I have a World Models 40 size P-51 Mustang with a flutter problem with an aileron on one side only.
It is powered by a OS 70 heli on tuned pipe spinning a APC 11X8 at 16K so the plane is going faster than originally intended. I need to fix this so that it’s safe to race, this has taken me out of two events this year.

The strip aileron is driven by a Hitec HS-5475HB servo (karbonite gears). The same side has blown out the gears in one servo completely and I replaced the gear train in a different (but same model) twice because the slop was extremely excessive in the center travel area. In other words, the flutter beats the tar out of a few teeth in the gear train in just a few flights.
The control surface was dead tight with no backlash or linklage slop at the start of the flights.
I did a high speed pass level flight and out of a dive and I can’t hear the flutter over the muffled tuned pipe.
I put a gap seal on the bottom side only, no help at all.

I was offered several suggestions;

1# Up reflex the ailerons, but a some point in flight it may still flutter when the aileron is used.
2# Cut away the last 6 ½” of the out board aileron and make it part of the wing (non movable).
3# Use a servo with metal or titanium gears, eventually the servo or the aileron may still fail since the flutter is still there.
4# remove the covering on the aileron and put a thin veneer of balsa on each side to make the aileron a bit thicker than the trailing edge on the wing.
5# Add a counter weight at the out board aileron end.
6# Increase the mechanical advantage in the servo’s favor, but this will amplify any apparent gear train slop at the control surface. It’s about one to one now, the servo is slightly advantage (shorter arm).


Too many choices
What would you guys do?

I would use some tape (like blemdurm) to seal the gap between the aileron and wing. Make sure that you deflect the aileron full in one direction and then apply the tape.

Cheers
Rick

What a hassle! You failed to mention which aileron is fluttering. Some of the solutions would probably work, and others would likely compound your problem.

First off, why is this bird using strip ailerons? The original design, of the Mustang, was to have slightly smaller than barn-door style ailerons, covering 60% of the outer trailing edge, and flaps utilizing the remaining trailing edge. The break in the leading edge, close to the root of the wing, creates a minor turbulence just at the root, and towards the trailing edge. It effects about 1/3rd of the supposed flap area, which is a problem onlyif the ailerons run all the way to the root. The right side less affected than the left, usually.

If it were my plane, depending on the manufacturer, I would install flaps and originally intended ailerons.

OR, if you are using a double servo setup, I have had success in moving the aileron control horn aft, just a scoche, behing the hinge line.

Don't give up on the bird, whatever you do! Trial and error, that will get you through this.

Keep your head up on a swivel,

Skratchbilt

The covering material that covers the wing goes in and out of the gap than on to the aileron in one piece, this was done on top and bottom, thinned Stix-It was used to make it adhere tight into the corner of the gap, so in effect it's double sealed already. The sail plane gap seal was used to try to smooth out the bottom. My logic was to make the sides different and thus out of balance. Fruitless effort.

This picture was taken before it's maiden flight and 3"black stripes added near the wing tips, also before it tip stalled and snapped inverted just before landing and ended up on grinding its lid because of a stuck down left aileron that I was compensating for. Almost had it down safe. Battle scared.

I would rebuild the aileron so it is stiffer and would definitely sheet it, maybe even with 1/64" ply on 1 side. Make sure the torque rod is well inbedded in hardened wood. I like to use epoxy "bearings" for torque rods instead of using tubing now for the least slop possible.

I think having control surfaces that are thicker than the wing would increase buffeting? Seems counter-intuitive.

Decreasing surface area of the flap is obviously going to help, I would look at other planes in your class and see what they get away with for roll control.

Funny how you helped me out of a flutter problem 2 years ago with my Nelson powered delta, that model is still with "the living", needs to be exercized soon.

Hi CP
There is no torque rod, it's a servo per wing.

On the Diamond Dust I was told by Jeff the inventor to leave the elevon thicker because it will flutter if it matches the TE of the wing, I had mentioned to him I wanted to match the lead off on the wing. I never would have thunk it.

I'm thinking off adding an oz. of weight under the aileron near the tip. I that doesn't work, cut it down.

There have been some strange plane losses, maybe this is happening to others too and the don't know it. There’s usually not much left to do autopsy on when the plane goes in at speed.[:@]

I don't recall what I said that helped you.

freakingfast:

I would follow advice #5.
I believe that any control surface flutters because it has mass.
That mass or weight is all on one side of the hinge or pivot line.
The turbulence of the air makes it reach the resonance frequency of vibration.
A balanced control surface cannot flutter because it has no mass, from the point of view of the flow of air (same weight on both sides of the fulcrum).
Also, adding less than the weight of the aileron as a counter-balance will change the resonance frequency of vibration to a different value, that your model may never reach again at those speeds.

