Test shows in-flight refuelling capabilities of HALE aircraft

DARPA’s two-year Autonomous High-Altitude Refueling (AHR) programme, which concluded on 30 September, explored the ability to safely conduct the fully autonomous refuelling of unmanned aerial vehicles (UAVs) in high-altitude flight conditions.

During its final test flight, two modified Global Hawk aircraft flew in close formation, 100ft (30m) or less between refuelling probe and receiver drogue, for most of a two-and-a-half-hour engagement at 44,800ft.

According to a statement, this demonstrated for the first time that HALE-class aircraft can safely and autonomously operate under in-flight refuelling conditions.

The flight was the ninth test and the first time the aircraft flew close enough to measure full aerodynamic and control interactions.

Flight data has been analysed over the past few months and fed back into simulations to verify system safety and performance through contact and fuel transfer, including the effects of turns and gusts up to 20 knots.

At the start of the programme, it was thought that only one of six attempts would achieve positive contact as HALE aircraft are designed for endurance at the expense of control authority. The final analysis, however, indicated that 60 per cent of the attempts would achieve contact.