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Rud-Ail mix and slow roll (roll rates) - 11/19/2012 1:07 PM   
KenChoo


 

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Last Login: 11/28/2012
From: Willetton, Western Australia, AUSTRALIA
Status: offline 		Hi everyone, I have rud-ail mix (same dir, i.e. left rud - left ail) and during slow roll I find the roll rate speeds up in the second half because of the application of different rudder in the first vs second half...that is, rudder in first half has ail from the mix opposite to the roll direction so the roll is slower, then after that opposite rudder has ail in the same direction as the roll rate speeds up.

Any suggestions to manage that? Or is it just varying ail input?

Thanks,
Ken

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RE: Rud-Ail mix and slow roll (roll rates) - 11/19/2012 4:13 PM   
jgg215


 

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From: Albuquerque, NM, USA
Status: offline 		Ken,
Put your rudder to aileron mix on a switch. Then try your slow rolls with the mix turned off. You may find that most of the roll rate variation is due to stick inputs rather than mixing. it is very diificult to maintain the same slow roll rate when you are also using the elevator and there is a pyschological tendancy to increase roll rate in the second half as well.
John


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RE: Rud-Ail mix and slow roll (roll rates) - 11/19/2012 9:44 PM   
bjr_93tz


 

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From: ToowoombaQLD, AUSTRALIA
Status: offline 		Seems odd?

If the mix is there to remove any roll coupling then it shouldn't be causing a variation in roll rate during a roll.

A quick and dirty way to check this is to see if you have any roll coupling during the knife edge points of a 4-point roll, if not then the mix isn't contributing to the change in roll rate. However all airplanes are different, the mix may need to be a multi-point mix and not a linear one so the mix is correct at the knife edge points AND during the transitions when the rudder (and yaw) is less?

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RE: Rud-Ail mix and slow roll (roll rates) - 11/19/2012 10:35 PM   
KenChoo


 

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Last Login: 11/28/2012
From: Willetton, Western Australia, AUSTRALIA
Status: offline 		D'oh! bjr, jgg, you're both right. Silly of me to think my mix is affecting the roll rate...thanks for putting me right on this one...more practice!

Ken

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RE: Rud-Ail mix and slow roll (roll rates) - 11/20/2012 5:16 AM   
Rendegade



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From: Perth, AUSTRALIA
Status: offline 		I've noticed it in almost every aircraft I've flown, rolling from inverted to upright (rudder and aileron in the same direction) the roll rate will increase. Some aircraft a little, some like my CAP 10, will damn near snap roll!

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RE: Rud-Ail mix and slow roll (roll rates) - 11/20/2012 8:31 AM   
matt13


 

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From: Adelaide, AUSTRALIA
Status: offline 		Full size aircraft have their roll rate increase as the "top rudder" is added in on the last part of the roll. ( Iuse to instruct in Cap 10's)
It is just easier to judge how much aileron to reduce to keep the rate constant when you are sitting in the real thing :-)

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RE: Rud-Ail mix and slow roll (roll rates) - 11/20/2012 11:38 AM   
bjr_93tz


 

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From: ToowoombaQLD, AUSTRALIA
Status: offline 		I'd concede that even if the rudder/aileron mix was set correctly to mitigate most roll coupling, that speeding up of the last 1/4 of the roll could happen if you were getting on the up elevator a bit hard coming out of the roll.

If you were to let the nose drop a bit while inverted and not get on the rudder hard enough during the 2nd knife edge bit, then there'd be a strong temptation to feed in a bit more up elevator than usual during the last 90 deg to correct the line. With the low wing yawed forward I'd expect a minor increase in roll rate in that case.

I agree with jgg215, if the mix is causing a problem for a given maneuver and/or you don't absolutely need it for the schedule you fly then switch it out.



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