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.