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Page 32
EXPOSING THE MYTH OF "WASTED ENERGY"



In the "Getting Started" section on Page 1, the dynamic forces involved in the launch of a drag car are discussed. Another analysis technique is to track the energy conversions involved.

Initially, the chemical energy of the fuel is the source of the car's performance. With combustion in the engine, approximately a third of the energy goes out the exhaust and another third goes into the engine's coolant. This leaves about a third to power the car down the strip. The rate at which that energy is consumed determines...for a given car speed...the maximum acceleration attainable.

Energy can appear in other forms, however. It is said, for instance, that any object has potential energy if it is possible for the object to descend to a lower elevation. That descent can be harnessed to do work. Examples would be the weights in an old pendulum clock or the water driving the turbines at a hydro-electric facility.

When the front end of a car rises during launch, then, it is recognized that a weight has been driven to a higher elevation and, consequently, some energy must have been required to achieve this change. Since the dragracer's goal is to quickly move the car forward and not upward, some have seized on this as evidence that energy which could have been used profitably has been "wasted" in this upward motion.

This is, however, not the proper conclusion.

Just as the fuel contains stored energy in the form of chemical energy, a deflected spring (compressed coil or twisted torsion bar) also contains stored energy. During launch, the vertical loading of the rear tires increases (weight transfer) and the vertical loading of the front tires decreases. With less upward force being applied to the front tires, the front suspension springs are no longer able to maintain their deflected shape. This loss in stored spring energy (as a coil spring or air bag lengthens or a torsioin bar "untwists") is exactly equal to the increase in potential energy (energy of elevation) gained by the car's front weight.

As far as the chemical energy of the fuel is concerned, nothing is "wasted" with this upward motion.

This does not mean, however, that the upward motion of the front of the car is of no concern. The upward motion increases the height of the center of gravity and, consequently, increases the potential for more weight transfer. This may or may not be beneficial. The best performing rear wheel drive cars are capable of unloading the front end completely, so they are set up to minimize front end lift and wheelie bar loading.

The point to remember is that front end rise does not constitute a "waste" of potentially usable energy and, as a corollary, there is no magic trick to somehow harness that energy of elevation to increase performance.

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