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: 34 of 171
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NACA TN 3790 33
at constant horsepower because of the relationship of thrust coefficient
and lift coefficient used in calculating the conditions (fig. 9). The
variations of the effects of the propeller slipstream with Mach number
were small, generally amounting to a change in pitching-moment-curve slope
of less than *0.05.
Effects of the Operating Propellers on the Stability
Contribution of the Horizontal Tail
The horizontal-tail contribution to stability is a function of the
downwash factor 1 - (de/da), the tail-efficiency factor t (qt/q), and
the ratio a. As in the low-speed case, calculations were made to
evaluate the effective downwash characteristics and the tail efficiency
factor with and without operating propellers. The force data presented
in reference 5 and the isolated tail-force data presented in reference 2
were used for the computations and the results are shown for several Mach
numbers in figures 62, 63, and 64 as functions of angle of attack. It
was assumed for the computation of downwash angle e and tail-efficiency
factor t(qt/q) that the Mach number at the tail was the same as the
free-stream Mach number. The effect of the propellers on downwash amounted
to a change in downwash angle of 0 .5 or less. At high angles of attack
the effects of the operating propellers on the factors mt(qt/q) and
r were sizable, however, these effects were compensating and their over-
all effect on tail effectiveness was small.
The variations with Mach number of the tail-effectiveness parameter,
dCm/dit, the isolated tail lift-curve slope, and the various factors
affecting the stability contribution of the tail are shown in figures 65,
66, and 67 for a representative level flight, high-speed attitude (a = 4o).
The effects of Mach number on dCm/dit were small with and without the
operating propellers. For the selected condition, operation of the pro-
pellers had little effect on the variations of the factors 1 - (de/da),
St(qt/q),, and with Mach number.
The effects of horizontal-tail height on the pitching-moment-curve
slopes of the model with and without operating propellers are shown in
figure 68 for several Mach. numbers. Raising the horizontal tail increased
the static longitudinal stability slightly with the propellers off at
Mach numbers less than 0.90, but was destabilizing over the Mach number
range of the investigation with the propellers operating.
-~-~L-- ~-~ TC- -~ ----- ---~~ --~~-- ----~- ~ '- -~ -~--C
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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/m1/34/: accessed May 24, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.