A gas turbine engine is, in simplest terms, nothing more than a precise, quiet and durable machine with a remarkable capacity for putting vast quantities of hot air to good use. In war and peace, in trucks, boats and helicopters, the particular gas turbine portrayed at the bottom of this page has been performing dependably for the past 10 years without getting many rave notices. This month it is making an appearance at the Indianapolis Speedway, where it is attracting a great deal of attention.
The General Electric engineers who designed and who have been refining this engine for a decade have faith in it, but in the Indianapolis 500—the grandest, most brawling dice game of them all—who really knows? It is safe to say that if all the hot air that has been expended by men arguing about the use of turbines in the Indianapolis race were somehow channeled through the bright, whining guts of this G.E. creation, it could probably run the entire 500 miles without fuel.
Last year, of course, Parnelli Jones's turbine car almost did win, leaving the rest of the field in its steaming wake until the 197th lap when, clunk, a transmission bearing failed. Although that lone turbine entry—the first ever to race in a 500—died on the track as piston cars have often done, the furor that it created lived on. Driver A. J. Foyt, who ultimately won the race in a rear-engined Ford, led the subsequent anti-turbine chant by insisting that " Indianapolis is for cars, not airplanes." Driver Mario Andretti claimed that the turbine was somewhat like a primordial screw worm—altogether too simple a creature ever to have enough sex appeal for the big Indy carnival. "I don't think the turbine is an interesting car," Andretti said.
As it happens, Mario's view is not shared by a good many fans, who regard turbine power as the good, the true and the beautiful; nor by Goodyear Tires, which has staked better than a million dollars on racers equipped with that G.E. engine; nor, oh Lord, by Andy Granatelli, the India rubber man who keeps bouncing back to Indy.
The turbine enthusiasts are mad as hell about the U.S. Auto Club's 1968 restrictions on turbine power. Since the car that nearly won last year was Granatelli's, and since this year he has six prospective entries whose United Aircraft turbines are now throttled to the point where they may have difficulty qualifying for the race, Granatelli has reason at the moment to be morose, if not irate.
By tradition, the 500 is a spawning ground of controversy. The flatulent din of cars has usually been accompanied by the wailing of competitors. This year is a vintage one for the wailers, and the best way for any buff to enjoy the show is to become an authority on turbine cars overnight and then jump into the middle of the current squabble loaded with half-baked opinions. Without toe-dancing through physical equations and theorems it is difficult to understand completely how a gas turbine works, but, in the interest of keeping a good controversy raging, it is worth a try.
A gas turbine and a traditional piston—or reciprocating—engine have one basic similarity: the power of both derives from expanding gas produced by a combustible mixture of air and fuel. As anyone knows who has rapped out a C—or better in elementary science, the combustion in a piston engine is not sustained but is a continuum of very rapid burnings in one or more cylinders. The expanding gas produced by each burning exerts force on a piston that is connected to the offset of a crankshaft in such a way that the linear force against the piston serves to rotate the shaft. The antique engine that powered the Apperson Jack Rabbit 60 clanking years ago operated in this fashion, and so do the engines in the latest chrome-bedecked thunder lizards from Detroit.
By contrast, in a gas turbine there is no violent burst of power. There is no sudden change in direction of any moving part, nor any eccentric motion. In a turbine, combustion is continuous; all parts of the engine that are integral to the production of power either stand dead still or simply spin at high speed. A gas turbine with a power output equal to that of the best piston engines competing at Indianapolis uses less fuel but requires a great deal more air.
To examine the matter in simple terms, air in its natural state is a loose confederation of restless molecules which, like emotional, antisocial little revolutionaries, do not really have a concerted mind of their own but can be very useful in the acquisition of power if their energy is channeled properly. Even under normal conditions, with no outside pressure on them, the little antisocial molecules of air are in an agitated state. Although they can be crowded together they resist the idea and become still more agitated. In the process, pressure builds up and the temperature rises.
In the front of the G.E. engine portrayed on page 50 there are 10 stages of rotating blades called, collectively, the compressor rotor. The purpose of this 10-stage rotor, in effect, is to draw in the little molecules and crowd them closer together while keeping the whole mob moving smartly along. There is so much pushing and shoving that as the rushing mob spins out of the last stage of the compressor rotor it is exerting about 8� times normal pressure and is quite hot—about 450� Fahrenheit.