"Twitchy" ailerons on my RV-7

My RV-7 has now been flying for just over two years. The Hobbs meter has clicked past 300 essentially trouble free hours. My wife and I have flown it from Maine to California and it has proven to be everything we wanted in a fast and efficient cross-country machine.

But.. since its first flight it has had ?twitchy? ailerons. So what does that mean? Well I truly think it could rival an Extra 300 in roll rate. It handled too nice. The lateral control seemed really fast? way fast. It was uncomfortable to fly in turbulence and if I hand flew it under IMC, I was ?this close? to declaring an emergency. My old RV-4 never flew like this. It was smooth and responsive but not overly so. I?ve got almost 2000 hours in RVs; made 12 initial test flights in all models and never did I find one that handled quite like my -7. Frankly I flew it on autopilot 95% of the time so I wouldn?t have to hand fly this hyper-active RV with a bad case of ADHD.

A few weeks ago I was flying another RV-7 and marveled at how it flew. Nice smooth ailerons, no snapback like I had in mine. That was enough. Time to look into this deeper. My -7 is a quick build and the ailerons came all finished and ready to install. I just assumed that they were built correctly. Hmm? maybe not. I really got to looking carefully at how the trailing edge was formed and discovered that they had the dreaded ?round? shape that Van warned about years and years ago when rolling your own ailerons. I closely looked at my hangar partner?s RV-7A and saw a nice ?sharp? trailing edge (his was a quickbuild also). A call to Van?s confirmed that not all quick-build ailerons are created equal. They suggested trying the ?squeeze-the-trailing-edge? technique to see if I could get back that nice RV feel.

So today I spent about an hour laying out two oak 1x3?s and a half dozen clamps and squeezing down the trailing edge on both ailerons (careful not to mar by multi-thousand dollar paint job). Mission accomplished, I headed out for a test flight. WOW?. I couldn?t believe this? a totally new airplane!!! Smooth ailerons... certainly not a competition acro machine anymore but no snap-back, no ultra-lightness, and no twitchiness. It handled WAY better in turbulence and even the autopilot now was 100% better in making turns, intercepting a course to a waypoint and tracking an LNAV path.

Moral of the story folks? check your trailing edges on even those pristine quickbuild ailerons. Lay a straight edge along the top and bottom and be sure they are flat right up about a quarter inch from the trailing edge (mine started curving about an inch from the TE). And remember to make the squeeze the same to both ailerons (if your effort results in a heavy wing, squeeze the radius a little more on the light side). Now that I have a ?new? RV-7, I might even be brave enough to try a little hand flown IFR!!

Here's the "before" photo. Note the rounded trailing edge compared to the ruler.




Here's the "after" shot. The aileron is flat (in my case a little concave) right up to the trailing edge.

I'm glad you achieved such a transformational result. I will check my QB ailerons tonight, although I can't remember offhand if they're AEX wedge (like the 9's empennage TEs) or folded.

I have this exact same issue, although I didn't know what to expect from the roll rate, other than my transition training in Mike Seager's -7. It seemed a little more jittery than Mike's 7, but I assumed that was because there was no Mike in the pax seat during my flight testing.

for me, the problem manifested itself in a divergent oscillation in the roll axis. A mild, imperceptible squeeze along the trailing edge reduced this issue to almost nothing, but it still twitches, and the autopilot has trouble keeping it under control. It could stand another round of squeeze, I think.

Yes, John... Try a little more squeezing and you likely will solve your issue.

Doug,
Your nine will not have this problem. It is built with the AEX trailing edge as you mention.

I would suggest that instead of squeezing the trailing edges trial and error style in an attempt to correct a handling problem, that you measure and adjust them to the specific shape they are supposed to be.

Section 5.7 in THIS document on the Van's web site gives details on how to do it.

Same QB 8

I just addressed the same issue. I always knew my aileron stick force was very light. I did some flights In RV7s and a friends 8 and they did not have the issue.

It was really nice having it be so responsive, but flying instruments was a chore, even the autopilot would get into a roll oscillation if I had the sensitivity too high.

I finally decided to do something about it when on my first flight with the Blackjack Formation group, the guy riding with me commented on my twitchy wings. I gave him the plane and he understood my issue.

There was an A&P on the field who was also a builder, he gently squeezed the trailing edges of my ailerons and I took it out for a test flight. He nailed it, less twitchy in roll and still balanced. It was like turning off super sensitive power steering.

The plane now handles much better on approach and in formation.

Cheers

rvbuilder2002 said:

I would suggest that instead of squeezing the trailing edges trial and error style in an attempt to correct a handling problem, that you measure and adjust them to the specific shape they are supposed to be.

Section 5.7 in THIS document on the Van's web site gives details on how to do it.

Click to expand...

Yep, just wish I had this info prior to finishing and painting my -6. The old manual was a little vague As it is, I was able to get my ailerons back to a correct shape but cracked a little paint doing it

I'm having a devil of a time seeing the difference in the pictures. Truth be told, I had a hard time seeing the difference in the instructions too.

You'll just have to come over and fly my 7.

