The Lotus turbine car

Let us get things straight from the start, in spite of what the Lotus publicity material said, the T56B Lotus is not a jet car. The exhaust from the Pratt & Whitney turbine is directed upwards at about 45-deg., there is only about 50 lb. thrust, and it exerts a downward pressure and not a propulsive force. The power from the turbine drives all four wheels through positive gearing, and because the engine is a two-shaft turbine there is no clutch mechanism, so forget any talk about "jet cars" and automatic transmissions.

This car may be the first turbine-powered Grand Prix car, but in the world of turbine cars it is not new, nor is it new in the world of racing, Indianapolis and sports car racing being way ahead of Grand Prix on technical development. It was while watching the Lotus turbine Formula One car during the first day of practice for the Race of Champions that the thought occurred to me that Formula One, or Grand Prix racing, is behind the times technically, for there have been turbine-powered cars at Indianapolis, Le Mans and the BOAC long-distance races, there have been Wankel-engined cars in hill-climbs, saloon-car racing and sports-car races, USAC racing is very advanced with turbo-charging, NASCAR racing is ahead on sheer speed, sports cars are faster on circuits like Spa and Monza, they also started the fashion of inboard brakes and side-radiators, and the only advantage the Grand Prix racing would appear to have would be on glamour, publicity and ballyhoo.

The origins of the Lotus turbine Formula One car go back to 1968 when Lotus designed the Type 56 for Indianapolis. In the same year they started on a similar car for Formula One, known as the Type 56B, but progress was stopped by various changes in the Lotus fortunes, and they side-stepped to the Type 63, which was a similar four-wheel-drive chassis, using a Cosworth V8 engine. They have now returned to the Type 56B, designated on its identity plate as T56B, but loosely referred to as the 56B. Like the Indianapolis cars and the Type 63, the chassis is an aluminium bath-like affair with a wheel at each corner, the driver in the front, and all the mechanism behind him, with a fibre-glass top clipped over the whole thing. The wheels are sprung on double links, the upper ones operating the spring units through rocker arms. The ventilated disc brakes are mounted inboard, but outside the "bath", with short drive shafts to the hubs. The front and rear differential units are on the left of the trans-axles, with the fore-and-aft drive shafts running along the left side of the "bath" to the centre differential, just to the left of the driving seat. From there, a drive case runs across behind the seat to the centre of the car, where it is joined to the output shaft of the turbine, this cross-drive being by a 2 in. internal tooth Morse Hy Vo chain.

The Pratt and Whitney STN6/76 turbine engine lies behind the driver, and it is a type of engine used in helicopters, boats and for industrial purposes. Basically it consists of two parts, the gas generator at the back and the power turbine at the front. In order to comply with the FIA rules equating turbine engines to piston engines, a lot of modifications have had to be made to the turbine, and these have been done by Pratt and Whitney. The cost of the engine in Formula One form is estimated at over £32,000, but it is purely academic because the engine in the Lotus belongs to Pratt and Whitney. Ducts on each side of the cockpit feed air into a sealed chamber on top of the engine, which feeds an annular entry into the gas generator; from there the high-speed air is delivered into the combustion annular chamber in which the kerosene injectors are situated, and where the burning takes place. The hot gas stream passes through a high-pressure nozzle to drive the gas generator, and the remaining energy in the gas stream passes through the power turbine and out through the upward facing exhaust outlet. The two parts are not connected, as in some turbine engines, hence the description two-shaft engine. From the power-turbine shaft an epicyclic gearing drives the output shaft coupled directly to the Hy Vo transverse drive.

It can be readily appreciated that with the car's brakes on the power turbine cannot turn, but the gas generator can, so that the air in the annular combustion chamber would be stirred up as the oil is in a fluid torque converter. However, with the fuel/air mixture burning, the heat inside the engine is enormous, as much as 1,000° Centigrade, so that the power unit does not like being held stationary for long. The temperature in the combustion space is the critical part of the turbine, so that the most important dial on the instrument panel is the temperature gauge coupled to this area, known as the ITT gauge, or inter-turbine temperature, and it is calibrated to 10 (X 100° C) with a danger line at 8 (800° C).

The speed at which a turbine revolves is of little importance, unlike a piston engine where crankshaft speed is all-important, so the Lotus has no form of rev-counter or tachometer at all. A turbine's main instrument, apart from the temperature gauge, is a dial that reads the percentage at which it is working, at full power reading 100 (100%), so that with this two-shaft engine there are two percentage gauges, N1 for the gas generator and N2 for the power turbine. At "all systems go" or maximum speed (dependent on axle ratios naturally), the driver would like to be able to read 100% on N1 and N2, with something under 8 on the ITT gauge. This would be like the driver of a Lotus 72 reading 10,000 r.p.m. in 5th gear. During practice at Brands Hatch the car was over-geared so that on the fastest part of the circuit Fittipaldi could only report 97% on N1 and 80% on N2. When they got the gearing right, by axle ratio changes for major steps, and sprocket sizes on the Hy Vo drive for minor ones, he reported 107% on NI and 103% on N2. This represented a slight under-gearing effect, but the safety margin on the Pratt and Whitney is enormous.

