SAE Paper

The Memorial Day "500" has long been referred to as a proving ground for automotive "firsts". Many engineering features in common use today have been developed and proved on the bricks at Indianapolis. It is altogether fitting that the automotive gas turbine be introduced there and given the opportunity to prove itself against the most successful racecar engines of our time. It is the author’s belief that the equipment and the know-how are available right now to build a turbine racing car that would not only be a serious threat at Indianapolis but would also stand a very real chance of winning.

Fig. 1 is presented for the benefit of those not familiar with the internal operation of the free wheel turbine. In the Boeing 502-10 gas turbine, air is drawn into the compressor where the pressure of the air mass is increased more than four times by the blades of a rotating impeller. The air is then discharged into the burners where fuel is added and combustion occurs. The combustion gases from the burners join in the nozzle box. At this point they expand through a ring of fixed vanes, which direct the gases as jets against the blades of the first turbine wheel, causing it to rotate at high speed. The first turbine wheel is directly connected by a shaft to the impeller to provide continuous compression of air for the gas producer. After leaving the first turbine wheel, the gases expand through another ring of fixed vanes, which direct the gases against the blades of the second turbine wheel. This wheel, through reduction gearing, drives the output shaft of the engine. After most of the energy of the gases has been thus converted into useful power, the gases are discharged through exhaust ducting to the atmosphere. Since the first and second turbine wheels are mechanically separate, their speeds are independent. The effect produced is the same as that of a hydraulic torque converter. The second turbine wheel can be stalled while the first turbine wheel is at rated speed, permitting the driven unit to start or change speed smoothly.

The gas turbine like any other type of engine has advantages and disadvantages which make it more or less desirable for a particular application. All things considered it appears that one application for which the gas turbine is particularly suited is in the field of automobile racing. The turbine’s chief advantage, high power to weight ratio, is of little concern in a stationary installation whereas it is of primary importance to the designer of a racecar. While it is generally acknowledged that the chief disadvantage of the turbine is its high specific fuel consumption, there are many applications where fuel consumption is of little importance. The racecar driver, for one, cares little about fuel consumption, as evidenced by the high fuel requirements of the conventional racing piston engines. At Indianapolis the tire stop is mandatory so there is no time lost in taking on additional fuel. Other advantages of the gas turbine are as follows: Gear shifting not required because of torque characteristics, clean exhaust, fewer parts than piston engines, ignition required only during starting, no vibration, insensitivity to fuel octane rating, and elimination of the water cooling system.

Now what about the turbine’s fuel consumption? Is it really as serious as is generally supposed? The specific fuel consumption of the Boeing Model 502-10F gas turbine is 1.0 lb/hp/hr. This means the turbine burns approximately 43 gal per hour at full power. The fuel consumption at idle is 10 gal per hour. Assuming the race to be 4 hours long (which leaves us a little margin) and assuming the engine is running at full power 80 per cent of the time, and idling 20 per cent of the time while braking, the total fuel consumption for the 4 hr would be 136 gal. The total fuel consumption for the average Offenhauser engine running at Indianapolis is understood to be about 150 gal.

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The turbine used in this analysis is the Boeing Gas Turbine Model 502-10F. This turbine is rated at 300 hp at 5680 output shaft rpm. Horsepower and torque curves are shown on Fig. 2. Here again, it is shown why the turbine fits so well into the racing business. This is a "hot rodder’s" version of the standard production 502-10C, which is rated at 240 hp at 5160 rpm. Hopping up a turbine consists of making it run faster and hotter which in turn is accomplished by increasing the fuel nozzle pressure and opening the gas flow nozzles. This is a fairly simple procedure. As with the piston engine, this increase in horsepower is accompanied by a corresponding decrease in engine life. The life of the 502-10F engine at full power is estimated to be more than ample for Indianapolis race requirements. An additional 15 hp can be gained at 175 mph by taking advantage of the ram effect of the air; however, this additional 15 hp was not used in the analysis.

