Tanker aircraft

The Airbus A330-based MRTT has scooped numerous tanker contracts around the world in recent years. This photo shows an Australian example refuelling an F-35. (Photo: Airbus)

A fine balance

Finding the right balance between proven and leading-edge technologies is a crucial concern for any service looking to extend the range of its combat aircraft, not least because the number of tanker aircraft solutions available on the market is limited.

Gordon Arthur

Air-to-air tankers are force multipliers, allowing platforms such as fighters to extend their range or remain on target longer. The number of tanker options available is rather limited for any air force wishing to add them to its fleet, however.

Continuous evolution

Airbus’ A330 Multi-Role Tanker Transport (MRTT) is currently the most popular air-to-air refuelling (AAR) platform, having racked up sales of 61 aircraft, of which 45 have been delivered. Converting a regular A330 into an MRTT with 111t fuel capacity takes about nine months.

Australia introduced its sixth and seventh KC-30As (as the MRTT is designated locally) in 2018-19, these being converted airliners. In October, a two-phase contract to modernise communications and mission systems on the RAAF fleet was announced.

Airbus highlights that the MRTT is continually being improved: ‘We have already tested in flight a fully automatic AAR solution that will relieve most of the workload for the refuelling operator when performing a contact with the Air Refuelling Boom System, increasing the efficiency and safety of this complex operation.’

Airbus secured a contract with Singapore for such a Smart MRTT ‘to take this innovative solution into reality, and very soon it will be in the field of operations’.

Airbus predicts future battlespaces will be truly connected environments, ‘so we are working towards this direction, in order to provide the MRTT with an advanced and flexible connectivity solution allowing it to expand its roles operating as a communication node or even a command and control station’.

 

🜂 Global orders and deliveries of tanker and tanker/transport aircraft. (Source: Shephard Defence Insight)

 

The UK RAF, for instance, is planning to use a Voyager MRTT as an airborne information node in its Babel Fish VII experiment.

Airbus’ spokesperson shared noted AAR has ‘evolved tremendously’ in recent years. ‘Some older tankers (still in operation) have their refuelling operator lying on the floor, looking through a glass window in order to perform the contact with the receiver. The A330 MRTT allows this same operator to sit comfortably in the cockpit, together with the pilots, performing the operation just using 3D glasses and a joystick.’

India is one market that has proved elusive for Airbus, with New Delhi’s 14-year search for tankers beset by mismoves. India has a few Il-78M tankers, and the MRTT had been selected twice in tenders before the procurement process collapsed. A 2018 RfI seeking six tankers was cancelled when the idea emerged to combine tanker and AEW capabilities in a single aircraft. With this notion curtailed, India’s latest thinking is to consider leasing tankers.

The MRTT is not Airbus’ only AAR option. The company spokesperson explained: ‘The A400M has a basic fuel capacity (wing fuel tanks) of almost 51t and is currently used in AAR missions… by the air forces of France, Germany, Spain and Malaysia. All delivered A400Ms have the basic built-up provisions for conversion into a tanker… The basic two-point tanker configuration includes two Cobham 908E underwing pods, external night/day video cameras and the software to allow supervision of the receiver’s approach and refuel operation from the cockpit.’

This system equips 26 of 93 A400Ms delivered so far. The OEM added that it is possible to refuel large aircraft by installing a hose-and-drum unit in the rear part of the cargo hold. ‘Additional enhancements are cargo hold fuel tanks and special pods for helicopter AAR.’

Complex competitor

The MRTT’s US competitor is the KC-46 Pegasus. Boeing has a long history in aerial tanking with aircraft like the KC-135 Stratotanker and KC-10 Extender that are mainstays in the USAF fleet (the first KC-10A was retired on 13 July). The USAF plans to buy 179 KC-46As, with 38 delivered so far.

Boeing explained that ‘the majority of the KC-46’s requirements are based upon and compared to KC-135 capability. Built upon Boeing’s 767 freighter, it delivers more fuel at all ranges and from shorter runways, carries three times more cargo pallets, up to twice as many passengers and over 30% more aeromedical evacuation patients than the KC-135.’ Indeed, it can be reconfigured within 2h to accommodate up to 18 pallets, 114 passengers or 54 medical patients.

