Precision landing system on trial

New aircraft navigation technology could allow aircraft to be landed at 40 degrees to an accuracy of up to 6cm.

A combination of aircraft navigation systems that enable precision landings at high angles were due to be tested for the first time in the US yesterday.

The technology is designed to allow military aircraft to make extremely short landings on aircraft carriers or temporary runways. It does this by allowing the plane to approach the landing area with its nose much higher than usual. This increases drag and cuts the speed of approach by more than a third.

The system is being developed in Maryland by a joint team of engineers from the US Navy, German government, Boeing’s Phantom Works R&D centre and the European Aeronautic Defence and Space company (EADS).

Saving wear and tear

If successful the technology, known as ESTOL (Extremely Short Take-off and Landing), will remove the need for ‘beefed-up’ carrier aircraft and save wear and tear on the undercarriage. It could also allow landings at sea without the need to dump fuel and stores.

Using the X-31, a unique tail-less test plane with thrust-vectoring flaps by the jet nozzle, the aim of the trial was to practise extreme-angle landings on a ‘virtual runway’ at 5,000ft above ground level.

Normal landing approaches are at around 12 degrees from the horizontal, but the team hopes to land the aircraft at about 40 degrees. The high-angle technique allows energy savings and low speeds of about 185km/h, compared to the usual 300km/h.The X-31 has been fitted with a sophisticated differential GPS system called the Integrity Beacon Landing System, developed at Stanford University. This helps the autopilot keep the back of the plane 60cm off the runway while it reverts to a more normal landing position at the last moment.

The system relies on extra transponders positioned near the landing surface to augment GPS satellite data.

Boeing Phantom Works programme manager and a former test pilot Gary Jennings said that unlike other automatic aircraft carrier landing systems under development, the IBLS could be accurate to up to 6cm.

Also on board the aircraft is EADS’ Advanced Flush Air Data System. Unlike other separate systems for measuring speed, altitude, angle of attack and so on, the all-purpose device does not need external booms or tubes. Instead it exploits non-protruding pressure ports positioned against the aircraft’s nose cone.

Enhanced aerodynamics

This improves aerodynamic and stealth qualities, and is ‘redundant’ in that, should any of the 12 sensors fail, the others can make up for its loss. It works in conjunction with the IBLS to produce the levels of accuracy required for ESTOL.

Mothballed from 1995 to 2001, the X-31 was originally designed for manoeuvrability demonstrations. ‘The aircraft has had a whole new avionics suite added,’ said Jennings. ‘Usually the multiple components would each need a test programme.’

After data has been extrapolated from the theoretical landing, tests on real runways are set for November. Commercial applications for the technologies could be developed in time, though whether high-angle landings could be suitable for passenger aircraft has yet to be seen.

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