2019 Abstracts – Research & Evaluation Stream

October 10, 2018   |   Categories:

2019 Abstract - Research & Evaluation Stream

Title of Abstract

Drag Sled Mechanics, a Fundamental Review

Background

There was a time during the late 1990s into the 2000s when the accident reconstruction community was embroiled in the “drag sled wars”. The dispute included questions about what the drag sled measured, how well and consistently it measured anything and how it should be used for collision reconstruction. The dispute intensified as new methods of analysis gave increased understanding of the breaking capabilities of motor vehicles. The dispute continues to stimulate debate and opinions.

Aims

The purpose of this paper is to outlines a new approach to drag sleds mechanics based on a firm engineering understanding. It illustrates that the drag sled, used correctly measures the tire pavement friction (traction) properties. The main aim of the paper is to remove any debate about the usefulness of the drag sled in collision reconstruction.

Methods

The analytical methods used are well known within the engineering community to solve statics equilibrium problems. The first method employed a very intuitive graphical analysis that was popular prior to the computer age. The second method is the now more popular analytic method. Preliminary experiments give numerical support to the conclusions.

Results

The drag sled when pulled at an angle that ensures that the three forces, Weight, Pull and Reaction are both coplanar and concurrent gives a system that by definition is in static equilibrium. The ratio of the Normal and Friction forces gives, by definition the tire pavement coefficient of kinetic friction. There is NO doubt as to the parameter being measured.
Simple adjustments to the angle of pull account for estimating the coefficient of kinetic friction on various grades.
Monte Carlo sensitivity analysis found that the standard error of the tire-pavement coefficient of kinetic friction was about +/- 3%. Error propagation analysis found the most sensitive variable to be the angle of pull which accounted for roughly 80 percent of the total error.

Discussion

Estimating a vehicles pre breaking speed from a the coefficient of kinetic friction requires a slight change in current analytical methods to estimate a vehicle’s speed specific drag factor or breaking coefficient. An estimate of a vehicle’s breaking efficiency is required, similar to a method used for bicycles or motorcycles.

Conclusions

The paper will be useful to police and engineers responsible for collision reconstruction. The new material removes any doubt as to what is being measured by a drag sled and exactly how to measure the tire pavement coefficient of kinetic friction.

What do you intend to be your final submission? Full Paper

What Topic does your paper relate to? Enforcement and Legal Issues