If you never have experienced a refueling operation from inside a tanker aircraft, you may think the process is relatively simple, involving little more than extending a boom and then letting the fuel flow. It is, in fact, a demanding operation that requires a high degree of precision and calculation. In a KC-135, the aerial refueling operator (ARO) lies on his stomach, with little cushion, for long periods of time (up to 30 minutes to refuel, say, a C-17), peering through a window in the back of the airplane. Using a long handle and cable-drive system, the ARO continually adjusts the pitch and angle of the aerial refueling boom as the receiver aircraft fills up with fuel. This is often referred to as "flying the boom" because, not unlike an airplane, the boom has a two-wing control system, called a "ruddevator." The ARO employs a "direct view system," so-called because he looks directly at the receiver aircraft through a window. If the ARO also manages refueling operations that employ a hose and drogue, his job becomes even more demanding.
But for the U.S. Air Force, the refueling task soon may become much easier for the ARO, as well as for the tanker pilots, thanks to new display technology, processing, digitally enhanced imaging and a state-of-the-art cockpit panel, all housed in a Boeing 767 with the nickname, "smart tanker." Boeing is a veteran in the tanker business, having delivered more than 1,900 refueling aircraft, ranging from the propeller-driven KB-29, flown in the 1940s, to a converted B747. It built 761 KC-135 tankers for the Air Force, 545 of which are still in operation. The average age of these aircraft is more than 40 years, which is why the service now seeks a replacement.
As a first step to modernize its tanker fleet, the Air Force plans to lease 100 commercial B767-200ER (extended range) aircraft. These planes would replace 132 KC-135Es (with Pratt&Whitney TF33 engines), which otherwise would have to be re-engined to become somewhat more modern KC-135R models (with CFM 56 engines). Boeing will produce the B767s at its Everett, Wash., facility, and then fly them to its Wichita (Kan.) Development and Modification Center to be fitted for the refueling mission.
A leasing arrangement allows the Air Force to get aircraft into operation more quickly than by acquisition, according to Brad Gorsuch, air vehicle integrated product team leader-767 programs at Boeing. The Air Force issued a draft statement of need in 1990, and in late 2001 the U.S. Congress authorized the service to negotiate a lease arrangement, which was scheduled to receive congressional approval in late 2002 or early this year. The plan would have deliveries made over a six-year period, beginning in early 2006.
The Air Force considers the 767 Tanker Transport to be technically a low-risk proposition. Boeing has delivered some 860 B767s to 85 operators, and the 767 fleet has amassed about 31 million flight hours. To "mitigate schedule risks" in fielding the 767 Tanker Transport (designated by the Air Force as the KC-767) within a short time frame, the Air Force will receive the first 50 aircraft equipped with a center line hose and drogue (called the hose drum unit) and a boom, but not with refueling pods and hoses on the wings, according to Gorsuch. "The wing pods may come with the second spiral of aircraft," he adds.
The RARO II
The heart of the 767 Tanker Transport and the feature that will allow the ARO to get up from his prone position is the second-generation version of the remote aerial refueling operator station (RARO II), a console positioned just behind the cockpit. Seated at the RARO station, the aerial refueling operator can plan, monitor and manage the refueling operation. His workload is greatly reduced. "Instead of continually flying the boom [manually], the ARO now has a ‘load alleviation system,’ which automatically keeps the boom where it is supposed to be," says Gorsuch. "It’s like an autopilot. It has sensors and a fly-by-wire control system, so it can detect a load in the boom and then relieve it automatically." The 767 Tanker Transport boom uses electronic actuators, reducing the number of hydraulic components in the boom system by 40 percent.
For planning, refueling management and monitoring, the RARO console will have an 18-inch diagonal, color active matrix liquid crystal display (AMLCD) and symbol generator, furnished by Exton, Pa.-based Innovative Solutions & Support (IS&S). The unit is called the aerial refueling operator control display unit (AROCDU). IS&S also provides a cockpit-based refueling display, known as the pilot mission display (PMD).
"The display computer–a powerful graphics processor–takes a lot of input, including video," says David Marvin, IS&S’ vice president-marketing and business development. "It is separate from the [AROCDU] display and located in the electronic bay." The IS&S processor also transfers mission data between the PMD and the AROCDU. The PMD allows the pilots to monitor the refueling operations (including video) on an 8.4-inch display, positioned in the center console. The multiyear agreement for the AROCDU and PMD is expected to bring some $10 million to IS&S.
Head-Mounted Display
At the RARO, the operator can view the fuel flow and the fuel quantities in the main and auxiliary tanks. He can summon aircraft specifications and create mission profiles for the refueling of multiple aircraft. The ARO also can preset the amount of fuel to give aircraft. On the AROCDU, the ARO can split the imagery to show simultaneously, for example, video from three externally mounted cameras along with the status of the refueling system.