Figs. 3 and 4 show what can be expected in the way of performance from a turbine powered racing car. Fig. 3 shows the available tractive effort and drag curves of both the turbine car and piston engine car versus miles per hour. Gear ratios chosen for both cars allow the engines to develop their peak power at 165 mph. This approximates conditions at the track and gives us a fair basis for comparison. As the curve shows, the higher horsepower of the Offenhauser engine gives it a higher top speed and greater acceleration in the high-speed range. But below the high-speed range the torque characteristics of the turbine give it a pronounced edge in acceleration. This torque advantage is down in the speed range where the cars are coming onto the straightaway.

Fig. 4 is based on the tractive effort and drag curves shown in Fig. 3 and on the following assumptions:

The cars start to accelerate during the last 500 ft of the turn and continue to accelerate for 3200 ft of the straightaway for a total of 3800 ft.

The cars start to accelerate from a speed of 125 mph.

The Offenhauser powered car weighs 1700 lb and the turbine powered car weights 1375 lb.

The effect of the inertia of the rotating masses such as the wheels, shafts, and gears is accounted for by adding 5 percent to the total mass.

The results show that the torque characteristic of the turbine will enable it to cover the distance approximately 0.25 seconds quicker than the Offenhauser and to be ahead by a distance of 65 ft. This shows that even though the turbine car is underpowered it has the low speed torque advantage and the light weight necessary for good acceleration.

A practical demonstration of this point was shown in a drag race between two Kenworth trucks several years ago. One was powered by a Boeing 175 hp turbine and the other by a 200 hp diesel. Both trucks were loaded to the same gross weight. Because of the low speed torque of the turbine it was ahead by about three truck-and-trailer lengths at the end of a half-mile. However, the extra horsepower of the diesel gave it a higher top speed and after both trucks had reached their top speed, the diesel eventually caught and passed the turbine.

One critical disadvantage of the turbine is the acceleration lag, that is, the amount of time required for the gas producer rotor to accelerate from idle rpm to full power. In the Model 502-10F gas turbine this is about three seconds. It is quite possible that this problem is not as serious as it sounds. In a race like Indianapolis, instantaneous response and sudden bursts of speed are not required as much as they would be in a race of shorter duration on a small track. Indianapolis is a race where the driver finds the "groove" and maintains a high average speed to win. In driving the turbine the driver will learn to anticipate power requirements and will know at what point to apply the throttle to maintain a high average lap speed. This is not the first time this problem of accelerating lag has shown up at Indianapolis. Fred Agabashian, driver of the turbo-super-charged Cummins diesel, was confronted with the same problem. Results showed that when Agabashian was out on the track all by him-self, as he was during qualifying, he learned to anticipate the power requirements and managed to set a qualifying speed record in the process. Results also showed that the diesel failed to respond after the pace car pulled aside on the initial lap and the diesel dropped from the pole position down to sixth. This happened because driver Agabashian had no way of knowing at what point the pace car would pull aside.

In the event that the drivers are unable to cope with this acceleration lag in the turbine there is still another method to overcome it. This is by means of a wastegate power control between the gas producer turbine wheel and the output section turbine wheel. This wastegate allows the high velocity gas to bypass the output turbine wheel while the gas producer is turning at about rated speed. When the wastegate closes, the gas is again directed against the output turbine wheel and the torque response is instantaneous. This method has been used successfully on several Boeing turbine applications.

Another advantage of the turbine over its four-cylinder counterpart is its smooth torque flow. The destructive qualities of the pounding power surges of the four cylinders are only too well known to be reiterated here. The turbine’s smooth torque flow will make itself felt not only in increased life of the driveline components but also in lessening of driver fatigue, an important factor in a four-hour race. The absence of vibration also means the chassis and driveline system can be of lighter construction, thereby effecting an additional weight saving. In all cases where gas turbines have replaced piston engines in helicopters, the life and reliability of the delicate and expensive transmission have been increased many fold.

Another important effect of the smooth torque flow is in the increased ability of the tire to transmit torque to the ground. When the torque comes in surges as it does with the four-cylinder engine, there is a tendency for the tires to break free and lose traction. The turbine approaches the traction limit of the tires gradually and the tires are less likely to break free. This point is illustrated in Fig. 5.

