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 degrees Page: 5 of 44
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INVESTIGATION OF THE AERODYNAMIC CHARACTERISTICS OF A MODEL WING-PROPELLER
COMBINATION AND OF THE WING AND PROPELLER SEPARATELY
AT ANGLES OF ATTACK UP TO 900t
By RICHARD E. KUHN and JOHN W. DRAPER
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 900, has been con-
ducted in the Langley 300 JMPH 7- by 10-foot tunnel. The
tests covered thrust coefficients corresponding to free-stream
velocities from zero forward speed to the normal range of cruis-
ing speeds. The results indicate that increasing the thrust
coefficient 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 qf an assumed airplane designed
for vertical take-of indicate that partial wing stalling would
be encountered at certain attitudes but sufficient power was
available for flight at any attitude. The effects of slipstream
on the variation of lift-curve slope with thrust coeficient 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 qf about 20 percent
of the propeller radius.
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 900, with the wing pro-
viding the lift and the propellers (acting as conventional
propellers) providing the thrust required for forward flight.
t Supersedes NACA Technical Note 3304 by John W. Draper and Richard E. Kuhn, 1954-
Results are presented of experimental data obtained with
a semispan wing immersed in the 'slipstream of two large-
diameter propellers, and a brief analysis of the application of
the data to aircraft combining flight characteristics of the
helicopter and conventional airplane. In addition, forces
and moments measured on the propeller, when combined
with the wing and when separated from the wing, are pre-
sented for an angle-of-attack range up to 900.
With a wing operating in the slipstream of a propeller,
large forces and moments can be produced even at very
small free-stream velocities. In this condition, coefficients
based on the free-stream dynamic pressure approach infinity
and therefore become meaningless. It appears appropriate,
therefore, to base the coefficients on the dynamic pressure in
the propeller slipstream. For the present investigation, the
coefficients based on this principle are indicated by the use
of a double prime and are defined in the list that follows.
The positive direction of forces, moments, and angles is
indicated in figure 1.
C, lift coefficient, qS/2
CL" lift coefficient, Lift
C," pitching-moment coefficient, Pitching moment
Cmp" pitching-moment coefficient of propeller,
Propeller pitching moment
AC,," increment of total model pitching moment due to
propellers, calculated from the measured propeller
cp C P inboard \"rap N0rp C /outboard
CN" normal-force coefficient of propeller,
Propeller normal force
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Kuhn, Richard E. & Draper, John W. 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 degrees, report, 1956; (digital.library.unt.edu/ark:/67531/metadc60654/m1/5/: accessed January 17, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.