What is the Aircraft Engine Starting System?
Despite being advanced machines, most types of aircraft engines require some sort of aid in the starting operation. An aircraft engine starting system is an electromechanical mechanism that applies mechanical energy to an engine, causing it to begin rotation. In both reciprocating and turbine engines, rotation enables the engine to begin its primary functions, allowing it to then take over and act in self-perpetuating motion. In this blog, we will discuss the aircraft engine starting system, as well as how it works in both reciprocating and turbine aircraft engines.
In the early days of aviation, reciprocating engines were typically started by manually pulling the propeller to begin its initial revolutions. This could be difficult in colder weather as lubricating oils would be in a nearly congealing state, and the magneto systems produced weaker starting sparks. As the reciprocating engine continued to develop, various starting systems began to develop that took the labor off of the pilot. In general, the two main types of starter systems that are used for such engines are the inertia starter and direct cranking electrical system.
Inertia starting systems may be operated by hand, electricity, or a combination of the two. The operation of each depends on the kinetic energy that may be stored within a quickly rotating flywheel, and energy is stored as the engine is cranked manually by hand or by a small electric motor. While the starter is energized, all of the moving parts within the apparatus are set in motion. Once the starter is able to reach a fully energized state, it is engaged to the engine crankshaft either manually or electrically. At this point, the flywheel energy of the starter is then transferred to the engine through reduction gears and a clutch.
The direct cranking electrical system is much more common to a majority of reciprocating engines, and it provides an instant and perpetual cranking once it reaches an energized stage. The starter type is composed of an electric motor, reduction gears, and an engaging and disengaging mechanism governed by a clutch. With a direct cranking electrical engine, the reciprocating engine is cranked directly as soon as the starter solenoid is closed. With the starter motor and clutch, the engine is sped up to a predetermined speed, in which the starter then automatically disengages from the engine.
For the turbine engine, the direct cranking electrical system and starter generator system are the most common. Direct cranking electrical systems are fairly common to small turbine engines, including APUs and smaller turboshaft engines. Meanwhile, starter generator engines are used for many gas turbine engines. The two starter types are fairly similar, though the starter generator has a second series of windings that is used to operate as a generator once the engine has reached a self-sustaining rotational speed. Because of this, aircraft that utilize such starters can save weight and space.
The starter generator is engaged to the engine shaft in a permanent fashion, and it serves as a shunt generator with heavy winding. With this heavy series of winding, the aircraft engine starting system can generate a strong field to provide high amounts of torque to start the engine. With their ability to act as a generator after starting the engine, starter generator systems are highly desired for aircraft applications when they can be used.
As starters provide for the initialization of operation for the aviation turbine engine and components, it is important that they are well maintained to ensure optimal performance. Whether an engine cannot rotate during a start attempt, or it fails to start when the throttle is placed in idle, it is recommended to troubleshoot the starter while following manufacturer instructions and maintenance directives.
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