what is aileron flutter?
 

what is aileron flutter?

RE: what is aileron flutter?
 

http://www.google.com/search?client=...=Google+Search

RE: what is aileron flutter?
 

The last sound you hear before the THUMP.:D

Cheers,

Colin

RE: what is aileron flutter?
 

Flutter is exactly that, a "flutter" or oscilation of the aileron during flight that is usually noticed due to the "rippling' sound it makes. It can also happen to the elevator and rudder. There is some debate as to its true cause, and I believe there can be more than one cause, but it can definitely bring your airplane down. The usual suspect is too large a gap in the hinge area between the aileron and the wing, but the construction of the aileron can also be part of the problem. I've only had aileron flutter occur on one plane so far. It was a Stick .40, and it only occurred comming out of high speed dives. I believe it was due to ailerons on this plane having a very large covering surface stretched over a minimal frame structure. This allowed too much flex in the covering and allowed a "billowing" effect in the covering that caused the "flutter".

RE: what is aileron flutter?
 

A sound that can freeze every person at a flying field in their tracks!!!! Trust me, when it's heard everybody will stop immediately and turn towards the sound!!! Why?? Because there's about to be a spectacular crash!!!!! ;)

Ken

RE: what is aileron flutter?
 

Google up "aeroelastic flutter".  The cause is the center of lift ahead or the center of gravity on a control surface.  The solution is to lighten the trailing edge ("back to the drawing board") or add weight at or ahead of the leading edge.  You'll see full-size planes with weights on the end of struts or with small surfaces out on the ailerons called "spades" that have a flutter-reducing effect. 

Many full size aircraft have an internal weight attached to a control surface that goes into the wing or fixed empennange to reduce flutter without being visible (or adding drag) outside of the plane.  That does limit the throw available

RE: what is aileron flutter?
 

I have heard guys say it is the gap that causes it, but to me I question this because I have seen planes with a huge gap in them and never a flutter at all. I believe it may be a combination of things.

We heard a Sig Cavalier flutter like crazy one time and we all looked because we knew it was going to hit the ground with a thud. The pilot slowed down and then landed and we looked it over and could not find one thing wrong with it. Everything on it was tight and well secure with very little aileron gap. We never heard the flutter return again.

RE: what is aileron flutter?
 

The biggest cause of flutter is the ability of the surface to move in the airstream. While a large gap can contribute to flutter it is rarely the cause. As you noted, many plane have large gap and never suffer flutter. The gap is more likely to affect the lift and effectiveness of the surface. For the flutter and type of movement can cause the flutter. Any slop in your control surfaces can lead to it. Control linkages that are too small for the application can lead to it. Weak or damaged servos can lead to it. Worn our servo arms and control arms can lead to it. Wallowed out holes in control arms can lead to it. There are several others that can lead to it as well, but these are the biggest causes that will usually be culprits in flutter. Check your control surface to see if there is any movement with the radio turned on. Any free movement in the control surface is going to put the plane at risk for flutter.

All of the above it good to prevent it, but sometimes a plane can be in perfect shape and suffer from flutter (although it's sometimes rare for this to happen). Flutter can actually start as a harmonic resonance in the airframe that moves to flutter. This can and does happen usually in a matter of seconds and the plane will literally come apart in the air. Sometimes with control surfaces flutter you can cut the throttle and get down immediately before the airframe is destroyed. If you do get your plane back on the ground never ever go back up again until you determine what was causing the flutter. Going back up again without fixing the problem is just inviting flutter to destroy your plane.

Ken</p>

RE: what is aileron flutter?
 

Exactly what happened to this Stick .40, no gap, and nothing else wrong with the aileron, other than large open areas in the frame work. I agree that there is probably not one simple cause. Gap may cause it, but I've never experienced it. In any given case it could be a combination of several things like the aileron construction, balance of lift, and the type of airfoils involved. This Stick .40 had a fully symetrical air foil in the wing, but the ailerons did not have any taper in the chord, just a flat constuction with beveled le and te on the aileron itself. I did not get a chance to experiment with the ailerons as a buddy borrowed and crashed it. But I would have liked to try adding counter weight to the ailerons, and/or building new ailerons with some sheeting over the large open areas.;)

RE: what is aileron flutter?
 

