roll tendency... different at low and high speed... thoughts?

[schristo@mac.com]

okay i am about out of ideas... what might be a rigging / wing loading condition that would yield a tendency to roll left when slow and right when fast? both rolls are well within trimming capacity when the fuel load is balanced.

[tcone1]

Stephen,

Search the forums for articles on heavy wings...chances are you'll end up squeezing an aileron and all will be well.

[Jamie]

Originally Posted by tcone1

Stephen,

Search the forums for articles on heavy wings...chances are you'll end up squeezing an aileron and all will be well.

I do believe that Stephen's question is a little more complex than that, as it rolls both ways.

EDIT: On second thought, it *could* still be heavy wing. If the perceived "trim center" is *not* centered but it is actually trimmed left...and a heavy right wing exists it will exhibit the described behavior.

I would disconnect the aileron trim, balance the airplane about the roll axis (equal fuel, etc -- much more easily done with centerline seating) and go fly.

[hevansrv7a]

In my experience, any GA airplane will tend to roll (to the right, if memory OK) as you go faster. The rudder (without trim) is perfect at only one IAS. Since this rolls both ways, it is likely a combination of a weak tendency to go one way due to rigging or similar and then a natural tendency to go the other way as IAS increases and overpowers it. The one that happens below the neutral point is the one to fix.

I am not an aero-engineer, don't even pretend to be one. This is merely based on experience and basic understanding of little airplanes. Worth the 2 cents but maybe not much more.

[Ironflight]

Stephen,

I have found this exact same behavior in my own RV-8, and I attribute it to the spring-bias aileron trim. While I haven't done the math to prove it, intuition (frequently wrong), says that if you trim for a stable roll condition at one speed, the ailerons are slightly deflected by the spring bias system to keep the wings level. If you increase or decrease the speed, then the forces acting on the ailerons from the airflow change, so their deflection will be different (assuming that you don't change the trim setting), and you will then be out of trim again. To see if you have a heavy wing, you want to set the aileron trim to neutral, then check. Once you have balanced the airplane (for instance, with an aileron squeeze), I bet you will still notice that the trim condition will change with speed if you have a fuel imbalance and use the aileron trim to compensate for it.

At least, that is my experience, and my theory for the behavior. Now, if you have an aileron trim tab, is the same thing true? I haven't noticed a trim change with speed in Louise's RV-6, with a tab - I'll have to check next time.

Paul

[schristo@mac.com]

Thanks. I think it is making sense. At high speed any spring trim force that balances the ailerons remains when the airflow is reduced and the spring force introduces the opposite roll since it is now greater than the air load on the aileron.

I am going to disconnect the springs to squeeze the ailerons for balanced flight at cruise.

[L.Adamson]

Originally Posted by Ironflight

At least, that is my experience, and my theory for the behavior. Now, if you have an aileron trim tab, is the same thing true? I haven't noticed a trim change with speed in Louise's RV-6, with a tab - I'll have to check next time.

I also have a 6(A) with the servo trim tab on the aileron, & haven't noticed the trim change. On the other hand, maybe I'm just automatically compensating with the trim button. But if not................then chalk one up for those "old fashioned" tabs...

Note: Others that do have spring tabs, have mentioned that my plane trims well.

L.Adamson --- RV6A

[rich]

Stephen,
If the aileron trim dosen't completely solve the problem try removing your gear leg fairings and see if you can elimate one of the Lt. or Rt. rolls. You may have two things going on here.

[billgill]

Steve,

I have the same issue with my 7. With balanced fuel and two folks in the RV, the aileron trim is dead center with no roll tendency at 150kts IAS, ball also centered. A higher IAS reults in a left roll tendency and a slower IAS results in a right roll. At 190kt IAS, there is not enough spring bias to trim out the left rolling tendency. If you get the roll issue solved, please advise.

Best regards,

Bill Gill
RV-7 N151WP
Barrett IO-390
Lee's Summit, MO

[jsharkey]

My RV-6 is perfectly balanced with no roll trim needed at cruise speed or above.

When I slow to pattern speed I need a small amount of right trim and slightly more when I deploy the flaps. All well within the range of the trim springs.

Jim Sharkey