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.
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, earning two Sports Car Club of America (SCCA) race victories and two qualifying sprint victories during its only year of competition. The TX later set six Fédération Internationale de l'Automobile (FIA) land speed records for turbines after being retired from racing.
Development
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, while British manufacturer Rover and racing team BRM combined to build a racing car for the 24 Hours of Le Mans in and . Both cars showed reliability but were unable to win over the public or to win at Le Mans respectively. 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. A similar attempt with a Lotus 56 in 1968 also led to retirement after showing winning potential.
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. 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.
Chassis
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. 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. The second car #GTP2 was built from scratch, allowing it to be purposely designed around the use of a turbine engine, including a chassis longer. The chassis were known as the Mk.9 to McKee, but only ever raced as turbines under the Howmet TX guise.
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 fuel tank was placed between the cockpit and turbine, housing Jet A fuel.
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. The loaned turbines weighed and were able to provide and of torque. A maximum of 57,000 rpm was able to be reached.
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.