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Aerial refueling

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Aerial refueling is the process of transferring aviation fuel from one aircraft to another while both are in flight. The aircraft providing the fuel is known as the tanker, while the one receiving it is called the receiver. This procedure is also referred to as in-flight refueling (IFR), air-to-air refueling (AAR), or tanking.

KC-135 refuels an F-16 Fighting Falcon
KC-135 refuels an F-16 Fighting Falcon

This capability is vital because it allows receiving aircraft to remain airborne much longer. It extends their flight range or their loiter time, which is the time they can spend circling an area. In some cases, a series of refuelings can extend a flight until the crew reaches physiological limits, such as fatigue, or until engineering factors like engine oil consumption become a concern.

There are two primary technical mechanisms used to move fuel between aircraft. The first is the flying boom system. This system utilizes a rigid pipe that can be guided into the receiver. The flying boom offers a faster rate of fuel transfer, but it requires a dedicated boom operator station on the tanker to manage the connection.

KC-135Boom-operator-521
KC-135Boom-operator-521

The second method is the probe-and-drogue system. This system is generally easier to adapt to existing aircraft designs. In this setup, the receiver aircraft uses a probe, which is a specialized nozzle, to connect with a basket-like device at the end of a hose trailed by the tanker.

Tu-95 filling rod and filling cone from Il-78M aircraft
Tu-95 filling rod and filling cone from Il-78M aircraft

Aerial refueling also offers significant advantages for aircraft weight management and payload capacity. An aircraft can take off with a greater payload of cargo, weapons, or personnel by carrying less fuel during takeoff. This allows the plane to maintain its maximum takeoff weight while staying light enough to get airborne safely. Once the aircraft is in flight, it can be topped off with extra fuel from a tanker.

Additionally, researchers have estimated that aerial refueling could reduce fuel consumption on long-haul flights by 35% to 40%, even when accounting for the fuel used by the tanker missions.

Early experiments in the 1920s involved slow-flying aircraft flying in formation. In these trials, a hose was run down from a hand-held fuel tank on one plane to the filler of another. On June 25, 1923, the first successful mid-air refueling occurred between two Airco DH-4B biplanes of the United States Army Air Service.

Refueling, 1923
Refueling, 1923

By August 1923, three DH-4B aircraft set an endurance record by remaining aloft for over 37 hours using nine mid-air refuels. In 1929, a Fokker C-2A named the Question Mark set a record of over 150 hours. Later, in 1930, the Hunter brothers set a record of 553 hours and 40 minutes using two Stinson SM-1 Detroiters.

Sir Alan Cobham was a key figure who revolutionized the field through his development of practical systems. In 1934, he founded Flight Refuelling Ltd (FRL) to advance in-flight refueling technology. One early method was the grappled-line looped-hose system. In this process, the receiver aircraft trailed a steel cable. The tanker then shot a line to grapple that cable, drawing it back into the tanker to connect the refueling hose.

'Lucky Lady II" being refuelled by B-29M 45-21708 061215-F-1234S-002
'Lucky Lady II" being refuelled by B-29M 45-21708 061215-F-1234S-002

This was eventually improved into the modern probe-and-drogue system, which was demonstrated by a Gloster Meteor jet in 1949, setting a new jet endurance record.

A major milestone occurred in 1949 when the B-50 Superfortress Lucky Lady II completed the first non-stop circumnavigation of the world. The flight lasted 94 hours and 1 minute. This feat was made possible by four aerial refuelings from four pairs of KB-29M tankers. These refuelings took place over the Azores, Saudi Arabia, the Pacific Ocean near Guam, and between Hawaii and the West Coast.

Refueling, 1923
Refueling, 1923

This mission demonstrated how refueling could overcome the geographic limitations of early long-distance aviation.

Despite its utility, aerial refueling is currently used almost exclusively in military operations. This is due to the high cost of specialized refueling equipment and the difficulty of the maneuvers required. Pilots must perform very close "line astern" formation flying to successfully connect the aircraft. While early pioneers like Cobham saw potential for long-distance commercial transoceanic flights, the complexity of the task has kept it within the military domain.

KC-10 Extender with the 76th Air Refueling Squadron
KC-10 Extender with the 76th Air Refueling Squadron
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🖼️ Images & Media (20)
File:KC-135 refuels an F-16 Fighting Falcon.jpg
KC-135 refuels an F-16 Fighting Falcon.jpg
File:Refueling, 1923.jpg
Refueling, 1923.jpg
File:'Lucky Lady II" being refuelled by B-29M 45-21708 061215-F-1234S-002.jpg
'Lucky Lady II" being refuelled by B-29M...
File:Eindhoven Air Base (8613167434).jpg
Eindhoven Air Base (8613167434).jpg
File:KC-135Boom-operator-521.jpg
KC-135Boom-operator-521.jpg
File:Fuel Prices Rise Again MOD 45146995.jpg
Fuel Prices Rise Again MOD 45146995.jpg
File:FA-18E of VFA-81 refuels Rafale of Flottille 11F in March 2015.JPG
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US Navy 110610-N-KA046-002 Two MH-53E...
File:20200311 KC-135 Stratotanker Tail 62-3565-Kadena AB-41.jpg
20200311 KC-135 Stratotanker Tail...
File:KC-10 Extender with the 76th Air Refueling Squadron.jpg
KC-10 Extender with the 76th Air...
File:A KC-135 Stratotanker from the 127th Air Refueling Group performs a night time refueling for a C-17 Globemaster III.jpg
A KC-135 Stratotanker from the 127th Air...
File:Wtaf-routes-1964.jpg
Wtaf-routes-1964.jpg

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