Which instrument measures the speed of the engine's crankshaft?

The tachometer is the instrument specifically designed to measure the speed of the engine's crankshaft, usually expressed in revolutions per minute (RPM). This measurement is critical for monitoring the performance of an engine, as it allows pilots and engineers to ensure that the engine operates within its optimal RPM range. Proper management of crankshaft speed is essential for efficiency, safety, and effective power production in various types of aircraft.

In contrast, the other instruments serve different functions. The attitude indicator provides information about the aircraft's orientation relative to the horizon, indicating whether the wings are level or if the aircraft is climbing, descending, or in a bank. The airspeed indicator measures the speed of the aircraft relative to the surrounding air, and the vertical velocity indicator shows the rate of ascent or descent. Each of these instruments is vital for different operational aspects of flying, but none of them measures the crankshaft speed specifically.