There are many different types of aircraft jacks currently in use, however, they all fall into two groups, mechanical and hydraulic.
Mechanical Lifting Jacks
The mechanical jacks operate on a simple ‘screw jack’ principle, where a ratchet mechanism is used to raise the telescopic ram by use of a square thread. These jacks are usually only used for raising small light aeroplanes, and some helicopters.
Hydraulic Lifting Jacks
The majority of aircraft lifting jacks operate on a hydraulic principle, which use the fact that oil will flow freely yet act as a solid, because it is in this context incompressible. Another advantage of using the hydraulic principle, is that a relatively small piston pump can generate a lot of pressure to move the jack ram and aircraft upwards, with only a moderate effort on the part of the operator.
