TECHNOLOGY FOR CHANGE

Listening for Small Aircraft

Dave Greenfield | Date: 05-26-10 | Comments

As the number of collisions between small aircraft increases, the need for better communication and detection equipment becomes more and more apparent. Acoustic vector sensors (AVS) may prove to be the right technology to prevent midair crashes.

In August 2009, a small plane and a tourist helicopter collided and plunged into the Hudson River between Manhattan�s West Side and Hoboken, N.J. The low-altitude crash was perfectly clear to thousands of bystanders, who saw the plane roll up and into the helicopter. Researchers from Holland and the United States now believe that the midair collision could have been avoided by better communication and detection equipment. These researchers are testing an acoustic vector sensor (AVS) that uses nanoscale materials that can be mounted on the outside of small aircraft to warn pilots of other craft within 10 kilometers.

A system like AVS is needed because smaller planes and aircraft are not required to have radio transponders, which track air traffic. Owners of small and private planes can opt to have transponders and/or GPS systems installed, but these only detect aircraft carrying similar gear. Instead of using radar, radio signals or echolocation, AVS listens for sounds of other aircraft. Flight sounds are used to determine speed, altitude and aircrafts� headings.

The vital component of the AVS is the anemometer. This device measures wind speed and can pick up sounds in a 360-degree sphere surrounding the plane. A bit smaller than a match head, the anemometer has two resistive platinum strips that measure 200 nanometers thick by 10 micrometers wide. These strips are placed across a gap in parallel with one another and heated to 200 degrees C. Temperature fluxes are created by particles of air, which flow through the gap and allow the anemometer to measure sound intensity and record particle movement. These measurements allow the device to calculate the x, y and z coordinates of the aircraft.

The AVS system has been used to track fly-bys of a small plane and helicopter, and was successful in tracking them within several feet. The sensor is typically mounted on the aircraft�s sink or in a wind shield on a wing�s leading edge. A problem that aerospace engineers have encountered is that the very small sensor can be degraded by �airborne grunge and water,� which decreases its efficacy. A team led by University of Kansas Aerospace Engineering Associate Professor Ron Barrett is working on the issue by developing �piezoelectric elements to induce infrasonic, sonic and ultrasonic vibrations in the strips. The vibrations atomize water droplets when they strike the strips and shake off solid particles.�

AVS has a few more obstacles to cross before (and if) use is to become widespread. With proper funding, a product will be available in about a year; without, it will be five to 10 years in the future. The FAA is backing a similar technology, ADS-B (automatic dependent surveillance-broadcast) and is not overly enthused about AVS. One further obstacle is the adoption by private pilots, who tend not to want more �stuff� and more expense when operating their planes. If adopted, however, AVS could be a valuable tool for preventing aircraft collisions.