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National Advisory Committee for Aeronautics, Technical Notes - Air Resistance Measurements on Actual Airplane Parts

The landing gear is shown in Figs. 1 and 8. In'
order that all parts, especially the wheels, might be well
surrounded by the stream of air, only half of the landing
gear was summed to the air stream. Otherwise the results
would have been unreliable, since the wheels would have been too
near the edge of the air stream. The results (Table I and Figure__
LS) were, however, multiplied by 2 and hence apply to the whole
’landing gear. The sides of the Wheels were covered with fabric
in the usual way. Besides the tests with the landing gear as‘a
whole, two other series of tests were carried out. In one, the
wheels were only attached as dummies, i.e., they were not rig—
idly connected to the landing gear, but were held by a special
device. In this way, the resistance without wheels was deter-
mined and yet the remaining parts were in a current of air in—
fluenced by the wheels. The third_test was carried out entire—
ly without the wheels. In Fig. 3 the equivalent resistance
surface SD in square meters is plotted against the pressure
q = p Va/ag kg/m2 (Resistance D = SD - q)«

On this occasion a few parallel experiments were carried
out, in order to throw light on the question as to whether the
sum of the resistances of the individual parts of the landing
gear gives the true total resistance. To this end, the resist—
ance of the wheels by themselves was determined. It was shown I
in this way that such addition is not permissible. this is
also comprehensible from the fact that the assembly of the in—
dividual parts sets up an essentially different disturbance of
the air stream from that set up by individual parts separately.

The "Luftfahrzeug—Gesellschaft" landing gear, Whichm
is somewhat larger than the Sienens—Schuckert, is shown in Figs-
4 and 5. The frontal projection of the wheels is 760 X 100 mm
(29.921 x 3.937 in) against 710 x 85 mm (27.955 x 5.346 in) _for_
the first landing gear (Figs. 1 and 2).