Boom Times

You want to be clear and understand how they react together.

Coordinating the project from the side of Air Mobility Group (AMG) is WGCDR Grant Kelly, 86 Wing’s KC‑30A transition manager. His job is to implement the schedule of clearances for receiver aircraft in the ADF, particularly for the boom.

“It’s a complicated procedure,” he said in outlining the organisational challenges posed by clearing the E-7A to tank from the KC-30A. “There’s a number of teams involved, each with a lot of expertise. In terms of flight test, engineering and flying, getting everyone together amongst a small Air Force to conduct activity, which is heavily tasked to do other things, is always a challenge. ” The nub of the exercise is how two aircraft – the tanker and receiver – will perform as they fly in tight formation at 300KIAS at night, day, or in turbulent air, transferring and receiving fuel.

“When you connect the two aircraft up, we call it a ‘coupled entity’. We have a tanker, a flying boom and a receiving aircraft. And you want to be clear and understand how they react together. That’s the nexus of our clearance activity – understanding the tanker/receiver pair and making sure it’s compatible within the envelope we want. ” Ensuring the safety of the coupled entity takes thorough planning and fastidiousness that are the hallmarks of ARDU flight testing.

“Each receiver clearance is a mini project where we assess what Once operational clearance for the Wedgetail to tank from the KC-30A is received, 2SQN pilots will be able to maintain air-to-air refuelling (AAR) currency and proficiency in both day and night conditions, facilitating not only training but deployed operational taskings, such as Operation Okra.

Illustrating the utility of AAR, aRAAF Wedgetail has been deployed to the Middle East in support of Operation Okra since October 2014, and it has been tanking over Iraq on every mission, receiving fuel from the USAF KC-135s and KC-10s. Tanking from these aircraft has proven crucial to extending the Wedgetail’s time on station, allowing it to sustain an average of 13. 5 hours flight time per mission.

Both the boom clearance and the ‘force multiplier’ it affords the Wedgetail are of themselves important milestones for the platforms and the Air Force as a whole, but it also heralds a wider program to clear the boom for useon the C-17 and the forthcoming P-8 and F-35.

On top of its operational success in Iraq, where it has been using its probe and drogue system to refuel RAAF Hornets and allied fighters over Iraq under Operation Okra, the trials mark something of a coming of age for the KC-30. So it was no surprise when, in July, the federal government announced the acquisition of an additional two KC‑30s to take the RAAF fleet of the type to seven.

Coupled Entity

But the KC-30’s overnight success has been a long time coming. The initial five KC-30s were delivered with their 17m‑long Aerial Refuelling Boom System (ARBS) booms attached but not cleared for use. Following a January 2011 incident where the boom of the RAAF’s first KC-30, which was being operated by Airbus Military, partially detached while refuelling an F-16, Defence deemed the boom’s flight control software as unacceptable.

Starting at 300ft astern we’d manoeuvre up and down in a box-type pattern. SQNLDR BOWES

info we have about a tanker and receiver,” WGCDR Kelly said. “It will involve a team from 33SQN and engineering support and analysis from both sides – tanker and receiver – and then for the boom clearances, it’s highly likely it will contain a flight test component – a team from ARDU will provide flight test engineers, test pilots and support people to assess, design and conduct flight testing. ” Clearance trials for the Wedgetail took place in airspace off the coast of northern NSW, midway between RAAF Amberley, home of the KC‑30A and RAAF Williamtown, base of 2SQN’s Wedgetail. Taking place in the first two weeks of June, the E-7A trials saw a total of 124 wet and dry midair contacts in which, for the first time in its operational history, a RAAF KC‑30A passed fuel to another aircraft via its ARBS.

Tanks A Lot

SQNLDR Paul Bowes is the ARDU qualified test pilot assigned to fly the E-7A during its receiver clearance trials, and was responsible for designing the test program, executing it and reporting its findings.

“We started with the envelope that we need to test – the Wedgetail’s operators (2SQN) tell us what sort of altitude and airspeed band that they want to tank in, and we take that, because that determines the number of test points we have to hit. In general terms, you want to examine the handling qualities of the receiver and tanker as a coupled entity at the four corners of the altitude/airspeed envelope,” SQNLDR Bowes explains.

“Within that, you need to look at tanker wake and receiver wake and centre of gravity position, particularly in receiver aircraft where the aft CG is more critical for handling qualities. A heavy tanker produces the most downwash and most intense wake. Also, the effect of having significant downwash is that if you run into performance limitations from a receiver – as the drag increases on the receiver (while behind the tanker), it may run out of engine thrust to fill up on gas at a particular airspeed. ” Other technical obstacles faced by the coupled entity were likewise the result of clashing with the laws of physics.

