RE: what causes flutter?
 

A loud buzzing noise usually, sometimes followed by a pop and then silence. And then, cursing, wailing, and gnashing of teeth.

RE: what causes flutter?
 

Here's another video of flutter. It's not obvious in the real time video but in the subsequent slow motion shots, the flutter is obvious. Oh yes, loss of control is another symptom of flutter.

http://www.youtube.com/watch?v=1Z6EctoAcXs

RE: what causes flutter?
 

Joco,
Yes, you should slow down. But you sould also IMMEDIATELY land. If you experience flutter you need to get your plane down as soon as you can, assuming that it's not already destroyed. Continuing to fly after you experience flutter, and haven't found the cause, is just begging for it to happen again.

Ken

RE: what causes flutter?
 

Minn,
The first thing you will notice is a very loud BUZZ. The best way I can describe it is when we used to put playing cards in the spokes of our bikes when we were kids. The buzzing that we got when we rode really fast sounds a lot like flutter in a plane.

Ken

RE: what causes flutter?
 

Actually, IF YOU'RE LUCKY the first thing you notice is the sound.

A good number........ uh, in a bad number of the incidents, you see an explosion of balsa about the time you hear the GRRRRR !!!

Light is faster than sound.

RE: what causes flutter?
 

Yup. Saw one flutter today. Called it out, but the pilot kept flying along. It stopped, but one of these times it is going to go POOF!

In general, if you experiecne flutter something is terribly wrong with either the desigm, setup, or flying style. Circumvent the issue by setting up the plane properly and use throttle restraint.

RE: what causes flutter?
 

Very often the first sign is a model on its way to eternity, most cases of severe flutter result in crashes. On minor cases, you hear it as a usually rapid or statico sound like a flag flapping in a breeze or a rapid fire machine gun off in the distance. In two personal cases, a sound like a shotgun going off and the disappearance of the covering on the top half of a wing (landed without further damage that time), again a rapid flapping of the left half of a stab/elevator followed by it seperating from the rest of the airplane (again landed without further damage).

RE: what causes flutter?
 

I've experienced flutter a few times. I have a SPAD Debonair that in a full powered dive will exhibit wild gyrations of the tail surfaces. Due to the flexibility and strength of the construction materials, simply reducing the throttle and adding up elevator immediately eliminates the gyrations. Inspections of the plane after each instance have revealed no harmful effects.

In the other case, a plane I designed myself (see my hanger for pictures) designated as the S-3, was a great flyer. One day (July 4), the throttle linkage came off, leaving the plane at about 3/4 throttle. I continued to fly it for about another 10 minutes trying to run out of fuel. At that point, I took the plane up to about 400 feet and put it into a 45 degree down line trying to get the klunk out of the fuel. The plane gained speed as expected, and at about 200 feet we hear a very loud POP. The horizontal stabilizer had sheared off both sides. It stayed attached to the elevators and actually remained connected to the plane. When the elevator carried away, it also snapped the rudder linkage and tore the rudder off its hinges.

The plane continued to fly for another 10 minutes (it reliably pullied toward the nose into a loop, which I could use in connection with the ailerons to keep the plane in the air and over the field. Finally it go to close to the ground before running out of fuel, and the resultant debris field.

Before and after pictures.

Brad

RE: what causes flutter?
 

BRAVO! Thank you!

I've been saying this, and have been met with disbelief.


Anything you can do to PREVENT harmonics helps.

This includeds, removing slop, using stronger stiffer pushrods and control horns, etc.

One particularly effective way of reducing flutter is using multiple servos.

The other servos stiffen the control surface, prevent blowback, and deaden or eliminate harmonics.

RE: what causes flutter?
 

............And do not forget the weakest link: the hinges.
It is there where all the destructive energy of the flutter converges.

I have seen several models loosing their ailerons in flight, right after that buzz has been heard.

Regards!!

RE: what causes flutter?
 

The end effect manifests on the hinges... but the hinges are not the point that needs reviewing to eliminate flutter.

As stated flutter is a side effect of turbulence. As the surfaces move in a harmonic fashion, undue stress is placed on the hinges.

If you eliminate or dampen the harmonic fluctuations, you likewise eliminate or greatly reduce the stress on the hinges.

Doing any of the above has a far more pronounced effect than anything you could do with the hinges....

RE: what causes flutter?
 

yeap land the model after a flutter, that's how i lost one of my models. I slowed down but the fluttering bent one of the
control rods. I jammed the sticks but it wasn't enough to prevent the model from rolling.
Come to think if it...it was the right airleron.

But if there's too much of a gap from not properly mounting CA hinges, this will enhance the fluttering.
Yeap the control horns from kits or Arf arn't exaclty precision...there's play in them.

