Thanks, David,

You mention 10,000 ft. Some of us are looking at FL 250 or so, and THAT'S
why there are so many tears and gnashing.

Any help?

Thanks again,

Jack Ford

Cozy MKIV #882

----- Original Message ----- From: "David Carter" <dcarter@datarecall.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Wednesday, January 05, 2005 2:32 PM
Subject: [FlyRotary] Re: IAS and Vne! Whoa!


 

Vne is principally a function of CAS (IAS corrected for instrument and
pitot-static system errors) as far as we are concerned flying below Mach
0.5.  Someone just observed TAS is also a factor - but not a significant
   

one
 

below jet aircraft speeds and altitudes.

As far as "Mach tuck", we are talking about pitch trim changes that are
related to/caused by shock waves on curved aircraft surfaces where the
local, repeat, local, air speed is reaching Mach 1.0 due to speeding up to
get around the curve.  It is not something you'll get at 250 CAS at 10,000
or below.  It is NOT the "normal"/predictable pitch trim change that
   

occurs
 

as the center of pressure moves aft (further behind CG)  as angle attack
decreases at high speed/very low angles of attack (high speed meaning
   

"above
 

cruise speed", "during descent with power on", NOT up near Mach 0.8 or
higher).
   -  Mach tuck is related to "Mach number" - shock wave formation.
   

There
 

is a TAS for each "Mach number" you may consider, but the effect is due to
Mach number, not TAS.  I.e., if you fly at that same TAS but at a lower
altitude (lower Mach number) you won't have the Mach tuck.

David
----- Original Message ----- From: "John Slade" <sladerj@bellsouth.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Tuesday, January 04, 2005 10:38 PM
Subject: [FlyRotary] Re: IAS and Vne! Whoa!


   

IAS is a pretty good indicator of the amount of force acting on the
       

airframe.
That's the way I understood it. The main issue for most of us with VNE
     

is
 

the potential for flutter, and catastrophic failure of control surfaces.
However, I've read that at high TAS there's another nasty little demon
lurking called "Mach Tuck". The problem is well named, since it can
     

cause
 

an
   

unrecoverable dive where the "tucked" part can be the wings :(.
I believe Mach tuck is more related to TAS.

Here's a quote from someone who "seems to know what he's talking about"
borrowed from another list.....

"Mach tuck is an interesting phenomenon, basically it is the result of
     

the
 

CL moving back as speed increases, increasing the twisting moment of the
main wing to the point where it overrides the horizontal stabilizers'
     

(or
 

canards') capability to counteract it causing the nose to suddenly pitch
forward, and in extreme cases twisting the wings off the aircraft
altogether."

I'd love to where these nasty little buggars live, so I can avoid the
neighborhood. Unfortunately without destructive wind tunnel testing we
     

don't
   

know where they are till we find them, then we don't get much of a
     

chance
 

to
   

document it. :(

Anyone know more?

John


     

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