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Stiff Ailerons

acam37

acam37

Well Known Member
During our break-in process of orbiting the airport Justin aborted the last flight early because he says that when the airspeed got over 150mph the stick was almost impossible to move the ailerons more than an inch or two from center position. (Major resistance) When he got below 150 everything went back to normal and made an uneventful landing. Post flight inspection showed no signs of binding or any obvious mechanical problems. we're scratching our heads on this one. We have not contacted Vans yet. Any suggestions?
I am leaning towards a problem in the bellcrank and torque tube rigging.
 
acam37 said:
During our break-in process of orbiting the airport Justin aborted the last flight early because he says that when the airspeed got over 150mph the stick was almost impossible to move the ailerons more than an inch or two from center position. (Major resistance) When he got below 150 everything went back to normal and made an uneventful landing. Post flight inspection showed no signs of binding or any obvious mechanical problems. we're scratching our heads on this one. We have not contacted Vans yet. Any suggestions?
Click to expand...

Perhaps these ailerons have a very small trailing edge radius?
 
Here is what the trailing edge looks like. I had another RV builder suggest that the trailing edge radius might be too large. If this is the culprit, how do I fix it and what is the physics behind this phenomenon?
4dfeb049ca588a09cb6fdc8eb628ac98_zpsvlymll09.jpg
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Aileron

Arlie,

I didn't build my RV-4 but I did have to rebuild the rudder and I remember squeezing the trailing edge to get the airplane to stop fish tailing. Don't know if that applies here but do the plans call for squeezing the aileron trailing edge? If it is done like I did the rudder (with Dave Domeier's help) then his can be accomplished easily on the airplane.

My ailerons have a much sharper, smaller radius.

My 2 cents,
Oly
 
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The way Justin described the aileron force was that the higher the speed the harder it got to move the ailerons, like trying to shut a door in a hurricane. So it appears that the slipstream over the wing is affecting the ailerons. I have flown an RV-7 and remembered little to no effort moving the stick. Like it almost had power steering. I haven't flown the -4 yet so I have no comparison. But this last event scared Justin bad enough to cause him real concern and he won't fly it again until we figure this out. Oh by the way, the elevator and rudder forces are just fine. Only the ailerons are affected.
 
If you have checked the control system for any problems that could cause binding, I would then check the trailing edge shape based on paragraph 5.7 of construction manual Section 5 (available HERE)
This would actually be a good idea to do on all the control surfaces for any new RV (without riveted training edges) before first flight.
 
acam37 said:
Here is what the trailing edge looks like. I had another RV builder suggest that the trailing edge radius might be too large. If this is the culprit, how do I fix it and what is the physics behind this phenomenon?
4dfeb049ca588a09cb6fdc8eb628ac98_zpsvlymll09.jpg
[/URL][/IMG]
Click to expand...

That is a very convex aileron! The straight upper and lower surfaces shoudl die into the final trailing edge radius - not bulge like it appears to do an inch or so forward of the TE - that can drastically affect handling qualities. Now that bulge might just be at the end rib, but if not - I'd do some squeezing. A very small amount makes a big difference in handling.
 
The radius pictured is similar to others I have seen I woud suggest checking distance between aileron and upper wing skin if too close will cause heavy aileron also have you cut control stick , too short = heavy .
 
Just to clarify, I didn't build this plane, and I re-attached the flight controls just like they came off. I'm still going to verify that the rigging is correct and that all the rod end bearings are lubed and not frozen up. I do have plans and a build manual so I will also go back and look at the aileron section. Since I've had several independent assessments of the trailing edge radius, that will get corrected for sure. I'm by no means an aeronautical engineer, so I am curious about the trailing edge effecting stick force so dramatically. Justin's description of his experience sounded a lot like what the old piston engine fighters and early jets suffered while in a high speed dive. Total loss of flight controls due to compresability factors. Am I on the right path?
 
Yes, trailing edge shape can have a huge effect on control force and centering ability, and effectiveness (a bulged trailing edge makes it act like the cord dimension of the surface is smaller).
As Jerry said, it usually makes forces lighter, but since the two ailerons are a coupled system, strange things can happen.
It is also possible that they feel so extremely light to the test pilot at slower speeds, that the normal increase in force as a result of a speed increase seems abnormally high.
 
