Contents
- 1 History and development
- 2 Aerial refueling systems
- 3 Compatibility Issues
- 4 Strategic and tactical implications
- 5 HIFR (Helicopter In-Flight Refueling)
- 6 Developments
- 7 Tanker aircraft by refueling system
- 8 Popular culture
- 9 Media
- 10 See also
- 11 References
- 12 External links
Aerial refueling
From Wikipedia, the free encyclopedia
Aerial refueling, also called air refueling, in-flight refueling (IFR), air-to-air refueling (AAR) or tanking, is the process of transferring fuel from one aircraft (the tanker) to another (the receiver) during flight. Applied to helicopters, it is known as HIFR for Helicopter IFR, pronounced "hi fur".[1] The procedure allows the receiving aircraft to remain airborne longer and, more important, to extend its range and therefore those of its weapons or its deployment radius. A series of air refuelings can give range limited only by crew fatigue and engineering factors such as engine oil consumption.
Because the receiver aircraft can be topped up with extra fuel in the air, air refueling can allow a take-off with a greater payload which could be weapons, cargo or personnel: the maximum take-off weight is maintained by balancing the larger payload with carriage of less fuel. Alternatively, a shorter take-off roll can be achieved because take-off can be at a lighter weight before refueling once airborne (as with the US SR-71 Blackbird reconnaissance aircraft).
Usually, the aircraft providing the fuel is specially designed for the task, although refueling pods can be fitted to existing aircraft designs if the "probe and drogue" system is to be used (see later). The cost of the refueling equipment on both tanker and receiver aircraft and the specialized aircraft handling of the aircraft to be refueled (very close "line astern" formation flying) has resulted in the activity only being used in military operations. There is no known regular civilian in-flight refueling activity. In large-scale military operations, air refueling is extensively used. For instance, in the Gulf War and the Iraqi invasion of Kuwait and the Iraq War, all coalition air sorties were air-refueled except for a few short-range ground attack sorties in the Kuwait area.
History and development
Pioneer experiments
Some of the earliest experiments in aerial refueling took place in the 1920s, when it was as simple as two slow-flying aircraft flying in formation, with a hose run down from a hand-held fuel tank on one aircraft and placed into the usual fuel filler of the other. The first mid-air refueling between two planes occurred June 27, 1923, between two Airco DH-4B biplanes of the United States Army Air Service. An endurance record was set by three DH-4Bs (a receiver and two tankers) on August 27-28, 1923, in which the receiver airplane remained aloft for more than 37 hours using nine mid-air refuelings to transfer 687 gallons of aviation gasoline and 38 gallons of engine oil. The same crews demonstrated the utility of the technique on October 25, 1923, when a DH-4 flew from Sumas, Washington, on the Canadian border to Tijuana, Mexico, landing in San Diego, using mid-air refuelings at Eugene, Oregon, and Sacramento, California.
In 1929, a group of U. S. Army Air Corps fliers, led by then Major Carl Spaatz, set an endurance record of over 150 hours with the Question Mark over Los Angeles. Between June 11 and July 4, 1930, the brothers John, Kenneth, Albert, and Walter Hunter set a new record of 553 hours 40 minutes over Chicago using two Stinson SM-1 Detroiters as refueler and receiver. Aerial refueling remained a very dangerous process until 1935 when brothers Fred and Al Key demonstrated the first spill-free refueling nozzle, designed by A. D. Hunter.[2] They exceeded the Hunters' record by nearly 100 hours in a Curtiss Robin monoplane [1], staying aloft for more than 27 days.[3]
In the UK, Alan Cobham bought the patent from David Nicolson and John Lord for £480 each and then pioneered research on the probe and drogue method, and gave public demonstrations of the system. In 1934, he founded Flight Refuelling Ltd. (FRL), and by 1938 had used an automatic system to refuel aircraft as large as the Short Empire flying boat Cambria from an Armstrong Whitworth AW.23.[3] Handley Page Harrows were used to refuel the Empire flying boats for regular transatlantic crossings. FRL still exists as part of Cobham plc.
Modern specialized tanker aircraft have equipment specially designed for the task of offloading fuel to the receiver aircraft, based on Hunter's design, even at the higher speeds modern jet aircraft typically need to remain airborne.
Operational air refueling
In January 1948, General Carl Spaatz made aerial refueling a top priority of the new United States Air Force. In March 1948 USAF purchased two sets of Cobham's refueling equipment, which had been in practical use with BOAC since 1946, and manufacturing rights to the system. FRL also provided a year of technical assistance. The sets were immediately installed in two B-29 Superfortresses, with plans to equip 80 B-29s.