“The engineers have to look at compatibility of the two aircrafts’ fuel systems, because even though the fuel is delivered at the same pressure as it is on the ground, the flow rate is much higher which means when the tank valves shut off in the receiver aircraft, it creates a water hammer type effect (or hydraulic shock wave) that can burst the pipes in the aircraft if they haven’t been tested or designed properly,” says SQNLDR Bowes.

“Also, the Wedgetail has a lot of transmitters that you’re putting in close proximity to an Airbus A330, which is all fly-by-wire. So, we needed to closely look at the vulnerability of the flight controls of the KC-30A green aircraft and the boom to particular transmitters that we either didn’t want to, or couldn’t, turn off on the Wedgetail when it tanked. ” Despite the Wedgetail’s plethora of excrescences, from its MESA Top Hat radar to ventral strakes and antennae, SQNLDR Bowes found the aircraft behaved well while locked in behind the KC-30.

“The Wedgetail, contrary to what you’d expect, flies quite nicely, despite the MESA radar. Once you put that big vertical surface behind the tanker you can find some unusual aspects. We found a few that weren’t unanticipated, but they didn’t preclude safe tanking by operational squadrons,” says SQNLDR Bowes. “Certainly the KC-30A also has quite a sizeable boom, compared to a KC-135 or KC‑10, so it throws off a wake of its own which can be felt in the Wedgetail as you move from astern to contact. But then the flipside is that the Airbus wing is a higher aspect ratio than the older Boeing [KC-135]or KC-10 wing, so the intensity of the downwash is less for the same sort of weight. ” Another benefit of the Airbus design is its supercritical wing – tailored to delay the formation of shockwaves just below the speed of sound – resulting in cleaner airflow coming off the wing, affording smoother tanking.

Gas And Go

Stakeholders in the Wedgetail booming trials – ARDU, 2SQN and 33SQN – would teleconference on the morning of flight to cover test points and outstanding maintenance issues. After a formal briefing, specific rendezvous times would be decided and the respective aircraftlaunched, meeting at the prearranged time in the restricted military airspace blocks (R662 and R671) off the coast of Coffs Harbour.

A typical complement on board consisted of flight test engineers from ARDU and Airbus, plus two ex‑USAF contracted test aerial refuelling operators, and two test pilots (including the highly experienced KC-30 test pilot SQNLDR Chet Takalkar, who participated in the KC‑30A boom clearance trials in Spain).

“We did seven flights but there were no contacts on the first flight, which was a wake survey – assessing the position of the approach line to the tanker at different distances,” says SQNLDR Bowes.

“The second flight looked at the boom envelope in terms of boom elevation and boom lateral roll connecting and disconnecting at different points in that envelope to see if there was any binding between boom and receptacle. That gave us the safe envelope to build the altitude/airspeed envelope. Starting at 300ft astern we’d manoeuvre up and down in a box‑type pattern, cued by the tanker flying the boom in a box‑type pattern, and we’d look for discontinuities in the wake, we’d look for vortices that were sudden onset and could cause a control problem. All that was done as part of a gradual process. ” The flight characteristics of the KC‑30’s flying boom and the Wedgetail, within touching distance, were explored next.

“We needed to do a wake survey behind the tanker, 1 to 2ft from the boom nozzle. We’d fly a pattern around the extent of the boom control envelope, looking for vortices, non‑linear control responses that would cause an issue for us if we ended up there. Because every operational pilot will always try to make contact on the centre elevation, different environments, as in night, poor lighting, or flying into the sun means they could find themselves off centre. And if there’sany sort of vortex off the tanker that’s highly localised, that could cause an unsafe control problem. ” Needless to say, the effect of flying an aircraft in the highly energised air behind a large tanker like the KC-30 imposes stresses on the receiver aircraft with the resultant fatiguing of its structure. The Wedgetail used in these trials was equipped with a structural load monitoring system, data from which was sent to Boeing at the end of each test flight to determine whether or not the loads encountered during trials exceeded the Wedgetail’s critical design limitations. Thankfully, Boeing was able to report that the data was well within design limits.

Further, explained SQNLDR Bowes: “This new generation of aircraft allows us to tap into the flight data recorder, which is a low cost, slightly less precise flight test instrumentation, but it gave useverything we needed for the test. On the KC-30A side, thanks to some foresight by Airbus and the RAAF project office, all five aircraft are wired up with the FTI (flight test instrumentation) needed to clear new receivers. ”

Boom With A View

Contact with the receiver aircraft is managed by the KC-30’s aerial refuelling operator (ARO), who sits in a rear-facing console immediately aft of the flightdeck.

The ARO’s display is fed with images from the aircraft’s 2D/3D high definition/digital enhanced video monitoring system which incorporates stereoscopic vision and laser-based infrared lighting systems. This enables the KC-30A to tank in adverse weather and at night.

