A Simple Method for Estimating Terminal Velocity Including Effect of Compressibility on Drag

Book excerpt: Summary: A generalized drag curve that provides an estimate for the drag rise due to compressibility has been obtained for an analysis of wind-tunnel data of several airfoils, fuselages, nacelles, and windshields at speeds up to and above the wing critical speed. The airfoils analyzed had little or no sweepback and effective aspect ratios above 6.5. A chart based on the generalized drag curve is presented from which the terminal velocity of a conventional airplane that employs a wing of moderate aspect ratio and very little sweepback in a vertical dive may be rapidly estimated. In order to use the chart, the only data that need be known about the airplane are a low-speed drag coefficient, the wing critical speed, and the wing loading. The terminal velocities for three airplanes were computed in order to illustrate the use of the method and chart. Good agreement between the estimated terminal velocity and the measured flight terminal velocity was indicated for all three airplanes.