Compressibility is not an issue at 150 mph.
Click to expand...
All I know is that it shouldn't take both hands to move a stick left to right. Something is happening at higher speeds to cause the stick to be harder move than at slower speeds. I'm sure that in the last 30 years since the RV-4 was designed my plane is not the only one that has experienced this. I sure hope we can figure this out so we can resume flying. Here are a few things to rule out; (1) the stick has not been cut down. (2) the control push rod is the bigger 1-1/8" and not 3/4". I'm going to do some more troubleshooting and post my findings, or lack of. I'm also going to give the Vans engineers a shout and see if they have any ideas. Thanks for all the input so far.
 
Check the aileron with a template

Arlie, have you checked the trailing edge of the ailerons with a template made directly from the plans? On my RV6, the aileron trailing edges "looked" ok, but it was only after I very carefully made a template out of hardwood that exactly matched the cross sectional profile on the plans, that I noticed small variations of the "squeeze" along the length of the ailerons. The template needs to be about 6" deep, so you catch any bulging of the top and bottom skins forward of the trailing edge. Check the template every inch along the length of the aileron. I bet you'll find some variations. Good luck with the trouble shooting.
 
acam37 said:
The way Justin described the aileron force was that the higher the speed the harder it got to move the ailerons, like trying to shut a door in a hurricane. So it appears that the slipstream over the wing is affecting the ailerons. I have flown an RV-7 and remembered little to no effort moving the stick. Like it almost had power steering. I haven't flown the -4 yet so I have no comparison. But this last event scared Justin bad enough to cause him real concern and he won't fly it again until we figure this out. Oh by the way, the elevator and rudder forces are just fine. Only the ailerons are affected.
Click to expand...

Arlie,
The slipstream over the wing does affect the control surface as does airspeed that is the nature of aerodynamics. Depending on the control hinge design, in this case the aileron, the force may change proportional to the airspeed. More speed = more control force required. That is the case on our wing but to a lesser effect than older wing/airfoil designs.

Has your bud flown an RV previously? If not, i would find someone close and get him a flight or two demonstrating maneuvers which would show him control force changes based on airspeed. i.e. slow flight (with 360 deg turns) to less than Vne, also steep turns at different airspeeds. That will get him some familiarity and confidence.

Break

I personally would not mess with the aileron trailing edge yet. I would look for potential places where higher airspeeds (resulting in higher aerodynamic forces) would cause things to flex and start binding. Is the wing skin flexing and touching the aileron? Is one of the ailerons' hinge bearing lose and the force causing the aileron to twist and bind? Is the force on the aileron causing the bellcrank to bind because there is too much play on the AN-3 hinge bolt or is it torque too tight? Is the belly of the aircraft flexing enough that the skin is touching the bottom of the control stick? Is one of the control rod bearings acting up under load? Did you replace them or reuse them?

Have someone hold the stick and someone put a load back and forward on the aileron. See what that feels like. If you are by yourself, clamp the aileron to your wing tip and then wiggle the stick (be careful).

Good luck.
 
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I went to the hangar today and disconnected all the torque tubes to check every component separately. I lubed all the bearings with LPS1 and re- checked the bellcrank rigging. The rigging was way off, so I set the bell cranks to neutral and re-adjusted the push rods. There is no binding what so ever. Smooth as silk. We get ready to do a test flight and the engine is running real rough so we start to pull the plugs. My brand new wiring harness has two broke insulators that go down into the spark plug barrel. So now we are down until I can get a new harness from Spruce. Man, I have the worst luck. I believe this plane is jinxed.
 
A word of caution.........

acam37 said:
I went to the hangar today and disconnected all the torque tubes to check every component separately. I lubed all the bearings with LPS1 and re- checked the bellcrank rigging. The rigging was way off, so I set the bell cranks to neutral and re-adjusted the push rods. There is no binding what so ever. Smooth as silk. We get ready to do a test flight and the engine is running real rough so we start to pull the plugs. My brand new wiring harness has two broke insulators that go down into the spark plug barrel. So now we are down until I can get a new harness from Spruce. Man, I have the worst luck. I believe this plane is jinxed.
Click to expand...

When re-rigging the aileron bel-cranks be sure that they cannot go over-center at either full travel extremes.
That is VERY possible on the RV-4 and -6.
 
Autopilot

Arlie,
Does your RV have an auto pilot? If so is there a chance it was inadvertently engaged and Justin was over riding the clutch. Just a thought. Stick forces should increase gradually with speed not all at once when you pass a certain speed.

