Air refueling includes the techniques, resources, and operations to refuel aircraft in flight. It extends the range of unrefueled aircraft, acts as a force multiplier, and provides other operational benefits for military aviation.
Aircraft purpose-built for refueling, or permanently modified for refueling duty, are called tankers, although they also have cargo transport capability; tanker aircraft are not filled with fuel but simply have supplemental tanks. The most common modern method of refueling is probe and drogue, in which the tanker trails one or more (usually two) hoses, each of which terminates in a drogue, an aerodynamically stabilized cone that contains a fuel valve and a connector that accepts a probe from the aircraft being refueled. When the probe makes positive contact and latches into the drogue's valve, fuel can flow. The other method, uses a rigid but steerable hollow boom at the rear of the tanker. The boom operator, who must be highly skilled, adjusts the position of the boom until it latches into a receptacle in the aircraft being refueled. Again, when the valve latches, fuel flows.
Other aircraft may be equipped temporarily with buddy stores to let them refuel other aircraft; this only is practical with the probe and drogue technique. The boom technique, used exclusively by the United States Air Force, can transfer fuel at a faster rate than can a probe and drogue, and was developed for the substantial fuel requirements of strategic bombers.
As mentioned, the only boom tankers are operated by the U.S. Air Force. The most common boom tanker is the KC-135 Stratotanker, which, while they have had numerous upgrades, approaching the end of their service lives. KC-10 Extender tankers were procured more recently, but a major replacement for the KC-135 fleet, but the procurement has been delayed by legal and competitive issues. Some boom tankers have been modified to support probe and drogue as well.
A substantial number of militaries have air refueling capabilities, but usually with buddy stores rather than dedicated aircraft. The United States Marine Corps does have a tanker version of the C-130 Hercules, the KC-135.
New capabilities for refueling come with the V-22 Osprey, with the lead being taken by the United States Navy. This aircraft has the extremely valuable, but rather rare, capability of both refueling and being refueled.
Historical air refueling
In 1917, a patent for air refueling, essentially with the probe and drogue method, was applied for Alexander de Seversky, later a noted aircraft designer but then a junior officer in the Imperial Russian Navy. . He received the patent in 1921, when the first actual refueling took place:
The first actual transfer of fuel from one aircraft to another was little more than a stunt. On November 12, 1921, wingwalker Wesley May climbed from a Lincoln Standard to a Curtiss JN-4 airplane with a can of fuel strapped to his back. When he reached the JN-4, he poured the fuel into its gas tank. Needless to say, this was not the most practical way of refueling an airplane in flight. — Dwayne A. Day
Practical probe-and-drogue refueling began in 1923.
Boom experiments began in 1948, conducted by the Boeing Company in response to a requirement from Air Force General Curtis LeMay, head of the Strategic Air Command (SAC). Even for SAC's heavy B-52 bombers, refueling was usually necessary to attack targets in the Soviet Union and have enough fuel for the return trip.
Initial SAC tankers were modified B-29 propeller-driven bombers and KC-97 propeller-driven transports, which were too slow for practical air refueling of jet aircraft. Speeds and capability matched only with the large-scale procurement of the KC-135 Stratotanker.
To meet the needs of long-range helicopter missions, typically for combat search and rescue, a KC-130 tanker first refueled a CH-3 in 1965. Today, helicopter refueling is a mission both for United States Coast Guard HC-130 aircraft used for long-range rescue, and U.S. Air Force MC-130 special operations transports. The MC-130 often is the navigation and communication center for a deep penetration helicopter mission.
- Day, Dwayne A., Aerial Refueling, U.S. Centennial of Flight Commission