Two modified RQ-4 Global Hawk unmanned aerial vehicles successfully
demonstrated technology that allows unmanned vehicles to be automatically
refueled in-flight, an important step in conducting surveillance and combat
duties, said the Defense Advanced Research Project Agency on Oct. 5.
Currently global military aviation relies on a key enabler – aerial
refueling. Fighters, bombers, reconnaissance and transport aircraft use “flying
gas stations” to go the extra mile, it said. Increasingly, it said UAVs are
conducting combat and Intelligence, Surveillance and Reconnaissance (ISR)
operations, but the aircraft aren’t designed to be refueled in flight.
DARPA said it teamed up with NASA in 2007 to show high-performance aircraft
can easily perform automated refueling from conventional tankers, but many
unmanned aircraft can’t match the speed, altitude and performance of the current
tanker fleet. The 2007 demonstration also required a pilot on board to set
conditions and monitor safety during autonomous refueling operations, it
said.
On Oct 5, DARPA’s two-year Autonomous High-Altitude Refueling (AHR) program,
which concluded Sep. 30, explored the ability to safely conduct fully autonomous
refueling of UAVs in challenging high-altitude flight conditions. During its
final test flight, two modified Global Hawk aircraft flew in close formation,
100 feet or less between refueling probe and receiver drogue, for the majority
of a 2.5-hour engagement at 44,800 feet, said the agency.
The manuever demonstrated for the first time that High Altitude Long
Endurance (HALE) class aircraft can safely and autonomously operate under
in-flight refueling conditions, it said. The flight was the ninth test and the
first time the aircraft flew close enough to measure the full aerodynamic and
control interactions, it added. Flight data was analyzed 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, it said.
According to the agency, since HALE aircraft are designed for endurance at
the expense of control authority, the program started with the expectation that
only one of six attempts would achieve positive contact (17 percent). The final
analysis, however, showed 60 percetn of the attempts would achieve contact, it
said. Multiple autonomous breakaway contingencies were successfully triggered
well in advance of potentially hazardous conditions, it said. Fuel systems were
also fully integrated and ground tested, demonstrating a novel “reverse-flow”
approach with the tanker in trail, said DARPA, opening up valuable trade space
for future developers to choose between various fixed and modular
implementations of proven probe and drogue hardware.
“The goal of this demonstration was to create the expectation that future
HALE aircraft will be refueled in flight,” said Jim McCormick, DARPA Program
Manager. “Such designs should be more affordable to own and operate across a
range of mission profiles than systems built to satisfy the most stressing case
without refueling. The lessons from AHR certainly extend beyond the HALE flight
regime, and insights into non-traditional tanker concepts may offer further
operational advantages.”
