Until now measurements of air speed, one of the most crucial measurements for a pilot, can be inaccurate and on occasion in icy conditions, non-existent. The current pitot tube system which protrudes from the aircraft, measuring airspeed by detecting changes in air pressure, has been prone to failures in icy conditions. In spite of heating the instruments, they have been known to fail, freeze and block with potentially catastrophic consequences. Pitot tubes have also been damaged as a result of their external position, with collisions with birds, for example, contributing to their demise.
BAE Systems has been developing a system, known as LASSI (Laser Air Speed Sensing Instrument), which could make these failures a thing of the past and air speed measurements more accurate.
To start with, LASSI is located completely inside the aircraft, meaning incidental damage and the effects of temperature will not impact on the system’s operational integrity. It operates on the same principle as roadside speed-guns, but instead of bouncing infrared light off cars, LASSI bounces an ultra violet laser off air molecules. As the light hits the air molecules, the reflections change colour due to the Doppler Effect. The system then measures this change in ‘colour’ of the reflections to determine the air speed. The further away from violet the reflection is, the faster the aircraft is travelling.
A significant benefit of LASSI is that it has the potential to detect air speed at a distance, meaning pilots could predict oncoming turbulence and change course accordingly, giving passengers a safer, more comfortable flight. Even more importantly, accurate airspeed measurements have a direct impact on the safe-running of an aircraft, allowing the pilot to keep the plane within its limits, as well as ensuring safe operation near to the ground or other aircraft.
LASSI has been successfully trailed by BAE Systems in wind tunnels and on ground vehicles. The next steps involve miniaturising the technology and investigating how it can be effectively integrated in to the aircraft. BAE Systems believe that LASSI could be rolled out within the next five years.
Credit: Dr Leslie Laycock, Executive Scientist at BAE Systems