For aerial refueling boom operations, the ARO wears a head-mounted display–Gorsuch calls it "quasi-helmet mounted"–which delivers a stereoscopic, three-dimensional view of the boom and receiver aircraft. This precise imagery, enhanced by processing, is critical for optimum depth perception to accurately extend and "fly" the boom, which is done using a joystick. In addition to video imagery, the head-mounted display also presents a scale to the left of the viewing area to indicate the length of the boom’s extension and one at the bottom, indicating the boom’s azimuth. Fuel flow rate also is presented.
To achieve the stereoscopic 3-D imagery, two digital cameras are mounted side by side just forward of the boom’s connection to the 767 Tanker Transport’s tail. The cameras must maintain precise alignment, so they are automatically synchronized, says Gorsuch, which means one camera "always knows where the other one is pointing."
Lights for Guidance
For wing pod operations, the aircraft is equipped with "situational awareness cameras." Three low-light digital cameras are centrally located on the tanker’s belly. One points straight back and the other two point outward, toward the two wing tips. Their fields of view overlap, so the ARO can monitor refueling using the hose drum unit, the wing pods, or both.
For refueling in low-light conditions, the 767 Tanker Transport has signal lights on the aircraft to guide the planes needing fuel," says Gorsuch. "The lights are like those on a runway, so the receiver aircraft can line up. It is a directional system." For more discreet refueling at night, pilots of the receiver aircraft can don night vision goggles and see drogues illuminated by compatible lighting attached to the tanker.
The ARO controls the lighting (as well as the digital cameras). He can preprogram various lighting configurations that subsequently can be called up by a single touch of the RARO screen.
Mission Management
Smiths Aerospace provides much of the 767 Tanker Transport’s mission equipment: the self-powered wing pods, palletized hose drum unit, and the boom actuator for refueling. In addition, it will outfit the aircraft with a mission control system (MCS), which replaces the flight management system (FMS). A derivative of Smiths FMS on the B737, the MCS is being developed especially for the refueling mission. (Honeywell supplies the FMS for the commercial 767-400.) The MCS "takes in such data as flight control, fuel storage and fuel flow," says Gorsuch. The ARO gains fuel quantity data through the RARO’s interface with the MCS.
In addition to the flight management tasks incorporated for commercial operations, the MCS will allow the input of refueling orbit patterns, rendezvous points and other mission-specific data. The pilot can enter the data manually or use a mission planning system on the ground and then transfer it to the MCS.
The MCS includes a liquid crystal, multifunction display (MFD) and a processor that is comparable to the computer for the C-130 AMP program, according to John Armendarez, Smiths’ director-military programs. This is a powerful processor. "A normal FMS would take only 15 percent of the processing capacity of this box," he claims.
The MCS uses VME interfaces and has open systems architecture and software partitioning, compliant with ARINC 653. "We use software partitioning to add new functions to the unit," says Armendarez. "One is an avionics control function to the RARO; this is what ties the mission control system with the RARO station and, therefore, to the refueling system."
The MCS’ partitioned, open architecture also will accommodate third-party communications software. Smiths will select the communications software supplier from a competition. The software will provide data link communications in compliance with ARINC 728.
"The system makes the 767 Tanker Transport GATM- [global air traffic management] compliant and, like the civil FMS, will accommodate an RNP [required navigation performance] capability and CPDLC [controller-pilot data link communications]," says Armendarez.
Much like the -400
The Air Force’s KC-767 will be a B767-200ER, but it will have an advanced B767-400 cockpit provided by Rockwell Collins. Five 8-by-8-inch color, liquid crystal displays (LCDs), replacing the old cathode ray tub (CRT) display in the commercial -200, grace the KC-767 cockpit panel. The primary display starts out by default, showing the standard, horizontal situation indicator (HSI) and attitude director indicator (ADI). But the display system is reconfigurable, so the pilots can present the information they choose on any of the five displays, according to Phil Jasper, Collins’ director of air mobility, bombers and special mission programs. Navigation and communications data can be presented, and the system includes an engine indication and crew alert system (EICAS).
Though the display system is the same as those in the commercial B767-400, it must be configured for the tanker mission. Take, for example, the display processing to show the orbit in which the aircraft flies during a refueling operation. Its mapping function will show the boundaries of the military operating areas (MOAs) and special use airspace (SUA).
"We are also installing a processor that allows Link 16 multifunction information distribution system to be integrated with the 767 avionics, providing tanker crews with even more situational awareness," says Jasper. "To grow beyond Link 16 and include other waveforms, the processor can be upgraded to ELINT [electronic intelligence] and SIGINT [signal intelligence]."
The KC-767 cockpit will include Collins’ WXR-2100 weather radar and multimode receiver (MMR), also taken from the B767-400. The tanker’s communications suite will include ARC 210, combined VHF-UHF radios plus ARC 190 military HF radios. (This varies from the commercial -400’s communications package, which includes three VHF radios.)
For navigation, the aircraft will be equipped with GPS and the Collins air-to-air tactical air navigation system (TACAN). The latter navaid gives tanker pilots the range and bearing of other aircraft in the battlefield arena.
