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National Advisory Committee for Aeronautics, Technical Notes - Procedure for Determining Speed and Climbing Performance of Airships

The procedure for obtaining air—speed and rate—of—
climb measurements in performance tests of airships is de~
scribed. Two methods of obtaining speed measurements, one
by means of instruments in the airship and the other by
flight over a measured ground course, are explained. In—
struments, their calibrations, necessary'correction fac—
tors. observations, and calculations are detailed fer each
method, and also for the rate-of—climb tests.

A method of correction for the effect on density of
moist air and a description of other methods of speed—
course testing are appended.

The procedure required to obtain accurate measure—
ments of air speed and rate of climb in performance tests
of airships is described herein for the instruction and
guidance of those.who, without having had the benefit of
previous experience, are required to conduct such tests.
Since it is important that those who conduct the tests
should appreciate the necessity of following the correct
procedure in all details, the basis for the recommended
procedure, as well as an outline of it. is briefly given.
The paper is Written-in an elementary form and the test
procedure is outlined in considerable detail so as to min»
imize as far as possible the necessity for previous knowl-
edge of the factors involved and to atoid the possibility
of error in following the correct procedure.

The general methods of measuring the air speed in
flight are: by means of instruments attached to the air—
ship and by means of timed flight over a measured course
on the ground. The instrument method may employ one of—
the numerous types of air—speed head that measure the dy—
namic pressure. from which instantaneous values of the
true air speed can be calculated when the air density is
known, or a windmill type of instrument independent of the
air density that gives a measure of either the instanta—
neous or the average true air speed directly, depending
on the type of mechanism.