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National Advisory Committee for Aeronautics, Report - Negative Thrust and Torque Characteristics of an Adjustable Pitch Metal Propeller

This paper presents the results of a series of negative
thrust and torque measurements made with a 4 foot
diameter model of a conventional aluminum—alloy
propeller. The tests were made in the 20-foot propeller-
research tunnel of the National Advisory Committee for
Aeronautics.
The propeller was tested for thrust and torque through
a blade-angle range from 22° to ~23° at 0.75 radius
and a V/nD range from zero to infinity, while mounted
in front of a cowled radial-engine nacelle. With this
arrangement the drag of the propeller was also measured
through a blade-angle range from 0° to 90° while locked
in a vertical position. Additional tests were made with
the propeller and nacelle located in two positions with
respect to both a monoplane wing and a biplane cellule,
in which smaller ranges of blade angles and values of
V/nD were covered.
The results show that the negative thrust is considerably
afiected by the shape and size of the body behind the
propeller, that the maximum negative thrust increases
with decrease in blade-angle setting, and that the drag
of a locked propeller may be greatly reduced by feathering
it into the wind. Several examples of possible applica-
tions thhe data are given.
Wind-tunnel tests of both model and full-scale
propellers through the ordinary ranges of air velocity
and revolution speed have been quite extensive. Very
few tests of propellers operating under conditions of
negative thrust and torque have been made, however,
because conditions of negative thrust and torque
are encountered’only in dives and fast glides and these
maneuvers in nonmilitary airplanes are relatively
unimportant. The recent development of the con-
trollable-pitch propeller has broadened the field of
use for negative propeller thrust and has therefore
created new interest in the subject.