Analysis of Wind-Tunnel Tests to a Mach Number of 0.90 of a Four-Engine Propeller-Driven Airplane Configuration Having a Wing With 40 Degrees of Sweepback and an Aspect Ratio of 10 Page: 10 of 171
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NACA TN 3790 9
At each angle of attack, the Mach number and the Reynolds number were
held constant while data were obtained for several propeller rotational
speeds from windmilling to the maximum attainable, the latter being lim-
ited by either the maximum power or the maximum rotational speed of the
Measurements of the static pressures on the wind-tunnel walls during
the tests at a Mach number of 0.90 indicated the possibility of partial
choking of the wind tunnel. It is believed that the force and moment data
shown for this Mach number are affected to some extent by this phenomenon.
The propellers were calibrated on a specially constructed calibration
nacelle. With this equipment the thrust and power characteristics of the
propellers in the presence of the spinner and nacelle forebody were meas-
ured at several angles of attack for the range of test conditions covered
in the tests of the complete model. Also measured were the normal force
characteristics of the propellers which included an increment of normal
force due to the effect of slipstream on the nacelle forebody.
REDUCTION OF DATA
The shaft thrust (parallel to the propeller shaft) and the normal
force (perpendicular to the propeller shaft) were determined from the pro-
peller calibration at Mach numbers, Reynolds numbers, propeller-blade
angles, advance ratios, and upflow angles A corresponding to the
complete-model test conditions. The upflow angle for the complete model
without flaps and with power off was the average at the 0.7 propeller
radius on the horizontal center line of the propeller plane and was based
on the measured values presented in reference 7. These propeller forces
were used to determine the thrust parallel to the free stream and hence
the thrust coefficient Tce used herein. This thrust coefficient is essen-
tially constant with.upflow angle. Typical variations of thrust coeffi-
cient Te with advance ratio J are shown in figures 4 and 5.
The results of the propeller normal-force measurements (which include
the increment of normal force due to slipstream effect on the nacelle
forebody) obtained during the calibration of the propellers are presented
in figures 6 and 7. The conditions for matching these data to those for
the complete model were similar to those for matching Tc, except that in
this case, the direct use of the measured values of A presented in ref-
erence 7 for the complete model without flaps and power off was not suffi-
ciently accurate because of the close dependence of normal force on the
value of A. Modification of these measured values of A was made to
allow for changes in upwash due to lift changes caused by slipstream on
the wing and by deflection of the flaps. The correction was made using
a theoretical value of the rate of change of upwash angle with lift
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Edwards, George G.; Buell, Donald A.; Demele, Fred A. & Sutton, Fred B. Analysis of Wind-Tunnel Tests to a Mach Number of 0.90 of a Four-Engine Propeller-Driven Airplane Configuration Having a Wing With 40 Degrees of Sweepback and an Aspect Ratio of 10, report, September 1956; (https://digital.library.unt.edu/ark:/67531/metadc56014/m1/10/: accessed May 21, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.