It's function is to lower the propellers speed and make it more controllable.
Not in the conventional sense, but some turbine aircraft can reverse the propeller thrust while on the ground.
Because the propeller would turn at excessive RPMS if it were coupled directly. If a propeller reaches supersonic speeds, it actually impedes the aircraft.
Most piston driven planes are a direct drive, some have a gear reduction between the engine and propeller. But no transmissions that I know of.
Some ships do. It is called a reduction gear and takes power from the engine and transmits it to the shaft and propeller. Other ships use direct drive, electric motors, steam or other schemes to power the propeller.
A "complex aircraft" is an aircraft which has a constant-speed propeller and/or retractable landing gear. The FAA requires pilots to attain the "complex aircraft" license endorsement before they are permitted to act as "Pilot in command" for such aircraft.
They use a fixed, gear reduction transmission which reduces the number of rotations of the propeller from the number of rotations of the crankshift. The pilot doesn't do any shifting.
The ground safety switch, often referred to as a weight-on-wheels (WOW) switch, is a critical component in an aircraft's landing gear system. Its primary function is to prevent certain systems, such as the landing gear retraction mechanism, from operating when the aircraft is on the ground. This ensures that the landing gear remains extended during ground operations, enhancing safety by preventing inadvertent gear retraction. Additionally, it helps in activating other systems only when the aircraft is airborne.
Jocelyn I. Pritchard has written: 'Sensitivity analysis and optimization of nodal point placement for vibration reduction' -- subject(s): Structural dynamics 'An overview of landing gear dynamics' -- subject(s): Landing gear, Aircraft landing, Aircraft brakes, Surveys, Dynamic characteristics, Structural vibration
Its an abbreviation for "offset gear reduction", another type of starter is PMGR or "permanent magnet gear reduction"
On the Landing gear
It was not strictly a differential gear, it was a reduction gear to reduce the relatively high engine revs by a fixed amount so that at full throttle at maximum speed in fine pitch the propeller tips would not go supersonic and break up through unstable shock wave generation. All high power propeller aero-engines had one, both piston types and turbo-props, especially turbo-props of which the turbine speed was very very much higher than the permissible propeller speed. Variable pitch controlled the speed of the propeller by varying the angle at which the blades met the airflow, the reduction gear was a fixed ratio which in turn governed the engine revs. Fine pitch = high revs, Coarse pitch = low revs. Engines like Hercules,Centaurus, Proteus (turbo-prop), Merlin, Griffon, etc. and their American counterparts all had one.
To increase torque.