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National Advisory Committee for Aeronautics, Report - The Vertical Wind Tunnel of the National Advisory Committee for Aeronautics

The vertical open-throat wind tunnel of the National
Advisory Committee for Aeronautics is described in this
report. .’l he tunnel was built mainly for studying the
spinning characteristics 'of airplane models, but may be
used as well for the usual types of wind-tunnel tests.
A special spinning balance is being developed to measure
the desired forces and moments with the model simulating
the actual spin of an airplane.

Satisfactory airflow has been attained with a velocity
that is uniform orer the jet to within $0.5 per cent. Ihe
turbulence present in the tunnel has been compared with
that of several other tunnels by means of the results of sphere
drag tests and was found to arerage urell with the values
of those tunnels. Included also in the report are compari-
sons oj results of stable autorotation and of rolling-
moment tests obtained both in the vertical tunnel and in
the old horizontal 5-foot atmospheric tunnel.

Some of the major problems under investigation by
the National Advisory Committee for Aeronautics may
be placed under the general heading of safety in flight.
One of the most important of these problems is the
study of spinning, both in the wind tunnel and in free
flight. In the usual horizontal type of wind tunnel,
however, considerable difficulty is encountered in mak-
ing spinning tests of airplane models owing to the
force of gravity acting with the rotation for part of a
revolution and against the rotation for the remainder.

This condition tends to give oscillating readings on the
measuring apparatus and can be avoided only by very
careful counterbalancing of the spinning model and
balance parts. This undesirable feature can be over-
come by locating the spin axis in the vertical rather
than in the horizontal position, because the effect of
gravity on the spin apparatus is then constant. In
addition, a vertical type of tunnel requires much less
floor space than the horizontal type of the same jet
diameter.