The boom is electrically powered, has a fly-by-wire flight control system and can pass fuel at a peak rate of 4,600lt/min.

WOFF Andrew Newman is an ARO instructor at 33SQN. A former flight engineer, in 2007 he was attached with the USAF to learn the art of flying a boom with the 92nd ARW in Fairchild, Washington.

“About 15 minutes prior to hookup, we conduct the preparation to contact checklist, then the rendezvous procedure would be conducted between the tanker and receiver,” he describes of how the KC-30 prepares for a typical contact.

“Once the receiver aircraft is visual, I will call it on visual and the pilots then hand me the radios and responsibility for the receiver’s management. Pilots say ‘ARO, your radios’, I make contact with the receiver, clear him into stern position behind the tanker, and the boom, and when the receiver is ready, I give a ‘clear to contact’ call and a signal light forward and they would proceed to contact position at 1ft per second. When the receiver is stabilised at the contact position we fly the boom and extend the telescopic beam to make the contact. ” WOFF Newman says AROs currently undergo five to six months training which involves qualifyingas a loadmaster after ground school, simulator training and flight training. Currently, the wing has 12 AROs trained, against a future requirement of roughly 20.

Describing the art of placing the boom safely in the receptacle, binding two aircraft together at altitude, WOFF Newman explained: “It’s a 3D system, so [the ARO has] depth perception and can judge it fairly well. There’s also cues from the shadows on receiver aircraft – it’s a matter of experience. In making a contact, if there’s movement between the two aircraft, it takes some skill to fly the boom and keep it aligned with the receptacle. You want to avoid scratches on the skin of the receiver, especially low observable aircraft and you have to be careful you don’t break small antennas that may be on a fighter. It’s quite precise and takes time to develop the skills.

At night, the KC-30 has IR illuminators; it’s black and white, rather than colour. That said, it’s easy to refuel at night in the KC-30A – the KC-135 has floodlighting which was more difficult. ” The ARO can effectively ‘tell’ the boom the size of the receiver aircraft to be refuelled, according to WOFF Newman, which then dictates the flight control laws of the boom. “There is a refuelling envelope, or cleared box that the boom will refuel in. The geometry between the two aircraft varies – if you look at a B-2 or F-16, they both have their optimum safe clearances determined. With the E-7A, this program determined that. For each size aircraft, there’s a refuelling limitation in elevation, in roll off the boom’s position and airspeed and altitude. ” Built into the software controlling the boom are numerous failsafes, given the potential hazards of air-to‑air refuelling, as demonstrated by the damage suffered by the KC-30A on the test flight in Spain which lost part

It takes some skill to fly the boom and keep it aligned with the receptacle. WOFF NEWMAN

of its boom to the Portuguese F-16.

“There are automatic disconnects in the system so that if the lower elevation limit of the boom was exceeded, the boom would disconnect before it allowed the receiver to take the boom down.

“If we didn’t you could wind up with nozzles being snapped off which does happen in the AAR world. ”

New Boom Sweeps Clean

The boom has clearly come a long way from the 2011 incident.

“Prior to this test program, the only real boom data in terms of its control handling qualities that we had was with respect to the KC-30A, or F-16, as receivers. When we looked at the Wedgetail, it sits roughly halfway between them. It’s a narrowbody aircraft, which weighs more than an F-16 but much less than a KC-30A. So we decided, with a lot of technical input, to try large receiver flight control laws first,” says SQNLDR Bowes.

“What we found was they were exceptional. The two test boom operators had not a bad word to say about the boom. They both said it was precise and easy to control throughout the envelope. ”

Future Clearances

Having successfully cleared the Wedgetail for boom use, 86WG and ARDU can turn their attention to clearing other receptacle-equipped aircraft operated (or soon to be) by the RAAF: the F-35, P-8 and C-17. There are plans to deploy a KC‑30A to the US to clear the F-35, while the US Navy is already receiving official briefings on the Wedgetail booming clearance effort ahead of P-8 boom trials.

As for AMG’s C-17 air-to-air refuelling trials, WGCDR Kelly states: “In US service, it’s already cleared to tank behind tanker aircraft. And it’s clearance behind the KC-30A is in our program, to be fitted in over the next 18 months where it’s a little bit fluid at the moment, but it will be one of the first things we look to clear. ” No doubt, these efforts will build the corporate knowledge to develop 33SQN’s ability to conduct boom refuelling. Using the boom on operations will require maturity across logistics, maintenance and operational areas. After its early hiccups, the boom is now winning plaudits from the AAR community, and is helping the KC-30A to deliver on its enormous potential and is helping the E-7A to do the same.