Flight testing began in May 1948 at Wright-Patterson Air Force Base, Ohio, and was so successful that in June orders went out to equip all new B-50's and subsequent bombers with receiving equipment. Two dedicated Air Refueling units were formed on June 30, 1948: the 43rd ARS at Davis-Monthan Air Force Base, Arizona, and the 509th ARS at Walker Air Force Base, New Mexico. The first ARS aircraft used a hose refueling system, but testing with a boom system followed quickly in the autumn of 1948.
In 1949 from February 26 to March 3 an American B-50 Superfortress Lucky Lady II of the 43rd Bomb Wing flew non-stop around the World in 94 hours, 1 min., a feat made possible by 3 aerial refuelings from 4 pairs of KB-29M tankers of the 43rd ARS. Before the mission, crews of the 43rd had experienced only a single operational air refueling contact. The flight started and ended at Carswell Air Force Base in Fort Worth, Texas with the refuelings accomplished over West Africa, the Pacific ocean near Guam and between Hawaii and the West Coast.
This first non-stop circumnavigation of the globe proved that, because of aerial refueling, vast distances and geographical barriers were no longer an obstacle to military air power. In 1949 four additional ARS units were organized by the USAF and both the 43rd and 509th ARS became fully operational.
The first use of aerial refueling in combat took place during the Korean War.
Aerial refueling systems
The two most common approaches for making the union between the two aircraft are the boom and receptacle system (sometimes called flying boom) and the probe and drogue system. There is also a combination “boom drogue adaptor” that combines the first two methods. Much less popular was the wing-to-wing system, which is no longer used.
Boom and receptacle (The Boeing "Flying Boom")
The “flying boom” is a rigid, telescoping tube that an operator on the tanker aircraft extends and inserts into a receptacle on the receiving aircraft. All boom-equipped tankers (i.e. KC-135, KC-10), have a single boom, and can refuel one aircraft at a time with this mechanism.
History of Flying Boom
In the late 1940s, General Curtis LeMay, commander of the Strategic Air Command (SAC), asked Boeing to develop a refueling system that could transfer fuel at a higher rate than had been possible with earlier systems using flexible hoses. Boeing engineers came up with the concept of the “Flying Boom” system. The B-29 was the first to employ the flying boom system, and between 1950 and 1951, 116 original B-29s, designated KB-29Ps, were converted at the Boeing plant at Renton, Washington State. Boeing went on to develop the world’s first production aerial tanker, the KC-97 Stratotanker, a piston-engined Boeing Stratocruiser (USAF designation C-97 StratoFreighter) with a Boeing-developed flying boom and extra kerosene (jet fuel) tanks feeding the boom. The Stratocruiser airliner itself was developed from the B-29 bomber after World War II. In the KC-97, the mixed gasoline/kerosene fuel system was clearly not desirable and it was obvious that a jet-powered tanker aircraft would be the next development, having a single type of fuel for both its own engines and for passing to receiver aircraft. It was no surprise that, after the KC-97, Boeing began receiving contracts from the USAF to build jet tankers based on the Boeing 367-80 (Dash-80) airframe. The result was the Boeing Model 707, Military designation KC-135, of which 732 were built.
Flying Boom Operation
The flying boom is attached to the rear of the tanker aircraft. The attachment is flexible allowing boom movement up to 25 degrees left or right, and from flush with the bottom of the aircraft up to 50 degrees down. Mounted within the outer structural portion of the boom is a rigid tube through which the fuel passes. The tip end of the fuel tube has a nozzle attached on a flexible ball joint. The nozzle mates to the "receptacle" in the receiver aircraft during fuel transfer. A poppet valve in the end of the nozzle prevents fuel from exiting the tube until "contact" is properly made between the nozzle and receptacle. Toggles in the receptacle engage the nozzle, holding it locked during contact. Mounted on the hollow shaft surrounding the fuel tube are a pair of control surfaces which equal the functionality of a conventional aircraft V-tail stabilizing surface setup, or alternatively, a four-surface arrangement closely resembling the tail surfaces of the late World War II Heinkel He 162 jet fighter, allowing aerodynamic control of the boom. The fuel tube extends and retracts hydraulically; it also "freewheels" in and out in response to the receiver's fore and aft movement during contact. The receiver's receptacle is typically fitted on the aircraft's centerline, but design considerations may require other locations.