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National Advisory Committee for Aeronautics, Technical Notes - The Dynamometer Hub for Testing Propellers and Engines During Flight

The need for a "FLYINGPTEST BENCH" to enable measurements
of filight resistance, engine and propeller power and efficienq
to be made during flight was experienced in interested circles
as early as 1915, and it grew in proportion to the constant de—
mand for increased flying capacity in our military types.of
aircraft.

The problem Was workedlout in various ways by the German
Aeronautical Laboratory (D.V.L.) at Adlershcf. Unlike the method
observed-in the actual flying test—bench, where the engine must
be so installed that it can work freely, a Dynamometer Hub was
inserted between the engine and the propeller by the D;V.L.

It was approved of as an accurate measuring device by the Pro—
peller Testing Department of the Technical Section of Aviation
(Flz.)-at Adlershof, and was accordingly constructed.there.
Measurements of stress are alga taken in this case by manometri-
cal pistons constructed by the D.V.L. in accordance with the
patent taken out by Professor BENDEMANN, who readily acnsented.
to its being utilized. by the D.V.L. -The Flz. developedi the :10-
vioe into a. thrust-d'miamometer only —- its. original purpose was.
that of measuring propeller thrust - while a. still newer type
rendered. it possible'to measure torque moment also. After fav—
orable test—bench results had been obtained, the first flight;
tests were made with the dynemometer hub in the spring of 1917,
.and further good.- results were obtained in numerous flights. '_ _
The efficiency of the engine could, however, -be determined}. by
the transposition: of calculations. of its. power at the'test—beneh.
It 'would. take up too much space to give a. detailedi account of
the tests, “which are but of minor importance.

e propeller is not rigidly secured. to the engine (zone,
but is free to revolve or to move: towards the; sense. The trans-
mission of torque from the engine to the propeller,- and. the:
tranmission of thrust“ from the inropeller to the engines takes
place: through dynamometrieal pistons by whimh both tor-ope and:
thrust. may he meashred'.