According to SQNLDR Bowes, “It was a very aggressive schedule, it relied on a lot of extra hours and a lot of hard work from people not just within ARDU but certain key individuals in 33SQN, 42WG, 2SQN and the aircraft systems program offices. We got assistance in terms of subject matter expert advice from Airbus and the USAF. We got it done quite successfully in the end. ”

Back for more

The RAAF fleet of five KC‑30As will soon grow to seven after Defence Minister Kevin Andrews announced on July 1 plans to acquire two additional aircraft.

“The two additional KC-30A aircraft will be delivered in 2018 and provide a substantial increase to the air-to-air refuelling capacity of the RAAF,” Andrews said in a statement.

“Defence has signed an update to the existing acquisition contract with Airbus Defence and Space for the two aircraft and associated conversion at a cost of approximately $408 million. ” The two ‘new’ aircraft are in fact secondhand airframes that have been operated by Qantas. The two airframes are VH-EBH (msn 892) and VH-EBI (msn 898), which were both built in 2007, and so are of a similar vintage to the existing RAAF KC-30s, and were leased by owner CIT Aerospace to Qantas. VH-EBH has already been withdrawn from Qantas service, operating its last service for the airline in May, while EBI is expected to be withdrawn by November.

“The aircraft were built in the same batch as the existing aircraft and are substantially the same configuration offering the Commonwealth an opportunity to deliver aircraft that are compatible with the in-service fleet and to minimise sustainment costs,” a Defence spokesperson told Australian Aviation. “The age and previous use of the aircraft is relatively low and Airbus Defence and Space have been contracted to provide a capability that achieves the life of type of the existing fleet. ” Although four of the original five aircraft were converted from ‘green’ A330 airframes to their KC-30 configuration by Qantas Defence Services (now Northrop Grumman Australia Integrated Defence Services) at Brisbane Airport, the two new aircraft will be converted to tanker configuration by Airbus Defence and Space at Getafe, Spain.

“The aircraft will be modified in Madrid using the existing production line to minimise cost as modification in Australia for only two aircraft is not viable,” the Defence spokesperson said.

The last KC-30 converted in Brisbane was delivered in 2012 and since then tooling has been returned to Spain and personnel who worked on the conversion program have dispersed.

Airbus also points out that since the end of the Australian program it has been performing MRTT conversions in Spain without interruption and “we have all the accumulated expertise of conversions for other A330 MRTT customers – so Spain currently represents the best solution,” the Airbus spokesperson said.

So does Airbus see a burgeoning market in ex-civil A330-to-tanker conversions? “We foresee a global market for strategic tankers of around 90 aircraft outside the USA and we believe that the vast majority will be based on new aircraft, while there may be a few exceptions to this general rule,” the spokesperson said. “The option of used aircraft was taken in this case in order to acquire aircraft with very similar configurations to the original A330 MRTTs built and converted for the RAAF. ” Sustainment of the expanded fleet, meanwhile, will be covered by the existing support agreements in place for the KC‑30. “The existing maintenance support agreement with Northrop Grumman IDS will be extended to cover the additional two aircraft,” Defence confirmed.

“The age and previous use of the aircraft is relatively low and Airbus Defence and Space has been contracted to provide a capability that achieves the life of type of the existing fleet. ” And like the existing fleet the new KC-30s will, at least initially, be configured with an airliner-style passenger interior, and not be fitted out for VIP transport.

“NSC [Cabinet’s National Security Council] has approved the acquisition of these two additional aircraft to be used as refuelling and transport aircraft in line with the current RAAF fleet,” the Defence spokesperson said in response to Australian Aviation’s inquiry if fitting one or both of these aircraft with a VIP/special purpose Interior was under consideration.

Instead, “The passenger interior delivered with the aircraft will be retained. ” Here the two new aircraft will differ from the existing fleet. The current aircraft were delivered with a 270-seat interior based on the original Qantas domesticA330-200 configuration, while EBI and EBH are fitted with an international configuration of 36 ‘Skybed’ lie flat business class seats and 199 economy class seats.

Both aircraft will wear the current all-grey wraparound camouflage scheme. And no new facilities will be built at RAAF Amberley to house the extra airframes.

The acquisition of extra KC‑30s was first publicly flagged by former Defence Minister Senator David Johnston in an interview in August last year.

“When you get good service from a platform it prompts you to say, ‘why don’t you get some more?’,” the then Minister was reported as saying.

So could the fleet of KC-30s expand beyond seven examples? Defence was non-specific, offering only that: ‘The Force Structure Review (FSR) is currently looking at a broad range of capabilities for the development of a balanced and affordable future force. This includes examining the full range of projects under way across Defence. To ensure a fully costed and affordable Australian Defence Force, capability and cost tradeoffs of all new and existing projects needs careful analysis. The FSR’s recommendations will be considered in the context of the Defence White Paper. ” We think that’s a no.