Aileron flutter, or "What the hell is that noise??"

[mrbonk]

I had a full-on 'brown trousers' moment with my Faser today. After hooking into some fabbo lift, I decided to do a speed run from *way* up there. About 1/2 way down, I suddenly heard "BRRRRR", which rapidly developed into "BRAAAAAAAAAAAAAP", after which I discovered I had no aileron control :eek: Dale reckons it sounded like the exhaust brake on a truck!! Turns out it broke the servo horns off both aileron servos at the same time. Not cool!!

I had to mush around with the flaps down to stop the ailerons from flapping while I was trying to get it on the ground using only the rudder for directional control. What a pig! Even with full rudder deflection, it would still turn the opposite way when the wind caught it. After narrowly missing the windsock pole, the pits and 2 parked cars, I finally got it down just next to the pits.

Total damage? 2 broken aileron servo horns and......that's it!! I reckon I was probably the luckiest guy in gliding today :D

[atmosteve]

Was there any slop to begin with, that can help set them off.

Did the horns seperate from the ailerons, or did they rods seperate from the servo arms - just curious.

Hey, I've almost hit that windsock pole too! I hope to see you guys at Goodwood soon, keep them thermals warm for me.

Cheers,
steve.

[Andy W]

http://awilletts.ezonemag.com/worthless.gif
..a

[mrbonk]

Was there any slop to begin with, that can help set them off.

Actually, the control system was pretty tight. It was *really* hammering down though....pretty much terminal velocity stuff :D

Did the horns seperate from the ailerons, or did they rods seperate from the servo arms - just curious.

The arms of the servo horns sheared off right at their bases.

[mrbonk]

http://awilletts.ezonemag.com/worthless.gif
..a

There's nothing to take pictures of (thankfully)! I've already thrown the broken servo horns in the bin...

[Andy W]

That's a weird one.
..a

[AstroDad]

Dale reckons it sounded like the exhaust brake on a truck!!

I have been there with my first trainer glow plane which was slightly overpowered and set up with a single servo to control both ailerons, there was a lot of slop in that system.

At first I thought the engine was roaring and did several high speed passes to admire the rumble, not understanding what flutter was. Then one of the ailerons busted off and I understood flutter and managed to land safely even though I was missing an aileron.

the noise was quite cool, while it lasted. It might be fun to design an accessory to an airplane that is designed to flutter and make that roaring noise without self-destructing.

[Libelle201B]

Actually, the control system was pretty tight. It was *really* hammering down though....pretty much terminal velocity stuff :D



The arms of the servo horns sheared off right at their bases.It would be interesting to set up a small jig of sorts and see how many inch pounds of force it takes to shear them like that. I'm also surprised that it didn't effect the servo gear train (metal Gears?) Glad that you were able to save your sailplane. I gues you now have a better idea of your planes VNE :)

[Anker]

Actually, the control system was pretty tight. It was *really* hammering down though....pretty much terminal velocity stuff :D



The arms of the servo horns sheared off right at their bases.

If the linkages were tight you probably had inadequate resistance to twist. The best way to increase twist resistance is to face the aileron control surface with bias S-glass (1.5 oz) or Kevlar (1 oz). In a pinch you can use regular glass, it will still help.

I face by first creating a sheet of glass and epoxy on a piece of Mylar. I lay the glass on the Mylar, saturate it with epoxy, lay a second sheet of Mylar on top and throw it in a vacuum bag to cure and pull excess epoxy out. Once its cured I cut it in bias strips that I epoxy to the exposed foam in the hinge cutouts. When the epoxy has set the excess is easily cut and sanded off.

Anker

[lesterpk]

One of the best way to stop flutter is to bond the servo to both wing skins. Some models have sub ribs in the wings which do the same thing as it helps prevent the wing from twisting and fluttering.
Les.

[mrbonk]

I'm also surprised that it didn't effect the servo gear train (metal Gears?)

Yeah, DS362s, both of which are fine.

Glad that you were able to save your sailplane. I guess you now have a better idea of your planes VNE :)

I don't think I'll be going back there for a while :eek:

[mrbonk]

If the linkages were tight you probably had inadequate resistance to twist. The best way to increase twist resistance is to face the aileron control surface with bias S-glass (1.5 oz) or Kevlar (1 oz). In a pinch you can use regular glass, it will still help.

It's a full carbon Faser, so I doubt I could improve the design beyond what it is already :) I suspect my problem was simply inadequate strength in the servo horns. It's been pointed out to me that I should have used the stronger horns that came with the servos, so they've now been changed!

[Anker]

One of the best way to stop flutter is to bond the servo to both wing skins. Some models have sub ribs in the wings which do the same thing as it helps prevent the wing from twisting and fluttering.
Les.

