Turboprop powered aircraft have two operating modes, Beta and flight. In the Beta mode, which is on the ground, the engine speed is variable according to power lever (not throttle, those are for reciprocating engines) angle. In flight the propeller is in the constant RPM mode and the propeller angle is varied by changing the power lever angle. Most later turboprops are totally constant speed, i. e. once you go into the flight mode on take-off the prop RPM is constant. On Rolls-Royce Dart powered airplanes, there is a different prop RPM for different flight modes, i.e. climb, cruise, descending. These airplanes are more difficult to ground run after engine changes and while trouble shooting in order to determine if the engine prop combination are operating OK.