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[OM] Re: OT Mustang

Subject: [OM] Re: OT Mustang
From: Chris Barker <ftog@xxxxxxxxxxxxxx>
Date: Sat, 10 Mar 2007 19:10:51 +0000
Well, it was meant to be a humorous play on words, Andrew :-)

There is no point in declaring the maximum groundspeed of an aircraft  
because it varies with the strength of the wind.  If I fly at 560  
knots true airspeed (TAS) into a wind of 100kts my groundspeed will  
be 460kts.  If I fly with that wind "up my chuff" it will be 660kts.   
Now the speed of sound at sea level is 660kts in a standard  
atmosphere, but having a groundspeed of 660kts does not mean that I  
am supersonic.

As an example, I once flew a Tornado GR1 from RAF Marham in Norfolk  
to RAF Laarbruch in Germany.  With a jetstream from the southwest at  
our cruising altitude of around 30,000ft, we had a groundspeed of  
nearly 1,000kts (according to the nav kit) but we were flying  
subsonic, at around M0.85.

I suppose "effective" speed depends on what you are trying to  
achieve.  If you are trying to get somewhere, the groundspeed is your  
effective speed.  But if you are trying to catch another aircraft to  
wreak destruction on it, TAS or Mach Number is your effective speed.   
You will both be affected equally by the wind and your groundspeeds  
are immaterial.  Finally, if you are trying to make your best climb  
angle, you will fly at the recommended indicated airspeed or Mach  
Number to achieve that goal.

Does that make sense? :-)

Chris

~~ >-)-
C M I Barker
Cambridgeshire, Great Britain.
+44 (0)7092 251126
www.threeshoes.net
homepage.mac.com/zuiko


On 10 Mar 2007, at 08:46, Andrew Fildes wrote:

>
> I hope that's a joke - I have enough trouble with reality as it is!
> If the earth is moving with the wind (or even my wind, being a
> certified old fart) then I'm in serious trouble.
> Surely groundspeed is effective speed?
> Andrew Fildes
> afildes@xxxxxxxxxxxxx
>
>
>
> On 10/03/2007, at 6:07 PM, Chris Barker wrote:
>
>> Groundspeed is immaterial, in
>> general terms, because it changes with the wind ... ;-)
>



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