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

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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.
 
Aileron squeezing

Stephen,

Search the forums for articles on heavy wings...chances are you'll end up squeezing an aileron and all will be well.
 
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.
 
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This is two things acting at once

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.
 
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
 
Spring force is constant but air load on aileron changes

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.
 
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
 
gear leg fairings

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.
 
Mine too

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
 
Data Point

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
 
Something to look at is the thrust line of the engine, tossing it out there since it's easy to check.
 
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.

On an RV-7 that I was involved with a while back, we had exactly this issue. After trying everything we could think of to rectify the situation it came down to a very simple fix - the left outer aileron bracket was shifted about 3/32" so that the aileron itself was relocated in the slipstream. I can't recall if the aileron was moved up or down (would have to check) but I recall that it was very sensitive to small movements.

To obtain the required movement of the bracket the bolt holes in the bracket were elongated slightly and once the adjustment was finalised, a cherrymax rivet was added to the bracket to prevent accidently slippage.

This pretty much eliminated the issue but, as with any RV, you will still require small amounts of aileron trim due to the large speed envelope of the aircraft.

Hope that helps.


Mike
 
i love my airplane...

just a followup to the thread. the beast is now balanced at all airspeeds and is an absolute joy to fly. i have not hooked the aileron trim back up yet and may not bother.

a couple of lessons learned in testing:

the spring bias system will completely mask what is going on with the ailerons and must be disconnected to evaluate properly. control inputs are so very small that you really cannot tell what is happening if the springs are attached.

only change one thing at a time and go fly... it is too easy to end up inadvertently canceling one change with another further masking what is going on.

if there is a differing roll tendency from slow to fast work toward making changes that bring the roll tendency to a common side then work the ailerons to eliminate the roll.
 
What was the solutions?

Stepehn,

What was your solutions to address the roll tendency at high v. low airspeed? I will disconnect the spring bias as you suggested and see where it leads...thanks for the information.

Best regards,

Bill Gill
RV-7 N151WP
Barrett IO-390
Lees Summit, MO
 
FYI for heavy left wing

My situation was different, as I had a left roll that got worse as speed increased. I spoke with other RV builders and everyone said "follow Vans procedure" Yakdriver who built a -7 QB, is on my speed dial. He said check the aileron position.......sure enough, my left aileron was sitting proud about 1/8". This apparently causes an imbalance in the ailerons.

Slotting the outboard left hinge dropped the aileron to a flush condition. Yesterdays test flight, she flew hands off at all speeds. Success took less than 30 minutes of effort.
 
My situation was different, as I had a left roll that got worse as speed increased. I spoke with other RV builders and everyone said "follow Vans procedure" Yakdriver who built a -7 QB, is on my speed dial. He said check the aileron position.......sure enough, my left aileron was sitting proud about 1/8". This apparently causes an imbalance in the ailerons.

Slotting the outboard left hinge dropped the aileron to a flush condition. Yesterdays test flight, she flew hands off at all speeds. Success took less than 30 minutes of effort.

Wanted to bring this thread back because I wanted to see if you guys could help me out. I am having a right heavy wing when slow, left heavy at cruise, increases with speed. Yesterday I removed the centering springs and flew again. I had a very very slight right heavy on landing, no noticeable on takeoff, and a left heavy in cruise. My right aileron is already squeezed down, cant do any more. I lowered the left aileron on the outboard hinge about 3/32 and haven't had the chance to fly yet. Hoping that reduces the left heavy in cruise. Any thoughts?
 
I had similar issues when I first got my -6. It was roll neutral at lower airspeeds, but got progressively left-heavy the faster I went. I noticed that at high cruise speeds, with the ailerons neutral (even with the wingtips) that my left flap was even with the left aileron, but the right flap was down just a bit below the trailing edge of the right aileron.

I raised the right flap up a little bit and that solved the problem, it flies roll-neutral at slow and high speeds now.

Funny thing though, is that when using a digital protractor to measure the flaps when fully retracted, is that now with the adjustments and the plane flying great, the right flap now measures about 0.8 degree reflexed upwards as compared to the left flap at 0 degrees.

Oh well, it *is* a homemade airplane, after all. :p

EDIT: Since the ailerons are interlinked, if you raise or lower one aileron, the ailerons together will just automatically find their own "happy center" in level flight, and will not really change a heavy wing situation at all.... it'll only change the amount of drag you get out of them. If you wish to raise or lower something on the wing in order to fine-tune the lift of that wing... you need to raise or lower something that stays in a "fixed position" on the wing while in straight and level cruise, such as a flap or a wingtip itself. Raising or lowering a flap's retracted position to adjust for a heavy wing was the only method we had in the old Piper PA28 Cherokees, and it was a pretty effective tool for doing that.... but at the expense of losing cruise speed if you had to lower one flap side too much.
 
