Turbines are extremely reliable in aircraft applications and can operate reliably at varying speeds and power levels. Failure rates are in the 1/100ths of a percent. the most critical aspect is the operating clearance between turbine blade tips and the shroud housing material, which is of the order of 5 thousandths of an inch. There are two problems in competition with piston engines like gasoline or diesel. One is cost and the other is part power fuel consumption. Piston engines have a thermodynamic cycle, which is constant over the operating speed range i.e. compression ratio. The equivalent thermodynamically of compression ratio in a gas turbine is compressor pressure ratio, which is a function of engine gas generator speed. Thus, a gas turbine with a regenerator can match the fuel consumption of a piston engine at its max power point, but as the gas generator speed drops to reduce power the pressure ratio falls accordingly and the thermodynamic efficiency drops exponentially raising the fuel consumption significantly. In a piston engine with its constant compression ratio the ideal thermodynamic efficiency remains constant over the speed range. However, at low speeds the internal friction in the cylinders is a dominant source of loss and at high speeds the air induction losses dominate as the friction losses diminish relative to the increasing power production. This results in a bucket shaped fuel consumption characteristic for pistons vs. a rectangular hyperbola shape vs. power for turbines with the fuel consumption rising rapidly as power diminishes from the max power point. Thus, gas turbines have much higher part power fuel consumption relative to pistons and it is inherent in the thermodynamic cycle. It is not a problem for aviation as aircraft are operated near their max thrust or power settings through most of a flight.
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Good article. Although I spent 40 years ( the last 10 as the engineering executive responsible for Design) designing jet engines at Pratt and Whitney Canada in Montreal, I never heard of Elsie MacGill. She is obviously an ideal role model and made well recognised contributions to the industry. We need more publicity for this kind of trailblazing excellence in Canada. I mention that the AVRO Arrow was not a fighter but was designed specifically to be a high altitude interceptor of Soviet bombers coming over the Pole. It successfully met that requirement, but was cancelled in disagreement between the then Prime Minister John Diefenbaker and the head of AVRO Canada Crawford Gordon, who fired the whole staff on Black Friday over the corporate intercom system. The Bomarc missiles, which were supposed to replace the Arrow, were unsuccessful and in the end the RCAF had to buy US aircraft. The Iriquois engines designed specifically for the Arrow mission were the first in aviation to have a two spool compressor and titanium alloy compressor rotors.
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