupling surfaces - mixing, or what?

Would it help if I said that mixing will help...A LOT?
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Old 10-27-2006, 11:11 PM
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Default RE: decoupling surfaces - mixing, or what?

hehehe yeah sure :P
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Old 10-27-2006, 11:20 PM
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Default RE: decoupling surfaces - mixing, or what?

Perhaps you could use this as an opportunity to hone your FLYING skills . Challenge yourself to master the control inputs that would reduce or eliminate the adverse couplings. You may get frustrated at times, but think of the satisfaction you'll gain as you can depend on your piloting skills rather than the computer.
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Old 10-28-2006, 08:10 AM
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Default RE: decoupling surfaces - mixing, or what?

You sound like a pattern flier in the making! There are lots of older pattern planes around that make good sport aerobats with very honest flying characteristics. I recently completed a Bridi Dirty Birdy and I love it http://www.rcuniverse.com/forum/m_4768795/tm.htm This plane lands a *little* faster than your four star . But something like a Bridi Vagabond would be a good next plane with minimal cross coupling. http://www.bridiairplanes.com/hangar/vagabond40.html

The throttle response you describe sounds like a thrust line issue. You might have a touch too much down thrust. Verify by trimming level flight for full throttle. Make a high speed pass and then chop the throttle. Does it climb? If so the down thrust is holding the nose of the plane down at higher throttle settings, try putting a washer under either the front engine bolts or the lower engine mount bolts and repeat the test.

Then, definitely use your transmitter's programmable mixing to help your knife edge.

Dave
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