Experiencing Flutter

[punkalouver]

Read something interesting on flutter in a safety article.

"Another area of concern is flutter, which can happen to an airplane flying too fast. The only solution is 'don't panic. Well, panic. But do it slowly. You can fly an aircraft beyond the flutter limits and recover. The last thing you want to do is jerk the controls. Panic slowly and smoothly. Don't extend the speed brakes.'"

Anybody else have advice or experience? Why not speed brakes?

I remember once as a passenger on a 727 while deviating around thunderstorms in cruise hearing some sort of wind noises and then a vibration. More than once over a period of perhaps 30 seconds, I saw the aileron vibrating rapidly for about a 3 second period. I belive it was the inboard aileron but I'm not 100% sure anymore.

[Milt]

Flutter and Buzz

Flutter usually runs away to destruction and is the bane of the test pilot. Often bonkers/exciters are fitted for flight tests near the speed boundaries to induce oscillations as forewarnings.

Modern design computer programs can predict most flutter situations as another giant leap along the track to enhanced safety.

Control surface buzz is usually transitory but should not be tolerated, often an indication of loose bearings, linkages, weakening ribs and the like.

[A and C]

Once had flutter on aleron flutter on a DR400, it started at about 110kt and dispite reducing airspeed it would not stop.

As a last resort I stalled the aircraft and this stopped the flutter and then returned to the airfield at 70kt

The problem was the aleron cables had been rigged in mid winter in a very cold hangar with a high humidity, the inccident happend in mid summer during a period of low humidity.

The cause of the flutter was low aleron cable tension as the result of expantion of the steel cables due to the summer heat and the contraction of the wooden airframe due to the low humidity.

[MrBernoulli]

"The cause of the flutter was low aleron cable tension as the result of expantion of the steel cables due to the summer heat and the contraction of the wooden airframe due to the low humidity."

Would never have happened to Biggles! He could have foreseen this problem.

[Graybeard]

Anybody else have advice or experience? Why not speed brakes?

I remember once as a passenger on a 727 while deviating around thunderstorms in cruise hearing some sort of wind noises and then a vibration. More than once over a period of perhaps 30 seconds, I saw the aileron vibrating rapidly for about a 3 second period. I believe it was the inboard aileron but I'm not 100% sure anymore.
On the 727-200, the outboard ailerons are locked out above 200 knots, so you're probably right, unless the lockout was sloppy.

[DesignerChappie]

Flutter and Buzz
Often bonkers/exciters are fitted for flight tests near the speed boundaries to induce oscillations as forewarnings.

It certainly was a requirement and probably still is to carry out flight tests with flutter exciters. Minimum crew and wearing parachutes just in case.
DC

[captjns]

On the 727-200, the outboard ailerons are locked out above 200 knots, so you're probably right, unless the lockout was sloppy.

Function of the outboard ailerons on the B-727 is based on position of outbard flaps and not speed. Movement of outoard ailerons commence with initial flap extion and increases as outboard flaps are extended to about the 15 degree position. The outboard ailerson are bused via cable from a concentric pully located just aft of the outboard ailerons when input is provided to the inboard ailerons.

[MarkMcC]

Interesting about the speed brakes...I'm not sure how I feel about that.

Depending on the nature of the flutter, I'd probably use body or tail mounted SB and be a bit more reluctant with spoilers.

In any case...if you do inadvertently overspeed the aircraft rest assured that the test folks will have anticipated the use of speedbrakes in this situation - throttle back, be smooth, and use 'em if you need 'em (unless, of course, the operators manual says otherwise!)