Investigations on the Downwash Behind a Tapered Wing With Fuselage and Propeller Page: 15 of 52
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N.A.C.A. Technical Memorandum No. 876
fcr nonrolled-up vortex sheet with the lift distribution
belonging to predetermined wing. This step was taken since
it became manifest that the "upper limit" of potential lift
distributions on tapered wings can be considerably more re-
mote from the trailing vortex curve than when distributed
elliptically and fits the experimental values better.
How essential this difference is may be seen from fig-
ure 20, which presents the "upper limits" for the different
lift distributions over the various wings. The expression
for these curves reads:
ai 2 1 a
The integral for Eq = 0 to 0.96 was obtainod
graphically, that for q -- 0.96 to 1.0 mathematically.
Figure 19 is very much like that obtained previously for
the elliptical wing. Due to the fact that the nonrolled-
up sheet affords the best actual values, provided the sink-
ing of the vortex train is allowed for, a tolerable agree-
ment of the measured curves with the "upper" limit must
follow if, instead of the values at Ch = 0 against qc
we plot the maximum values of these measured on the verti-
cal axes. Plotting in.figure 21 the maximum values of
the normal axis downwash curve-s of all recorded angles of
attack, it is seen that, as in figure 8, they lie in prox-
imity of the upper limit curve.
Figure 22 presents the corresponding data for all an-
glee of attack of the earlier elliptical wing study (ref-
erence "1). Tho greater the angle of attack is the closer,
in both cases, the maximum experimental values with dual-
tube recor'der approach the'"upper" limit. On the tapered
wing, the difference is only about 10, on the elliptical
wing only about 0.50. On the rectangular wing, it should
beo even less and on the wing with tapered lift distribution
Lateral axes.- As example of the .measurements .on the
lateral axes of "wing alone" at a = 8.80, see figure 5.
The marked change in downwash in relation to e q in con-
trast to the earlier measurements on the elliptical and
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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/m1/15/: accessed April 26, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.