I also had a great discussion about the rear of the control surfaces. Some people say to round them.
I wasn't really sure..but I remember doing reserch on this matter. I read that you should leave them square.
Untappered control surfaces such as the airleron of a 4*

Yeah..you can hit natrual harmonics at the 12 fret or the 5th fret of the guitar. Some guitar neck are actaully not flat.
It's bowed and the lowest piont is between 5th and 7th fret becuase that's where the string vibrate back and forth the most.
It also depends on how the angle of neck is mounted to the guitar body.

Kind of like not all model's wings are flat...they'll either have wash in or wash out.

It's pretty neat to get into hobbies and learn the variouse details.

RE: what causes flutter?
 

edit: Nevermind - I heard flutter on 2 bigger planes this summer - like a machine gun, I knew exactly what it was when I heard it.

I don't know what flutter on a .40 would sound like - is it really loud?

RE: what causes flutter?
 

Loud enough that everyone at the field will look up. And it's one of those sounds that everyone agrees is a "bad" sound.

RE: what causes flutter?
 

thought so.

RE: what causes flutter?
 

Yes.

I've arrived to the field only to hear a plane fluttering like crazy, because the pilot did not recognize the sound.

Often they think that there is some loose covering or something else causing the "buzzing" sound.

RE: what causes flutter?
 

Can sound remarkably like the cyclic rate of an M60C on a doormount of a UH-1.

RE: what causes flutter?
 

Worst I ever heard and almost caused a loss of control of my own aircraft it was so sudden and frightening.

It was a three pole 428 (Q-500) race at Speedworld (PHX) The teams fly from roughly not quite between the #2 and #3 poles and you are rather close as the airplanes round two and three. The airplane that suffered the flutter occured between two and three and it was not a control surface flutter but instead the entire wing. The sudden burst of high frequency wing flutter was extrodinary.

Even more extraordinary was the fact that the airplane did not crash. Of course the airvalve was shut down immediately and the gentleman was able to land. On that shoulderwing airplane four bolts secure the wing and both rear bolts were missing. Its not clear if the ossilations backed out the bolts or perhaps poorly tightened bolts had precipitated the incident. The only thing holding the wing was the two forward bolts at the leading edge and the trailing edge could flop up and down about an inch.

John

RE: what causes flutter?
 

Yeah, that is a very scary sound on a large or fast model. I saw a 35% flutter off a wing on a maiden flight. One of the most terrifying things I have ever seen as it happened on a pass right down the runway. The whole wing fluttered, snapped the wing tube, total loss. The pilot you mentioned was very lucky to have a plane after the flutter.

RE: what causes flutter?
 

Nobody here has mentioned using adequate servo's. Or am I way off base here?

RE: what causes flutter?
 

Using adequate servos is an obvious help - as is good linkages with no slop. But on some planes, especially those with large control surfaces, even proper setups won't help IF you hit the right frequency.

RE: what causes flutter?
 

Weezle, true, looking at the high end, jets, giant scale, etc., where flutter would be a total disaster, the issue is generally circumvented by proper selection of servo and linkage and good building techniques such as decent hinges, proper installation, and minimal hinge gaps. Basically everything mentioned in this thread EXCEPT the mass balance. You will rarely if ever see mass balances in jets/giant scale 3D, etc. This is because the mass balance often creates more problems than it solves in our models due to the lack of stiffness in the control surfaces, which is in turn due to the building materials we use.

RE: what causes flutter?
 

I have a model that suffered flutter, the Dynaflite Fun Scale P51D 40 size in my avitar beside this post. It was on an early flight in its life, maybe it's 6th or so. The airframe was built by a friend many moons ago, never flown, and given to me.

That friend flies with us now, so I offered him a chance at the stix on his old airframe. He was used to lightweight parkfliers, and found the power of this plane intoxicating (AX46, 105mph s&l, unlimited vert). He roared about at full throttle at least 4 mistakes up, grinning from ear to ear. He dove full throttle, and abruptly pulled out.

It sounded like the engine had lost a muffler and was running roughly (it wasn't). Didn't take us long to spot the right side hori stab doing a good impression of a flag in a huricane. The plane handled normally. It did sorta sound like automatic weapons fire.

We got her back, and post mortem revealed a failed glue joint on the elevator joiner. With the non-driven elevator half free, it fluttered and tore the stab half-off.

Ran outa elevator on approach, and had to land hot, but landed anyway. Rebuilt the stab (harder balsa, thicker, carefully airfoiled), and now she happily stands hard pull-outs from terminal power dives.

J

RE: what causes flutter?
 

Bump this thread up for Bret

RE: what causes flutter?
 

That'll make for a fun landing! :D