Date: Thu, 08 Jun 2000 10:58:10 -0700
From: fmoreno4@postoffice.pacbell.net
Subject: speed vs altitude
To: lancair.list@olsusa.com
Reply-to: fmoreno4@pacbell.net
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References: <20000608045058.AAA8100@ns1.olsusa.com>
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The formula cited:

-------Rule of thumb for TAS:  TAS = [IAS x 2%] x [ALT/1,000 ft] +
IAS------

I believe will lead to overly optimistic results.  I have flown a Turbo Skylane RG
for 20 years and found that a closer approximation is that True Air Speed goes up
about 1% for every 1000 feet of altitude at constant horsepower.  I have used this
rule to check data from a number of other turbo aircraft and found it to be quite
close for altitude changes of up to 10-15,000 feet, and it does not deviate that
much for altitude ranges beyond this.  Thus if you assume 240 knots True Air Speed
at 3000 feet, I would guess that at the same power setting, you would get 288 knots
(plus or minus a bit due to the approximation) True Air Speed at 23,000 feet.
Incidentally, these figures are are very close to the actual performance of the
Lancair IV.

Fred Moreno.


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