Retractable Undercarriages: A Historical Review with Descriptions of Examples of the Latest Practice

Retracting mechanisms may be operated either manually or by power systems, according to the type and size of aircraft. Manual systems may be classified into two main groups, mechanical and hydraulic. The mechanical group may be further sub‐divided according to the form of mechanism; e.g., cable and pulley, screw and nut, worm and other gears, all of which have been used for retraction schemes at some time or another. Power systems are even more diverse, many of them being of recent birth and, therefore, still in the experimental stage. Some of the various ways in which power can be applied to drive the retracting mechanism are by: electric motor and mechanical coupling; electric motor and hydraulic pump; aero engine coupling to hydraulic pump; compressed air motor and hydraulic pump; and other pneumatic systems.