Howmet TX
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| Category | Group 6 sports prototype | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| Constructor | McKee Engineering | ||||||||
| Designer(s) |  Ray Heppenstall Bob McKee | ||||||||
| Technical specifications | |||||||||
| Chassis | Tubular space frame | ||||||||
| Suspension (front) | Double wishbone with coil spring | ||||||||
| Suspension (rear) | Double wishbone with coil spring | ||||||||
| Length | 154 in (3,900 mm) [1] | ||||||||
| Width | 71.5 in (1,820 mm)[1] | ||||||||
| Height | 46.5 in (1,180 mm)[1] | ||||||||
| Axle track | Front: 58.5 in (1,490 mm) Rear: 56.5 in (1,440 mm)[1] | ||||||||
| Wheelbase | 93.5 in (2,370 mm) or 91.25 in (2,318 mm)[1] | ||||||||
| Engine | Continental TS325-1 2,960 cc (181 cu in) two-stage gas turbine mid-mounted | ||||||||
| Transmission | 1-speed (electric motor for reverse) | ||||||||
| Fuel | Jet A | ||||||||
| Tyres | Goodyear | ||||||||
| Competition history | |||||||||
| Notable entrants | Howmet Corporation | ||||||||
| Notable drivers | Ray Heppenstall Dick Thompson Ed Lowther Bob Tullius Hugh Dibley | ||||||||
| Debut | 1968 24 Hours of Daytona | ||||||||
| Last season | 1968 | ||||||||
| |||||||||
| Constructors' Championships | 0 | ||||||||
| Drivers' Championships | 0 | ||||||||
The Howmet TX (Turbine eXperimental) is 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.[2]
Although not the first attempt at using a turbine powerplant in auto racing, the Howmet TX was the first and is still the only turbine to win a race,[2] earning two Sports Car Club of America (SCCA) race victories and two qualifying sprint victories during its only year of competition.[3] The TX later set six Fédération Internationale de l'Automobile (FIA) land speed records for turbines after being retired from racing.[2]
Chassis
Interest in the use of gas turbines as an alternative to the piston engine had been gaining support in the automobile industry during the 1960s. Chrysler had begun testing in the 1950s and began leasing their Turbine Car to the public in 1963,[4] while British manufacturer Rover and racing team BRM combined to build a racing car for the 24 Hours of Le Mans in 1963 and 1965.[5] Both cars showed reliability but were unable to win over the public or to win at Le Mans respectively.[6] By 1967, team owner and car developer Andy Granatelli had created the STP-Paxton Turbocar for the Indianapolis 500. The car nearly won the race driven by Parnelli Jones, but suffered a mechanical failure after leading over two-thirds of the event.[7] A similar attempt with a Lotus 56 in 1968 also led to retirement after showing winning potential.[6]
At the same time as Granatelli's turbine debut at Indy, racer Ray Heppenstall began to conceive a design for his own sports car to make use of a gas turbine, improving in some areas where the Rover-BRM had failed several years before. Heppenstall felt that a more simplified design for the chassis could make a turbine-powered car more competitive. Heppenstall originally proposed the car to Allison Engine Company and later to Williams Research.[8] He eventually turned to fellow racer Tom Fleming for aid. Fleming was at the time vice-president of Howmet Corporation, which provided castings for turbines in the aerospace industry. Heppenstall and Fleming were able to convince Howmet that their backing of a competitive and unique sports car could promote public awareness of the company. Howmet agreed to fund the project, lending their name to the car.[2]
Heppenstall began the project by purchasing a Cooper Monaco sports car, but later decided it was not the best choice for a turbine and the car was sold off.[8] Bob McKee, owner of McKee Engineering, was then contracted by Heppenstall to build two cars brand new. The first space frame chassis was actually built from an older McKee car initially built for the Can Am series in 1966, but adapted to house the turbine engine.[6][9] The second car #GTP2 was built from scratch, allowing it to be purposely designed around the use of a turbine engine, including a chassis 2.25 inches (57 mm) longer.[2] The chassis were known as the Mk.9 to McKee, but only ever raced as turbines under the Howmet TX guise.[9]
The Mk.9 was designed around the FIA's Group 6 regulations for sports prototypes, allowing for a completely custom mid-engine layout that was only limited in terms of engine sizes available to competitors. Closed cockpit bodywork with gullwing doors was designed by Bob McKee to shroud the mid-engine layout. Standard double wishbone suspension with coil springs were used with disc brakes on each wheel. A 32-US-gallon (120 L) fuel tank was placed between the cockpit and turbine, housing Jet A fuel.[6]
Turbine
The turbines to power the two Howmet TXs were leased from Continental Aviation & Engineering. The TS325-1 gas turbines were prototypes from an aborted bid for a military helicopter contract which Continental was not putting to use at the time.[10] The loaned turbines weighed 170 pounds (77 kg) and were able to provide 350 bhp (260 kW) and 650 lbf⋅ft (880 N⋅m) of torque.[2] A maximum of 57,000 rpm was able to be reached.[10]
A two-stage setup used an internal power turbine to drive the rear wheels through the use of reduction gearing. Due to the wide variable output of the turbine and the high level of torque, a standard gearbox was not necessary, leaving the Howmet TX with only a single gearing speed. However, the gearing ratios were able to be quickly changed in the differential, allowing the car to be adapted to various circuits. Due to the use of a single-speed transmission, there was no gearing for reverse. Although Heppenstall initially wished to do without reverse, the FIA mandated its use and a small electric motor powered by the turbine was installed, allowing the car to move in reverse.[2][8]
The turbine itself used two large exhaust pipes. However, a third pipe was situated off-center for use with a wastegate. The wastegate was designed to eliminate the lag between the driver pressing the accelerator and the turbine increasing its revolutions. Once the turbine was at its maximum revolutions, the wastegate helped regulate the flow of hot gas from the core to the power-turbine, thus increasing or decreasing the power output to the gearbox far quicker than the core could adjust mass-flow by itself.[2][8]
Although turbines cannot have their displacement measured in the same way as a piston engine, the FIA used an equivalence formula to determine the Continental TS325-1's displacement of 2,960 cubic centimetres (181 cu in),[10] although Heppenstall has since admitted that the engine was actually above the three litre limit.[8] This allowed the Howmet to compete in the Prototype Under 3000 cc category of the Group 6 formula.[6]
