High-speed wind-tunnel tests of a 1/14-scale model of a four-engine cargo airplane Page: 4 of 32
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Pitching moments are given about the center of gravity as
located in figure 1.
The following tunnel-wall corrections were applied to the test
results (reference 1):
1 a = 0.310 CL
CD = 0.0054O CL2
OCm = 0.0057 CL (tall-on runs only)
Approximate lift, drag, and pitching-moment taros were obtained
with the -model removed leaving the struts with failings on their
upper ends, as in fIgure 4. These tares are shown in figure 5.
Since no corrections for buoyancy, stream inclination, or interference
have been applied to the drag data, they should be used for compara-
tive purposes only. The pitchiYd mrments .ave been torreted for
the downflow of the air stream at the tail position of the model
(fig. 6). This downflow was measured with the " 1I sr ov.
DISCUSSION OF RESULTS
The characteristics of the model in vari ous stages of comiplto-
ness are shown in figures 7, 8, and 9. Figures 7 rAd indic e
tht the tail-off instability increased at Mach nuhcarc above 0.675.
Figure 9, which shows the characteristics of the compoe nodel,
indicates no appreciable change in pictclhing mom._t or static lonng--
tudinal stability through the range of Mach numbers from 0.3 to 0.5.
As th; Mach number increased fr om 0.5 to 0.65, the stability
decreased at negative lift coefficients, but remained about the
same at positive lift coefficients. About 0.65 Mach number, the
stability increased and a large change in the lift coefficient for
balance occurred. The increase in stability appeared first at the
higher lift coefficients, as indicated by the breaks in the moment
curves of figure 9(d). Because of the increase in stability and the
change in lift coOfficiOnt for balance, a greater incromnrt of
pitching moment is required of the c ovator in order to control the
airplane. At lift coefficients corresponding to level flight this
increase in stability appeared spds ranging rom 60 miles r
hour at 29,000 fooeet altitude to 515 miles per hour at sea level. This
result indicates a considerable margin of safety over the prodCicted
maximum speeds in level flight of 247 miles per hour at 29,000 feet
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Hamilton, William T. High-speed wind-tunnel tests of a 1/14-scale model of a four-engine cargo airplane, report, February 1943; (digital.library.unt.edu/ark:/67531/metadc61219/m1/4/: accessed July 17, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.