Flutter

[NeilG 0]

Having just watched a documentary on the development if the 747, it seems that one of the phenomena that needed to be contended with was something called ‘flutter’, a massive vibration throughout the aircraft at certain speeds and height which was capable of breaking an aircraft, even a 747, apart. I couldn’t quite tell what was done to allow the aircraft to contend with this problem so am putting the question out there. Also was wondering if there are conditions now in which an aircraft could encounter this difficulty and what it is that a pilot might have to do to deal with it.

[skelsey 765]

There may well be some aeronautical engineers around who would be able to answer this in a better way than me, but fundamentally flutter is a situation where one or more control surfaces begins to oscillate, usually as a result of the nature of the airflow (particularly, but not exclusively, at higher Mach numbers where the movement of the shock wave from supersonic airflow over the wing may cause a disturbance/a different pressure distribution over the affected control surface etc).

Solutions can include balancing the affected control surface with weights, for example, or a more high-tech approach could use flight augmentation computers as part of a fly by wire system. 

High-speed (as in >200kt or so) aircraft can be very sensitive to flutter. As aircraft speeds increased through the 1930s the RAF had to move the roundel markings from the tail/rudder area to the fuselage on some types as it was discovered that the thickness of the paint used to depict the roundel or fin flash was sufficient to unbalance the control surfaces and induce quite severe flutter.

[Ephedrin 418]

Fluttering is actually nothing that is restricted to aircraft but can occur to anything that is exceeding its structural limits in a certain medium. An airplane obviously moves through air and at a certain mach level the airflow will cause these flutters. The how and why will be down to the explanation of an aviation engineer but I know you can also find this effect on cutting tools. For example a hard metal milling cutter will start to flutter when its capability (rpm, feed) is exceeded which will be audible as a sqeaking sound like chalk on a blackboard. It doesn’t mean that it will break immediately but the risk is high. It‘s relatively similar in its cause although obviously looks differently. 

[downscc 1,327]

Flutter was a major design hurdle during the 50s when the Air Force was testing the first trans-sonic and super-sonic aircraft.  A few tests simply self destructed.  Today the engineers have a thorough understanding of this and the tools to avoid it before they even get to a wind tunnel.

[overspeed3 410]

Is it time for a FlutterNutter?

 

                                                                 Jerry Neidick

Edited February 21, 2019 by overspeed3

[jcomm 5,889]

Glider pilots know it well...

We hate it....