I saw some surface counterweights weights on here that were made from regular pushrod wire and the round fishing weights with a hole through them. The fellow said that changing the CG of the surface a little would stop most flutter.

RE: what is aileron flutter?
 

Here are some made from 140 grain .270 bullets silver soldered to a 4-40 rod in a drilled center-line hole I did as an experiment. Made no difference I could detect with or without . . . but the ailerons are still attached so it peobably doesn't flutter either way.

.

RE: what is aileron flutter?
 

The are called mass balance and will work every time on any of our airplanes and the speed ranges we operate in, that demonstrate the onset of flutter. Its also easy for any of our surfaces that have aerodynamic balance forward of the hingeline to simply imbed a ball of lead in it.

John

RE: what is aileron flutter?
 

Ken in post number 8 above, gave the best description. Everything will flutter if given the proper stimulus, even an iron bar. The only thing that will not flutter is something with infinite stiffness and zero mass, an impossibility. As Ken said, gaps do not cause flutter. The most common cause in models is sloppy hinges, spongy control rods (to small and they flex under load) or insufficient stiffness in the structure itself.

RE: what is aileron flutter?
 

I didnt know flutter had so many causes. Always thought that

If you had a thick airfoil and flew it too fast, the air flow would seperate over the tapering part of the foil (part after the main spar when the cross-section starts reducing). This would induce turbulence causing sudden high and low pressure pockets to form on the same side of the control surface. This would cause the surface to move exagerating any play in the linkages.

I also thought that aileron hinge gaps would allow air to "leak" from the higher pressure undersurface to the lower pressure upper surface and this crossing of flows would induce the flutter.

Is my understanding of the issue wrong?

Ameyam

RE: what is aileron flutter?
 

Ameyam flutter analysis is an aeronautical engineering displine in itself, careers are devoted to aeronautical flutter analysis.

Therefore the facts of what can happen and what works in its prevention gets lost in the discussion of theory and argument.

In the context of our model airplanes and the range of speeds at which we operate them, yes flutter can happen to any portion of the airplane with the most common being in order: ailerons-elevator then rudder.

I agree gap sealing has little effect in inducing flutter and trying to cure flutter with ever more expensive servos is most often disappointing.

Poor linkage geometry as well as sloppy linkage and strutural elasticity of both the airfame and the control surface are all contributors however you can still flutter after 'fixing' all these things.

But its easily fixable;)

Its called mass balance. First dicovered in the twentys When during the Pulitzer races and internationally during the Schneider Cups races and simple mass balance stopped the carnage of lost control surfaces and flailing wings.

It will do the same for us if your airplane ever demonstrates the onset in flight. It only takes moments to attach one to any of the three axis's for most smaller airplanes like Charlie P and I posted.

For years frequenting the old SWRA and later PCPro warbird races sometimes up to 13 races a year all over the soutwest where arf's with roughly twice the normal displacements were the norm, flutter incidents were constantly happening both in practice and heats. I took to makeing up pocket fulls of the simple widgit I posted in my first post and gave them away to folks who survived the first incident so they could make their next heat. It never failed and I seldom went home with any.

Its also rather simple to imbed mass balance on any airplane that has aerodynamic balance surface forward of the hingeline. Works just as well except that requires a tiny bit of surgery and adding a pittance of weight during assembly/construction and folks will fight that to the death untill they do suffer a loss to flutter.

John

RE: what is aileron flutter?
 

besides sound is flutter visible from the ground?

RE: what is aileron flutter?
 

That just looks kewl, flutter or not!http://www.rcuniverse.com/forum/js/f...ades_smile.gif

RE: what is aileron flutter?
 

I beleve flutter is not always detectible by either sound or visually. This brings to mind the classic cases where a single hinge or more hinges fail continually frequently on ailerons and no once see's or hears it. Thats why the hinge type or hingeing workmanship is blamed when in fact its flutter.

