Each time a new undercarriage design is laid down by an aeroplane or undercarriage designer, the geometry of the undercarriage retraction system nas to be investigated. This often involves a review of known solutions and since the designer cannot be expected to remember all these known solutions, the following notes have been prepared to put on record most of, and possibly all, the known solutions.

The basic linkage from which nearly all solutions are derived is the well-known fourbar linkage, as illustrated in Fig. 1. Links A and C rotate, link B is “floating,” while the airframe forms the fourth link.