Gas turbine on and off to run it only at high efficiency. The emergence of the continuously variable transmission may also alleviate the responsiveness problem. Turbines have historically been more expensive to produce than piston engines, though this is partly because piston engines have been mass-produced in huge quantities for decades, while small gas turbine engines are rarities; however, turbines are mass-produced in the closely related form of the turbocharger. The turbocharger is basically a compact and simple free shaft radial gas turbine which is driven by the piston engine's exhaust gas. The centripetal turbine wheel drives a centrifugal compressor wheel through
Free-turbine turboshaft Free-turbine turboshaft A free-turbine turboshaft is a form of turboshaft or turboprop gas turbine engine where the power is extracted from the exhaust stream of a gas turbine by a separate turbine, downstream of the gas turbine and is not connected to the gas turbine (the exhaust airflow is what spins the turbine that is connected to the shaft hence the term "free"). This is opposed to the power being extracted from the power spool via a gear box. The advantage of the free turbine is that the two turbines can operate at different speeds, and that these speeds can