How about this classic the aileron servo out there in its box just keeps mysteriously losing its mounting screws. Worse found just flopping around in the wing but no one heard or saw a thing. Throw a mass balance on it and just as mysteriously the screws stay in place no problem

John

RE: what is aileron flutter?
 

There was a problem in my execution. The Giant Super Sportster apparanty has sheeted ailerons that do not have internal ribs. Ipoked about 30 holes with a needle searching for the internal framing and never found any. Finding none Iwent to the outside edge (I researched several models that put the weights there). They did alright until I lost a wheel collar and threw the wheel - resulting in a ground loop. Tore the starboard weight and strut off. Did not hurt the hinges or aileron, amazingly.By luck it just spun around on the axis instead of pulling straight back.Still, that might not be the ideal location for a low-wing model.

Best solution Ihave seen for flutter is to SLOWDOWN. Most guys who seem to have trouble are playing the throttle like an on/off switch. The other best proactive remedy, as John said, is to eliminate slop in the linkage. The DuBro syle (aka: relatively inexpensive")ball-and-socket connectors have simplified this immensly.

RE: what is aileron flutter?
 

charlie i love it!

mine are usually 9mm.

Ed H. had a flutter problem on one of his planes on the Elevator. this E had spoons so he drilled a hole into the LE of the spoon and screwed in a bolt. problem solved.

Joe

RE: what is aileron flutter?
 

Missed you at the picnic.  Weather held out and it was a good day.

RE: what is aileron flutter?
 

I hate to disagree with Mr. Buckner as he is most often right on when it comes to a solution to a problem; but, mass balancing will not necessarily cure any flutter. Perfectly balanced systems can and do oscillate or flutter if given the impulse or input to generate the frequency at which they are resonant and mass balancing a surface that will flex or maintain oscillation does nothing to cure that. I'm a firm believer in mass balance, especially on elevators and ailerons but not for the reason that it prevents flutter.

RE: what is aileron flutter?
 

Rodney perhaps in the strictest sense you are correct with a couple of caviets . The first is absolutely, we are not curing the flutter but the application of a percentage of mass balance is moving the onset to a higher speed that we will not ever be capable of reaching.

The second caviet is "perfectly balanced" it is not the goal Indeed 100% may even be more likely to induce.

In the early ninetys I did my first expeiments with flutter stired on by the fun fly airplane rage which being the predesesors to the modern 3d were interesting but not as good in many respects. With all the hugh surfaces, fat airfoils extreme lightness adding to flexability and worse fiber glass tube fuse's or aeroshafts. All the worst case senarios and mostly powered by 25, 32's. The were flying rubber bands. You remember and sure you also messed with them also.

Anyway most of these could never use full throttle unless on the vertical line, any other time you were certain to loose an aileron or elevator. It was very easy at the time with the square surfaces to just use wire extension at the outboard ends with a ball of lead. At first I disconnected the pushrods and did set a perfect 100% balance, took more lead than I thought. It was kinda cool that old elevator or aileron would just set there bout neutral and thump it with your finger and it would just wave at you for a while and settle back bout neutral. OK now came the test flights guess what no real detectable change except I lost another elevator.

Back to the drawing board and the next ship (I built bunchs of these things) I balanced only perhaps around 10%, That did the trick all my later fun flys had no problem with loosing surfaces to flutter never happened agine to any of mine.

I don,t know what to say but every ship I have added mass to since were airplanes that survived their first encounter and it never happened agine after adding the mass. That includes a small percentage of my normal airplanes a few other folks here and there and an awfull lot airplanes at the races.

John

RE: what is aileron flutter?
 

I had aileron flutter with a Tiger 3 (40 sized low wing). I could hear it flutter quite clearly but was able to bring the plane down without incident. Others in our club have had the same problem with this particular model and solve it by replacing the single servo (with longish linkages) for the ailerons with a separate servo for each aileron.

An old timer at the field who heard my aileron flutter applied a long strip of cellophane tape along the forward edge of the aileron and the flutter didn't come back. Unfortunately I crashed the plane only a couple of flights later due to a completely different reason.

I have another Tiger 3 now and have fitted dual servos and it has no aileron flutter although I've only flown it a few times.

