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One important step needs to be added for you brave souls
anticipating flutter testing.
When you "slap" the stick you need to ensure your aircraft
is in a gentle climb so that any excitation of surfaces face a decreasing
airspeed situation (putting your further way each millisecond from the critical
airspeed that might cause flutter). Also, I would not count a whole
lot on the usefulness of a parachute if you should encounter flutter - the
potentially extremely rapid disintegration of the airframe may well preclude
being able to get out and be conscious enough to deploy it. But, hey, I
would rather have one than not {:>)
Also worthy of note, a lot of debate raged about
the following viewpoint - a case was made in one of Van's Rvatiors that
flutter was a function of True Airspeed rather than
indicated Airspeed. The point was that while all other
airspeed restrictions could safely be related to indicate airspeed, Vne could
not.
The argument was that flutter was a
function of the velocity of the moving air molecules
flowing across the control surface/wing. Further while the dynamic
pressure encountered varied with both the density and velocity of the air
molecules, the excitation force (causing the flutter) was a function of velocity
of the molecules and not their density. Well, not being an aerodynamic
engineer - it got beyond me.
The point was that the True velocity of the
air molecules of an IAS reached at 3000 feet was far different
than when that same IAS was reached at 20,000 ft. And that
IF the argument was correct, then you could be far in excess of the
intended Vne airspeed.
This was all in the context of turbocharged engines
as the power output of NA engines falls off proportional to altitude and
therefore did not present the same problem relative to Vne as a engine capable
of full power at 18000.
Me? I should be so lucky to have to worry
about Vne {:>)
Just thought I would pass it one.
Ed
Sent: Sunday, July 03, 2011 3:41 PM
Subject: [FlyRotary] Re: VNE / Flutter Testing
I read somewhere (I can't recall, sorry) that basically you speed
up a couple of knots, let go of the stick, and then bump it forward and see what
happens (being ready to grab it in a hurry). the the same with elevator,
rudder, and aileron. Speed up a couple of more knots, try it
again.
The idea is that you can have a "metastable" situation where there
is no flutter until a gust of wind comes by, at which point you're 30 knots over
where it can happen, so it happens in a hurry. Creating the disturbance
yourself prevents it from being a metastable condition.
Dustin
On Sun, Jul 3, 2011 at 2:29 PM, Ernest Christley <echristley@nc.rr.com>
wrote:
On 07/03/2011 03:24 PM, Kelly Troyer wrote:
Ernest,
The procedure is to test with many steps increasing
speed in small increments always ready
to reduce throttle and increase AOA at the
slightest indication of flutter..............
Dang! I was hoping
somebody had come up with something better than that. Oh, well.
At least that gives me a "reason" to take up parachuting
8*)
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