Date: Sat, 02 Jan 1999 13:15:32 -0500
From: bil kleb
Subject: Re: COZY: Flutter?????
mikefly@juno.com wrote:
>
> Flutter is a function of IAS.
it is also of Mach number as Mach approaches unity. however,
for our "slow" birds it can be considered a function IAS only.
(recall IAS is measuring dynamic pressure, a.k.a., q).
a simple way to examine the importance of Mach number w.r.t.
flutter is to look at the linear behavior of the coefficient of
the lift-curve slope, c_l_alpha, which is a directly related
to the pitch-induced flutter point. c_l_alpha equals,
2*pi/beta, for M < 1 and 4/beta, for M > 1,
where beta is the sqrt(|1-M^2|). so, if you plot c_l_alpha
as a function of Mach from 0 to 2, you'll find that c_l_alpha
goes to infinity at Mach one due to beta going to zero. this is
referred to as the transonic singularity. what it means is that
a small change in angle of attack (alpha) causes a huge change
in the amount of lift (c_l) produced. therefore, any small
disturbance to the angle of attack and, whammo, off go your wings.
note: we've used the _coefficient_ of lift here to "divide-out"
the effects of the dynamic pressure, q. recall, lift = C_l * q.
note: in real, non-linear life, c_l_alpha is not infinite at
Mach one due to non-linear effects, but i hope you get the idea
that Mach one is pretty special as far as flutter is concerned.
--
bil
Date: Mon, 04 Jan 1999 08:10 -0600 (CST)
From: Michael Pollock
Subject: Re: COZY: Flutter?????
re "Flutter airspeed is a function of Indicated airspeed. Right??"
Flutter is a mostly a function of CAS (Calabrated Air Speed). TAS corrected
for position and installation error. That is why one places a redline
at a maximum IAS on your airspeed indicator. There are other forces
at work at higher speeds, but much higher than your Cozy or EZ can
ever go.
Date: Mon, 04 Jan 1999 10:07:23 -0500
From: bil kleb
Subject: Re: COZY: Flutter?????
Michael Pollock wrote:
>
> Flutter is a mostly a function of CAS (Calabrated Air Speed).
true, you really want IAS corrected for position and installation
error; i.e., accurate dynamic pressure.
> TAS corrected for position and installation error.
(?) i don't understand what you're trying to say here.
CAS is IAS corrected for position and installation error.
TAS is CAS corrected for non-standard conditions.
(see http://vweb1.hiway.co.uk/aviation/pterms2.html)
--
bil
Date: Mon, 04 Jan 1999 10:44 -0600 (CST)
From: Michael Pollock
Subject: Re: COZY: Flutter?????
Michael Pollock incorrectly wrote:
> TAS corrected for position and installation error.
Bill Kleb wrote:
>(?) i don't understand what you're trying to say here.
>CAS is IAS corrected for position and installation error.
>TAS is CAS corrected for non-standard conditions.
Yes Bill, you are right. My fingers were typing faster than my brain
was thinking.