gaarder (09/10/82)
Previous article had error which is corrected in this reprint. Error was
in units for Rs (sink rate); corrected to fpm instead of fps.
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A neat way to determine where to begin descent is as follows:
Beforehand; decide what approach speed(V) and rate of sink(Rs) you like
and compute;
F=(100*V(mph)) / (6*Rs(fpm)); units are miles/1000ft
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Now suppose you are at 9000ft(MSL) and wish to descend to a pattern altitude
of 2000ft(MSL):
(1) Divide 9000 & 2000 by 1000=9 & 2
(2) Subtract 9-2=7
(3) Multiply 7*F= Distance required to decrease present altitude to
pattern altitude
Example:
Suppose V=120mph and Rs=500fpm
then F=4; A factor good for all still air 120mph,500fpm approaches
and for this example 7*F=7*4=28 miles
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This method can be used for ascending, using rate of climb, instead of sink.
If you prefer knots, substitute accordingly for mph and miles.
Gene Gaarder -WECO