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: 18 of 171
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NACA TN 3790
pitching-moment characteristics with the low tail that resemble those
with the higher tail, flaps up.
The various factors affecting the tail contribution to dCm/dCL
vill now be examined to provide the basis for explaining and interpreting
the large changes in power-on pitching-moment characteristics accompany-
ing changes in tail height or deflection of the flaps. Using the relation
expressing the pitching-moment coefficient due to the tail, equation 1,
the following expression can be written (for a constant thrust or power
condition and a constant angle-of-tail incidence):
dCmtata 1 -tail V de ld at dc I
dCL a w dc aw L d q a
at = m+ it-
and the subscript
neglected. A more
w refers to the complete model less tail. It is
that dCmti d that is, the tail lift is
accurate expression is
The values of at/aw, l-(de/d), and nt(qt/lq) which appear in equa-
tion 4 and are assumed independent of tail incidence, are presented in
figure 32 for various thrust conditions, flaps up. Similar information
is given in figures 33 and 34 for two cases of flaps deflected. The
effect of power-induced lift changes on dCL was significant as shown
by the changes in at/aw with Tc (which reflect the changes in aw). For
example, at an angle of attack of 50, flaps up, at/aw decreased from 0.74
to 0.52 as Tc increased from 0 to 0.80. By itself, this represents a
30-percent change in dCmtail. The value of at/aw with flaps up was
about the same as that wit t flaps deflected except at high angles of
The effect of power on the effective-downwash term, 1-(de/da), was
erratic (figs. 32, 33, and 34), depending as it does on such diverse
factors as changes in wing-generated downwash, changes in downwash from
--I ---- I C~-~- CC -C~eer~CTr -,~cc~Cc~--
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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/m1/18/: accessed May 23, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.