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horizontal tail not in plane of the wings?

I have seen this behavior before. If the horizontal tail is not "level" with the wings, it can cause this. Hard to see how this could happen in an RV because the pre-punch kits jig straight "every" time. So I kind of doubt it in your case, but I'll mention it anyway.

Another possibility is a small misalignment of the left and right elevators.

One way to test to see if it is caused by an out-of-plane stabilizer is to see if it gets worse with rearward c.g. and less noticeable with fwd c.g.

What causes this is that at low speed, there is very little download on the tail, and probably even some up-load on the tail if you have rearward c.g. (yes, it is still stable that way, contrary to popular misconception). At high speed, you have a lot of download on the tail. So, if the tail is out of plane, the download has a side-force component that causes a yaw, and the yaw couples with the dihedral to cause roll. At low speed, with a small amount of upload on the tail, it will pull one way, and at high speed with a large download, it will pull the other way. This would show up more as a yaw offset requiring rudder trim, but depending on whether you ALSO have a heavy aileron, the two effects can interact and show up as roll trim.
 
Production methouds

"Another possibility is a small misalignment of the left and right elevators"

Cessna 207's deliberately have elevator positions that are not the same. The torque tube holes are elongated and the bolts are installed wet with structural adhesive.

I am also curious if the a 3/16" or 1/4" NAS bolt with an eccentric bushing is as strong as a 5/16" AN bolt for the aft spar attach. Move the whole trailing edge up and down. Anyone interested??
 
During my Phase 1 testing I had a heavy Left wing. I didn't notice anything at low speed, but did once speed got above 180mph. I was breaking in my engine so didn't spend much time at lower speeds. At 200mph, if I relaxed my hold on the stick, the plane took a hard roll left, the faster I went the faster it rolled. At WOT it was scary for a lowtimer like myself. As I released the stick, My ailerons would deflect (left went up, right went down). So after making many calls to RV'rs, I measured the aileron outboard hinge placement. Sure enough my left aileron hinge pushed the outboard leading edge above the wingskin. slotting and dropping the hinge and I was flying balanced at cruise and higher. I still don't know how it affects slow speed, but I don't notice any adverse effect.

pic of aileron to wingskin alignment
photobucket-7921-1345060962625.jpg


Then during more high speed testing I found a new problem. Unstable in roll axis. I would tap the stick sideways to check stability, but instead of damping out, it would rock back and forth getting worse with each oscillation. After 4 or 5 rocks, I had to tighten my grip to keep things in check. A check of the trailing edges of the ailerons revealed a bloated radius edge instead of a flatter profile. I fixed this using 2 paint sticks with tape for scuff resistance and my seaming pliers. A very subtle squeeze on both ailerons took care of the unstable roll.

hope this helps
 
During my Phase 1 testing I had a heavy Left wing. I didn't notice anything at low speed, but did once speed got above 180mph. I was breaking in my engine so didn't spend much time at lower speeds. At 200mph, if I relaxed my hold on the stick, the plane took a hard roll left, the faster I went the faster it rolled. At WOT it was scary for a lowtimer like myself. As I released the stick, My ailerons would deflect (left went up, right went down). So after making many calls to RV'rs, I measured the aileron outboard hinge placement. Sure enough my left aileron hinge pushed the outboard leading edge above the wingskin. slotting and dropping the hinge and I was flying balanced at cruise and higher. I still don't know how it affects slow speed, but I don't notice any adverse effect.

pic of aileron to wingskin alignment
photobucket-7921-1345060962625.jpg


Then during more high speed testing I found a new problem. Unstable in roll axis. I would tap the stick sideways to check stability, but instead of damping out, it would rock back and forth getting worse with each oscillation. After 4 or 5 rocks, I had to tighten my grip to keep things in check. A check of the trailing edges of the ailerons revealed a bloated radius edge instead of a flatter profile. I fixed this using 2 paint sticks with tape for scuff resistance and my seaming pliers. A very subtle squeeze on both ailerons took care of the unstable roll.

hope this helps

This worked for curing our hard left roll when at high speeds, but we still have a right roll at low speeds (landing and takeoff speeds)
 
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