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National Advisory Committee for Aeronautics, Technical Notes - Determination of Propeller Deflection by Means of Static Load Tests on Models

This note describes a simple and inexpensive method for de~
termining the deflection of propeller blades under operating
loads. Both the centrifugal force and air force loads are ap—
plied statically as a number of concentrated loads by means of
weights and wires. Two methods Of attaching the wires to the
propeller blades have been tested, both giving approximately the
same deflections. The method is considered useful for studying
the deflections of propellers of different shapes under various
operating conditions.

Aeronautical propellers deflect when operating. In fact,
for every different condition of operation, i.e., every combina—
tion of air speed, revolutions, altitude, etc., a propeller has
a somewhat different shape. This is because the centrifugal
force and air force loads, which produce the deflections, vary in
magnitude individually and in relation to each other. The great—
est deflections take the form of a bending and a twisting of the
propeller blades, both of which are an indication of stresses in
the material. The twisting, however, also affects the pitch of
the propeller and consequently its aerodynamic performance. A
knowledge of the deflections is therefore of interest both from
the aerodynamic and the structural points of view.

Unfortunately, the stresses in a propeller are of so compli—
cated a nature that it is practically impossible to calculate
either the stresses or deflections with any degree of accuracy by
means of methods known at the present time. This makes experi~
mental methods necessary in order to study deflections. A simple
method has been devised in which both the air load and the load
due to centrifugal force are applied_to a propeller blade static—
ally by means of weights, and a description of crude apparatus
which was used for a preliminary trial of the method is given in
this paper.