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"Any help?"
Well, to comment on the 25,000' arena: From my "Standard Atmosphere ICAO
Standard Day" chart from A-7D flight manual, at 25,000' the temp is -34.5
deg C & -30.2 deg F. Speed of sound at those temps is 602.1 KTAS.
Most "Mach effects" won't manifiest themselves below maybe .8 (maybe .7 on
really thick wings?). .7 X 602.1 = 421 KTAS.
- Anyone going to be going 421 KTAS in their prop home builts?
- If so, consider me for a sponsor at the next Reno Air Races. (grins)
The A-7D "Airspeed-Mach Number Conversion" chart converts .70 Mach at
25,000' to 290 KCAS (IAS if no pitot-static and instrument error).
- If you are cruising up there with a turbo at 200 KIAS/200KCAS, then
your Mach is 0.49
- If you nose it over for your descent to landing and want to "go fast"
(don't we all!!), just keep it below 290KCAS near 25,000, 320KCAS at 20,000,
350 at 15,000', 390 at 10,000', 430 at 5,000' (if you're outside the area
where you're supposed to be at or below 250 IAS below 10,000).
- What was the Vne again? (grins)
I wouldn't worry about "Mach tuck".
David
----- Original Message ----- From: "Jack Ford" <jackoford@theofficenet.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Wednesday, January 05, 2005 7:18 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
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