Estimating updraft velocity from an airplane response.

Abstract

Aeroplanes have been used to estimate the magnitude and shape of thunderstorm updrafts by assuming that the aeroplane follows the updraft when the thrust, mass and pitch angle are held constant. This assumption is shown to be satisfactory, using simplified aerbplane equations of motion , for a Beechcraft Queem Air and a North American T-28 , if the updraft is large with respect to the contribution of the drift of the pitch angle reference to the airplane vertical velocity. For thunderstorms, where updrafts greater than 8msSUB-SUB1 with a diameter of 3km are expected, the aeroplanes should follow the updraft closely enough that a smooth updraft profile can be distinguished from a top hat profile. The contribution to the vertical aeroplane velocity from horizontal wind variations is less than 20percent of the horizontal wind variation if the pitch angle is held constant. If, instead, the airspeed is held constant, the contribution to the vertical airplane velocity would be as much as 100percent of the horizontal wind variation. A Queen Air, instrumented with a complete air motion sensing system, was flown through the updraft over an isolated mountazn peak, which was similar in size and shape to a thunderstorm updraft, to check the analysis. The results verified the desirability of flying a constant pitch angle. (A)