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National Advisory Committee for Aeronautics, Technical Notes - Full Scale Drag Tests on Various Parts of Sperry Messenger Airplane

The drag of a Sperry Hessenger airplane with the wings re—
moved, and also the drag of its various component parts, was
measured in the 20—foot air stream of the N-A.G»A- propeller
research tunnel at air speeds from 50 to 100 M.P.H. It was
found that the three-cylinder radial air—cooled engine nearly
doubled the drag of the bare fuselage, and the drag of the land—
ing gear was about the same as that of the fuselage and engine
combined.

Heretofore, measurements of the drag of airplane fuse—
lages, landing gears, and other large parts have been limited
by the size of available wind tunnels to tests on relatively
small models. It has been necessary to calculate the full
scale drag from the results of the model tests upon the basis
of the principle of mechanical shnilitude. Since all of the
conditions of this principle are not fulfilled in the model
tests, the calculated full scale drag is at best more or less
an approximation. The approximation may become very poor for
bodies having complicated shapes such as airhcooled engine cyl—
inders and landing gears in which the model cannot easily be
made similar in all details to the full size object. It is de—
sirable, therefore, to test these objects at full scale. This
is now possible in the 20~foot air stream of the now propeller
research wind tunnel of the National Advisory Committee for
Aeronautics.

The Sperry Messenger airplane was originally mounted in
the tunnel for prepeller tests. This note describes a series
of tests made on the drag of various parts of the airplane
without wings. Since the wings have about the same Span as
the diameter of the air jet their drag as measured in the tunnel
would not be the same as their drag in flight. The tests were
therefore confined to drag measurements with the wings and wing
bracing removed. The drag of the whole airplane without wings
was obtained for air velocities of from 50 to 100 M-P.H., and
the drag due to the landing gear, tail surfaces, windshield,
cockpit, and the radial air-cooled engine, were measured at ve—
locities frmn 50 to 80 M.P.H.