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Should I Adjust My Aileron Rigging?

iamtheari

Well Known Member
My RV-14 is done with Phase I, not painted yet, and a blast to fly. In cruise, the ailerons are drooped a little bit, maybe 1/2" or 3/4" on each side at the trailing edge, relative to the wingtips and flaps in reflex. I rigged everything according to the plans. Should I adjust the ailerons upward a bit to get a closer match with the reflect flaps in cruise?
 
Because of the design shape of the RV-14 (and 10) airfoil, the ailerons are top loaded in high speed cruise flight so they can droop just a bit because of the slight elasticity in the control system.
A small adjustment to remove this is fine, but I highly doubt you are seeing anything approaching 1/2" let alone 3/4".
I would expect closer to about 1/8" or so.
Before you make any adjustments I would recommend some careful measuring to determine exactly what amount it is. If it is actually 1/2 or more, I suggest some serious investigating to find the cause because that is not normal.
 
Thanks, Scott. I don't have a ruler that works on the exterior of the plane in flight so I was eyeballing it and you're probably right that I am overestimating the deflection. I took pictures so I can study it when I have more free time. Given how well the plane flies, I'm not likely to chase this much since you said it's normal in these wings.

But I wonder: Has anyone experimented with performance between the drooping-in-cruise vs reflex-on-ground rigging?
 
Yes

I have experimented with this. You are paying a small trim drag penalty for not having the ailerons in line with the flaps and wingtip at cruise. The -10 and -14 are designed to cruise at -3 degrees. The penalty will vary with altitude. You can find threads here on VAF from both Rvbuilder2002 and scsmith that address the subject. Now, is the penalty enough that you care? That one is very subjective, but I’m glad I addressed it on my plane.
 
Marvin, could you please elaborate on your before and after performance numbers? Thank you very much.
 
Trim drag

Gash,
Trim drag is a very minor drag component. The before and after will be dependent on the individual aircraft. If your aircraft is only slightly out you may see no measurable difference. If the OPs aircraft is as far out as described the change could be worthwhile.

In my case, the before and after was in the 1 to 2 knot difference arena , at 9000DA, which is difficult to measure with confidence.
 
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When I was rigging my ailerons I simulated the aerodynamic down load on the ailerons by cutting a 2x4 to the length of the ailerons and putting them on Both sides with a 2 LB weight. The deflection was right around 1/8” when in the reflex position. What it did show me was that I had a slight twist in my right aileron that you can barely see in flight and does not impact handling characteristics.
 
Thanks, Scott. I don't have a ruler that works on the exterior of the plane in flight

Neither do I, but in the spirit of home building I often assume that people reason through a way to do something, without making a suggestion of my own.

In instances like this, I do as you have done. Take a photo and then on the ground position the surface to mimic what you see in the photo, and then take a measurement.
 
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