 

🜂 The Boeing KC-46A ordered by the USAF has encountered a number of teething problems, but it is a critical platform needed to replace ageing tankers. (Photo: Boeing)

 

The KC-46’s fly-by-wire boom is based upon the KC-10 outer mould line, but is completely revamped on the inside. It has three times the refuelling envelope of its predecessor, offloading 1,200+ gallons per minute. Each KC-46 has a centreline drogue system, ensuring it can ‘rapidly transition from boom air refuelling to hose-and-drogue refuelling during flight in only a matter of minutes’, according to Tim Flood, director of international sales, commercial derivative aircraft, at Boeing Defense, Space & Security. Every KC-46 also has a removable Wing Air Refueling Pod on each side to enable simultaneous refuelling.

Unfortunately, the KC-46’s fielding has been beset by well-publicised problems. Boeing has halted deliveries several times because of foreign object debris in completed aircraft, plus there have been wiring issues. Flood responded: ‘With 38 aircraft delivered to the USAF at four main operating locations, it’s important to note the KC-46 has successfully flown aeromedical evacuation missions and transported cargo. Most importantly, it is regularly used for refuelling training and exercises.’

Serious issues concern the Remote Vision System (RVS), where the operator’s station utilises panoramic, long-wave IR cameras providing a 185° view behind the aircraft. Flood stated: ‘In close coordination with the USAF, Boeing has jointly developed a technology enhancement plan for the RVS. These new capabilities will be installed using a phased approach. This plan required extensive engineering, analysis and coordination between the air force and Boeing. While time-consuming, it was essential to complete this engineering coordination to ensure the technological enhancements match the needs of the warfighter well into the future.’

 


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Boeing completed the first round of flight testing on initial RVS 1.5 enhancements in July. Flood elaborated: ‘We will have additional testing to collect data in the coming months as we continue to work toward a final design. The enhancements include upgrades to the current cameras as well as a new sensor that provides additional information on the distance between the boom and receiver aircraft.’

The Boeing executive added: ‘If the USAF decides to implement the interim RVS enhancements, we expect the first phase to be available for aircraft modifications on previously delivered aircraft in the second half of 2021. The second phase, which incorporates state-of-the-art advancements for the entire system, should be available for aircraft modification and incorporation into the production line in late 2023 or early 2024.’

 

🜂 This is an H-6U tanker of the PLAAF. It is converted from an H-6 bomber and can only carry 30t of fuel for offload to other Chinese aircraft. (Photo: author)

 

Media have reported that cost overruns on the KC-46A have reached $4.6 billion. Considering that Boeing’s fixed-price development contract was worth $4.9 billion, it appears the OEM has paid almost as much on development as the USAF.

Two export customers for the KC-46A have emerged: Israel and Japan. The latter has contracted for two so far under a 2015 request for four aircraft, but the two extras are expected. Flood added: ‘We’re engaged in discussions with other potential international customers.’

Just as the A400M transporter turns into a refuelling aircraft, so can Lockheed Martin’s C-130 Hercules. Indeed, the USMC utilises a number of KC-130s to refuel fixed-wing aircraft, tiltrotors and helicopters. The latest iteration is the KC-130J (carrying 27.8t of fuel), with the HC-130J combat rescue tanker and MC-130J special operations tanker being sub-variants. Around 60 of 110 KC-130J models on order for the US military have already been delivered. Other customers are France, Germany, Italy, Kuwait and Saudi Arabia.

A newcomer emanating from Embraer in Brazil is the KC-390 tactical tanker-transport fitted with a probe-and-drogue system. The first two customers for the KC-390 so far are Brazil and Portugal, with production at an early stage. Hungary also signed an order for two aircraft in November 2020.

Eastern ambitions

The Russian Air Force’s mainstay tanker is the Il-78, with about 19 in service. Although many Russian fighters and bombers can be aerially refuelled, the country’s tanker fleet is comparatively small. The first Il-78M-90A tanker with 126t fuel capacity and three hose-and-drogue pods achieved its maiden flight in January 2018, and tests should conclude next year before any order for this new model is lodged.

China relies on about ten rather inefficient H-6U tankers (based on the H-6 bomber) as well as three Il-78s. The People’s Liberation Army Air Force (PLAAF) is underequipped with tankers, especially as it roams farther from home.

