General Motors Firebird

1950s prototype cars by General Motors
the later General Motors produced vehicle

The General Motors Firebird comprises a quartet of prototype cars that General Motors (GM) engineered for the 1953, 1956, and 1959 Motorama auto shows. The cars' designers, headed by Harley Earl, took Earl's inspiration from the innovations in fighter aircraft design at the time. General Motors never intended the cars for production, but rather to showcase the extremes in technology and design that the company was able to achieve. GM preserved the prototype cars at the GM Heritage Center in Sterling Heights, Michigan. Models of the cars are in the permanent collection of the Henry Ford Museum in Dearborn, and the cars still make regular appearances at car shows. The tradition of offering prototype vehicles continued with the Pontiac Banshee series. From 1967 to 2002, the Pontiac division of GM marketed its Firebird line of pony cars, which had no direct relation to these series of Firebird concept cars.

General Motors researched the feasibility of gas turbine engines in cars as early as the 1940s. It was not until the early 1950s that the company began building an actual engine, under the direction of Charles L. McCuen, general manager of General Motors Research Laboratories, with Emmett Conklin leading the project. The fanciful top speed of all four concept cars is "200 MPH." As these concept cars were not specifically tied to any one division of GM, the Firebird I, II, and III were adorned with the logo of the General Motors Air Transport Section (GMATS).

The 1956 Motorama movie Key to the Future projected a vision of the future. It shows a nuclear family that are hot and perspiring in a convertible on their way to a day at the beach, but they are stuck in a freeway traffic jam. In a flashforward to the future, they are cruising at a high speed in air conditioned comfort along an automated freeway with no other vehicles (except once a Firebird I) to be seen in a turbine powered Firebird II. The movie's concept was that General Motors would provide such a future. An example of this type of forecast is the approach in vehicle infrastructure integration using electronic vehicle control and improved highway infrastructure.

The Whirlfire gas turbine engines fitted to the Firebird concept cars and other GM concept buses and trucks are free turbine turboshaft machines with two spools: one compressor/gasifier turboshaft and one power/output turboshaft sharing a common axis without a mechanical coupling between them. Initially, the first engines developed (GT 300 and 302) did not have a regenerator, but adding regeneration to recapture heat from the exhaust gases was found to reduce fuel consumption by 1/2 in the second generation GT 304 fitted to Firebird II, so subsequent generations of GM Whirlfire turbines incorporated a regenerator. The single stage rotary compressor pushes compressed air out radially into the combustors, where it is mixed with fuel and burned, and the resulting combustion gases are expanded through first the gasifier turbine, which is on the same shaft and is used to drive the rotary compressor, then through the power turbine, which is on the output shaft. The power shaft speed is stepped down through reduction gearing at the output shaft to make it compatible with automotive components. The GT 300 had an output of when the gasifier (compressor) turbine was spinning at 26,000 RPM and the free (power) turbine was spinning at 13,000 RPM. The weight of the entire engine unit was With a second burner, the engine was re designated GT 302 and fitted to Firebird I (XP 21). Brake specific fuel consumption (BSFC) was a notable issue, which at 1.63 lb/hp·h was significantly greater than that of a comparable Detroit Diesel 8V71 diesel engine (approximately 0.40 lb/hp·h), even though the turbine was lighter. Other planned improvements would target throttle lag, caused by accelerating the gasifier turbine to peak speed, and lack of engine braking. GT 304 (1956) was the first GM gas turbine to include a regenerator, which used exhaust heat to warm intake air, improving fuel consumption to 0.77 lb/hp·h. The GT 305 (1958) fitted to Firebird III had an output of (at turbine speeds of 33,000 RPM gasifier / 27,000 RPM power) and weight of With a regenerator and additional component refinements, GT 305 achieved a brake specific fuel consumption of 0.55 lb/hp·h.