Final answer:
The smallest cable size in an aircraft's primary control system is based on compliance with regulatory standards like FARs and is chosen to handle specified current loads safely.
Step-by-step explanation:
The smallest size cable allowed to be used in the primary control system of an aircraft is determined by the regulatory standards such as the Federal Aviation Regulations (FARs) and aircraft manufacturer requirements. These standards take into account the electrical load, safety factors, and the environmental conditions the cables will face. Typically, the size is specified in American Wire Gauge (AWG), and while the exact gauge can vary, it is imperative that the chosen cable must be able to handle the current specified for the system without overheating or suffering from excessive voltage drop. The determination of cable size must also consider the installation environment within the aircraft, including temperature, vibration, and potential exposure to fluids or chemicals.
These cables are typically made of stainless steel, which provides strength and durability while also being resistant to corrosion. The small size of the cable allows for precise control of the aircraft's surfaces, such as the ailerons and elevators.Using a smaller cable size also reduces the weight of the control system, which is important for aircraft efficiency and performance.