Aerospace

All modern aircraft flight control systems are literally ‘fly-by-computer‘ systems. The flight management computer (FMC) receives the command signal from position sensors mounted in the control column, pedals and thrust levers to electro-mechanically actuate the movement of the flight control surfaces (ailerons, elevators, rudder) and the power to the engines. An aircraft’s electro-hydraulic control system consists of control electronics (command signal), a servo-amplifier, a servo-valve, an electro-hydraulic actuator and a feedback sensor, which measures the position of the actuator. These position sensors are usually high specification contactless LVDT (Linear Variable Differential Transformer).

Contactless LVDT sensors are chosen due to their ‘long operational life’ and high reliability in extreme operating conditions. 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.

Primary Flight Controls

Most large fixed winged aircraft have primary flight controls consisting of a control column (alternatively known as a yoke), foot pedals and thrust control levers. The command signals from the control column are from position sensors mounted in the column and pedal assemblies, and are usually high specification ‘contactless’ LVDT (Linear Variable Differential Transformer).

Secondary Flight Controls

The most common secondary controls are ‘trim tabs’ which keep the aircraft at a desired altitude by making small adjustments to the ailerons and rudder without the need for the pilot to make constant primary control adjustments. All trimming surfaces are electrically operated and controlled from the cockpit. The control and feedback signals are from position sensors and are usually high specification ‘contactless’ LVDT (Linear Variable Differential Transfers).

Landing Gear Systems

An important part of the aircraft’s landing gear is the nose wheel steering system which enables the pilot to carry out safe aircraft steering while on the ground. Despite only being used for relatively short periods of time, the landing gear is vitally important for controlled aircraft maneuverability.

Engine Controls

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 benefit of fly-by-wire systems for military aircraft is improved manoeuvrability and flight performance. The system also improves combat survivability as damage to hydraulic systems causes leaks that can lead to loss of aircraft control. Electrical wires can be more flexibly routed compared to hydraulic lines and are less susceptible to damage. The ‘on-board’ aircraft computer also offers flight envelope protection, which prevents the aircraft from exceeding pre-set limits such as stall or spin. A fly-by-wire system also improves flight economy through weight reduction, by the elimination of some of the heavy mechanical components.

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.

For further information about Active Sensors aerospace sensor design, manufacturing and environmental testing capabilities, please contact sales@activesensors.com.