Innovative AARD system

The US’ Defense Advanced Research Projects Agency (DARPA) could breathe easy even in the nightmare scenario. The agency successfully tested a fully autonomous robotic system to refuel in mid-air.

Picture this: you’re flying in an aero plane, looking out the window, when all of a sudden you feel the plane shudder. Then the rumbling kicks in. the pilot announces that the plane is running out of fuel and there’s no place to land. Then the plane is in desperate need of fuel. This is where this innovation system of Air refueling comes as a great rescue saving all the passengers and crew.

Refueling in mid-air is one of the most difficult and dangerous maneuvers for a pilot. However, the success of the autonomous airborne refueling demonstration (AARD) showed the unmanned aircraft can autonomously perform in-flight refueling under operational conditions.

The revolutionary AARD used precise inertial, GPS and video measurements, combined with advanced guidance and control methods, to plug a refueling probe into the centre of the drogue-a 32-inch basket trailed behind a tanker.

Several control techniques were tested on the aircraft – a NASA Dryden Flight Research Centre F/A-18 and the best was 100 percent effective in 18 attempted probe and Drogue connections.

Each attempt was made flying across a range of turbulent conditions.

In a significant break through, the system demonstrated the ability to make contact during turns. Although pilots routinely follow a tanker through turns while connected, they typically do not attempt to make contact in a turn.

In AARD program, fuel was routinely transferred in turns as well as during normal Flight. The system further demonstrated the ability to join the tanker from almost 4 km behind, 1000 feet below, and 30 degrees off heading: this provides a ready transition from the way point control approach-locking on a target point and following it used by almost unmanned aircraft to a fully autonomous refueling mode.

The exceptional performance ultimately achieved by the program was made possible by two major enhancements to the System. First, improved video processing eliminated troublesome dropouts, allowing the system to conduct four times as many plug attempts per flight.

Secondly, advanced control algorithm proved capable of anticipating much of the overall drogue motion. These algorithms were actually able to precisely match the drogue motion an aspect that pilots are specifically taught to avoid.

In one case, the system followed the drogue through a full three-foot cycle in the two seconds before making contact, never deviating more than four inches from the exact centerline of the drogue; and all of this while traveling at 400 kmph,18000 feet in the air.

Automatic sequencing has improved tremendously. While NASA test pilot characterized some of the less mature version of AARD software as “flying like a Second Lieutenant” he found the final configuration “better than a skilled pilot”. Skilled pilots can actually save some tricky, last second movement that the basket has a habit of making. But in doing so, they set themselves up for a basket strike, ripping off the basket from the hose, or sometimes breaking the probe or parts of the airplane. Autonomous in flight refueling is a critical aspect of unmanned strike systems. The technology could revolutionize unmanned air operations. It could enhance the reliability, safety, and range of operating conditions for in-flight refueling of manned aircraft, be it military jets or passenger airplanes.

The innovative refueling idea is being commercialized and will prove to be a boon to long haul passenger jets where they can avoid technical stoppages including change of Aircraft. For the airlines it will be an immense cost savings and higher passenger turnout.