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 8½ times normal pressure and is quite hot—about 450° Fahrenheit.
At this point the antisocialites have been marshaled in sufficient numbers and are emotionally ready, as it were, for some kind of incendiary action. And that is exactly what they get when they rush into the turbine's combustion chamber, where fuel is constantly being injected to feed a constant flame. The situation in the combustion chamber is such a highly inflammatory one that it could easily get out of control. In the same way that men who drink cheap gin in excess sometimes start smashing furniture, if the air molecules suddenly tie into too much fuel in the combustion chamber there can be trouble. The trick is to serve up enough fuel to keep things going at a fever pitch, yet control the activity in such a way that there is no risk of burning up the joint. Considering that the air-fuel mixture in the chamber burns at around 3,500°, while the walls of the chamber cannot withstand much more than 2,000°, this takes some doing.
The G.E. engine does it successfully. Even when it is operating at maximum the fuel supply is limited so that only a quarter of the air is needed for efficient combustion. The balance, called secondary air, serves to keep things under control. The combustion chamber lining is pocked and stippled with a seemingly haphazard arrangement of holes, flanges and ducts. The flow of secondary air around and through these configurations tends to confine the 3,500° flame in the center of the chamber while at the same time keeping the lining of the chamber tolerably cool. By mixing with the rapidly expanding hot gas produced by combustion, the secondary air also reduces the overall temperature to around 1,650°. And thus, in a neatly controlled state of seething unrest, the agitated molecules rush out the rear end of the combustion chamber and at increasing velocity on through two stages of gas generator turbine blades. The effluence of hot, expanded gas causes the gas generator turbine to rotate at high speed (at 26,300 rpm maximum). Since the 10-stage compressor rotor at the front of the engine is affixed to the same shaft as the gas generator turbine, it also rotates, pulling in more air and keeping the action going.
In the extreme rear of the engine there is a third disc of turbine blades in line with the two-stage gas generator turbine but larger and rotating independently on a separate shaft. Although the energy of the effluent gas is diminished by the time it reaches this third disc—called the power turbine—it is still considerable. It is the spinning of this disc (at a maximum rpm of 19,500) that furnishes usable power.
Like a piston engine, a gas turbine depends on an electrical starter, but, once a sufficient mass of air is flowing into the combustion chamber and the air-fuel mixture has been ignited electrically, the action is virtually self-sustaining. A turbine does require a relatively simple lubricating system and a pumping system to keep fuel coming into the combustion chamber, but it needs no generator, water cooling system, distributor, nor any number of other knickknacks that get out of kilter on the traditional piston engines currently being used by leadfoots at Indianapolis and by little old ladies in Pasadena.
A piston-type Indianapolis engine, including all the knickknacks, weighs around 400 pounds and is capable of producing about 600 horsepower. The G.E. engine shown here weighs only 350 pounds but can put out more than 1,250 horsepower. However, because of the restrictions placed on turbines by the USAC, the two G.E. engines competing at Indianapolis will be producing far less.
For many years the power of piston engines has been restricted in a comprehensible way at Indianapolis: by limiting cylinder capacity—or, to put it more accurately, limiting piston displacement in the cylinders. Since there is this restriction on traditional engines, no one in his right mind is arguing today that turbines should go unlimited. The controversy persists primarily because the rating of turbines for the Indy race is a new and inexact science, particularly so because the engines available were not designed for such specialized use and vary considerably from make to make.
In the very front of the G.E. engine there is an annular (i.e., ringlike) inlet through which air passes on the way to the first stage of the compressor rotor. In the motor as originally designed, and as shown here, the area of this annular inlet is 41.6 square inches. To limit the power of turbines the USAC has ruled that the area of the annular inlet at the leading edge of the first set of compressor blades cannot exceed 15.999 square inches. To comply with the rule the Wallis Engineering Company, which designed and built the two G.E.-powered cars for Indianapolis, actually reduced the size of the first stage of the compressor rotor. Such a large reduction in inlet area quite naturally means a reduced mass flow of air and, consequently, a reduction of power unless some desperate measure is taken. Actually, because the engine has so much power to give away, Wallis Engineering has found no emergency action necessary. While he will not reveal exactly what the restricted engines will put out, Designer Ken Wallis will say that, even while keeping temperatures within safe limits, the G.E. should hold its own against the best of the pistons in the 500.
Andy Granatelli has had the most to say against the USAC restrictions, and understandably, since the five new engines in his racing stable have an output of only 620 horsepower as originally designed by United Aircraft of Canada. The Canadian-made engines have a four-stage compressor rotor, but to reduce the annular inlet area to the limit specified by the USAC, because of the basic configuration of the engine it was necessary to remove the first two stages and reduce the size of the third. In consequence some desperate measure is required to get the same lively action in the combustion chamber. To compensate for this emasculation the Granatelli team is going to gamble on a richer fuel mixture, thereby upping the temperature of the gas leaving the combustion chamber from a recommended 1,650° to around 1,850°. Thus more of the little molecules will be used in the process of combustion, and there will be less available to keep things under control. You can get more action that way, regaining power, but you also run a risk of burning up. "We want to race," Granatelli says. "We'll run the engines to the ragged edge if we have to."
The many virtues of the turbine engine—notably its simplicity, durability and high power-to-weight ratio—provoke an obvious question: Why aren't there two turbine-powered cars in every American garage today? The principal reason is that man, the inventive ape, has not always advanced at the same pace on all fronts.
Generally speaking, in a simple turbine the fuel consumption is too high for ordinary highway use, and exhaust temperatures are also too high, particularly if you consider the excess heat already being generated in the public streets by placard bearers and window smashers. The Chrysler Corporation, the pacesetter in the street turbine field, solved the fuel and exhaust problems with a single approach, employing a regenerating system that, in effect, passed the hot exhaust back through the combustion chamber. Between late '63 and early '66, Chrysler let 203 typical U.S. drivers—of various ages and both sexes—use 50 hand-built turbine Chryslers as their workaday cars. Eventually, Chrysler did prove that fuel cost could be no more than for a medium-powered piston car. However, the price of a turbine engine would still be high—too high for the ordinary car simply because the alloys are expensive; the trace metals in them are still in short supply. The typical, crude, clunking, ancient, four-barreled, multicammed Ford engine that has been running at Indianapolis for four years now costs a mere $23,000. By contrast, the G.E. turbine, sold right off the shelf with no alterations—simply with a guarantee of 3,000 hours between overhaul—costs $75,000.
GAS GENERATOR TURBINE