I suggest you to read through these old threads:

http://www.rcuniverse.com/forum/m_77...tm.htm#7766711
(Check pictures of Post #5)

http://www.rcuniverse.com/forum/m_79..._1/key_/tm.htm

Best regards!

I don't think you can truly counterbalance a built up balsa aileron by hanging a weight off the end. I think the problem is a run-away flexing condition. A servo could be added to the outboard end of the ailerons to see if the problem goes away. I'd be willing to bet that a pair of standard servos per flap would do the job, it isn't a matter of torque or holding power, it's about controlling vibration by adding another control point.

The counter weight or BALANCE is the way.

My understanding is that every airplane (yes full scale too) has a 'flutter' speed __ period.
Get to that speed and you've got flutter.

Over the years I have had 'flutter' remove ailerons, aileron servos (yep, the whole thing) etc. but it has been a very sparce occurence. Perhaps three aircraft out of roughly fifty year's worth.
The elevator on a P-38 Lightning is the most visible "flutter band-aid" I can think of at the moment.
http://upload.wikimedia.org/wikipedi...tning_USAF.JPG

Most models, including my few that had a flutter were overcome (it's a 'fix' not a cure) by your #1. Incidentally, it can work with the reflex either + or -.
I cannot buy your reason for not trying it. I have simply never experienced that which you have stated as a reason not to. I have used refexed airfoils for a variety of reasons, flutter is but one.
I also do not agree with removing the outer portion (6.5" you stated). Removing the whole aileron will stop the flutter too. Need I say more?

I am NOT an aerodynamcist, but we have several on these threads who are.
Hopefully they will chime in

Let's try the easy stuff first.  Fluttering ailerons was always a potential problem on Formula One pylon racers that I built and flew in competition for many years.  They were running between 175 on the course but could reach about 200 after a long straight run.

Tape the ends of the ailerons solid to the wingtip with plastic tape.  In most cases, this will solve the problem.  Those long strip ailerons are pretty flexible, so you will be twisting the ailerons for control.

If building up a speed airplane, it is best to stop the ailerons 4 to 6 inches from the tip.  Even then, tape is often needed.

The suggestion to "thicken" the ailerons is OK.  It helps to reattach the air to the aileron in theory, but a pain to do in practice.

Generally, adding weight to the aileron makes the problem worse.  That is, weight in trying to make it stiffer.  The extra mass lowers the flutter speed.  On full size, just adding the weight of paint has been found to lower the flutter speed.

In full scale, the practice is to add a counterbalance ahead of the hinge line.

The shape of the trailing edge can also contribute to the tendency to flutter.  Sharp edges are good, rounded edges tend to flutter.  A square edge is better than rounded.

I've seen the taped down tips work wonders, some guys set their planes up like this from the get go.

This is what I use for the P-51s. Plenty of roll control for the whole flight from the hand launch all the way to the dead stick landing. Once in a bank, the plane stays there [if you'll let it]. I'll bet the same proportions would work well for a .60 sized Stang, too.

4# remove the covering on the aileron and put a thin veneer of balsa on each side to make the aileron a bit thicker than the trailing edge on the wing.

or

6#

#6 also has some flawed logic Increasing the mechanical advantage in the servo's favor, will reduce the load the servo sees and reduce any geartrain slop.

More than likely the problem is vortex shedding around the aileron, making it thicker will change the airflow around the hinge gap. more than likely this will kill the flutter problem. I don't think alieronmass is your problem, changing the effective mass of the aileron will only change the speed at which the flutter occours, not get rid of it.

Investigate the cause of the flutter. Think about why it only occurs on one side of the airplane. Flutter needs a small harmonic excitation force. Find and eliminate that and your problem will disappear. Start upstream and ask yourself why a (seemingly) symmetrical airplane would only generate flutter in one aileron? Whats different about the two sides? I already have a suspect....

We are glad you are back posting, CrateCruncher.[sm=thumbs_up.gif][sm=teeth_smile.gif]

Reducing slop in the system from the servo to the aileron works. Loose connections allow the aileron to start a small flutter. That flutter works away to get more room and on and on.

Fixing an outboard length of the aileron to the wing also works, and doesn't require more than 3-4". Decide the amount after locating the hinges. You won't notice much roll rate change. And you might get less yaw.

It's so simple and easy to try that reflex trick, what's stopping you. I've seen it done and never seen it work. But what'ya got to lose? Tell us how it comes out.

Reducing the mass of the ailerons works, but isn't easy. The easiest way that I've done was to use a Forstner bit or two. That's when the aileron stock was good stuff but heavy. Strip the covering, drill some holes about half as wide as the surface chord and recover. It's actually quite simple and easy. The one I did took about an hour. Gotta admit it wasn't done because of flutter. It was back when servos weren't as powerful as today's, and I'd used some pretty brutal balsa for the ailerons. I was trying to get a bit quicker movement. Reducing mass works but results depend on how heavy the suckers were to begin with.

