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Help me tune the Pico Cub Roll - Adverse Yaw

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Help me tune the Pico Cub Roll - Adverse Yaw

Old 07-01-2005, 05:21 PM
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stealth916
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Default Help me tune the Pico Cub Roll - Adverse Yaw

Hi all,

I just added ailerons to a Multiplex Pico Cub given to me by a friend, along with a gear drive and new prop for the Speed 400 motor. I built this plane for him about 7 years ago or so, and it has just come back around to me. I used data which I found online in order to size the ailerons to proper cub dimensions, relative to the overall wing size.

I am using 2 servos and a Futaba 9CHPS, so I can do differential with ease. I did not remove any dihedral, because the wing was built pretty well way back, and I couldn't bring myself to saw through the kevlar wrapped spar or the fiberglass wrapped seam. I also didn't want to reshape the wing saddle, etc. Ok - lazy I know... but these mods would also take me beyond the point of no return should I decide to retreat and leave it a 3 channel ship.

This plane has a healthy dose of dihedral - sorry I don't have the exact number right now. The first few test flights indicate adverse yaw from hell. I have set end points to 140% up and 90% down on the ailerons to start, so whatever that ratio works out to be is the differential I have tried. I have also tried moving to nearly no differential, with maybe worse results. Coordinating rudder helps to a degree, but I am looking for some smoother performance. Is there any hope for this baby without getting rid of some dihedral? Should I increase differential further, by reducing the amount of down aileron to reduce the drag on the up-rolling wing panel? Should I just go with spoiler rolls? Should I consider increasing the rudder area by some percentage?

Thanks for any suggestions!
Old 07-01-2005, 08:41 PM
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stealth916
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Default RE: Help me tune the Pico Cub Roll - Adverse Yaw

Extra info: Dihedral ~12 degrees, Chord ~8.75", Span ~46", Weight ~18.5 oz, Area ~440 sq in, Loading ~6.1 oz/sq ft, Airfoil is undercambered
Old 07-02-2005, 09:19 AM
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Flypaper 2
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Default RE: Help me tune the Pico Cub Roll - Adverse Yaw

Try more diff. Full size Ercoupe had 30 degrees up and 10 degrees down. Might try coupling rudder, ails. too. with mixing.
Old 07-02-2005, 03:00 PM
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LouW
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Default RE: Help me tune the Pico Cub Roll - Adverse Yaw

Adverse yaw isn't much affected by dihedral, so removing it wouldn't help. Diferential aileron throw is a good bet. Of course using generous rudder with aileron deflection is the method used on full scale cubs. Mixing to provide rudder and aileron together is effective and reduces dependence on thumbs.
Old 07-02-2005, 05:21 PM
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stealth916
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Default RE: Help me tune the Pico Cub Roll - Adverse Yaw

OK this morning I did another test flight, with 140% up and 40% down (more differential) on the aileron end points. This produced better turns with much less adverse yaw, although it could be better. I should have mentioned that I did program coordinated (coupled) rudder on a Tx switch, so I can turn it on and off. On this bird I would usually only turn it off for landings, especially in a crosswind when I need to slip... But really I don't need computer coupling - flying 3D Bipes and 3D Helis has taught my thumbs & brain to work together just fine :-) I typically prefer to couple myself, since speed & flying conditions will dynamically vary the amount of coupling needed at any given time...

So the adverse yaw is less with increased differential, although a good amount of rudder coupling is still required without a doubt for actual turns. I guess due to the dihedral, the plane has no chance of smooth axial type rolling maneuvers (I'm not talking full barrel/360 rolls), and when the roll angle gets over 15-20 degrees things get messy. So with this much dihedral I do not have much axial roll action.

Anyhow, I may try increasing the DIFF some more to toally eliminate the yaw - but I am starting to approach spoileron only rolls if I take any more down aileron out. I guess if it works, who cares :-) Someday I may go ahead and section the wing, by removing the center & regluing without Dihedral for more axial roll action.... (Clipper Cub?).



Thanks for the tips!

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