adjust rod end bearings for heavy wing?

[dbhill916]

Hi All,

due to some hangar rash, I had to replace the outside skins on my left flaperon. Predictably, the plane is no longer balanced and the left wing is now distinctly heavy. I don't mind approaching the problem with the traditional skin massage techniques, but I wanted to poll the group mind regarding possibly trimming the heavy wing by adjusting the rod end bearings (MDM3614M) slightly away from the book spec of 11/32".

Does anyone have any experience with raising/lowering the flaperon by turning the rod end bearing to effect a change in roll balance? If no direct experience, anyone with enough aeronautical engineering to predict which direction (raising/lowering) which (left/right) flaperon to reduce the heavy left wing?

Any reasons *not* to make such a change?

Thanks in advance,
-dbh

[Piper J3]

Look here at Post #5..... https://vansairforce.net/community/s...ght=heavy+wing

[Taltruda]

If the plane flew straight before the repair of reskinning the flapperon, why would you expect the plane to no longer fly straight? Was the new flapperon not built straight? What changed besides re skinning?

[Piper J3]

Originally Posted by Taltruda

What changed besides re skinning?

The pinch radius on the trailing edge has direct correlation to wing heaviness...

[dbhill916]

Originally Posted by Piper J3

Look here at Post #5..... https://vansairforce.net/community/s...ght=heavy+wing

Thanks, Jim. Lots of good stuff there.
-dbh

[scsmith]

HI all,

I've posted about this before, but I figured I would chime in here.

A major cause of 'heavy wing' is that the aileron brackets do not necessarily hold the aileron at the same height compared to the wing skin at the gap.

Ideally you would like to have the aileron surface just slightly above the tangent line off of the upper surface wing skin -- this helps keep the airflow attached. As the flow off of the wing encounters the slightly higher surface of the aileron, with the rounded nose on it, the flow accelerates a little, and this tends to 'suck' the aileron up. In other words, the natural free-floating position of the aileron is slightly trailing edge high.

Now, if both the left and the right aileron are up by the same amount, then the floating tendency is balanced and there is no stick force required to keep the wings level. But if one aileron is mounted slightly higher than the other, then that one will tend to float higher, causing that wing to feel 'heavy'.

So - step one is to set a straight edge on your wing skin and aileron skin spanning the gap and see how much higher (or lower) the aileron is relative to the wing. You should do this at each hinge bracket. Use a feeler gage if you like to measure the gap under the straight edge and write it down. Then you can develop a picture of where the left and right ailerons differ.

To give you a sense of the matter of degree you are looking for, it would be great to have both ailerons uniformly high by about 0.020--0.040". If one aileron is flush and one is 0.040" high, you will have a heavy aileron.

Now - how to fix it? Well, you can buy aileron brackets from Vans that have not been drilled yet. You can elongate the holes on your existing brackets until you get them symmetrical left and right, and then use them as patterns to drill new brackets. Odds are, you will only need to fix one, or at most two, brackets.

[dbhill916]

Originally Posted by scsmith

HI all,

I've posted about this before, but I figured I would chime in here.

A major cause of 'heavy wing' is that the aileron brackets do not necessarily hold the aileron at the same height compared to the wing skin at the gap.

(edited...)

To give you a sense of the matter of degree you are looking for, it would be great to have both ailerons uniformly high by about 0.020--0.040". If one aileron is flush and one is 0.040" high, you will have a heavy aileron.
(edited...)

Thank you, scsmith, that was exactly the information I was looking for. My L flaperon was noticeably higher than the R when examined with a straight-edge. I was able to lower it by 1 full turn of the outboard bearing rod (and 1/2 turn of the inboard). This improved the situation. I ran out of threads on the Left, so raised the R by the same amount and now the wings are almost perfectly balanced. I can fly hands-off at low speed, and there is perceptible L heaviness only at high speeds (e.g., ~125 KIAS).

Thanks again,
-dbh

[rvbuilder2002]

The aileron hinge bracket design on the RV-12 is very different than all of the other RV's.
It is almost impossible for the elevation of the hinge point to be wrong.
Trailing edge shape can have an effect on roll trim and should always be checked / adjusted first, and then adjust rod ends if needed, if adjusting the T.E. to proper shape doesn't solve it. I.E., adjusting rod ends without correcting T.E. shape can induce other control problems.

[revenson]

Originally Posted by scsmith

HI all,

Ideally you would like to have the aileron surface just slightly above the tangent line off of the upper surface wing skin -- this helps keep the airflow attached.

To give you a sense of the matter of degree you are looking for, it would be great to have both ailerons uniformly high by about 0.020--0.040".

Steve: Other than minimizing wing heaviness, what is the implication of having the ailerons 'uniformly high by about 0.020--0.040"'? In other words, what practical benefit can be expected with better airflow attachment. Can one expect to notice lower stall speed? Less drag? more speed?

[RFSchaller]

I had a heavy wing. I chose a less elegant solution. I installed aileron trim tabs. I also put a tab on the rudder. I like the ability to quickly adjust them on the ground.