BAE Systems develops laser airspeed sensor for aircraft

14 Jul 2016

UV-based “LASSI” system more accurate and sturdy than conventional pitot systems.

In what they are claiming is “an aviation first”, British scientists at BAE Systems, Chelmsford, UK, have successfully trialled a highly accurate laser-based airspeed sensor, which is designed for use in the next generation of high altitude aircraft. The team says this development will increase survivability while improving aircraft performance and fuel efficiency.

The Laser Air Speed Sensing Instrument (LASSI) which is being exhibited at this year’s Farnborough International Airshow is different from conventional airspeed measurement methods because it can accurately measure velocity even at low speeds, say the developers.

Conventionally, air speed is determined using pitot tubes, which protrude from aircraft and sense variations in air pressure with speed. Although usually heated, these tubes are vulnerable to blockage in icy conditions. They can also be damaged by collisions with birds and when the aircraft is on the ground.

Doppler Effect

The new laser-based system operates on the same principle as roadside speed-guns: the technique works by bouncing ultraviolet laser light off air molecules and measuring the change in “color” of the reflections caused by the Doppler Effect. The further away from the ultraviolet light wavelength the reflection is, the faster the aircraft is travelling. The detector identifies minute changes in wavelength, which indicates the aircraft’s airspeed.

Dr Leslie Laycock, Executive Scientist at BAE Systems said, “LASSI challenges the established method of measuring air speed. “Conventional air data sensors which protrude from the sides of aircraft must be carefully located to work properly and are inaccurate at low airspeeds. Instead, LASSI can be located completely inside the aircraft and is accurate at low airspeeds. It can even measure negative air velocities. These features should ensure that the equipment is robust against damage, require less maintenance and be easier to operate at lower airspeeds.”

He added, “A significant benefit is that LASSI has the potential to detect air speed at a distance, meaning an aircraft could predict oncoming turbulence and change course accordingly.”

BAE Systems says it has successfully trialled LASSI in a low speed wind tunnel and on ground vehicles. Engineers from the company predict the component technology could be miniaturized and actually be in use “within the next five years”. They are currently investigating how the system could be integrated in future aircraft.