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The Gas-Turbine Chevrolet “Turbo Titan III”


kscarbel
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Leading up to the GT-304 gas-turbine powered Turbo-Titan III, the Chevrolet Division of General Motors built the 200 horsepower GT-304 powered Turbo-Titan I of 1956, and 225 horsepower GT-305 powered Turbo-Titan II in 1959. Despite the dramatic names, both of these gas-turbine testbeds externally resembled stock Chevrolet COEs (I suspect the test chassis were respectively a GMC F-series and DF-series “Crackerbox”).

However the Turbo-Titan III (XP809) introduced by Chevrolet in 1965 was altogether different. GM put the truck concept on display in 1966 at the 1964-1966 New York World’s Fair and said the truck was five to ten years away from commercial production.

Developed by the General Motors Research Laboratories, the GT-309 gas-turbine delivered 280hp at 4,000rpm (an upper shaft speed of 4,000 rpm, reduction geared downward from 35,000 rpm). Because turbine engines deliver their highest torque levels at stall (0 rpm), the turbine developed a maximum torque rating of 875 ft-lb (1,152 N.m) at idle.

An operational prototype, three of the advanced Turbo-Titan IIIs were built on modified GMC COE truck chassis (I assume DF-Series “Crackerbox”) and paired with a specially built aerodynamic side skirt-equipped 40-foot Fruehauf stainless steel trailer.

The tractor-trailer combination had a 50-foot overall length and GCW of 76,800 pounds.

The General Motors GT-309 was a conventional turbine including a compressor, gasifier, power turbine and regenerator. The gasifier was mounted on the same shaft as the compressor. The power turbine gear was connected to the output shaft.

A 6-speed Allison MT-40 automatic transmission with the torque converter and hydraulic retarder omitted was coupled to the turbine with a special aluminum adapter.

Chevrolet claimed the Turbo-Titan III’s turbine engine to be lighter, quieter and longer-lasting than conventional diesels (350,000 miles versus 250,000 miles), however fuel costs were higher.

Engine: General Motors GT-309

Horsepower: 280 @ 4,000

Torque: 875 ft-lb (1152 Nm) @ stall (0 rpm)

Engine Weight 1,425 lb

Specific Fuel Consumption 0.45 lbs per horsepower·hour

Transmission: Allison MT-40 less torque converter and hydraulic retarder

Front axle: 15,000 lb

Front Springs: 2 x 7,500 lb

Rear Bogie: Hendrickson 34,000 lb

Rear Axles: Eaton 2-speed (7.17/9.77) spiral bevel drive axles

Rear Springs: 2 x 17,000 lb

Frame: Ladder type, channel section side rails, 10-1/16 x 3-1/2 x 5/16”

Brakes: Full air, Rockwell 17-1/4 x 3-1/2 (front), Rockwell Stopmaster 15 x 7 (rear)

Wheels: Budd heavy-duty

Tires: 10.00-20 (front), low-profile 18-19.5 16-ply (rear)

The cab consisted of fiberglass-reinforced polyester exterior panels with a steel framework. Molded side chassis air fairings followed the cab’s futuristic styling theme and enhanced aerodynamics.

Left and right side sections of the side chassis air fairings, just behind the cab, tilted upward to provide access to dual batteries and other components.

An electro-hydraulic cab tilt system provided quick and easy access to the GT-309 gas-turbine engine.

Top-hinged power-operated swing-up door windows provided driver entry when the key was inserted into the door lock.

Triple rectangular headlamp assemblies in the left and right side engine air intake scoops, retracting into the sidewalls when not in use for an optimized aerodynamic profile.

The front turn signals were retractable, emerging from the front fenders only when actuated.

The rear 3-bulb turn signals operated in an inboard-out sequence, indicating motion in the direction you were turning.

A flat exhaust stack exited through the roof.

Inside the cab, "Astronaut Seats" with full headrests were mounted on each side of a center console.

A T-handle controlling the 6-speed Allison transmission was mounted on a pedestal that pivoted forward and back along with the panel to provide drivers of all sized with an optimized driving position.

Full interior carpeting was included along with retractable seatbelts, air-operated windshield wipers, full tinted glass and air conditioning.

A 4-speaker AM/FM stereo radio and a 2-way telephone were featured for the first time in a heavy truck.

Mounted on a pedestal in front of the driver, the GM designed and engineered dual steering system replaced the conventional steering column and wheel. Twin dials mounted on a padded vinyl panel operated the platforms power steering. An auxiliary pump driven from the propeller shaft provided emergency usage if the main pump failed for any reason when the truck was in motion.

One of the Chevrolet engineers who designed and drove the Turbo-Titan III had these comments:

"At the time Chevrolet was getting very serious about turbine engines. Although the Turbo-Titan III was highly experimental, the key advantages were power, fuel economy and cheap fuel (kerosene). The driveability was outstanding. However, the driver had to be extremely careful about monitoring turbine temperatures. The engine could not be used for braking as in internal combustion engines. I have no idea what happened to the vehicle. Since it was one of a kind, I assume they kept it in storage or scrapped it. As an added thought, the disc steering wheels (the truck did not have a steering wheel--it had two small discs in front of the driver), I had them installed on a passenger car for evaluation in normal driving situations. This type of steering system was very novel at the time and required a lot of attention to normal driving. I kind of liked it but I do not think anybody else did!"

When driving the Turbo-Titan III through Pennsylvania on the way to the New York World’s Fair, he encountered a large hill that other trucks had trouble climbing. The Turbo-Titan went over it "like nobody's business."

After appearing in various auto shows, the three working prototypes entered service with GM’s own truck fleet. I don’t know what became of these trucks, an important piece of trucking history.

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The GT-309 gas-turbine was designed to be a series of four engines with power ratings up to 2,000 horsepower.

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 the rotating regenerators, discs which recover more than 90 percent of the exhaust heat. As they rotate, the discs transfer heat to the relatively cool air flowing to the burner.

Regeneration pays three principal dividends. First, it cuts fuel usage. A regenerative engine will use only 50% of the fuel of a non-regenerative engine in a comparable application. Second, it cools the exhaust gases. The exhaust is in the 200° to 500°F range, depending on load. Third, thanks to the regenerator, a muffler isn’t necessary.

While some earlier gas-turbine engines used regenerators, the GT-309's claim to uniqueness was “power transfer”, a patented GM development of the GM Research Laboratories and Allison Division.

Power transfer transmits a scheduled amount of power from the gasifier turbine to the output shaft, thus stabilizing the turbine inlet temperature over much of the engine operating range. A direct result is improved fuel economy at partial throttle, where the engine operates most of the time.

When the vehicle decelerates, power transfer couples the driving wheels to the compressor, providing engine braking power two to three times greater than that of a conventional diesel-powered truck.

The power transfer system of the 280 horsepower GT-309 gas-turbine engine provided over 1000 lb. ft. of torque at stalled output rpm. Power transfer allowed trucks to make faster and safer descents, controlling downhill speeds while extending service brake and wheel-end life.

Another function of Power transfer was to prevent turbine overspeed if the load suddenly is disconnected from the engine.

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