The Traffic Accident Reconstruction Origin -ARnews-

Re: Rotating Vehicles Drag Factor

Ed Phillips (EPHILLPW@CO.SAN-DIEGO.CA.US)
Mon, 10 Mar 1997 15:14:22 -0500 (EST)

Art,

You may have opened a can of worms, and if you haven't my response probably will. I have opposed (one fellow in particular) those with many letters after their names that say that this dynamic demands the use of a Runge-Kutta form of differential equation for the numerical intergration. I disagreed then, and still do today. A good deal of empirical testing, and other independant evidence has shown that separating the vehicle motion during the cycloidial motion into increments of varying distance and resistance (rolling friction when warranted and locked wheel for side slipping) allows one to reasonably sum up the amount of Kinetic Energy transformed during such an event. When do you assign friction values as locked wheel is debateable. Most agree that once a vehicle approaches 30 degrees off its initial tangent, recovery is extremely unlikely. Some others measure the c.g. translation and assign a mid range friction value, between lock-up and about 0.25g where viewable tire marks
may initiate, for the translational distance and solve a speed from skid type of equation. Both methods have yielded similar results. For references, you might try an oldie but goodie, "Highway Collision Analysis" by Collins and Morris, SAE 890857 "Reconstruction of Rollover Collisions" by Orlowski, Moffatt, Bundorf and Holcomb; or another good one is an SAE paper from the 70's by Alan Nahum and Arnie Siegel. I apologize, we are in the process of moving, and that data is boxed away. Try the SAE search site for further.

Ed
Ed Phillips
EPHILLPW@CO.SAN-DIEGO.CA.US

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