Joe
 
Mel, I set the bellcrank to the neutral position per the plans. They don't go over center, and Joe, I thought of the auto pilot servo. Justin said it was powered off but for the next flight I removed the linkage so that it can be completely ruled out.
 
Stiff controls

Check very closely for scraping marks where the aileron push rod goes thru the rear spars. If the washers on the aileron hinges and push rod horn were not put back exactly as the original sequence, the rod could bind with the hole. Also I seem to remember on '6s that the rod end bolts need to be oriented in a specific way, either facing up or down on the bell crank.
 
Aileron Bellcranks...

Arlie,

One thing I just thought of with the aileron bellcranks in the RV4 wings. When you said the "rigging was way off", it sort of went along with what I was about to type when I got to the bottom of the thread. IS It possible, that you installed the aileron bellcranks backwards? If you measure, the distance between the bellcrank hinge point, and the hole that goes to the stick, it is NOT the same distance as from the hinge point to the hole to the aileron. It is possible, and in fact easy, to get the backwards. (I had mine backwards when checking travels the first time - DOH!)

This will not give proper travels, or the proper leverage to the surface. The odds are high that the bellcranks are NOT your issue, but it doesn't take long to pull that access panels and check.

You'll beat this thing!

Gregg
 
Alright, I have taken everyone's advice and checked everything that was mentioned that could be a problem. The bellcranks were never removed for the rebuild but I did verify they were oriented correctly. All the pushrods were checked for binding and rubbing. All clear and operating smoothly. So the only thing left is to fix the trailing edge radius. There is nothing else that can be done. If the stick resistance still persists, then it is what it is.
 
Nothing else that can be done?
The ailerons should be operable with finge tip pressures at 150kts.
The trailing edge radius looks OK to me, but maybe that is the problem. Otherwise there is something still to be found. Have you had any feedback from Vans?
 
Normal?

Arlie, at great risk of insulting your intelligence, I'll say this. Frankly, what the you (and Justin) describe sounds perfectly normal to me. It is, of course, all a matter of degrees. But in my RV-4, the aileron control forces are much higher at speeds above Vno and especially approaching Vne. And, that is by design. Too much control authority at those higher speeds would increase the risk of a pilot inadvertently over stressing the structure. The maximum airspeed for full control inputs in my airplane is only 115 knots. That's my design maneuvering speed, above which it is unwise to make full application of any single flight control (or "pull to the stops") as it may generate a force greater than the aircraft's structural limitations.

I think a better test would be to see if you can generate acceptable roll rates at higher speeds. Ailerons that appear "stiffer" at higher speeds may be operating perfectly normally.
 
Randy, like I said previously. I have not flown it yet and I'm just going by what Justin is telling me. After re-rigging the ailerons and lubeing/inspecting all the rod end bearings. The controls are now silky smooth as compared to before. After he flies again I will post the results. I agree that the controls are going to have more resistance the faster you go, but when someone lands and is physically shaking, I tend to believe he encountered a serious problem. Justin is not a new pilot and flies a banner plane in his spare time. Let's see how the controls feel after what has been done since the last flight?
 
acam37 said:
Randy, like I said previously. I have not flown it yet and I'm just going by what Justin is telling me. After re-rigging the ailerons and lubeing/inspecting all the rod end bearings. The controls are now silky smooth as compared to before. After he flies again I will post the results. I agree that the controls are going to have more resistance the faster you go, but when someone lands and is physically shaking, I tend to believe he encountered a serious problem. Justin is not a new pilot and flies a banner plane in his spare time. Let's see how the controls feel after what has been done since the last flight?
Click to expand...

Thanks Arlie,
Looking forward to hearing the results of the next test flight!
Randy
 
Update

We flew again today for the sole purpose of narrowing down this control stick phenominom. At 4000ft and circling the airport Justin put the plane through a bunch of steep bank turns and rocked the wings. While doing this and looking at the ailerons he described to me that they appeared to be Warping and flexing at the trailing edge, basically changing shape. After landing I grabbed the trailing edge and can easily bend the ends and they oil can pretty bad. Maybe it's time to build a new set of ailerons?
Justin also told me that while he observed the aileron "warp" at the same time it would almost jerk the stick out of his hand.
 
Ailerons

Arlie
I had to build new ailerons for my project. I got lucky and found someone with a left aileron already built but I had to order parts for the right side. If you want I can get you the part numbers you will need for the ailerons if you go that route. For what it is worth you can order quick build ailerons for the -8 they come already built and the -4 uses the same aileron. I chose to buy the kit it will arrive on Monday. I believe it might be pre drilled but not to sure about that. I can let you know when my box arrives.
 