You can tell from the frequency whether its the wing or its the aileron. The brrrrrraaaap is typical for aileron flutter. Wing flutter is more of a whop-whop-whop sound.

Anker

[bundyglida]

The issue was with the horn used on the servo. They were the smallest ones that are attached to the servo when you pull it out of the box.
I would have suggested that MRBONK change them before flying if I had known that he had used them.
We don't show to much respect to our mouldies sometimes....'beefy' makes for much stronger fun times...or something like that :confused:

[mrbonk]

"Whoops, I did it again....."

I got another HUGE "get out of jail free" today. I blew another aileron on the Fazer, but this time it was because I'd used the nylon clevises that were supplied with the glider. In a speed run, one of them ripped off the end of the pushrod.......oh man. After it detatched from the rod, it flipped up and jammed between the upper skin of the wing and the aileron, locking the aileron into a ~15deg down position. Not good! With full right aileron, full right rudder and full flap, I could *just* get it to go straight. If I backed off any of the controls, it went into a spin almost immediately. Luckily I still had some height to come to grips with the new method of control and I managed to get it down unharmed again. Needless to say I'll be changing to steel clevises now!

[Mark Miller]

We had a fellow club member who used the smallest arms that come with the JR 368's. He blew his aileron arms up on the transition in the zoom. The Perfect is now repaired and he is using the regular arms. Rock solid now.

Mark

[mrbonk]

I seriously underestimated the potential stresses on the hardware in one of these comp gliders. I figured if my 3D heli can get away with plastic ball links etc, I should be fine. Clearly I was mistaken!

[tonyestep]

Ah, Mr Bonk, you are reliving my worst moments. I have sheared clevis pins, ripped clevises out by stripping all their threads, and sheared the arms off right at the servo wheel. When you launch an F3B plane like the Fazer from mono, your ailerons want to flutter if they can. A slop-free linkage with unbreakable parts and a solidly mounted servo will hold everything.

To get a typical F3B zoom, the plane will be traveling between 105 and 115 mph at the bottom of the zoom. And a properly set-up plane will have elevator to flap mixing, which adds to the loads on the flap and aileron linkages at pushover and pullout.

The Fazer is a strong, strong plane. Make the linkages strong too, and it'll survive any launch. For a lot of planes, the next thing to go will be that the stab will fold, but that probably won't happen with your plane.

Good luck!!

[lineofsight]

... For a lot of planes, the next thing to go will be that the stab will fold, but that probably won't happen with your plane.



How do you know that, Tony?

Chris

[tonyestep]

Becuz if the stab on any plane will fold, I will be the guy who folds it. Actually I've never had a Fazer but I have a Stratos 6. It's so similar that I am assuming that since I've never folded the Stratos stab, the Fazer won't fold either. Besides, I watched Ben Clerx launch his Fazer in the most stressful way possible with no flex in anything.

[bundyglida]

Mr. Bonk, If you had bought a better quality airframe like my EUROPHIA, then you probably wouldn't have these problems :p
About the only thing standing up to your punishing flying is the servoframes that I gave you.
But you are learning 'grasshopper' strength and slop free, is key to many happy flight

Oh, by the way, that's the last time I chase you down from 1500ft :D
Let me go first next time to avoid being 'flown through' :cool:

[mrbonk]

Mr. Bonk, If you had bought a better quality airframe like my EUROPHIA, then you probably wouldn't have these problems :p

Or maybe like that Exploder you were thinking about getting :eek: At least I wouldn't have to worry about flutter.....it'd already have blown up on the winch :o

[bundyglida]

Yes! for once, I made a good choice I think, the PIKE PERFECT should serve me nicely in the very near future......now hurry up and get my servos in you slack '#*#'
Or maybe like that Exploder you were thinking about getting :eek: At least I wouldn't have to worry about flutter.....it'd already have blown up on the winch :o

[tom43004]

I've heard wing flutter at the higher frequency as well. It depends on the stiffness of the airframe. Often the frequency of aileron flutter is so high (buzzing) that you don't recognize it as flutter, or it's so high that you don't hear it until it develops into a more serious condition.

Even molded ships have their limits. I would do things with my Pike Giant that I would never consider doing with my Eraser (very similar to the Fazer.) They're different airframes and the Pike is made to go fast. The Eraser not so much.

Consider yourself lucky to have the ship safe and sound, and NEVER use nylon on anything that will go faster than you can run.

Fazer = $1300
A dozen steel clevices = $6
Tide stain stick for your undergarments = $4

Tom Siler
Columbus, OH

[rdeis]

I remember an old floating poly giant that would flutter at ~15mph.

The thing sounded like a B-17.

Then there was the Legionaire with the divergent flutter mode- I never saw one come apart, but I'm told that it never buzzed first because you only got 1/2 of one flutter cycle before the wing exploded.