Cactus.

My Feedback: (1)

i do remember seeing ages ago from the back of a boat that little wirlpools would form on one side, detach and float away, then one would form on the other side and float off, this kept going. i was told this is the same on the control surface and this caused flutter. it is also what causes skyscrapers to sway.

JimTrainor

Somewhere on the net there is a video of scale model glider, fiberglass, with the entire wing oscillating badly. The movie shows the pilot gliding it for a safe return - the whole way the wing is oscillating. The sound is something like a saw blade flexing back and forth. The wing deformations are plain to see.

I've seen it.... but I can't locate it now. Perhaps someone else knows of it and can post link.

Rotaryphile

The surest way that I can think of to get intentional rudder flutter would be to add weight to the trailing edge at the top. This will have the opposite effect to that of a mass balancer. I would gradually add weight (assuming that your CG can stand it) until flutter starts. Flexibility in the rudder and fin will also tend to cause flutter, and less weight will be needed at the trailing edge with a somewhat flexible vertical tail.

whiplash2

Attached, is an image of a “just for the fun of it” type experiment. This airplane was built in about an hour, using only ¼ Luan ply-wood [the cheap stuff], dry-wall screws and a piece of 2x4. Total weight was about 6 pounds, wing plan was Q-500, 50”x10”, no airfoil shape, the wing was not stiffened in any way, the leading edge was just a flat cut edge with no taper. We had a worn-out K&B .61 on the nose with muffler, 3 channel control, throttle aileron, elevator. The idea was really just to see if it would fly. The big surprise was that it flew very well, better than a few trainers I have flown. The only bad habit it had was, ‘Wing Flutter” above ¾ throttle. Above a certain flight speed (I’m guessing about 50-60 mph) the wing (the entire wing) would start to oscillate span-wise at 3-4 HZ . This phenomenon was very predictable and controllable with changes in throttle in level flight. And yes you could see it happening very easily.

This experiment eventually lead me to build another airplane I refer to as the “Twister”. I used this airplane to explore minimum wing torsional stiffness. The right wing panel is made of segments that are allowed to rotate about the M.A.C., two elastic spars run thru the segments and are controlled by a small winch at the root section. The aero-elastic properties of the wing can be changed in flight.

Montague

Ok, so, would that first one be a SWAD?

William Robison

My Feedback: (3)

Montague:

Nope. Still a SPAD. Instead of "Plastic," this time it's "Plywood."

Just like your girl's new sleek dress of "Man-made" fiber is a Simple Polyester Attractive Dress.

Haw.

Bill.

PigMan Buggerus

My Feedback: (6)

I gotta tell you Bill, you truly are a bird of a different feather. Keep 'em coming they're great!

William Robison

My Feedback: (3)

Allan:

One for you from a newspaper item:

Stealing Pigs? Allan Denies!

or:

Sauteed Pork, Allan Dines.

And a last one, from recent history:

Spinning Propellor -> Allan's Digits.

Do you have them working OK now? Hope so.

Bill.

PigMan Buggerus

My Feedback: (6)

Yeah they are doing OK. The middle finger is just a little shorter, so I guess I can't flip people off as well with my left hand now. The index finger is shorter as well, but it is from the break, nothing was actually removed from the end. Both fingers have almost full range of motion again. The only thing that really isn't up to snuff yet is the motion in the last joint on my index finger. But all in all, I can't complain after the damage I put them through.

William Robison

My Feedback: (3)

Piggy:

Good to hear you've gotten that much back.

It was a gruesome affair, an experience which I'm pleased to say I have not experienced.

At least to that extent.

Many is the time I've had skin removed, but that was in the days of almost everything being hand propped.

A hazard of the game, one that got everybody.

Bill.

JimTrainor

Flutter video:

http://www.beardsleys.net/dave/index.htm

Go the the "Videos" page, then select the forth link on the page, titled "Shaking Apart".

The video shows a glider's wings fluttering in flight.

Ben Lanterman

Very impressive, is that ailerons I see trying to depart the wing? I think I will chick out my hinges before I fly the next time.

Rotaryphile

Having been bitten by destructive flutter too many times, I now put mass balancers on the ailerons and elevators of everything I build. They would, in all likelyhood, have prevented that glider's flutter.

William Robison

My Feedback: (3)

Rotaryphile:
Disagree sir. The control surfaces were not in flutter, it was the wings themselves. The flapping ailerons were the effect, not the cause.

Bill.

Rotaryphile

It is entirely true that a wing does not require ailerons to get into flutter, but in this case, the ailerons appear to be deflecting downward as the wing deflects upward, and upward as the wing deflects downward. This is the classic mechanism for aileron-induced flutter, where the out-of-phase movement of the ailerons generates aerodynamic forces that reinforce the flutter. When an aileron deflects downward as the wing is moving upward, the downward movement of the aileron imparts additional lift to the wingtip, tending to cause the wingtip to deflect farther upward. Then, when the wing rebounds, the aileron deflects upward, producing additional force in the opposite direction, and thus continuing to reinforce the vibration.

Ben Lanterman

Right, there are several mechanisms for flutter of a wing with and without ailerons. Applies to any aerodynamic surface. The magnitude and rate are dependent on structural rigidity or lack of and the magnitude of driving aero forces.

The first is flutter on a wing that is being driven by the unsteady aerodynamics about the wing spanwise axis. The ailerons are rigid or not there at all.

The second case is when the wing is rigid but the ailerons and or their mechnaism are loose or flexible allowing flutter of the surface.

The Third is the flutter of both at the same time and is probably the worst case in magnitude of the oscillations.

For the distance the movies were taken it was difficult to determine which came first but surely regardless of whether it was one or two that started it the third case developed almost instantly.

Flutter being the destructive force that it is often causes a tight aileron to become loose. That can be recovered from, maybe, as long as the wing doesn't disappear :-)

As soon as flutter appears it would be advisable (in the case of a glider) to pull up and knock off some airspeed.

William Robison

My Feedback: (3)

Rotaryphile:

No argument. But in this case the period is way too long for it to be aileron induced.

Bill.