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

[flyboyedwards]

My 4 has this same issue, please advise if you find that answer.
Thanks!!!

[Rick S.]

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

[planenutz]

Originally Posted by 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.

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

[schristo@mac.com]

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.

[billgill]

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

[hydroguy2]

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.

[flyenforfun]

Originally Posted by hydroguy2

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?

[Neal@F14]

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.

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.

[scsmith]

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.

[Andrew M]

"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??