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From: "Jack Ford" <jackoford@theofficenet.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-593631@logan.com>
Subject: Re: [FlyRotary] Re: IAS and Vne! Whoa!
Date: Thu, 6 Jan 2005 11:40:31 -0800
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Bless you Brother!

John, give us some more turbo reports.

Jack Ford

----- Original Message ----- 
From: "David Carter" <dcarter@datarecall.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Thursday, January 06, 2005 11:22 AM
Subject: [FlyRotary] Re: IAS and Vne! Whoa!


> "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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