The turbine provides absolutely no vehicle retarding force. There have been methods suggested for using the compressor as a power absorption device, but all methods are both complicated and at the present time unproven. In this installation, all braking will have to be done by the wheel brakes. The condition of the presently used spot brakes at the end of 500 miles indicate that they are more than ample for their present job and should be able to handle the job of slowing down the turbine car. If not, higher capacity brakes could be developed.

Today’s turbines are selling for about $14,000. This is a little more than twice the cost of the Offenhauser engine. While this price is high, it is not unreasonably high to the extent that it places the turbine completely out of reach to the racecar owner. Certainly many owners have spent considerably more than this to develop other experimental engines. Perhaps with the increased reliability and longer life of the turbine, it will prove to be less expensive in the long run. This price is, of course, being substantially reduced as the production of gas turbines increases.

Fig. 6 shows one possible arrangement of the engine and chassis. This chassis shown is a Kurtis 500D. Later refinements of the chassis and suspension culminating in the 500F can also be incorporated in this design. The engine fits in quite nicely with the standard six-inch offset. Cooling air coming in the front would be divided between the oil cooler and the engine compartment. The air inlet is located on top of the engine compartment to prevent the influx of dirt and rubber from the track. The installation is shown with a simple dog clutch to couple the engine to the driveline. Because the turbine has its own built-in torque converter the standard two-speed transmission is not required. The dog clutch could be replaced with a marine reverse gear if reverse is required. For the ultimate in reliability the conventional Indianapolis clutch and transmission with one gear removed could be used.

The turbine exhaust has always been a problem. The exhaust gas temperature is 1150 degrees Fahrenheit and requires a duct with a cross-sectional area of 80 square inches. In this installation it is placed in the conventional location with a large duct running down the upper-left-hand part of the car. The exhaust can be deflected upward in the event of objections for other drivers.

The weight of the turbine engine and transmission is 425 pounds as compared with the weight of the Offenhauser engine and transmission of 550 lb. An additional saving of 75 lb of the radiator, water, and fittings means a total saving of 200 lb in the engine compartment. This lighter engine and the absence of vibration means that the chassis and driveline could be of lighter construction, thereby affecting a weight saving of about 50 lb. The turbine contains its own oil sump, which holds six quarts. Normal oil consumption is less than one quart in 15 hours of operation; therefore, this is all that need be carried. The weight saving here over the piston engine is approximately eight gallons of oil plus the oil tank, which is estimated to be 75 lb. This makes a total weight saving of 325 lb. This will have a tremendous effect on tire life, a problem that has plagued racecar drivers for years. It also means increased acceleration as mentioned previously. Less weight in the forepart of the car means a change in weight distribution. This can be compensated for by locating the fuel tank amidship instead of over the rear axle. This has been done on the Italian Lancia and several other European cars. This position provides the desirable characteristic of having a constant weight distribution with either a full or empty tank. This midship position has often been criticized by drivers as being a potential fire hazard in the event of an accident. It should be remembered at this point that the turbine uses diesel fuel and not highly explosive gasoline or methanol.

Fig. 7 shows the famous SAC Fireboid. This has a Boeing Model 502-8C 175 hp turbine installed in a Kurtis 3000 series chassis. The car turned a speed of 107 mph in 13.14 seconds in a standing quarter mile. Time and speed were recorded during the 1955 National Drag Meet at Great Bend, Kansas. At the Fireboid’s home base in Omaha, it had no trouble dusting off a 300 hp Chrysler Allard in a quarter-mile drag. This car also made a demonstration run at Indianapolis just before the 1955 race, which could very well be considered symbolic of things to come. Replacing the 502-8C engine with the 502-10F engine shown in Fig. 8 and using a car designed specifically for the turbine will result in a combination that will be pretty hard to beat. The day is not far off when the awesome scream of the turbines will be intermixed with the mighty roar of the "Offy’s" as the starter announces "Gentlemen, start your engines."

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