Aircraft were originally controlled by small aerodynamic surfaces operated by cables, attached to levers that magnified the pilot's input, using mechanical advantage.
Numerous aircraft in the early stages of World War II suffered from these problems, notably the Mitsubishi Zero and P-38 Lightning.
In their early incarnations, hydraulic pumps attached to the engines fed high-pressure oil through tubes to the various control surfaces.
One of the earliest fittings of a hydraulic boost system was to ailerons on late-war models of the P-38L, removing the need for great human strength to achieve a higher rate of roll.
[7] Stepper motors are designed to move through a fixed angle with every pulse of current and do so repeatedly in an extremely precise fashion.
The entire system, consisting of the pump, the cylinder and a reservoir of hydraulic fluid, is packaged into a single self-contained unit.