RE: what is aileron flutter?
 

So, aileron flutter is the moving of the aileron? Not the wings flapping? I have not seen a plane flutter but if I do witness one and inspect the plane, would there be significant play between the servo and aileron (somewhere in the linkage)?

RE: what is aileron flutter?
 

HI
I THINK THE FORCES ON THE CONTROL SURFACE MAY EXCEED THE OUTPUT FORCE OF THE SERVO (IN OUNCES ) THAT IN ADDITION TO SERVO WEAR ( MOTOR,GEARS,ETC ) AND SLOP THAT DEVELOPES IN THE LINKAGES-( PROPER MAINTENANCE SHOULD BE PREVENTING AND IDENTIFING THIS CONDITION ) ALL ADD TO THE FLUTTER PROBLEM DEVELOPING- QUICK IDENTIFICATION OF THE SOUND OF FLUTTERING AND PULLING BACK THE TROTTLE ( QUICKLY ) TO LAND QUICKLY MIGHT BE YOUR ONLY SAVIOR-THE FLUTTER IF LEFT TO CONTINUE WILL DESTROY YOUR SERVO GEARS AND TAKE YOUR CONTROL SURFACE OUT !!-LOSS OF THE PLANE WILL FOLLOW-,TWO SERVOS ON 40 AND UP AIRFRAMES IS RECOMENDED ESPECIALLY IF YOU OVER POWER YOUR AIR FRAMES AS I CHOOSE TO DO ALWAYS (HOT ROD RC ) I MUST SAY AFTER FLYING FOR OVER 20 YEARS A LOTIN SOME WAY THE PLANE USUALLY GIVES YOU A SIGN THAT A PROBLEM WILL FOLLOW-LEARNING TO READ THAT SIGN WILL OFTEN PREVENT THE LOSS OF THE PLANE -( REQUIRING YOU TO THINK AND REACT FAST ) TO FLY ANOTHER DAY ENJOY BEST REGARDS TONY

RE: what is aileron flutter?
 

So servo buzzing=/=flutter?

RE: what is aileron flutter?
 

Aileron flutter can progress to flutter of the wing, depending on the stiffness (mostly torsional) of the wing and control surfaces and mechanical interplay between the wing and offending aileron. It can actually happen the other way around, with the wing driving flutter of the control surface.

This kind of interplay is what is suspected to have caused the wing to fail in the Gee Bee crash from the early 1930's that was captured on film and has probably been seen by most of us. Keep in mind, however, that a WING can actually flutter independently of the control surface. It is rare, but can and does happen occasionally. I have had it happen wilth glider wings with high aspect ratios and relatively inadequate torsional stiffness. You can make a yard stick (wooden only) do this by whipping it like a sword in your hand. Try it! You will also hear the sound of flutter, which of course has come to be known as the death rattle of any airplane that is experiencing it.

Any wing or aileron (or other control surface for that matter) can flutter under the right conditions. Mass balance and proper stiffness are employed on full size aircraft and by modelers if they are smart. The stiffness and balance serve to keep the flutter "envelope" outside of the operational envelope (mostly speed, but load and other factors to a smaller extent) of the airplane.

Keep in mind that on a typical light aircraft the control systems are "free floating." They are tied to movable controls. Our models controls are tied to servos that are not easily moved by aerodynamic inputs from the control surfaces. When connected by properly stiff control rods and cables, this arrangement tends to prevent (damp) the onset of flutter in MOST (NOT ALL) cases. This is why we typically get by with improperly hinged, improperly balanced, and improperly aligned control surfaces without disaster.

Regards
littlera (aerospace engineer)

RE: what is aileron flutter?
 

No. No. You generally can't hear servo buzzing over the sound of the engine and from 100 feet away. You can aileron flutter. It varies from a baseball card in the spokes sound to a leaf in the car's defroster sound. Veryrapid, Problem is occasionally about the time you hear it the damage is done. That'swhy a maiden flight shouldstart gentle.

Warning signs for a less severe casemight be the holes in theservo arm and control horn elongating or opening up, servoteeth breaking, hinges failing, a shimmering reflection off the covering in flight, any loud buzzing heard on the ground from the model overhead.

