Turbofan engines power most of today's airliners. A turbofan engine has a large fan at the front, which sucks in air. In old turbojet engines all the air entering the intake passed through the engine combustion chamber, but in turbofans, most of the air flows around the outside of the engine (bypasses), making the engine quieter and giving more thrust at low speeds. The term 'bypass' relates to the ratio between the flow of air drawn in by the fan but bypassing the engine to the air passing through the engine. A high bypass (big fan), gives greater fuel efficiency but also reduces the top speed. The air taken into the engine is compressed up to 12 times its original pressure and fuel is added.
A modern aircrafts fuel system is fly-by-wire (electro-hydraulic), and consists of control electronics, a servo-amplifier, a servo-valve, an actuator and a feedback sensor. In a fuel sytem these position sensors are usually high specification contactless RVDT (Rotary Variable Differential Transformer) or LVDT (Linear Variable Differential Transformer) types. Virtually all 'fly-by-wire' systems have built in redundancy, duplex or quadruplex systems (multi-channel), which mean that each control function will have up to four sensors and control wires. If the signal is lost from one or two sensors, the others will continue working on a separate electrical system. The fuel is added to the engine when the pilot operates the thrust levers in the cockpit. The thrust lever will contain up to four RVDT sensors (quadruplex arrangement), and the actuator will have a similar multi-channel LVDT sensor fitted that provides the closed loop control function.
Active Sensors design and manufacture LVDT sensors for primary and secondary flight control electro-hydraulic actuators, engine control valves, brake-by-wire systems and much more... We meet customers' system development needs by offering a complete sensor design and delivery service for fixed and rotary wing aircraft.
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