tony0707

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

FlyingGatsby

So servo buzzing=/=flutter?

littlera

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)

Charlie P.

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.

Charlie P.

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.

Lnewqban

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

freakingfast

My Feedback: (3)

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.

RCER88

My Feedback: (25)

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.

opjose

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.

Gooseman240

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?

littlera

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

Charlie P.

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 & 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.

combatpigg

My Feedback: (3)

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.

Charlie P.

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!"

FlyingGatsby

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

opjose

Well not really... ( with exceptions... )

This indicates that the servos still want to travel more, but the control surface is at it's limit.

With the plane on, put your computer controlled TX into setup mode, and LOWER the travel adjustments as you keep the sticks to their extremes.

Try to adjust the TX so that the sticks can still move to the extreme, but the servo buzzing stops.

combatpigg

My Feedback: (3)

The better fix is to rearrange the linkage to limit the amount of excess travel. In doing so, you will also increase the control resolution [finer control] and allow the servo to operate closer to it's max rated torque.

FlyingGatsby

How do I do this?

opjose

Yup, he is correct. That is a better solution.

What you do is move the the point where the linkages connect to the servo horn "in" towards the servo horn screw, and then the linkage at the control surface "out".

You can do this a hole or two at a time.

As you move the servo linkage side in and the other out, you increase the lever moment of the servo, increasing force.

As you'll recall from high school physics, you are adjusting the fulcrum.

At the same time this reduces the amount of control surface travel.

Typically I will turn the TX's travel rates UP as high as possible then make these adjustments so that I get the movement I desire from the control surface.

In your case the servo is trying to push the control surface futher than it will move, causing the binding you are experiencing.

With the above you are effectively reducing the total travel amount and at the same time gaining more torque, which will help prevent flutter and give you more precise TX control.

Remember that ideally at ANY stick extreme on the TX, your servos should move to the extreme, then go quiet, having reached the commanded position.

If they are not able to get there, you get buzz.

Lnewqban

Graphically:

FlyingGatsby

Thanks for the explanation, and the diagram, guys

And ophose, what about if my ailerons use torque rods? The torque rod out has 1 hole, on the controll surface.

Lnewqban

The torque rod should be threaded and the horn should be able to be lowered or rised for adjustment.

Check this thread with a good diagram:

http://www.rcuniverse.com/forum/m_60...tm.htm#6088779