Roll Response/Sensitivity

[Janekom]

We have built a standard kit RV7A some about two years ago and now recently a QB 7A. I am busy test flying it and find the roll response, or rather the roll sensitivity much more sensitive than on the old one that we fly on a daily basis. On the old RV there is some roll resistance or in other words you have to push the stick to roll, although only gently. With the new one it feels as if it rolls just by touching the stick - very sensitive. I did ask Van's but I am still waiting for a reply.

Could this be from the difference in trailing edge radius on the home built one against the QB or could this be because the fairings and spats are still off (long shot here) ?

 

[Kevin Horton]

Yes, a difference in aileron trailing edge radius could affect the stick force required for a given amount of aileron deflection. It is possible that the vertical location of the aileron with respect to the wing could also be a factor.

 

[pierre smith]

Droopy ailerons...

.....on my buddy's -4 really made them heavy. They were 1/4" below the bottom skins since the previous builder hadn't rivetted the attach brackets up high enough. We drilled them out and now they're flush with the bottom of the wings, where they should be. If they have any droop, i.e. downward deflection, they're gonna be heavier on the stick.

My Air Tractor's flaps go down 7 degrees with full flap and boy-oh-boy, do they get heavy....as in two hands to move the ailerons!

Regards,

 

[N733JJ]

Yes, the trailing edge radius has a major effect on stick forces! Van's suggestion to squeze the trailing edge to counter a heavy wing will have an effect with anything but the very smallest of changes. This was enough of a factor to get me to build a new aileron.
A much better way to solve a heavy wing, as Kevin eluded to, is to change the vertical placement of the aileron. A 1/16" displacement makes a significant change with no cahnge in tht great RV feel.

Scott A. Jordan
N733JJ

 

[RV7Guy]

Other factors

The weight of the airframe and CG could be affecting the sensitivity. Aft CG will give you a quicker roll rate and pitching moment.

 

[Stephen Lindberg]

Can you explain?

Roll rate changes with a change in longitudinal cg? I hadn't heard that before. Can you explain? I have never noticed it but I will look for it.

 

[rvbuilder2002]

Yes, the trailing edge radius has a major effect on stick forces! Van's suggestion to squeze the trailing edge to counter a heavy wing will have an effect with anything but the very smallest of changes. This was enough of a factor to get me to build a new aileron.
A much better way to solve a heavy wing, as Kevin eluded to, is to change the vertical placement of the aileron. A 1/16" displacement makes a significant change with no cahnge in tht great RV feel.

Scott A. Jordan
N733JJ

Before squeezing or repositioning anything, you should use a straight edge and check the skin flatness at the trailing edges of both the ailerons. (actually all builders should do this on all of the control surfaces as a final check before flying, regardless of who built the parts). Lay the straight edge cord wise and check that the skin is flat all the way back to the start of the bend radius. If not, then make adjustments until it is. Then you can can start looking at other causes if the stick forces are still excessively light.

 

[Janekom]

Thanks for all the ideas guys!!
One thing I should have mentioned is that the ailerons are very slightly "up" in the neutral position. In other words - if I align the LH one with the wingtip, the RH one will be slightly up (about 4mm at the back) and obviously also the other way round as well.

So I think I will do the straight edge check suggested by rvbuilder2002 first thing on Saturday morning and report back.

 

[Kevin Horton]

The weight of the airframe and CG could be affecting the sensitivity. Aft CG will give you a quicker roll rate and pitching moment.

Differences in fuel weight could certainly make a difference in roll acceleration, due to the effect on moment of inertia.

Movement of the CG in the aft direction causes a small reduction in directional stability, as there is now a shorter moment arm between the CG and the vertical tail, combined with additional fuselage side area ahead of the CG location. This reduction in directional stability has a small effect on roll performance, as lateral and direction motions are coupled. But, the effect of an aft CG movement on roll performance is usually very, very small, and it would not likely be possible to detect it without on board instrumentation to record data for post-flight analysis, and a very careful test program.

 

[Janekom]

The end result and solution was to pinch the aileron trailing edges ever so slightly. Feels like a different AC now and I am very happy with the result

 

[Janekom]

Seeing that there is another thread also on this topic, I would like to describe my actions in more detail:
1) Panic
2) Asked a few local guys who are experts on RV's and they confirmed the TE theory
3) Asked Vans and they confirmed that one can (read - is allowed to) do it
4) Very careful pinched only one third of each aileron very slightly
5) Test fly
6) HAPPINES IS ........