The 90-kilovolt-ampere (kVA) generators in the 767-200 have been swapped out for 120-kVA generators to accommodate the KC-767 digital architecture.
Testing and Training
The KC-767 configuration has been established, and design and development is under way. Although a B767 has yet to be equipped for the refueling mission, Boeing and the Air Force have been able to test the aircraft suitability for the mission.
"We’ve done proximity testing, flying aircraft close to the 767," says Gorsuch. "At Patuxtent River [Naval Air Station], we conducted tests with the F/A-18 and S-3 in 2000, and in the summer of 2002, we tested with the C-17. The test showed that the 767 is an extremely stable platform for refueling small and large aircraft alike."
Aerial refueling operators have had a chance to evaluate the RARO, as well, and "they were impressed," says Gorsuch. The Boeing official believes it will take no more time to train operators on the RARO than it did training them to work the old way, on their stomachs.
Tankers Around the World
The United States isn’t alone in seeking a new tanker aircraft. The Japanese and Italian governments have joined the U.S. Air Force in selecting a Boeing 767 variant to satisfy their tanker needs. The UK also seeks a modern tanker but is weighing a choice between the B767 and its chief rival, the Airbus A330 Multirole Tanker Transport (MRTT). These two aircraft are competing in a global market that Boeing estimates to be about 500 aircraft, worth some $100 million over the next 30 years.
Japan, which has acquired from Boeing 767 AWACS aircraft, made a decision in December 2001 to order four 767 tankers. Boeing expects a contract early this year, and deliveries are expected to run from the fourth quarter of 2006 to 2009. The Japanese aircraft, like the U.S. Air Force’s KC-767, will be equipped with the remote aerial refueling operator (RARO) station and boom. But unlike the KC-767, it will maintain the cockpit and 90-kVA generators used in commercial B767-200s.
Italy will be the first customer to receive 767 tankers, beginning in 2004. In a competition, Italy selected the Boeing candidate in July 2001 and signed a contract in September 2002. The Italians have ordered four aircraft and, like the Japanese, have chosen to retain the -200 cockpit and generators. The Italians also chose to have their tankers fitted with a hose drum unit, boom and wing pods. One aircraft will be modified at Boeing’s Wichita facility and three by Aeronovali, part of Alenia, in Naples. Deliveries are to be completed in 2008.
Boeing offers two versions of 767 tankers: a convertible freighter, which can be reconfigured for cargo transport or personnel transport, and a convertible combi, which can be fitted for cargo or personnel transport or both at the same time. Japan has selected the convertible freighter option, while the U.S. Air Force and Italy have selected the convertible combi.
The downselect for a new tanker in the UK is expected in the summer of 2003, with a contract to follow in 2004. The UK does not want to buy or lease tankers, but has set aside some $20.5 billion for a highly unusual service delivery arrangement. For 27 years, the winning bidder would provide a tanker service with aircraft that could otherwise be in other service. On tanker missions, the aircraft would be flown by Royal Air Force crews. Should Boeing be the winner, the UK military would employ B767-300ERs (instead of B767-200s) taken from the British Airways fleet. The aircraft would be fitted with wing air refueling pods and a centerline hose and drogue system but not a refueling boom. Teaming arrangements have been made for the UK deal. The Boeing team that would provide the refueling service is called the Tanker & Transport Service Co. Ltd. and includes BAE Systems, SERCO and Spectrum Capital. The competitive team, AirTanker, which would offer the A330, includes EADS, Rolls-Royce, Cobham, Brown & Root Services and Thales Defense.
Aerial Refueling 101
Aerial tankers can refuel aircraft in three ways:
A boom, positioned below the aircraft tail; it has a "ruddevator," a V-shape wing system with control surfaces to allow the operator to maintain the boom’s consistent elevation and azimuth;
A center line hose and drogue, called a hose drum unit; the hose is extended from the tanker aircraft’s belly; and
Wing pods, which extend a hose and drogue from the tanker wings.
The various refueling devices exist for redundancy and to accommodate aircraft with different refueling probes. For example, the U.S. Navy aircraft refuel from a hose and drogue system, which can connect to the shorter, lighter probes fitted to carrier-based planes. Air Force aircraft, fitted with receptacles, can hook up to the refueling boom.
The fuel flow rate varies among refueling devices. The wing pods dispense fuel at a rate of 400 gallons per minute; the center line drogue dispenses at 600 gallons per minute, and the boom, which commonly fuels the larger bombers, puts out 900+ gallons per minute. The KC-135 has a boom, as well as a hose and drogue, but it cannot perform the two types of refueling simultaneously. The B767 Tanker Transport proposed for the Air Force can.
How much fuel can the 767 Tanker Transport hold? The B767’s normal fuel load is 161,000 pounds, but with auxiliary tanks installed in the cargo hold, an additional 41,000 pounds are brought on board. The 767 Tanker Transport also can perform as a receiver and be refueled in-flight from another tanker.