What kind of tachometer is used on most small single-engine airplanes?

What kind of tachometer is used on most small single-engine airplanes?

• A. A mechanical gear-driven tachometer
• B. A magnetic drag tachometer that is similar to an automobile speedometer
• C. A digital quartz tachometer
• D. A three-phase AC tachometer

Answer: (B)

In small piston airplanes, the tachometer most often used is an electric magnetic drag type. This system gets a signal from a magnetic pickup or small generator driven by the engine, so the RPM is converted into an electrical signal that the gauge reads. The “drag” aspect refers to the small electromagnetic load the generator imposes, but it’s minimal and mainly serves to produce a proportional voltage (or current) for the tachometer to display RPM. The big advantage is fewer moving parts than a mechanical cable-driven tachometer, which means less wear, easier maintenance, and reliable operation under vibration. It’s also similar in concept to a car speedometer, which uses a magnetic mechanism to translate rotational speed into an electrical signal for the gauge. Digital quartz tachometers exist, but they’re not as universally used as the magnetic drag type on most light aircraft. A three-phase AC tachometer isn’t typical for small single-engine airplanes because those systems require a three-phase generator setup that isn’t standard on piston engines.

In small piston airplanes, the tachometer most often used is an electric magnetic drag type. This system gets a signal from a magnetic pickup or small generator driven by the engine, so the RPM is converted into an electrical signal that the gauge reads. The “drag” aspect refers to the small electromagnetic load the generator imposes, but it’s minimal and mainly serves to produce a proportional voltage (or current) for the tachometer to display RPM. The big advantage is fewer moving parts than a mechanical cable-driven tachometer, which means less wear, easier maintenance, and reliable operation under vibration. It’s also similar in concept to a car speedometer, which uses a magnetic mechanism to translate rotational speed into an electrical signal for the gauge. Digital quartz tachometers exist, but they’re not as universally used as the magnetic drag type on most light aircraft. A three-phase AC tachometer isn’t typical for small single-engine airplanes because those systems require a three-phase generator setup that isn’t standard on piston engines.