Types Of Sensors Used In An Aircraft

Flying an aircraft safely and effectively relies on feedback on flight conditions from a wide variety of sensors and equipment. These sensors monitor conditions and effects on the aircraft and feed this information to flight computers for processing before being displayed to the pilot.

Flow sensors monitor the amount of lubricating oil and liquid coolant in motion, as well as any fluid moving in fuel transfer and bleed air systems. Liquid level sensors monitor fuel, oil, and coolant levels, as well as potable and gray (or waste) water reservoirs, collection sumps, and hydraulic reservoirs. Pressure sensors monitor the pressure in hydraulic systems, including those used for moving control surfaces, braking, and raising and lowering the aircraft’s landing gear.

Position sensors such as linear variable differential transformers and rotary variable differential transformers sense the displacement of various aircraft components, such as the status of the thrust reversers. Force and vibration sensors are also used to measure torque and force in braking and actuation systems and flight controls.

Temperature sensors play a key role in monitoring conditions of hydraulic oils, fuels, and refrigerants, as well as temperatures in environmental cooling systems in the cockpit and passenger seating. Types include bimetallic pressure gauges, electrical resistance thermometers, and thermocouple temperature indicators.

Outside the aircraft, the pitot-static system is one of the most important and provides the source of pressure for a variety of instruments including airspeed indicators, vertical speed indicators, and altimeters. Pitot static systems gather two air pressures from separate ports: the pitot static tube collects impact air pressure measuring the full force of the air as the aircraft moves forward through the atmosphere, while the static port gathers static air pressure representing atmospheric pressure outside the airplane in still conditions. By comparing these two, the aircraft’s speed can be determined. Other pressure management systems include the bourdon tube, diaphragm, aneroid and bellows mechanisms, and solid-state sensors. Solid-state sensors, like crystalline piezoelectric, piezoresistive, and semiconductor chip sensors, use changes in pressure to cause a deflection on the material resulting in a current or change in resistance proportional to the pressure chage.

Digital technology and the advent of “glass cockpits” has revolutionized sensor technology. Attitude heading and references systems now use GPS, MEMS devices, and solid-state magnetometers and accelerometers to display attitude information such as roll, pitch, and yaw as well as aircraft heading. Digital instrument systems (or glass cockpits) receive data from various sensors, and process these inputs, applying compensating factors and present information on flight displays to the pilot. Analog-to-digital converters process electrical output from analog sensors, while solid-state sensor data can be handled directly. Flight control systems in modern aircraft work in concert with signals from sensors monitoring control surfaces and the flight stick, ensuring that operation is safe and effective.