Contents
- 1 History and development
- 2 Systems
- 3 Compatibility issues
- 4 Uses and considerations
- 5 Helicopters
- 6 Developments
- 7 Tanker aircraft by refueling system
- 8 Operators
- 9 Popular culture
- 10 Media
- 11 See also
- 12 References
- 13 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 HAR for Helicopter Aerial Refueling.[citation needed][1]
The procedure allows the receiving (generally military) aircraft to remain airborne longer, extending 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 carrying less fuel and topping up once airborne. Alternatively, a shorter take-off roll can be achieved because take-off can be at a lighter weight before refueling once airborne.
The two main refueling systems are probe and drogue, which is simpler to adapt to existing aircraft, and the flying boom, which offers greater fuel transfer capacity, but requires a dedicated operator station and specially designed receiving receptacle.
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. Originally employed to extend the range of intercontinental strategic bombers, air refueling since the Vietnam War has been extensively used in large-scale military operations for many different aircraft and helicopters. 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; two slow-flying aircraft flew 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 on 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 a 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]
There were parallel experiments conducted in Europe; at Le Bourget the Aéro-Club de France and the 34th Aviation Regiment of the French Air Force were able to demonstrate passing fuel between machines at the annual aviation fete at Vincennes in 1928.[4] The UK's Royal Aircraft Establishment was also trialling refuelling-in-mid-air, with the aim to use this technique to extend the range of the long-distance flying boats that serviced the British Empire. By 1931 they had demonstrated refueling between two Vickers Virginias, with fuel flow controlled by an automatic valve on the hose which would cut off if contact was lost.[5] The aviation pioneer Alan Cobham bought a patent from David Nicolson and John Lord for £480 each and then developed 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. During the closing months of World War II it had been intended that Tiger Force's Lancaster and Lincoln bombers would be flight refulled in operations against the Japanese homelands, but the war ended before the aircraft could be deployed. FRL's post-war trials used a Lancaster tanker trailing the hose and drogue from an HDU, and the modified Meteor III, EE397, fitted with a nose-mounted probe[6]. On 7th August 1949, the Meteor flown by FRL test pilot Pat Hornidge took-off from Tarrant Rushton and, refulled ten times by the Lancaster tanker, remained airborne for 12 hours and 3 minutes, receiving 2,352 gallons of fuel from the tanker in ten tanker contacts and flying an overall distance of 3,600 miles, achieving a new jet endurance record.[7] 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 use
In January 1948, General Carl Spaatz, then the first Chief of Staff of the new United States Air Force made aerial refueling a top priority of the service. In March 1948 USAF purchased two sets of Cobham's refueling equipment, which had been in practical use with British Overseas Airways Corporation (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 three aerial refuelings from four 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. Though the KC-135 was envisaged for refueling strategic bombers, it saw extensive use refueling smaller tactical aircraft in the Vietnam War supporting large strike packages. It also was used for in Desert Storm and current US air warfare doctrine. The HC-130 and KC-130 Hercules is used by the US Marine Corps and Navy to refuel jets, and by the US Air Force to refuel helicopters.
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
Often called the Boeing "flying boom”, this system uses a rigid, telescoping tube controlled by two small wings that an operator on the tanker aircraft extends and inserts into a receptacle on the receiving aircraft. In practice, the pilot of the aircraft being refueled must position the aircraft so that the boom can be engaged, using visual references, including lights used during night refueling. All boom-equipped tankers (i.e. KC-135 Stratotanker, KC-10 Extender), have a single boom, and can refuel one aircraft at a time with this mechanism.