Dear All
Wikipedia has a small entry on flutter (see below). This refers to a
critical airspeed for a given system. It reminded me that on the only
occasion I flew an aircraft which fluttered (ailerons on a badly
rigged Jodel D9) there was a critical airspeed above which the
flutter started, below which it stopped (it never progressed to
anything more than a side to side shaking of the stick and we cured
it eventually by reducing the droop of the ailerons). Anyway, the
issue about a critical speed begs the following question: if, despite
all the measures we are all about to take to prevent flutter on our
Europas, it does start to happen again to one of us, would there be
time to arrest the flutter by smartly reducing airspeed before
catastrophic damage occurs?
In addition to the many other unanswered questions about William's
crash is this: Why did it happen WHEN it happened? If there was slop
somewhere in the system, it would presumably have built up slowly
over time, so why did it go catastrophic when it did? Someone said
yesterday, I believe, that the aircraft had just had its Permit
Renewal Inspection, which is normally followed by the test flight
including Vne dive. So, could it have been a speed-triggered flutter?
By the way, correspondence on this site some time ago about what Vne
really means revealed that some people do not regard the 165kts Vne
as a velocity never to be exceeded. Could the crash aircraft have
been going faster than 165kts? Or maybe it was just going a lot
faster than it had been for a year and that was enough.
The link to the story of the Tacoma Narrows Bridge in the Wikipedia
entry is worth following. Also, worth watching the video link in the
same entry of the bridge fluttering towards its collapse - like a
slow motion version of a tailplane. The bridge was resonating in
torsion but other modes of vibration, including bending can be
involved. Can anyone comment on whether tailplane flutter is more
likely to involve torsional or bending motion (in the torque tube and/
or the fuseage)?
Willie Harrison
Flutter
Flutter in aircraft structures, control surfaces and bridge
engineering, aeroelastic flutter is a rapid self-excited motion,
potentially destructive, usually present above some limiting aircraft
speed
Flutter is a self-starting vibration that occurs when a lifting
surface bends under aerodynamic load. Once the load reduces, the
deflection also reduces, restoring the original shape, which restores
the original load and starts the cycle again. In extreme cases the
elasticity of the structure means that when the load is reduced the
structure springs back so far that it overshoots and causes a new
aerodynamic load in the opposite direction to the original. Even
changing the mass distribution of an aircraft or the stiffness of one
component can induce flutter in an apparently unrelated aerodynamic
component.
At its mildest this can appear as a "buzz" in the aircraft structure,
but at its most violent it can develop uncontrollably with great
speed and cause serious damage to or the destruction of the aircraft.
Flutter can also occur on structures other than aircraft. One famous
example of flutter phenomena is the Tacoma Narrows Bridge
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