Howmet TX Gas Turbine Prototype - Le Mans 1968
|Johann and Piet van Biljon|
I have done some research on the car. This is what I found.
BackgroundThe 1960's was a time when there were fewer restrictions placed on race car designers than today, and that period saw the appearance of gas turbine powered cars, such as Andy Granatelli's STP-Paxton and Lotus 56 cars and the American Howmet Corporation's TX sports-racing machine of 1968.
The Howmet TX (Turbine eXperimental) was an American sports prototype racing car designed in 1968 to test the competitive use of a gas turbine engine in sports car racing. Planned by racing driver Ray Heppenstall, the TX combined a chassis built by McKee Engineering, turbine engines leased from Continental Aviation & Engineering, and financial backing and materials from the Howmet Corporation.
The Howmet project was conceived early in 1967 by Ray Heppenstall, a sports car racer from Philadelphia. Heppenstall reckoned that a suitable lightweight turbine mounted in the back of a conventional sports-racing chassis would be a competitive proposit ion. He also convinced one of his racing friends, Tom Fleming, then the sales vice-president of Howmet, one of the United States leading metal companies and a major supplier of precision castings to the aircraft gas-turbine industry. Fleming and Heppenstall convinced the Howmet board that running a race-car program would be an ideal promotional tool.
|The turbine engine|
A suitable power unit was found at Continental Aviation & Engineering, who had recently lost out in a bid for a
contract for a light observation helicopter engine and had ten TS325-1
turboshaft engines left on the shelf from its development work. This unit
developed a nominal 325 bhp at the output shaft, 650 lbs. ft. of torque at
stall, and weighed 170 lbs. Applying the FIA's engine equivalency formula it
was rated at 2960 cc, slotting it neatly into the Group 6 sports-prototype
three litre class. Continental contributed two of these engines for
installation in a relatively conventional tubular space-frame chassis built by
Bob McKee. US
The turbine was mounted at the rear, above a single speed transmission driving the rear wheels through a specially designed quick-change differential which allowed ratio changes. The necessary reverse was provided by a separate electric motor drive. A 32 gallon fuel tank was mounted centrally between the cockpit and the engine. Suspension was by conventional wishbone and coil spring/shock absorber units, with outboard disc brakes.
The TS325 engine comprised a two-stage gas generating turbine driving the two-stage compressor while also providing gas to the power turbine whose output shaft, via reduction gearing, drove the rear wheels. Heppenstall's solution to the turbine lag was to insert a wastegate bet ween the gas-generating and the power turbines. The first third of throttle pedal movement controlled fuel supply to the combustion chambers, and thus the speed of the engine. But once spinning at its maximum 57,500 rpm and delivering full power, the final two-thirds throttle movement activated the wastegate, thus controlling the amount of gas directed to the power turbine, and hence the rear wheels.
The 1968 Racing Season
The TX's first race was the Daytona 24 hours in February and two cars were brought, a newer car with 2.25 inch longer chassis and the original as spare; drivers were Dick Thompson, Ed Lowther, and Heppenstall. After 34 laps, and running as high as third, the waste-gate valve stayed shut as Lowther arrived at a tight corner leading from the infield to the banking, the resultant contact with the wall putting the car out.
At the Sebring 12 hours the car was qualified third, just 1.2 seconds adrift of the pole. In the race, the TX was running seventh when one of the engine mountings broke, and retired just before the seventh hour.
At the BOAC 500 at Brands Hatch in April British pilot Hugh Dibley joined Thompson and the TX qualified seventh. In the race the wastegate problems struck again, sending Thompson into the bank at Druids after seven laps. Dibley then drove in the Guards Spring Cup at
Park the following weekend. Here he qualified second, and was
running in fourth place until he pitted for fuel, but the starter failed and
there was no way he could rejoin.
Heppenstall then campaigned the cars in a number of SCCA regional events. The first race finish came in May in the
200. Then on June 8th Heppenstall won the qualifier for the Heart of Dixie race
at Huntsville, and then the main race the
following day, the first race win for a turbine powered car. The following
weekend at Marlboro, Dick Thompson joined him for the 4.5 hour 300 mile race.
Thompson won the qualifier, then the following day with Heppenstall the feature
race also, leading from start to finish.
The Watkins Glen 6 hours in July was the next FIA Championship outing, and for the first time both TX's were raced, with Thompson/Heppenstall being joined by Hugh Dibley/Bob Tullius in the older car. The cars qualified 8th and 9th, and were running well in third and fourth places, until the final hour. Heppenstall and Thompson maintained third spot until the end, but the transmission of the Dibley/Tullius car broke, although they managed to cross the finish line and be classified 12th.
|Howmet TX at Classic Le Mans 2012|
Le Mans 24 hours on 28/29th September
turned out to be something of a disaster. After only three laps Thompson came
back in to hand over to Heppenstall, feeling that his car wasn't quite right. A
fuel system problem limited the engine to 70% power and strangled the speed on
the straight. They kept going however, and had worked up to 29th place when, at
9.45pm, Thompson crashed at Indianapolis
corner and rolled, severely damaging the car although being unhurt himself. A
rear wheel bearing broke on the Tullius/Dibley car after less than two hours.
Although repaired in a lengthy 3 hour rebuild, it was finally disqualified in
the seventh hour having covered insufficient distance.
Gas turbine operating principle explained
A gas turbine operating principle is simpler than a reciprocating piston engine. There are only three rotating parts not in rubbing contact with their surrounding cases as shown in the above simplified diagram. There are two shafts. The first shaft supports the air compressor and the primary turbine while the second shaft supports the power turbine and transfers the power by gear reduction to the wheels. An electric starter provides assistance by rotating the air compressor for the starting procedure. Compressed air is fed to a combustion chamber where it is mixed with kerosene fuel and ignited. Hot and high pressure gases are generated and sent to the primary turbine before reaching the power turbine. The primary turbine rotates with the air compressor. Hot gases are then sent to the exhaust system. In the case of the Howmet TX, there are two ways to adjust the power transferred to the wheels. The first method is the conventional approach with a gas turbine and operates with the variation of the fuel quantity injected in the combustion chamber. This conventional method, however, is known for a response time unwanted with racing cars. A second method utilizes a variable vane system on the hot gases admitted to the power turbine. This system also called waste-gate, allows to adjust the quantity of hot gases sent to the power turbine while sending the remaining portion directly to an exhaust pipe. This second method allows to keep the combustion chamber at full power and adjust the power sent to the wheels. The third exhaust pipe at the rear is dedicated to this waste-gate.
The Howmet TX gas turbine rated at an equivalent 3000cc produced nearly 400 hp at 55,000 rpm. The power transfer system contains a gear reduction that set the proper rotation to the wheels.
Reproduced from Wikipedia and various other sources