International’s gas turbine trucks
In the late 1960s International was convinced that the gas turbine would be the truck powerplant of the future. What happened?
“From fifty feet away all you hear is the sound of the tyres on the road.” Was this the claim being made about a new whisper-quiet passenger vehicle? No, it was actually a prototype heavy truck and the result of many years’ engineering work at International Harvester’s US head office.
The truck was a modified CO-4000 6×4 and demonstrated its grunt by hauling two semi-trailers converted to drawbar units with dollies around several test tracks.
The engine was a gas turbine, produced by IH’s own Solar Division and intended to replace diesels in the 300hp+ range. Plusses for the gas turbine were said to be installed weight and package size, economy, maintenance and reliability.
The prototype engined weighed an impressive 720kg – around half the weight of a six-cylinder diesel of the period – and measured a metre wide, just over a metre high and 1.25 metres long.
Just as a gas turbine turboprop engine drives a shaft, the Solar gas turbine drove an output shaft and then the rear wheels, via a step-down transmission that dropped shaft speed form 34,000rpm to 4000rpm.
Unlike a diesel engine, the gas turbine was said to be stall-proof and the output shaft could be stopped, while the gas producer section of the engine kept running.
A heat exchanger, called a ‘recuperator’ captured waste heat from the exhaust to prove fuel economy, particularly in part-load conditions. The recuperator also acted to ‘chop up’ the exhaust sound waves, greatly reducing exhaust noise.
IH selected a stationary recuperator, rather than a rotary regenerator, because it was inherently rugged, required little maintenance and was durable.
Fabricated stainless steel parts, including honeycomb structures, achieved high efficiency in a compact stationary heat exchanger.
Other features of the power unit included variable-geometry nozzles which were reported to have brought fuel economy of the turbine much closer to that of a diesel.
The IH gas turbine research project began in 1955, with the aim of producing turbines for agricultural and construction equipment, as well as for trucks.
In late 1959, the Solar Aircraft Company lost several key military contracts for its turbine engines and so decided to court an investor. The one that best suited was IH and the relationship was mutual. The IH leadership team was keen on the idea of buying Solar Aircraft Company and developing turbine engines for its trucks, tractors and construction equipment.
The Solar Aircraft Company had been producing gas turbines for stationary and marine power for the previous 20 years. Its range included gas turbines from 700hp to 5000hp that had clocked up a collective 10 million operating hours in global applications.
IH also demonstrated Solar gas-turbine-powered agricultural tractors and one of the prototypes is in the Smithsonian Collection.
After initial hype the Turbostar gas turbine truck failed to make it to market.