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This article first appeared in Aerospace Daily & Defense Report.
LONDON -- AirTanker, the consortium charged with the provision of air-to-air refueling services for the U.K. Royal Air Force, says it hopes to be cleared to start tanker work in the coming weeks.
Although AirTanker is not due to take on the aerial refueling role until March 2014, efforts to clear the Airbus A330 Voyager tankers have been hampered by a series of issues involving the hose-and-drogue system used to refuel receivers.
Without certification, the three Voyager aircraft have been relegated to air transport duties only, but the company hopes to begin operational tanking missions in the next few months.
Phill Blundell, CEO of AirTanker, told Aviation Week that military certification authorities have been unhappy with the flight characteristics of the Cobham-designed High Speed-Variable Drag Drogue (HSVDD) fitted to the hoses of the Voyager, and have changed back to the standard Sergeant-Fletcher-designed drogue currently fitted to the VC-10 and Tristars, as well as tankers from other countries.
"The Military Aviation Authorities simply weren't happy with the flight characteristics of the HSVDD, and they didn't have enough inflight data so they went back to what they know," Blundell says.
The HSVDD is designed to refuel aircraft at between 180 and 300 kt., a much wider speed range than previous drogue systems. However, a series of flight trials in 2011 found that the drogue or basket was venting and separately spinning, causing hose oscillation.
Both of these issues were resolved by mid-2012. More recent tests with fully instrumented Panavia Tornado aircraft found that as the receiver's probe inserted into the drogue, the drogue would "tip," causing an issue when trying to connect. With adoption of the old drogue system, a series of test refuelings using both Tornado and Typhoon aircraft have been successful. Airtanker says it is "waiting for ‘paper' approval from the MOD [Ministry of Defense]. It is our expectation that this will be given imminently."
The HSVDD is in use on the A330s employed by the other three customers who have ordered the tanker and has been cleared for refueling types such as the F/A-18 Hornet.
The HSVDD will be retained for use on the centerline hose-drogue (HDU) unit for the three-point RAF Voyager tankers and will also be used to refuel larger types such as the Lockheed Martin C-130J Hercules and the Boeing E-3D Sentry. The Sergeant-Fletcher drogue will be fitted to the wing-tip HDUs, which are most commonly used for the refueling of fast-jet aircraft. Tests with the C-130J have been successfully completed, while refueling tests for the E-3D are scheduled to take place in 2014.
AirTanker is now operating three Voyagers, a pair of two-point tankers and a single, civilian-registered A330. The company received its Air Operating Certificate (AOC) from the U.K. Civil Aviation Authority on Dec. 13 and is applying for civil and military ETOPS certification. Additional paperwork is required to demonstrate that the extra military systems installed on the aircraft will not interfere with safe ETOPS operations. AirTanker will eventually operate 14 Voyagers, with nine of the aircraft fitted out for aerial refueling. The other five will be provided as an "optional additional capability."
Voyagers will eventually replace the Vickers VC-10 and Lockheed Tristar, which currently provide air transport and air-to-air refueling capability for the RAF. The VC-10 is now expected to exit service in September 2013, while the Tristar will be retired in the summer of 2014.
Credit: Airbus Military