The turboprop is the least expensive turbine to operate, due to the fact that there is a prop, pushing lots of air, at a relatively slow speed. It is usually most efficient in the .3-.5 mach range.
The piston often cant go as high as a turboprop, since it relies on normal aspiration to feed the engine. A turboprop uses a turbine, which is relatively the same pressure in the air, as on the ground.
Two all beef patties, special sauce, lettuce, cheese, pickles, onions on a sesame seed bun.