Tach Generators

An aircraft tach generator is an electromechanical device that is capable of determining the speed of motors, engines, and other various rotational devices. When implemented on an aircraft, such devices are regularly used to measure the revolutions of the engine, indicating engine RPM and/or rotor RPM. As tach generator devices are common to aircraft applications, understanding how they are designed and how they function can be useful for any pilot or aircraft engineer.

While tach generators will often differ in their overall design, the most common variations utilize a permanent magnet for their operation. With the formation of a fixed magnetic field, a rotating armature is attached to the machine shaft and can rotate within the field in order to measure rotational speed. As the armature rotates through the magnetic field, its movement will induce an electromotive force that is proportionate to the speed of the shaft. The armature also has contacts that are attached to a voltmeter circuit, and they allow for the induced voltage to be translated into a measurement of speed. If the permanent magnet of the tach generator is a direct current magnet, the current from the AC generator can be converted into DC by a commutator located between the armature and voltmeter circuit.

As an aircraft device, a tach generator may be used to find the rate of rotation of the engine’s crankshaft. Often, the tach generator will also provide speed ranges for rotation, and these can permit the operator to select the safest throttle and gear settings for current conditions. The warnings for speed ranges are highly beneficial as prolonged operations at high speeds can result in the wear of assemblies, a loss in lubrication, or affect fuel efficiency for flight planning. Generally, a green arc will be provided on the face of the correlating cockpit instrument that denotes the safe cruise speed for the particular aircraft model.

Beyond measuring the revolutions of an aircraft engine, the tach generator may also prove very useful for a number of power equipment applications such as mixers, conveyors, machine tools, and more. As such, they are often implemented within speed control circuits as a feedback component. They may also be a feedback source for the voltage control of a motor. In the instance that a motor needs a large amount of current only for starting, the tach generator can ensure that the motor starts and then has a continuous and proportional supply of voltage.

When discussing the tach generator, one should know that they are not the same as the tachometer. While the tach generator is a device that measures the engine’s rotational speed, the tachometer itself is a gauge that displays the RPM of systems for the pilot. While related, the two components do serve their unique functions and thus should be differentiated. Tach generators and tachometers may both be governed by standards as well, often falling under SAE standardization or those from other jurisdictions.

As maintaining a safe engine RPM is beneficial for efficient flight, having a functional and reliable tach generator is very important for any aircraft. At ASAP NSN Distribution, we serve as a premier online distributor of aircraft parts with a multitude of new, used, and obsolete items readily available for purchase on our website. As the only independent distributor with a no China sourcing pledge, we ensure that each and every item comes from a leading global manufacturer and has been sufficiently inspected and tested for quality assurance. With our adherence to such quality standards, we operate with AS9120B, ISO 9001:2015, and FAA AC 00-56B certification and accreditation. Experience how we can serve as your strategic sourcing partner today when you fill out and submit an Instant RFQ form as provided on our website.


April 8, 2021

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