Switches

Switches are electronic gadgets that allow you to open and close circuits. They are made up of one or more contact pairs. Momentary contact switches actuate the circuit for a brief period before returning to their original position with the help of an internal spring when the switch is released. When a switch with continuous contacts is actuated, it stays in place. By installing switches logically and consistently, dangerous errors in switch operation can be avoided. By installing proper protection above the switch, inadvertent switch operation can be avoided.

In any circuits where a switch failure might be dangerous, a specially engineered switch should be utilized These switches are made to last, with enough contact capacity to constantly break, create, and carry the connected load current. The typical aircraft switch’s nominal current rating is normally stamped on the switch casing. With the connections closed, this rating shows the continuous current rating.

• SPST is a type of switch that opens and shuts a single circuit. The number of different circuits that can be activated is indicated by the pole, while the number of current routes is shown by the throw.
• DPST Turn two circuits on and off with one lever
• SPDT switches allow circuit current to flow in one of two directions. In both locations, the switch is turned on.
• DPDT (dual-pole double-throw) switch activates two circuits at the same time. Switches with two or three locations are known as double-throw switches.

Rocker and toggle switches

These are the most common type of switches that control the majority of aircrafts electromechanical components. Push buttons are frequently used to control electrical components on aircraft with a glass cockpit.

Rotary Switches 

Rotating a knob or shaft activates rotary switches, which are commonly found on radio control panels. Rotary switches can be used to regulate more than two circuits.

Precision Switches 

Micro switches are activated with very little pressure. These switches are spring-loaded, which means that when the pressure is released, the contacts return to their original position. To detect and limit the movement of moving parts like landing gear, flaps, and spoilers, micro switches are used

Solenoids and Relays 

Solenoids

A solenoid is a particular type of relay with a moving core. In a relay, the electromagnet core is fixed. Solenoids are commonly employed as mechanical actuators, but they can also switch huge currents. Only currents are switched via relays. Solenoids are employed as switching devices when weight savings or simplified electrical controls are desired. The preceding description of switch ratings applies to solenoid contact ratings as well. Solenoids have a moveable core/armature, which is commonly constructed of steel or iron, with a coil wrapped around it.

Relays

Relays are used to employ a tiny current to control the flow of big currents A low-power DC circuit is utilized to trigger the relay and control the flow of massive AC currents. They’re used to turn on and off motors and other electrical equipment, as well as to keep them from overheating. Electromechanical and solid-state relays are the two primary types of relays. Solid-state relays work similarly to transistors and have no moving parts, whereas electromechanical relays have a permanent core and a movable plate with contacts. A magnetic field is created by current flowing through the coil of an electromechanical relay, which attracts a lever and switches he switches contacts. Because a relay is an electrically powered switch, it is susceptible to dropout when the system voltage is low. Relays enable one circuit to control a second circuit that is fully independent of the first.

Current Limiting Devices

Fuses

A fuse is connected to the voltage source in series, and all current must pass through it. The fuse is made up of a metal strip that is housed in a glass or plastic casing. The metal strip is commonly constructed of lead, tin, or copper and has a low melting point. The metal strip heats up and disconnects when the current surpasses the fuse’s capacity. As a result, the circuit’s current flow comes to a halt.

Circuit Breaker

A circuit breaker is an automatic electrical switch that protects a circuit from damage due to power fluctuation. Any fluctuation in the current can damage the circuit. Its primary role is to identify a fault state and cut off electrical flow instantly. As we know that a fuse can only be used once, whereas a circuit breaker can be reset and resume its function. Trip-free circuit breakers are those that do not trip. As the name implies, Circuit breakers that automatically reset themselves are called automatic reset circuit breakers. In aviation, they should not be utilized as circuit breakers.

In Short

Everything from lights and avionics to the auxiliary fuel pump and engine starter motor is controlled by the electronic switches system, which is vital to the proper operation of any modern aircraft.