REFLECTOR: How Fast-flutter
Chuck Harbert
c.harbert at comcast.net
Thu Mar 22 12:11:02 CDT 2007
I think we've covered this a couple times before, but as I recall, the gist
of it was that the IAS is the thing you need to watch, but that TAS also
affects what the actual forces that can induce flutter. IOW is really both,
but for practical purposes IAS is the one you need to watch. If the Vne
(IAS) is 200 kts, you better be careful reaching or exceeding it, especially
at higher altitudes (at higher TAS), because the air load change is not
linear. The IAS Vne reduces slightly (<5%) at higher altitudes as I
understand it.
I think the more important point is what part of the V is likely to flutter.
Flutter is basically an undamped resonant vibration of a movable flight
control surface caused by air pressure loadings. From what I've read and the
responses I've seen on the Reflector, the rudders are the most likely (in a
turn), assuming you've properly balanced the elevators and ailerons. I
believe that the rudder in a turn is the weak point because it is only
positively controlled in one direction (spring loaded in the other
direction) thus allowing high airloads to overcome the spring pressure load.
The big problem with flutter is that once it starts it can very rapidly rip
the control surface from the plane which can result in a loss of control. I
think "stabbing" the controls at high speed is intended to see if flutter
shows up because it can be induced with a airfoil change. If you get a
flutter indication at less than Vne, you need to "fix it" before you attempt
higher speeds.
> From: "Tom Martino" <tmartino at troubleshooter.com>
> Date: 2007/03/18 Sun PM 11:22:24 EST
> To: "Velocity List" <reflector at tvbf.org>
> Subject: REFLECTOR: HOW FAST?
>
> OK, in speed tests this weekend, I was able to true out at 210 knots
> pretty consistently. I was at 23 inches and 2400 RPM. I still had
> throttle travel left. Flight controls were solid and no sign of
> flutter. Should I push it even further? At what point do I know I have
> gone far enough?
>
> Tom Martino
> 173 Elite RG - 300 HP (IO-540)
>
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