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This paper describes the development of a hybrid-computer simulation of a recreational snowmobile. The vehicle has been mathematically represented by a displacement-driven, damped nonlinear spring-mass system with two degrees of freedom. The analog circuit and the logic level control system of the analog/hybrid computer is discussed. The use of a hybrid system using Hytran Operational Interpreter to perform OFF-LINE and ON-LINE checks is also discussed. Finally, a method to display a visual representation of the vehicle on an oscilloscope screen is presented. The simulation permits vehicle designers to vary at will the various design parameters and to observe immediately the effect of so doing.

The validity and appropriateness of the application of the Head Injury Criterion (HICm) concept to motorcycle helmet testing has been examined. Its derivation has been reviewed and its logic assessed. It is shown to be an inconsistent and unreliable criterion for helmet performance evaluation. This inconsistency stems primarily from its poor correlation with experimental data and from the basic assumption that the seriousness of a head impact can be ascertained by considering only a portion of the test headform acceleration pulse. Several alternative criteria which all are physically sound and mathematically consistent and which are more amenable to protective headgear design and testing are proposed. These criteria include force and loading time minimization; load distribution; minimization of loading rate and maximization of energy dissipation.