 

🜂 A KC-707 tanker from Omega transfers fuel to an F-35 fighter. Omega was the first private company to successfully provide contracted tanker services to the US military. (Photo: Omega Aerial Refueling Services)

 

However, it is assumed that a tanker version of China’s Y-20 transporter will eventuate, with a prototype first spotted in 2018 satellite images. It appears to use one fuselage and two wing hose units; it could be five years before China develops a viable boom. Teng Hui, commander of a PLAAF aviation regiment, said on CCTV in February: ‘I believe that people will see our Y-20 aerial tanker debut on the battlefield in the not-too-distant future.’ It should be able to carry up to 80t of fuel, helping the Chinese military’s strategic ambitions.

Conversions and leasing

Other tanking options exist. Rafi Matalon, EVP marketing of Israel Aerospace Industries’ (IAI’s) Aviation Group, spoke of Multi-Mission Tanker Transport (MMTT) conversions: ‘Right now we are focusing on the Boeing 767 platform and look forward to develop on the Airbus 330.’ IAI literature lists ‘more than 12 customers worldwide including the Israeli Air Force’.

When asked about to compare IAI conversions to new-build OEM platforms, Matalon said: ‘IAI’s MMTT 767-300ER has a take-off fuel amount of over 216,000lb [98,000kg]. Therefore, its fuel transfer capability is higher than our current competitors in the market. Moreover, since IAI offers a “vintage” aircraft, the total price of the tanker is lower than our competitors’ price…

‘These aircraft can be operated for many more years for aerial refuelling missions after its original role in an airline as passenger aircraft. An additional advantage is IAI’s capability to “tailor” the tanker in accordance with customer requirements.’

Matalon elaborated: ‘The major problem of air refuelling missions is the duration time for fighters refuelling and refuelling as many fighters at the same time… especially in operational missions in a threatened zone… Most important is the ability to perform the mission when there are not enough tankers available. Based on IAI’s past experience with tanker system development, our engineers are working hard to find the right solutions with the most up-to-date technology for the above-mentioned requirements.’

 

🜂 The USMC relies on a KC-130 Hercules fleet for aerial replenishment. This particular KC-130J of Marine Aerial Refueler Transport Squadron 152 was lost in a refuelling crash near Japan in December 2018, illustrating the inherent danger of such missions. (Photo: author)

 

Air forces can also lease tankers. Omega Aerial Refueling Services currently has six such aircraft, three of which are in regular USN service. Omega’s fleet includes: a Boeing KC-707A with dual centreline FR-300 hose reels (one more entering service by mid-2021); two KC-707Bs equipped with MK32B wing pods; one KC-707C; a KDC-10/MPTT with dual 909E wing pods; and a KDC-10 (plus one coming next year).

Ulick McEvaddy, owner and founder of Omega, told Shephard: ‘We offer a low-cost, highly reliable alternative to ensure readiness of receiver units, expedite delivery of receiver units to/from exercises or other deployments, be available for initial or recurring aerial refuelling training and provide an excellent AAR R&D platform to improve products or services.’

Omega was the first to conduct autonomous refuelling in 2006. This led to the first AI-controlled refuelling of an X-47 UAV by an Omega KC-707 in 2015. McEvaddy continued: ‘This project paved the way for the MQ-25 Stingray which will be fielded in the next few years. Now Omega is studying the option of having boom refuelling stores in the wing pod position to permit multi-point boom-type refuelling. This project is several years out, and the wing-mounted boom will be controlled entirely by AI.’

Short supply

The USAF’s Air Mobility Command has an annual shortfall of 7,000-15,000 flight hours of tanker support. A 2020 report to Congress indicated that, once remaining regulatory issues are resolved, the air force will move to meet this shortfall using commercial assets. Omega estimates that ‘contract refuelling is 25-30% more cost-effective than USAF-owned assets providing the same service’.

Competition is heating up for Omega too, with another lessor to join the race being UK-headquartered Meta Aerospace. It recently took receipt of four retired ex-Singaporean KC-135Rs so it can begin offering private AAR services to the US.

McEvaddy concluded: ‘There is a fine balance that needs to be maintained between maintaining proven reliable systems and incorporating leading-edge technology. Often in the AAR business, operators are quick to throw out perfectly good technology for the latest high-tech but unproven solutions. We introduce our own new technologies to help improve ruggedness, reliability and maintainability of our fleet, while also embracing new testing of new technologies to support receiver requirements.’