Scale models of automobile collisions with breakaway obstacles. Paper presented at 1971 SESA Fall Meeting held in Milwaukee, WI, on October 19–22, 1971.

In a new approach to scale modeling, the model rules, as well as the essential pi-numbers, are obtained directly from the physical laws identified as governing a phenomenon. Contrary to the widely used parameter approach with dimensional analysis, the new approach simplifies the derivation of model rules and gives a clearer physical meaning topi-numbers. As an application of the method, a study of automobile collisions in which roadside obstacles, such as signposts and lightposts, are made to break away when struck to lessen injuries is described. Both an analytical approach and full-scale testing are difficult for studying the collisions, the one because of the complexity of the phenomenon and the other because a systematic study of parameters that influence the effectiveness of a design is prohibitive in both time and cost. Laboratory tests by scale models conducted according to the established model rules were photographed with high-speed motion pictures. Agreement of the breakaway motion with that of full-scale counterparts proved the feasibility of using scale models for design improvements of such obstacles.