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: 35 of 171
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NACA TN 3790
Longitudinal Characteristics of an Assumed Airplane
Figure 69 presents a summation of the longitudinal characteristics,
as calculated from the results of the subject investigation, of an assumed
airplane operating with the power required for level flight at an altitude
of 40,000 feet. These characteristics are presented as functions of Mach
number or normal-acceleration factor. The lift coefficients shown are
computed values based on a wing loading of 65 pounds per square foot and
the assumed airplane altitude.
The effects of propeller operation at the power for level flight on
the static longitudinal stability of the airplane were small (fig. 69).
Compared to propellers-off stability a maximum decrease in pitching-moment-
curve slope of 0.04 was indicated at a Mach number of 0.70. Only a small
change was indicated in the stable variation of tail incidence for trim
with Mach number between the conditions of propellers off and propellers
operating at the power required for level flight. At constant Mach number,
the variation of tail incidence for trim with normal acceleration was not
greatly affected by the operation of the propellers at the power required
for level flight.
Figure 70 presents, for an upflow angle of approximately 00 and a
Mach number of 0.80, a comparison of the characteristics of the isolated
propeller with the propulsive characteristics of the model. Also shown
is a comparison of the variations with Mach number of the efficiency of
the isolated propeller and the propulsive efficiency of the model at a
constant thrust coefficient of 0.04.
The propulsive characteristics include the lift due to the propeller
slipstream (ref. 12) and the effects of the operating propellers on longi-
tudinal .force characteristics previously discussed. The method of cred-
iting the propellers for these effects differs from the method applied
in the low-speed case in that the effective thrust is determined on the
basis of constant lift coefficient. This is permissible whenever the
effects of operating propellers on the wing lift are small. The following
relationships were used in determining the effective thrust coefficients
and propulsive efficiencies of the model:
eff -2 (CXp on - Crops o)=cons t.
_ I ____I _I _ __
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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/m1/35/: accessed May 20, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.