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National Advisory Committee for Aeronautics, Report - Investigation of the Aerodynamic Characteristics of a Model Wing Propeller Combination and of the Wing and Propeller Separately at Angles of Attack up to 90°

An investigation of the aerodynamic characteristics of a
model wing-propeller combination, and of the wing and pro-
peller separately at angles of attack up to 90°, has been con-
ducted in the Langley 300 MPH 7- by 10-foot tunnel. The
tests covered thrust coeflicients corresponding to free-stream
velocities from zero forward speed to the normal range of cruis-
ing speeds. The results indicate that increasing the thrust
coefiicient increases the angle of attack for maximum lift and
greatly diminishes the usual reduction in lift above the angle of
attack for maximum lift.

Predicted characteristics of an assumed airplane designed
for vertical take-off indicate that partial wing stalling would
be encountered at certain attitudes but sufliciem‘ power was
available for flight at any attitude. The ejects of slipstream
on the variation of lift—curve slope with thrust coefficient for
this model could be satisfactorily estimated by means of a
modified form of a method formulated by Smelt and Davies.
The variation of propeller normal force with angle of attack
compared favorably with calculated values. An appreciable
direct pitching moment was found to exist on the propeller
itself at high angles of attack. This pitching moment was
approximately doubled when the propeller was operated in
the presence of the wing and corresponded to a downward
movement of the effective center of thrust of about 20 percent
of the propeller radius.

INTRODUCTION

Numerous schemes have been suggested in an effort to
design aircraft that would combine the take-off and landing
characteristics of a helicopter with the high-speed potential
of a conventional fixed-wing airplane. One of the proposed
arrangements involves the use of large-diameter propellers
as lifting rotors for the take-off and landing conditions. The

cruising attitude is achieved by rotation of the wing-propeller '

combination through approximately 90°, with the Wing pro—
viding the lift and the propellers (acting as conventional
propellers) providing the thrust required for forward flight.