William, At the PFA today I was told that the radar trace of William's plane
showed it was going at 90 knots or so. He would have done his Vne dive
somewhere on the way back from Cornwall - all very perplexing.
Did my Permit renewal test flying today and didn't like to ask
someone to come along as ballast/observer!
Regards, David Joyce
----- Original Message -----
From: "William Harrison" <willie.harrison@tinyonline.co.uk>
Sent: Friday, June 22, 2007 5:31 PM
Subject: Europa-List: Wikipedia's entry on flutter
> 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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