Investigations on the Downwash Behind a Tapered Wing With Fuselage and Propeller Page: 18 of 52
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N.A.OC..A. Technical. Memorandum No. 876
As .to the course of the downwash on the lateral axle
at height Eh = 0.0, that is, at .height of,.slipstream aris,
figure 23 further zid&ifests. aside from the already men-
tioned ono in which -though reduced by the wide fuselage
and the wing acting as guide apparatu - the twist of the
slipstream occurs two other zones may be distinguished.
They lie to the right and left of the slipstream approxi-
mately between tcq = 0.14 to, 0.45. In these transition
zones there is a marked rise of downwash over the right
half of the wing and a somewhat lesser downwash decrease
over the left half, These deviations have therefore the .
opposite signs of those on the same half due to the twist.
As the sense of rotation of the slipstream changes the de-
viations in the transition zones themselves change signs.
The counter-rotating downwash changes to both sides of the
slipstream are therefore directly related to the slipstream
rotation (fig. 25).
The total downwash zone of the lateral axes disturbed
by the propeller - that is, into which the disturbances
enter as a result of the axial supplementary velocities in
the' slipstream -' is on the average about twice as great as
the propeller diameter, while according to Koning (reference
13) this zone should amount to about four times the propel-
ler diameter. Strictly speaking the disturbed curve an-
. preaches the undisturbed curve asymptotically, although the
- limit can be fairly well gaged by the eye.
Mention should also be made of the attempt at simple
qualitative derivation of this downwash distribution from
the lift distribution modified by slipstream twist and sup-
plementary axial slipstream velocity. But it was impossi-
ble .to obtain an agreement between the theoretical and the
experimental downwash distribution.
Figures 26 and'27 (vertical axes) complement figure
23. They indicate that the downwash changes relative to
the reference curves on the pressure side are curiously
still traceable at great distance from the wing, but die-
appear at shorter distance on the suction side. The same
is seen in figure 28, which illustrates the angle of down-
wash at height Eh.= 0.2 on two longitudinal axes in the
plane of symmetry. -
a = 6.8o.-.Figure 29 presents the results of downwash
measurements o the .lateral axes at distance c = 1.0 for
a = 6.80. Hereby A = D.188 and a correspondingly higher
thrust coefficient than at a = 3.150. It is c = 0.486
and ca = 1.18.
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Muttray, H. Investigations on the Downwash Behind a Tapered Wing With Fuselage and Propeller, report, September 1938; (https://digital.library.unt.edu/ark:/67531/metadc63295/m1/18/: accessed April 22, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.