LettersFromFlyoverCountry said:

I'm having a devil of a time seeing the difference in the pictures. Truth be told, I had a hard time seeing the difference in the instructions too.
You'll just have to come over and fly my 7.

Click to expand...

Look closely. In picture #1 from the 4" mark aft the scale does not touch the surface. Aileron surface is convex.
In picture #2, the 4" mark has a gap between the surface and the scale and the aft end of the scale is sitting on the aileron surface. Surface is concave.

Guys this is a very well known thing. Luckily it is so easy to squeeze and go test. My advise after having done several is to start gently and maybe only do about 12 inches at a time.

It really work well to stop it from being twitchy and also "snatching" a bit into the turn as you start to apply aileron.

The problem is comparing to the experiences here is I don't really know what either "twitchy" or "snatching" means or feels like. I have no frame of reference.

Mel said:

Look closely. In picture #1 from the 4" mark aft the scale does not touch the surface. Aileron surface is convex.
In picture #2, the 4" mark has a gap between the surface and the scale and the aft end of the scale is sitting on the aileron surface. Surface is concave.

Click to expand...

OK, so as I understand it, the key here is not the trailing edge (the bend itself) but what is forward of the bend?

Reiterating for those that are interested in making their RV fly/handle the way it is intended to.

Proper adjustment of a critical flight control surface like ailerons, elevators, or rudder should not be done in a guess work, little here / little there process.

There is a very specific shape control surfaces should be to perform properly. This can be checked/measured easily (see link to document in my previous post).

Once the surface(s) has had the shape set properly, minor adjustment can be made to to the ailerons to tweak the roll trim if needed.

I have corrected severe handling issues on many RV's with just adjusting tools and a straight edge. Most of the time no further adjustment is needed after making a test flight.

Side note....
A mis-shaped (bulged trailing edge) control surface is actually causing the surface to act as if it were smaller in cord than it really is. This means that it also has less effectiveness than is intended.
Some people may like the lighter feel on the ailerons or elevator (or even rudder), but that lighter feel also means you have a lower level of control effectiveness.
It will also effect the natural centering action of the surface, which can have effects on stability in all axis. Particularly on a control surface that has more hinging friction than is ideal.

Trailing edge

It is the trailing edge, the aileron had a very rounded shape at the aft edge. Crimping this down ever so slightly helps with the aileron feel. If you go too far you will see the aileron skin dish in the middle which you don't want.

What I meant by "twitchy" is that it takes little stick pressure to move the aileron, this leads to over control in the roll axis, just a slight touch on the stick rolls the plane, same with wind gusts.

I was used to this but it makes precise control very difficult.

Cheers

LettersFromFlyoverCountry said:

The problem is comparing to the experiences here is I don't really know what either "twitchy" or "snatching" means or feels like. I have no frame of reference.

Click to expand...

That is why I am recommending that the surfaces be measured and adjusted as needed.
Not guessing if it is "feeling" correct and then guessing at what adjustments to make to correct it.

That's pretty much what I did: I checked the skin with a straightedge. It was bulging slightly. I was afraid to oversqueeze it, especially since I had fairly poor lighting conditions at the time and I wanted to do an incremental adjustment if I could. It's time for another increment.

Went thru this process this weekend.

I have always had a heavy left wing and very light ailerons and have seen it impact AP performance as well resulting in having to run low gains to prevent oscillations.

Taking Scott's advice I put the straight edge on the skins and did have a slight bulge. Squeezed the right aileron and went up for a test flight.

Immediately I realized that I had gone too far and I now had a very heavy right wing. I also instantly noticed how much more solid the ailerons felt at the stick.

Came back and very lightly worked on the left aileron in a similar manner just much more lightly. Went back up for another test.

Rinse and repeat 2 more times and by the end of the 4th flight I had the airplane flying hands off for several minutes at a time.

Not only is the heavy wing gone but now the stick forces in roll are much more matched with the elevator. The neutral point is much more defined and the airplane handles much better in turns and when landing.

Can't wait to do more testing to see how much it will improve my AP performance in roll. It looks like I should be able to run a much higher gain now without running into oscillations and that will allow the AP to track at its peak performance.

My only regret is that I did not do this sooner!

My only advice is to take it easy as this is a very very effective procedure!

Man if my RV's ailerons felt like the elevator I'd throw rocks at it!

Brantel said:

Not only is the heavy wing gone but now the stick forces in roll are much more matched with the elevator.

My only advice is to take it easy as this is a very very effective procedure!

Click to expand...

My assumption is he meant matched as far as roll / pitch harmony goes, not matched in equal amount of force.
Improperly shaped ailerons can make the roll forces extremely light... way outside of a good balance between pitch and roll

Glad to hear it worked for you Brian. My advice is to start with a straight edge and make both ailerons flat. This often gets roll trim to neutral right away. If it doesn't, then make adjustments to just one as necessary.

Keep in mind, the same goes for the elevators and rudder. If they are not flat cord wise, they are not performing as they should.

rvbuilder2002 said:

My assumption is he meant matched as far as roll / pitch harmony goes, not matched in equal amount of force.
Improperly shaped ailerons can make the roll forces extremely light... way outside of a good balance between pitch and roll

Click to expand...

Yep, what Scott said!