The driver has but two pedals, a brake pedal for the left foot, and an accelerator pedal for the right foot. The accelerator pedal is linked directly to a fuel-metering unit mounted on the rear of the car and this controls the flow of kerosene to the injector nozzles. It does not shut off completely, or the flame would go out, so it is set to a determined idling speed for the gas generator. On the steering wheel is a "kill-switch" which shuts off the fuel at the nozzles by an electrical system, and on the left of the cockpit is a T-handle push-pull control that also opens and shuts the fuel-flow valve.

To start the engine an electric motor, that also acts as a generator, turns the gas generator, the N2 gauge rising as the shaft speed increases. A form of glow-plug in the combustion chamber is switched on and the T-handle in the cockpit is slid forward, opening the fuel valve. Burning starts up in the combustion space, and as the flame starts the ITT gauge rushes up to 900° C, and as the heat flow passes through the power turbine and out through the exhaust outlet the temperature settles back to 600° C. The driver holds his left foot on the brake, thus keeping the power turbine stationary, but the moment he lets them off the car moves forward, its acceleration depending on the percentage output of the gas generator, which in turn depends on the amount of fuel being fed to the combustion space by the accelerator movement. It would not be possible to hold the car on the brakes with 100% on the gas generator, and apart from that, trying to do so would put the reading of the ITT gauge way up in the danger zone.

For take-off the driver has to balance temperature with percentage reading on N1 in the same way that a driver of a conventional racing car balances engine r.p.m. with wheelspin and clutch movement when starting off. The turbine car will not spin its wheels on initial take-off, but at about 60 m.p.h. it could start spinning all four wheels. Into corners the driver has to lift off early, keep the N1 gauge indicating as much percentage as he feels he can use round the corner, and slow the car with the brakes. When he estimates his cornering speed has been reached, he releases the brakes and corners with the power on, rather like a racing motorcyclist does. Too much opening on the fuel valve will either overheat the brakes or raise the ITT gauge too high, so he has to balance temperature against braking against cornering power. It can be appreciated that a driver who is steeped in tradition with piston-engined cars would find it difficult to adapt himself to the new technique. A driver without belief in turbine cars would be wasting his time trying to drive one, like a driver who doesn't believe in mid-engined coupés trying to drive a Lotus Europa.

It was this mental attitude that allowed Andretti to lap Indianapolis some 10 m.p.h. faster than Hill and Rindt in the Indianapolis STP-turbine Lotus cars. It is also applicable to four-wheel-drive, which is the main reason why all the four-wheel-drive projects in 1969 floundered. In Emerson Fittipaldi Lotus have an ideal "new boy" who is prepared to develop himself with the turbine car.

The life of the Pratt and Whitney turbine engine is 1,000 hours, not 100 as mentioned in some journals, and on the rear of the chassis is a recording clock counting up the hours that the engine has run. When the car appeared at Brands Hatch for the first time it had run just over 20 hours. In order to make the car comply with Formula One rules a reverse mechanism, using an electric starter motor and cog-belt drive, is attached to the transfer case, turning the power turbine in reverse and driving the power train in reverse, but naturally the gas generator must be stationary when doing so. Fuel consumption of Shell Aviation kerosene is pretty heavy, and at the moment the 60 gallons the car carries would only take it about 160-180 miles. The wheelbase is 102 in., the track 62.5 in., overall length 170 in. and 15 in. diameter wheels are used.

Needless to say, the introduction of such a car to road-racing, as distinct from oval racing where constant throttle can be used, has posed numerous problems, especially as regards instant pick-up and the method of cornering when in company with other cars. At Brands Hatch, had Fittipaldi been on the front row of the grid he could have let the turbine car accelerate to its maximum, and it would certainly have beaten everyone to the first corner, but he would then have had to lift off early and the other cars could have stormed past on the over-run with locking brakes, and scrabbled round in the lead. At Monza where the first corner is a long way from the start, it would be a different story.

However, one of the big problems that Gold Leaf Team Lotus will be faced with is dealing with the "barrack room lawyers", which abound in Grand Prix racing these days, for they will certainly try and get it banned if it proves competitive. If it ever wins a race I can hardly wait for the screams of protest from those who do not win. Another problem facing Lotus is that the FIA view a Lotus-Cosworth and a Lotus-Pratt & Whitney as two different makes of car, so that any points each might gain in the Manufacturers' Championship events cannot be added together, and Lotus are very keen on winning that Championship.—D. S. J.