GM’s Turbo-Titan gas turbine trucks
In the 1950s and 1960s, several global car companies experimented with gas turbine power. Prominent among them was General Motors, who built gas turbine powered experimental cars and trucks.
GM’s best-known experiments with the gas turbine engine were Firebird concept cars, but there were gas-turbine truck ventures. The truck experiments ran concurrently with the car efforts in the late-1950s.
Two prototypes were based on production trucks: the 200 horsepower, GT-304 turbine powered Turbo-Titan I of 1956 and the 225 horsepower GT-305 powered Turbo-Titan II of 1959. Both gas-turbine testbeds externally resembled stock Chevrolet GMC F-series and DF-series COE trucks.
GM must have realised by the early 1960s that gas turbine power wasn’t going to work in passenger cars and the principal interest turned to trucks – and heavy ones at that. The GT-gas-turbine engine family was was to be a series of four engines with power ratings up to 2000 horsepower.
The Turbo-Titan III (XP809) introduced by Chevrolet in 1965 was put on display in 1966 at the New York World’s Fair and GM predicted that it was five to 10 years away from commercial production.
Developed by General Motors’ Research Laboratories, the GT-309 gas-turbine delivered 280hp at 35,000rpm and that was geared down to driveline entry speed of 4000rpm. The peak torque rating at stall was 875 -1000 lb ft (1152 – 1356Nm).
Two significant technological advancements that distinguished GM’s GT-309 gas turbine engine design were the regenerative system and ‘power transfer’.
The regenerator recovered energy from hot exhaust gases. Instead of being exhausted directly into the atmosphere, the gases passed through rotating regenerator discs that recovered more than 90 percent of the exhaust heat. As they rotated, the discs transferred heat to the relatively cool air flowing to the burner.
Regeneration had three principal uses. Firstly, it cut fuel usage to around half that of a non-regenerative engine in a comparable application. Secondly, it cooled the exhaust gases (more on that topic later). Thirdly, the regenerator’s silencing action meant that a muffler wasn’t necessary.
While some earlier gas-turbine engines used regenerators, the GT-309’s claim to uniqueness was ‘power transfer’ – a patented development of the GM Research Laboratories and Allison Division.
Power transfer transmitted a scheduled amount of power from the gasifier turbine to the output shaft, thus stabilising the turbine inlet temperature over much of the engine operating range. A direct result was improved fuel economy at partial throttle, where the engine operated most of the time.
When the vehicle decelerated, power transfer coupled the driving wheels to the compressor, providing engine braking power two to three times greater than that of a conventional diesel-powered truck.
Another function of power transfer was to prevent turbine overspeed if the load suddenly was disconnected from the engine.
In the Turbo-Titan III a six-speed Allison MT-40 automatic transmission, with the torque converter and hydraulic retarder omitted, was coupled to the turbine via an adapter plate.
Interestingly, the drive tandem was Eaton deep-reduction (7.17/9.77) two-speed.
Three uniquely-bodied Turbo-Titan IIIs were built on modified GMC COE truck chassis and paired with aerodynamic side skirt-equipped 40-foot (12.2m) Fruehauf stainless steel trailers.
Each combination had a 50-foot (15.2m) overall length and GCM of 76,800 pounds (34.8t.)
Claimed fuel consumption was 0.45lb per hp hr (278g/hp hr) and the nominal fuel was Jet A1 (kerosene).
Electro-hydraulic tilt-cab construction was FRP panels over steel framing, with ‘gull-wing’ lift-up access doors and streamlined FRP chassis-side fairings. Streamlining extended to retractable headlights and indicators.
Inside the cab, ‘astronaut seats’ flanked a centre console and the transmission ’T-bar’ was adjustable for reach.
GM-engineered ‘dual steering’ replaced a conventional column and wheel, with twin discs operating the power steering. This Twin Dial steering system was developed by GM’s Saginaw division and was remarkably similar to Ford Motor Company’s Wrist Twist system that was created at almost exactly the same time.
GM engineers liked the Turbo-Titan III’s drive-ability and it showed diesel-powered tucks of the period a clean pair of heels when hill climbing. However, the driver had to monitor turbine temperature carefully. The steering system required a different technique that most testers didn’t like.
There’s an anecdote related by one of the test drivers, Bob Carlson. He brought a Turbo-Titan III into the Chevrolet Engineering Centre in Warren, Michigan, for a company function.
There was an outdoor viewing deck on the third floor of the Engineering Centre and a hydraulically powered freight elevator lifted vehicles to the deck.
On this occasion, the Titan was parked, turbine running, in the hallway waiting to be loaded on the elevator. Unbeknown to the driver, the vertical exhaust stacks were aimed directly at the ceiling-mounted, fire-suppression sprinkler heads.
When the sprinklers came on and dirty water showered the cab, Bob thought the engine had failed so he immediately shut it down and then realised what had happened. He sat there until someone was found who could turn the sprinklers off.
There was a minor flood on the floor of this hallway before the water flow was stopped.