The Traffic Accident Reconstruction Origin -ARnews-

Re: Rotating Vehicles Drag Factor

Brian McHenry (mchenry@interpath.com)
Thu, 20 Mar 1997 11:51:34 -0500 (EST)

Ed:

By no means did I mean to imply that is it improper or impossible to reasonably approximate the energy dissipated and therefore the speed required for a vehicle to travel a given distance with a given amount of rotation.
It is however improper to assign some arbitrarily % of full lockup.

The total distance traveled, the total amount of rotation, the amount of drag on each wheel and elevation changes in the terrain must be considered to approximate the energy dissipated as a vehicle travels from separation to rest.
My reasons for referring interested individuals earlier in this thread to our recent SAE paper and/or the CRASH research summarized in the NHTSA document is that although CRASH currently is being used mainly (by NASS and many accident reconstructionists) for damage based analysis, the fundamental research that went into CRASH was to investigate all aspects of a reconstruction (damage AND trajectory) to determine a reasonable approximation of the impact speeds and impact speed changes. The papers cited contain a large collection of references related to trajectory reconstructions, including relatively simple hand calculations. These would be preferred to some arbitrary % factor.

My recommendation that accident reconstructionists also consider performing a trajectory simulation is in recognition of the fact that the common desktop PC (Pentium, etc.) is a major powerhorse sitting idle on your desktop which is quite capable of performing simulations. All that is required is to obtain software and/or do a little research to accomplish the task.

On our website (http://www.mchenrysoftware.com) you will find further discussions on accident reconstruction, our 4 recent SAE papers, information on obtaining various public domain databases of crash tests and vehicle specifications and software information (from us as well as others).

Brian McHenry
mchenry@interpath.com

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