The bi-pod jack consists of a hydraulic unit supported by two fixed legs and one adjustable leg.This jack is suitable for arc lifting.
The two fixed legs provide support on two opposite sides while the adjustable leg gives support on the third side. The two fixed legs rest upon swiveling feet. These legs support the load and may be tilted through a small angle, usually not exceeding 6°. The adjustable leg is adjusted to steady the bipod legs as they move the jack body towards the vertical position during an arc lift.
The jacking point moves laterally as the aircraft is raised because the aircraft pivots about the wheels of the other undercarriage units
The tripod jack consists of a hydraulic unit supported by three fixed legs.This jack is suitable for vertical lifting.
It is not suitable for lifting where lateral movement of the jack develops during the jacking operation. Lateral movement of the jack might occur when raising the aircraft to change a wheel after a tyre has deflated.
The quadropod jack consists of a hydraulic unit supported by two fixed legs and two adjustable legs.
This jack possesses all the advantages of the bipod, and consists of attaching an additional leg to the bipod jack.
The use of this additional leg gives increased stability to the jack. It also forms the legs into a trestle, which can be rigidly locked when the jack is supporting an aircraft.
This jack can be used for an arc lift in a similar manner to the bipod jack.