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This may have been mentioned already...
From what I've read the Vne is an IAS restriction. The structure reacts
negatively to apparent flow of air. The exception is with higher speed
aircraft like military jets that approach the speed of sound. Sonic waves
against the structure are the issue then and not the force of apparent wind.
The speed of sound decreases as you gain altitude so mach 1.00 is actually
slower the higher you go so the Vne must decrease (if the Vne is due to the
sonic shock waves and the aircraft cannot break the sound barrier).
Of course we are not that fast so Vne is based on indicated without threat
of encroaching on the speed of sound. At least that's the way I understand
it. ;-)
Well... that's my story and I'm sticking to it! Now back to lurking.
-Tim Peters (close to Farr)
Dalton, GA.
----- Original Message ----- From: "Jack Ford" <jackoford@theofficenet.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Wednesday, January 05, 2005 8:18 PM
Subject: [FlyRotary] Re: IAS and Vne! Whoa!
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
> >
> >
> > >> Homepage: http://www.flyrotary.com/
> > >> Archive: http://lancaironline.net/lists/flyrotary/List.html
> >
>
>
>
> >> Homepage: http://www.flyrotary.com/
> >> Archive: http://lancaironline.net/lists/flyrotary/List.html
>
>> Homepage: http://www.flyrotary.com/
>> Archive: http://lancaironline.net/lists/flyrotary/List.html
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