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From: "DaveLeonard" <daveleonard@cox.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Subject: RE: [FlyRotary] Re: IAS and Vne! Whoa!
Date: Wed, 5 Jan 2005 06:22:01 -0800
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Importance: Normal

My RMI encoder has the ability to display speed in Mach number as well.
However, I believe that when top speed is a function of Mach number it is
not a flutter issue, but an issue of localized trans-sonic airflow on the
airframe - usually around the engine intake.  I doubt that the Lancairs are
experiencing issues with near sonic air flow except possibly at the
propeller tips.

That being said, mach number is going to more accurately represent a given
TAS than would the IAS (mach number would be even more conservative as it
will increase slightly as you go higher while IAS decreases significantly -
given you are flying at a fixed TAS).  I am sure the Chelton has the ability
to display TAS as well, so I wonder why they use mach number instead of TAS.
It could be for the propeller tips but more likely just to sound cool.

Maybe I will start flying around with mach number on display and see how it
goes.  ;-)

Dave Leonard


>
> "Ed Anderson" <eanderson@carolina.rr.com> wrote:
>
> """
>   The bottom line is that at the higher altitudes your indicated airspeed
> gauge
> can be showing you safely below the Red Vne mark but, your True
> Airspeed may
> be exceeding Vne by a considerably margin putting your airframe in a
> potentially danger zone of flutter.
> """
>
> The Lancair IVPs, being designed for turbocharged flight, spend
> most of their
> cruise time in the flight levels.  Vne for that aircraft is mach
> .52... the
> Cheltons (and other glass cockpits, I imagine) have the ability
> to monitor
> that speed directly, and Vne is adjusted and displayed based on
> altitude, OAT,
> etc (ie, TAS).  The Vne parameter is entered as a mach number in
> the Chelton's
> setup mode.  Pretty amazing stuff.
>
>    <Marv>
>
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