This is a longshot, but after looking at some build log pictures I noticed that my ailerons have large lightening holes on the outside ribs leading edge and others I've seen don't. Could air be getting inside the aileron through these openings causing the skins to balloon and drastically change the airfoil shape? I'm going to tape them up and see what happens. It's worth a try anyway.
 
acam37 said:
Justin put the plane through a bunch of steep bank turns and rocked the wings. While doing this and looking at the ailerons he described to me that they appeared to be Warping and flexing at the trailing edge, basically changing shape.
Click to expand...

I find this rather disturbing...........

acam37 said:
After landing I grabbed the trailing edge and can easily bend the ends ----------

Justin also told me that while he observed the aileron "warp" at the same time it would almost jerk the stick out of his hand.
Click to expand...

And this even more so.

I think you need to get some expert "hands on" assistance here.

Take care, fly safe.
 
Mike, you find this disturbing? How do you think we feel? I have reached out to several RV builders over here and no one is willing to help. Yesterday evening I let an A&P mech look at everything. He said the controls are fine and that the ailerons felt like all the other RV's he has worked on over the years. So at this point I have a very expensive lawn ornament.
 
Have you considered taking photos/videos of the flexibility you mentioned in post 27?? Also, the hole you mentioned in post 29-----------

Send them to the factory and get their input.

You already had----have?--- Scott (rvbuilder2002) from VANs looking at this thread, he is a very good contact and has been incredibly helpful to folks here in the past.

An inflight video of the ailerons changing shape could be useful to them as well, but at this time is your pilot even willing to continue flying the plane with this issue unresolved?
 
Let's imagine for a second that for a reason the ailerons might both bulge and both become lift generating devices...

It would probably be more difficult to move them as they would both want to raise and somewhat block the control stick...

Just a theory... And worth what you paid for...
 
Mike, Justin isn't afraid to fly the plane. He is orbiting the airport at altitude and wearing a parachute. It handles great at lower speeds with full response of the flight controls. Just imagine your power steering going out in your car. That's how he described it to me yesterday. It's easy then gets hard then easy again. That's why I think air is getting inside aileron through those big holes. I took some pictures and emailed Vans of what is happening. I'm going to point a GoPro camera right at the ailerons and see exactly what they are doing in flight. If we can't resolve the problem I'm just going to build a new set of ailerons. Earlier I may have used a poor choice of words describing how the ailerons felt on the ground.
 
Holes

Hi

There should not be any holes so tape them up and report back.

Do you have any photos of them.
 
We taped the holes and think that solved the problem. The jerking motion he described went away and the stick is much more responsive. Justin said he is now comfortable with the way it handles. We are going to let another RV-4 pilot fly it and see if ours is now normal.
 
If someone added lightening holes or something that are not supposed to be there I think that I would build some new ailerons.
 
You said the ailerons warpped in flight and you could do same on the ground with your hands. I tried that with my -3 and they are very stiff and cannot be wrapped I recently built the ailerons for my -8 project and they also are very stiff. In fact they have to be built on a flat surface to avoid building in a warp that cannot be removed. It sounds like something is not right with your ailerons and you are on the right track to replace them with either new or borrowed ones. If they have been modified from plans there may also be flutter awaiting at higher speeds.
 
Since I believe I narrowed the problem down to the ailerons themselves, I think it's time to just build a new set. The prop is going back to Catto for a re-pitch so this will give me time to change them out.
 
acam37 said:
Since I believe I narrowed the problem down to the ailerons themselves, I think it's time to just build a new set. The prop is going back to Catto for a re-pitch so this will give me time to change them out.
Click to expand...

That sounds like a very well reasoned approach after reading this whole thread. With as much as you've done to get this arplane right, building a set of ailerons is a very small time investment to be sure you are happy with the performance and safety of the craft.

Paul
 
Yes sir, I hate that it went to 5 pages, but this is why I go here. To echange information so that the next poor soul that runs into this problem will have the resources to troubleshoot. If you look at my picture in post #3 you can barely see the hole that I was talking about in the rib.
 
I remember a hole there but a much smaller one. It was there to allow you to tighten a nut that held the metal bracket in place. Required on the inboard aileron bracket but not the smaller outboard bracket.
It is hard to imagine this hole, although larger, causing an issue. Perhaps combined with an incorrect trailing edge?
 
some ideas

I've been following this thread and thinking about it, although I can't say I've read every post, so apologies if someone already mentioned these.

