Date: Sat, 02 Jan 1999 13:15:32 -0500
From: bil kleb <w.l.kleb@larc.nasa.gov>
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 <mailto:w.l.kleb@larc.nasa.gov>

Date: Mon, 04 Jan 1999 08:10 -0600 (CST)
From: Michael Pollock <Michael.Pollock@mci.com>
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 <w.l.kleb@larc.nasa.gov>
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 <mailto:w.l.kleb@larc.nasa.gov>

Date: Mon, 04 Jan 1999 10:44 -0600 (CST)
From: Michael Pollock <Michael.Pollock@mci.com>
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.


