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This note is to follow up the earlier comments about Mach effects and
(more importantly) frictional heating effects on true air speed
calculations. Mike Guth wrote me and noted that his Sierra Flight
Systems instrumentation takes these effects into account, and he finds
the TAS from the SFS units to be consistently 15-20 knots lower than
that calculated with the traditional round gage corrected with an E6B.
This is consistent with what one would expect.
This stimulated an old thought. I did a presentation years ago at the
Lancair builders symposium at OSH, and I presented some charts showing
the effect. To minimize download times, I attach only one chart, for
20,000 feet. If some of you want the charts for 10,000 and 30,000 feet,
drop me a line and I will email them along.
Fred Moreno (correction curve attached)
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