You can get many 3-D models to flutter because the control surfaces are so large and the model so overpowered. Not a design flaw really, just a misuse of the excesive power inflight. It's like the speed rating on car tires. Just because the engine can pull you at 140 mph doesn't mean your P rated tires won't disintegrate after a few minutesof doing it. Ihave no doubt Icould have torn the ailerons and probably elevator off my Hot Stik in level flight if Iflew at full throttle. That same powder allowed a torque-rollwith a ballistic exit. But if you fly fast you'd better correct it even faster.

RE: what is aileron flutter?
 

Oh - PS - servo buzzing can just be the natural complaining of a digital servo or may indicate a servo that is binding because of stiff conrol play.  If you ever watch a voltmeter in the circuit you will see buzzing can mean power is being consumed at a high rate.  Address that, too.  A little is OK.  A lot is bad news.  For the servo and your receiver battery life.

RE: what is aileron flutter?
 

nrad2000

So, aileron flutter is the moving of the aileron? Not the wings flapping?

Any surface and structure flexible enough to oscillate, will flutter within turbulent airstream.
It is not possible for any aileron to be shaken to destruction and not to transfer some of that shaking to the wing to which it is attached.
A rigid flag will not flutter in the wing.


I have not seen a plane flutter but if I do witness one and inspect the plane, would there be significant play between the servo and aileron (somewhere in the linkage)?

You will see surfaces of two airplanes fluttering here:

http://www.youtube.com/watch?v=vRoyk...eature=related

http://www.youtube.com/watch?v=wAiOcPVXW0c

RE: what is aileron flutter?
 

Twice I have seen two identical planes, one with flutter and the other without. And they had different causes. One plane had sharpened trailing edges on the aileron VS blunt, the sharpened aileron fluttered. When the aileron was replaced with blunt TE, it stop fluttering (the replacement was actually softer lighter balsa!). Another had thinner ailerons then another plane. The plane with the thicker stock did not flutter (it even had a larger hinge gap). The leading edge of that aileron was a bit thicker than the trailing wing edge just ahead of it. Thin balsa veneers were applied to the aileron sides on the plane that had the thin ones and the problem was again solved. I'm guessing this kept the control surface in contact with the air flow. Linkage and servos were tight in all cases.

If you hear flutter, dump throttle, pull up to dump speed and load control surfaces, land and fix.

RE: what is aileron flutter?
 

Guys, "Flutter" is cause by exceeding the airframes capabilities(flying faster than the airframe can handle). Gap has very little to do with it. Slop in the control surface can cause it.

Many planes with airelons are very capable of creating Flutter. If the airelon goes all the way out to the edge of the wing. Especially if the airelon is very "Soft" "(ie twists easily) then in flight it flops like laundry on the clothes line. Look at a flag in a high wind. That is what the surface is doing.

In twenty plus years I have had quite a few different airplanes "flutter" during high speed flight. Most are overpowered.

It is very easy to "stop" the flutter. Slow the airplane down. Quit exceeding power requirements. build a fixed area on the outboard area of the wing and shorten the airelon one to two inches. Thus the airflow around the tip is not amplifying the flutter and the airelon end is not in the tip vortex.

I had a 60 size pattern plane not overpowered and the airelons fluttered during high speed flight. Upon inspection I found the servo arm (gear lash) had "slop" thus causing the the airelon to flutter, putting a small input stopped it. I replaced the servo and no more flutter.

In most cases there is a "Mechanical" problem that is causing the flutter. A proper detailed inspection can find the cause.

RE: what is aileron flutter?
 

SOOOO TRUE!

Ironically, this past weekend this very thing occurred at our field, when someone was flying an overpowered Giant Super Sportster. ( Charlie P. that you? )

We all heard that loud BZZZZZZRMP noise from flutter as he did a diving pass over the field. Everyone turned to look and we watched the elevator disintegrate followed by a spectacular crash.

RE: what is aileron flutter?
 

