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: 13 of 171
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NACA TN 3790
propeller operating with wing flaps up or with either of the two flap
configurations. A check showed the differences in lift-coefficient incre-
ment for these various conditions to amount to less than 0.01.
Increment of lift from slipstream on the wing.- The increments of
lift coefficient attributable to the effects of the propeller slipstream
on the wing and rear portion of the nacelles have been calculated from the
data for various model configurations and are shown in figures 16 and 17.
The method of obtaining this incremental lift coefficient, CLwjng, was
ACOLing = CL - CL - ACLropeller-nacelle - p 'Apropeller shaft
normal force thrust
OCL lift coefficient of the model with tail off and with propellers
operating at given thrust coefficient
CL2 lift coefficient of the model with tail off and with propellers off
This increment in lift coefficient includes power effects on the rear por-
tion of the nacelle and all wing-nacelle interference resulting from the
slipstream. Referring to figure 16, it may be se8n that with flaps up,
ACI ring wqs negative at angles of attack below 4 or 50, despite the
fact that portions of the wing immersed in the slipstream were operating
at section lift coefficients of the order of 0.35, power off. Comparison
of ACwIng for both propellers operating (flaps up or flaps down) with
the sum of values of ACwin measured for inboard and outboard propellers
operated independently generally shows some positive interference lift.
In regard to figure 17, it is noted that changing from inboard flaps to
outboard flaps decreased AC but had little effect on the rate of
change of ACrng with angle of attack.
Increment of lift from tail.- For a constant tail incidence the
increment of lift due to the effects of power on the tail is dependent
upon tail height and incidence as well as on flap configuration. However,
the increment of lift due to the effects of power on the tail can hardly
be discussed without reference to the pitching-moment changes involved,
since the lift on the tail must be that to balance the airplane. This
will be discussed in succeeding paragraphs.
Components of the Pitching-Moment Changes Due to
The application of power results in changes of pitching moment, due
in a large measure to the fact that the centers of the lift increments
previously discussed are at some distance from the reference center of
moments. The various components of the change in pitching moment can
therefore be classified in the same manner as the lift changes of the
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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/m1/13/: accessed May 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.