1) I do not see the tooling alignment hole in the ribs, as pictured in post #3, causing this. It is possible for air to get inside the aileron, and 'might' tend to pillow the skin a bit, but not something I think would cause the problem. Anyway, taping over the hole will eliminate this as a possibility.

2) the trailing edge, as shown in post #3, is not ideal, but I don't think it would cause the symptoms you are struggling with. It would make the ailerons very light, maybe have a kind of bi-stable behavior, where they don't want to stay perfectly neutral, but always bias slightly to one side or the other. But I doubt they would make them get very heavy at high speed.
(I can explain why the TE effects are the way they are, if anyone is interested off line).

3) The flexibility you describe by flexing the aileron with your hands on the ground - this really disturbs me. I am suspicious that the ailerons were not built as designed. Maybe they left out every other rivet for time saving, maybe they left some component out, maybe there are components inside that were not final-riveted together. Something is not right if you can manually warp the aileron.

4) there is one other item that can effect aileron feel, and that is the location of the aileron, as installed on the wing. If it is mounted just slightly high, so the aileron skin forms a contour that is slightly above the extension of the wing airfoil, that is a good thing. If it is mounted too far forward, so that both the upper and lower aileron surfaces contours nest "inside" the extended wing airfoil contours, that is a bad thing.

5) both the warping (3) and the surfaces below the wing contour (4) will effect aileron RESPONSIVENESS, and therefore indirectly the stick force. You will have to deflect them farther to get the response you expect, so the force is higher. The warping, in particular, would be very speed dependent.

Easiest thing maybe is build a new set, as you suggested. Be sure to locate them with respect to the wing as shown on the plans.
 
How does the flap and aileron trailing edge compare?

acam37 said:
Yes sir, I hate that it went to 5 pages, but this is why I go here. To echange information so that the next poor soul that runs into this problem will have the resources to troubleshoot. If you look at my picture in post #3 you can barely see the hole that I was talking about in the rib.
Click to expand...

This is one of my flaps with a straight edge laid along it. Notice that the top skin is flat all the way to the exact point where the curve radius starts. Its hard to tell from your picture, but it does look like you have a large radius curve back there instead of a crisp curve. Lay a straight edge on yours and see how it compares.
FP14022013A0003O.jpg


Also, I have not seen such a large hole at the forward edge of the end rib. Instructions were to create a small mouse hole (like less that 1/2 a full hole, only to allow a wrench to get in there. I'm no engineer, but for you to say you can manipulate your aileron by hand, you can be sure 150 MPH air can do the same and more.

Here is what my aileron end rib access hole looks like. Smaller.
FP29102012A000D7.jpg


I'm guessing that big radius on the back of both ailerons would almost create lift on both ailerons at the same time, adding to pressure on your stick. Just guessing, though.
 
Steve and Wendell, awesome posts. I do believe that the ailerons are the culprit as everything else has been checked and re-checked. I cant explain how covering up a few holes made a dramatic improvement on the stick force, but it did. Anyway, aileron replacement seems to be the consensus of the forum, so that's what I'll do.
 
Hmmmmm!

Sorry I missed the earlier post where you gave the results after taping over the holes and found great improvement. Hmmm, I'm really surprised by that, which is fun for me, not often surprised by something aerodynamic. I will have to stew on it for awhile.

thanks!
 
Update

Justin called the factory and explained the stick force to an engineer. even though it got better by taping up the holes, it still wasn't right. They told him it should be almost effortless even at high speed. They told Justin that this problem has never been reported and they are just as baffled as everyone here on the forum. I am going to get a seasoned RV-4 builder to fly it and see what he thinks. After Christmas I will order a new set of ailerons and go from there.
 
acam37 said:
Justin called the factory and explained the stick force to an engineer. even though it got better by taping up the holes, it still wasn't right. They told him it should be almost effortless even at high speed. They told Justin that this problem has never been reported
Click to expand...

Did he mention that the plane had been in a hangar collapse ???

I wonder if there could be some hidden damage that you did not find???

Your photos show damage to the tail, http://www.vansairforce.com/community/showthread.php?t=107227 , but did the wings get any damage also? Didnt you have to replace some of the spar?? Is it possible you inadvertently got something out of kilter when you had the wing apart?

Not trying to scare you, just dont want to see anyone hurt, or another bent plane.

Have you discussed the flight characteristics with the previous owner?
 
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