What is the Function of a Tachometer in an Aircraft

A tachometer is an instrument that measures the rotational speed of a shaft or disk, and it is responsible for measuring the RPM of a moving object such as a plane. As such, they are usually found in the aviation and automotive industries. Within the automotive industry, tachometers are displayed on the dashboard of the car, informing the driver when to shift gears by taking the rotational speed of the shaft into consideration.  

However, aircraft tachometer systems are furnished with AC generators on the gear cases of reciprocating engines or drive sections of turbine engines. When a turbine engine turns, the AC generator converts it to a digital setting. It is important to note that generators produce varying rates of output in direct proportion to engine speed. 

Essentially, a tachometer is a motor speed gauge that is driven by the speed of its exhaust valve. In simplistic terms, tachometers are dials with a needle pointing to the current speed in RPM. However, the use of digital tachometers has garnered popularity. Regardless of the type, they are found in various machinery to hold and control fuel, and will usually always consist of a dial display and/or display screen with an LED signal. 

While some tachometers measure engine hours from the aircraft’s engine records, others calculate at what intervals planes need to be inspected. Beyond record keeping, tachometers serve to inform both pilots and drivers when they should slow down. Keep in mind that for aircraft, in particular, engines must maintain a constant speed of at least 2700 RPM. To better understand the importance of tachometers, the next section will cover electronic, mechanical, contact, and non-contact tachometers.

Electronic Tachometers

Featuring numerical readings and data storage capabilities, electronic tachometers are often preferred over their counterparts. With this type of tachometer, the ignition system generates a voltage pulse whenever the spark plug fires at the output of the electromechanical part. As a result, this part of the tachometer corresponds to the average voltage of this series of pulses as directly proportional to the engine speed. This signal can then be transmitted to the indicator through a twin screened cable and displayed to the user via the LED or LCD readout. 

Mechanical Tachometers

Mechanical tachometers, on the other hand, work by using the centrifugal force on a rotating mass and rotating speed. This force has the ability to compress or stretch mechanical springs. Resonance tachometers are a subtype of mechanical tachometers. This subtype uses a set of highly-tuned reeds to determine the speed of an engine. Furthermore, they function by identifying the machine’s vibration frequency. 

Contact Tachometers

Contact tachometers necessitate, as their name suggests, contact with the rotating object to determine its RPM. They utilize an optical encoder or magnetic sensor, depending on the model of the tachometer, and they must make direct contact with the shaft or rotating component to acquire an accurate reading. 

Non-contact Tachometers 

Non-contact tachometers can achieve accurate measurement without the need for contact and they work alongside lasers or infrared light. More than that, they are perfect for operating conditions that have hard-to-access, hazardous, or mobile objects. 


If you find yourself in need of tachometer indicators, tachometer sensing devices, or other aircraft engine parts and accessories, rely on Aviation Orbit. Aviation Orbit is a premier distributor of top-quality aircraft products that have been vetted for quality, reliability, and functionality. Kickoff the procurement process with a competitive quote and see how Aviation Orbit can serve as your strategic sourcing partner!


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