Squared off trailing edges work but that's a job best done during construction. Tapering the aileron works too, both the benefit is from the mass reduction that results and from reducing the area back there where flutter can start. The thicker the TE, no matter what shape, the more area in which the flutter can build, and more force it can generate right off. Square off any rounded TE and you further reduce the dead zone.

Static balance, square T.E., seal gaps, aileron horn near outboard end, hinge a little behind L.E. so that L.E. projects into airstream (tubulates)- pretty much the things recom. in this thread that I've done. Never 'taped' an ail. but have seen pics of it. Of course, the ail. servo can't be at this end..... 'Model Aircraft Aerodynamics' is a good book if available.

Well, I up reflexed both ailerons about 3/32" and added some lead to the out board trailing edge. After three flights I didn't blowout a servo...........instead I blew out both aileron servos![:@]
Landing was.....er.. uh.....exciting. I was flying a real fast & fun practice pylon circuit when I noticed a sound in the turns. I would roll the plane on it's side than pull elevator and when I pulled, that's when I thought I heard a sound .....VOOOOOOOOM! The next turn and I knew I heard it for sure. I had decided at that moment that I would land and investigate but the decision had just been made for me as the roll control was wild and lots of new flutter noise. I chopped power and landed with a squirrely rudder/elevator plane.

The strip aileron is going to go. I'm putting in new ailerons that will be shorter, a bit wider (deeper), and centered along each wings length. they will also be thicker than the wing's trailing edge. I may move the servos outboard two bays to make control stiffer.

I guess this is what you get when you push a plane much further than it was designed for. This plane has been a PITA from the time I pulled it out of the box. It's cursed I tell ya

Man! Good job!

I haven't built much in the way of big and fast, but isn't hard / firm balsa usually good enough for ailerons? At some point the size of the model dictates built up ailerons, sounds like this plane is a "tweener".

I'll bet a layer of 2 oz cloth on both sides would stiffen up the balsa enough.

Adding lead to the outboard trailing edge is the opposite of what was required. The idea is to balance the aileron about the hinge line. The weight should have been forward of the aileron leading edge, preferably on a horn type arrangement attached close to, or part of, the aileron horn. Try again.
Evan, WB #12.

Ok, I think it's fixed.
I made 6 3/4" of the outboard end of the strip aileron fixed and cut to free the rest. I did this by removing the covering material in the gap on each side and glued in a strip of tri-stock than made the cut. Then I sanded flush and recovered. Instead of karbonite geared servos, I went with HS-9585MG, over kill I know but I want to be done with it. No weights were used.

I must have nailed the position of the new outboard trailing edge because I needed zero trim adjustments. As a matter of fact all control surfaces are perfectly centered for level flight. After three hard flights with speed dives, all linkages are tight with no sign of trauma from flutter nor could I hear any flutter. I dialed up the servo travel to help make up for the control surface area I took out.
It's slightly less responsive at landing approach and consecutive roll rate at speed is less, but stetting up for a pylon turn it's hard to tell any difference from before.

Nice job! Make sure your high rate's cranked up enough to counteract a wind gust when you've got low airspeed.

I know what you mean CP. It's done.

If you look at some of the 428 Q-500 aircraft, they have wide chord ailerons that are short. Also set closer to the root of the wing than the tip. The wide chord gives better slow speed aileron effectiveness by increasing aileron area. Being inboard helps with flutter issues.
My recommendation would have been to do this and also move the servo to be centered on the aileron.
Just for anyone else, If the ailerons are going all the way out to the tip, one other trick is to taper the aileron at the wing tip to eliminate the vortex effect on the T.E. of the aileron. This works well. Also, stiff aileron material needs to be used to start with as light, flexible ailerons are prone to flutter.
Congratulations on solving your problem.

If aileron flutter is a problem, always have the aileron horn at an odd number of divisions; i.e. at 1/3 span, 1/5 span,2/3 span etc. , never at an even spacing as this will help to prevent some of the components causing flutter. Reasons are quite complex but if interested, check into vibrations of structures.

You have investigated everything except stiffer control horns. The molded plastic ones that come with the kit are kinda limp and if they are not installed over a hard-point, they can dent the balsa that they are sitting on and work in some slop. Trim out some control horns from3/32 ply or carbon fiber sheet. Slice full depth through the aileron, and epoxy the new stiffer horns in place. Make sure all the geometry matches wing-to-wing, that the linkage hole is aligned with the hinge line, and the hinge holes have the same height in both wings. Heavy-duty servo arms, and beefy pushrods complete the triad.