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: 14 of 171
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NACA TN 3790
previous section, that is, according to whether they arise from the
direct forces of the propeller (normal force and thrust), or whether they
result from the effects of the propeller slipstream on the wing or on the
tail. The components will be considered in that order.
Increments of pitching moment from direct propeller forces. - The
normal force of the propeller (including the increment in normal force
due to slipstream effect on the nacelle forebody) can be considered to act
in the plane of the propeller2 and the pitching moment from this source
is simply the normal force times the distance to the moment center. The
increments of pitching-moment coefficient due to normal forces created by
the operating propellers are shown in figure 18. The swept-wing configu-
ration with tractor propellers inherently has larger pitching-moment incre-
ments from propeller normal force than a corresponding straight-wing con-
figuration because the propeller must be farther forward to maintain a
given clearance between the wing and the inboard propeller tip.
The increments of pitching-moment coefficient due to shaft thrust of
the operating propellers (thrust parallel to the shaft times the distance
to the moment center) are shown in figure 19. It is obvious that changes
in the vertical location of the propellers with respect to the center of
gravity can materially affect the magnitude of these increments in
Increment of pitching moment from slipstream on the wing.- The incre-
ments of pitching-moment coefficient attributable to the effects of the
propeller slipstream on the wing and on the rear portion of the nacelles
have been calculated from the data for various model configurations and
are shown in figures 20 and 21. The method of obtaining this incremental
pitching-moment coefficient, ACmwing, was as follows:
ACmwing = Cm1 - Cm2 - aA0propeller-nacelle - Alpropeller shaft
normal force thrust
Cm1 pitching-moment coefficient of the model with tail off and with
propellers operating at the given thrust coefficient
Cm2 the pitching-moment coefficient of the model with tail off and with
and all pitching-moment coefficients are referred to the 1/4 point of the
mean aerodynamic chord.
The increments of pitching-moment coefficient due to the effects of
the slipstream on the wing are closely related to the local lift changes
which occur and their location along the span of the wing. Hence, such
configuration characteristics as spanwise position of the nacelles and
spanwise extent of the flaps are dominant factors affecting the magnitude
of this increment of pitching-moment coefficient. Referring to figure 20,
aThe pitching moment of the propeller-nacelle combination about the
intersection of the thrust axis with the plane of the propeller was found
to be negligible.
V r ---- --- - -- - ~~- -~ --~ -- --
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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/m1/14/: accessed May 22, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.