Investigations on the Downwash Behind a Tapered Wing With Fuselage and Propeller Page: 25 of 52
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N.A.0.A. Technical Memorandum No. 876
Measurement with detector vane accordingly gives a
lower figure than with point-by-point measurement. In a
comparison of angles of downwash defined according to dif-
ferent test method this fact should be borne in mind.
E. VELOCITY DISTRIBUTION IN THE SLIPSTREAM
Figures 59 to 61 show the velocity distribution in
the slipstream of the low-wing model with angular fuselage
at a = 6.8 and the coefficient of advance ) = 0.1865
at E = 1.0. Again the lateral axis measurement indicates
a stronger thrust on the left- than on the right-hand side.
The slipstream center lies approximately at h = 0.03.
Figure 62 illustrates the velocity distribution averaged
over the range of eq = -0.3 -to +0.3 against Eh. The
horizontal tail surfaces of an airplane on passing through
the slipstream are, if the angle of attack is changed, on
the average in a wind of constant mean dynamic pressure,
unless they reach the Jet boundary or emerge from it.
In the velocity distribution test, the static pres-
sure was measured separately from the total head. For the
latter, a pitot-venturi was used of directional .insensi-
tivity within a range of 450. The static tube was turned
into the previously measured flow direction.
Our velocity distribution measurements in the slip-
stream were confined to the low-wing model with angular
fuselage and a = 6.8 and A = 0.1865, although for
stability .studies (section r), the knowledge of the addi-
tional velocity in the slipstream - whose mean value re-
ferred to lateral tail axis is according to figure 62,
approximately unaffected by the height level of the tail -
of both models and at several a and ? is necessary.
These additionally needed values were mathematically approx-
imated on the basis df an assumed dependence of A but not
of a or the model form.
The additional axial velocity in the slipstream far
downstream .from the propeller is
w k,(l .+ 2 )
2a - In(l + -
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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/m1/25/: accessed April 18, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.