Question for Aeronautical Engineer?

[snopercod]

The simplest thing to do is adjust your fuel load to compensate. I weigh 250 and sit in the left seat, so I always have a "heavy left wing". Putting 5 more gallons in the right wing tank than in the left perfectly balances me out. (I do have a servo-controlled 1" x 6" trim tab on the left aileron which will also do the trick.)

[Mike S]

Originally Posted by snopercod

The simplest thing to do is adjust your fuel load to compensate. I weigh 250 and sit in the left seat, so I always have a "heavy left wing". Putting 5 more gallons in the right wing tank than in the left perfectly balances me out. (I do have a servo-controlled 1" x 6" trim tab on the left aileron which will also do the trick.)

RV 12, no wing tanks........

[Piper J3]

Update... This afternoon we went out to plane with a long straight edge to determine if flaperons were installed at correct pivot height with respect to the top wing surface. We ended up adjusting pivot heights to raise the left flaperon and lower the right flaperon in small successive steps. It took six flights but now the plane flies hands-off with no trim tab. Flap deployment is hands-off straight also.

Thanks to all for providing valuable information and for boosting my confidence to alter flaperon pivot heights slightly outside of the spec dimension.

VAF is the best source of information. This flying fraternity is the greatest?

[redbaron]

Go back to basics, under the flap arm there is a mix box and a 3 to 4 " bolt that sets the mix box correctly before drilling the 4 bolts under the baggage floor to set the flaps. Check the build manual for the instruction. Good luck

[DaleB]

Originally Posted by redbaron

Go back to basics, under the flap arm there is a mix box and a 3 to 4 " bolt that sets the mix box correctly before drilling the 4 bolts under the baggage floor to set the flaps. Check the build manual for the instruction. Good luck

Having just finished doing some work in that area... It is quite possible to have the torque tubes drilled incorrectly, the pushrods different lengths, and still have the plane fly straight hands-off.

We had noticed a little "something" at full right aileron deflection with flaps up. Of course the only time most people normally ever do that in an RV-12 is during pre-flight checks. Anyway, it took is a while to track down the source of the odd feeling/sound we had noticed, but something was obviously not right with the flaperon rigging. The right torque arm was at the wrong angle, rotated forward (downward) compared to the left. With flaps up and full right aileron, the pushrod would bump against the top of the fuel pump.

I just finished replacing the right torque tube a couple days ago. We set everything up per plans, drilled the new torque tube and set everything dead to spec (though now I need to go back and check the pivot height -- thanks scsmith and Piper J3 for that!) I was at a loss as to how it could have been done so wrong. What we figured out along the way was apparently the setup was originally done while the flap lever was UP rather than down as specified in the plans.

But -- my long delayed point is, the airplane flew just fine. The stick was centered, ball centered, no heavy wing that wasn't explained by fuel and pilot/passenger loading. And fortunately, the interference was not enough to cause any damage to the pushrod or the fuel pump.

[Pat Stewart]

I have seen this a couple of times on the 12. First make sure the rod end dimension is correct on the flaperons. If you decide to squeeze the trailing edge it's the opposite the heavy wing that you squeeze. Tourque tubes are the last check. If none of this works a minor half turn to the rod ends of the heavy wing will make changes as it sounds like you found.

[Piper J3]

Yes, rod end adjustment to raise/lower vertical flaperon position with respect to upper wing surface is very effective. I had a very pronounced heavy wing which I countered by raising flaperon on one wing and lowering flaperon on the other wing.

I don't know the aerodynamic theory but I suspect that changing relative height must change induced drag. Maybe just magic, I've been flying for more than 50 years and I still marvel at how airplanes fly through the air...

[John-G]

Hey Jim .... Just another thought that may work well for you so you don't need to fly with the airplane rigged slightly off to compensate for your heavy wing.

When I first flew my RV-12 I had a heavy left wing and tried to tweak the flaperons a tad to make things better .. but before getting draconian I ran across a post here in the forums that solved my issue.

Long story short, the aluminum that overhangs the rear spar by 2" or so was not flat with the skin on the wing. Some places were high and some places were low. I lowered the flapperons and using a thin metal 12" ruler on edge made sure the skin extending aft of the rear spar was totally even with the skin on the wing forward of the rear spar. A thin block of wood was used to tweak the aluminum up or down as necessary. After tweaking both wings the RV-12 now flies straight. The amount the skin was actually off was not that much seemingly ... but guess the airflow over the flapperons was affected just enough to make a difference.

Not saying that is your issue, but it sure is an easy fix if it is.

Happy flying,

[Piper J3]

John

Yes, I knew about the cantilever top skin behind the rear spar and already tried that. What I didn't know about, until this thread, was the effect of raising/lowering the flaperon pivots. Worked a charm...

[scsmith]

Originally Posted by Piper J3

Yes, rod end adjustment to raise/lower vertical flaperon position with respect to upper wing surface is very effective. I had a very pronounced heavy wing which I countered by raising flaperon on one wing and lowering flaperon on the other wing.

I don't know the aerodynamic theory but I suspect that changing relative height must change induced drag. Maybe just magic, I've been flying for more than 50 years and I still marvel at how airplanes fly through the air...

What causes the perception of a heavy wing is an asymmetry in the natural float position of the ailerons. When you fly hands-off, the ailerons seek a compromise position between where the two ailerons separately would like to float to, a position where the hinge moments (pushrod forces) are balanced. But that position may not be aerodynamically balanced in terms of the whole wing. You can end up with the natural float position such that one aileron is slightly trailing-edge up compared to the other one, making that wing seem heavy.

When you raise the aileron hinge axis slightly, the raising the aileron surface with respect to the wing skin at the hinge gap, you create slightly more suction on the upper surface of that aileron as the flow goes over the slight bump or curve in transitioning from the wing to the aileron. That slight increase in suction causes that aileron to want to float a little bit more trailing-edge high. The two ailerons together find a new natural float position with that aileron slightly higher. With that new balance position, that wing gets a little bit 'heavier'. So you want to raise the hinge axis slightly on the "light wing" side.