Soooooooooooo



The message here is, follow manufacture recommendations for engine size and this can be avoided. I would like to think that they test for this type of thing if it is so well know that engine size can cause catastrophic failer of the airplane and internal workings, do they not?

RE: what is aileron flutter?
 

Many years ago a now long departed older friend asked me to do the maiden on his just completed Pilot Pacemaker old timer style plane. He was one of the best builders around, but not the best mechanically when it came to setup. I had flown many of his planes without incident, so I took the box and pushed the thorttle stick forward.

When the plane got up to speed and altitude, the sound of flutter was heard and we could SEE the elevator flapping like a flag so fast it looked like a humming bird wing! I immediately throttled back and was able to land, although had to hold almost full DOWN elevator to do it, as pieces of balsa and covering were flying out the back of the plane.

The Csuse: Readily apparent, he had connected the elevator with a 4 - 5" piece of unuspported inner Nyrod instead of using metal pushrod after the Nyrod exited the outer tube as it exited the fusealge.

Damage: Horizontal stab rear (main) spar broken on both sides; most covering on horizontal stab shredded or missing; elevator horn hanging by one screw.

One could deflect the elevator almost 90 degrees down by pushing it with a finger. The inner Nyrod of course just bent like a soda straw.

Moral: Always test stiffness of your control linkages. ALL flutter is caused by aerodynamics, but can usually be prevented with proper control linkages.

littlera

RE: what is aileron flutter?
 

http://www.rcuniverse.com/forum/js/f...sn/biggrin.gifhttp://www.rcuniverse.com/forum/js/f...sn/biggrin.gifhttp://www.rcuniverse.com/forum/js/f...sn/biggrin.gif

Igot out pretty far at one point chasing an eagle awayfrom a flock of'lectricsbut it was headed North, not South-East.

My GSS is not overpowered, just at a gentlemanly adequate 34cc. I was doing slow rolls, huge &amp; slow loops, hammerhead stalls and tail-slides at 40% to 60% throttle. Nothing like a slow, aerobaticgasser on a Sunday afternoon with a tummy full of BBQ chicken.

Well, OK, steamed blue-crab and clams would have been better, but since there was no beer what's the point, though the flying couldn't have been. Well, OK, a better pilot could have done the complete circular roll but I'm still learning theGSS. http://www.rcuniverse.com/forum/js/f...sn/biggrin.gif

RE: what is aileron flutter?
 

A real good inspection of the plane beginning in the building stages will prevent flutter. As you progress through any build, you're constantly scrutinizing your work against several pitfalls..one of which is potential flutter. If you have solid goals for the plane to begin with [fast, slow, 3D, etc.] then you'll be better able to set the plane up accordingly.

There are areodynamic considerations, structural considerations and linkage considerations already covered here. The controls need to be tested against manual pressure and the control surfaces need to be operated against manual pressure to see if they are stiff enough. In some cases you need to either fiberglass the control surface or add another linkage/control point.
Take the time to see how "flexxy or twisty" this stuff is before you find out later at the field.

If the servos are hooked up with the best mechanical advantage [linkage geometry], then that will go a long way to help limit [postpone] flutter. Unless you are flying 3D, it takes very little aileron movement to control a high speed plane. Using the inner hole at the servo arm and being about an inch up on the control horn end will give the best mechanical advantage [leverage] and control resolution.

RE: what is aileron flutter?
 

Yes and no. Not all pilots are fast pilots. Everyone has their own style and preference. In some cases the added power is handy. Say you're building a biplane that usually calls for a pound of added nose-weight. Why not go bigger with the engine, add no lead and run it at 75% instead of flat out for cooler running and longer life? Or, to get an upline at the same speed as a downline in IMAC or pattern. You need plenty ofpower to do that. You just have to have the discipline not to go full throttle on a level or declining course. Iknow some guys who do loops at speedwithout changing throttle. They are cantidates for catastrophic aeroelasatic flutter and it ususlly happens with the nose pointed down at the lowest altitude.


ReowoooooooowwwwzzzzzzZZZGH-BAM! "I got hit!"

RE: what is aileron flutter?
 

Ya, my servos only buzz, if I push the control sticks all the way. So it's okay like that?