Propeller speed reduction unit

[1] This allows the use of small displacement internal combustion engines to turn aircraft propellers within an efficient speed range.

[3] The challenge with coupling gearboxes to internal combustion engines is primarily the torsional resonance that can develop at certain speeds.

The load of a propeller and reduction unit can alter the resonant frequencies of the crankshaft, allowing torsional vibration to increase rapidly to high levels at certain rotational speeds.

Clutches and/or flexible couplings are sometimes used to prevent torsional resonance from reaching damaging levels.

The use of a reduction unit is common in the construction of experimental homebuilt aircraft when automotive engines may be used.