Measurements were made of the base pressure distribution and the aerodynamic drag of a variety of 1/8th-scale tractor-trailer truck models in a wind tunnel at yaw angles ranging from 0° to 20°. Base-drag coefficients and overall aerodynamic-drag coefficients were calculated from this data. The measurements show that the base-drag coefficient of typical tractor-trailer trucks does not vary much with vehicle configuration, and that base drag constitutes approximately 13 to 15 percent of the total aerodynamic drag at zero yaw. The base drag increases in magnitude and also becomes a larger part of the overall aerodynamic drag as yaw angle increases, reaching about 18 to 25 percent of the overall drag at 20° yaw. Streamlining the forebody of the vehicle has little effect on the base-drag coefficient, but increases the fraction of the overall aerodynamic drag due to the base.

Stability characteristics of an overhanging shaft immersed in a viscous fluid are investigated experimentally. The predominance of two effects, damping and virtual mass, are separated and explored as they affect amplitude and critical speed. A correlation equation for amplitude as a function of viscosity, velocity, and mass is developed with the aid of statistical regression analysis. The techniques of regression analysis are summarized in the Appendix.