The U.S. Vertical Wind Tunnel: A Full Description with Details of Calibration Tests and Some Preliminary Experiments

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 making spinning tests of aeroplane 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 overcome 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.