A
erial refueling, also
referred to as air refueling,
in-flight refueling (IFR),
air-to-air refueling (AAR), and
tanking, is the process of
transferring aviation fuel from one
military aircraft (the tanker) to
another (the receiver) during
flight. The procedure allows the
receiving aircraft to remain
airborne longer, extending its
range or loiter time on station. 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 takeoff with a
greater payload which could be
weapons, cargo, or personnel: the
maximum takeoff 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. Aerial
refueling has also been considered
as a means to reduce fuel
consumption on long-distance
flights greater than 3,000 nautical
miles (5,600 km; 3,500 mi).
Potential fuel savings in the range
of 35-40% have been estimated for
long haul flights (including the fuel
used during the tanker missions).
The two main refueling systems are
probe-and-drogue, which is
simpler to adapt to existing
aircraft, and the flying boom,
which offers faster fuel transfer, but
requires a dedicated operator
station. 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. 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 shortly before World
War II on a very limited scale to
extend the range of British civilian
transatlantic flying boats, and then
after World War II on a large scale
to extend the range of strategic
bombers, aerial refueling since the
Vietnam War has been extensively
used in large-scale military
operations for many different
military aircraft operations. 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. 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, based on the
development of Alexander P. de
Seversky, between two planes
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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
US gallons (2,600 L) of aviation
gasoline and 38 US gallons (140 L)
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 Canada–
United States border, to Tijuana,
Mexico, landing in San Diego,
using mid-air refuelings at Eugene,
Oregon, and Sacramento,
California. Similar trial
demonstrations of mid-air
refueling technique took place at
the Royal Aircraft Establishment in
England and by the Armée de l’Air
in France in the same year, but
these early experiments were not
yet regarded as a practical
proposition, and were generally
dismissed as stunts. As the 1920s
progressed, greater numbers of
aviation enthusiasts vied to set new
aerial long-distance records, using
inflight air refueling. One such
enthusiast, who would
revolutionize aerial refueling was
Sir Alan Cobham, member of the
Royal Flying Corps in World War
I, and a pioneer of long-distance
aviation. During the 1920s, he
made long-distance flights to
places as far afield as Africa and
Australia and he began
experimenting with the
possibilities of in-flight refueling to
extend the range of flight.
Cobham was one of the founding
directors of Airspeed Limited, an
aircraft manufacturing company
which went on to produce a
specially adapted Airspeed Courier
that Cobham used for his early
experiments with in-flight
refueling. This craft was eventually
modified by Airspeed to Cobham’s
specification, for a non-stop flight
from London to India, using
in-flight refueling to extend the
plane’s flight duration. Meanwhile,
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. They exceeded the
Hunters’ record by nearly 100
hours in a Curtiss Robin
monoplane, staying aloft for more
than 27 days. The US was mainly
concerned about transatlantic
flights for faster postal service
between Europe and America. In
1931 W. Irving Glover, the second
assistant postmaster, wrote an
extensive article for Popular
Mechanics concerning the
challenges and the need for such a
regular service. In his article he
even mentioned the use of Aerial
refueling after takeoff as a possible
solution. At Le Bourget Airport
near Paris, the Aéro-Club de
France and the 34th Aviation
R egiment of the French Air Force
were able to demonstrate passing
fuel between machines at the
annual aviation fete at Vincennes
in 1928. The UK’s Royal Aircraft
Establishment was also running
mid-air refueling trials, 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. Royal Air
Force officer Richard Atcherley
had observed the dangerous
aerial-refueling techniques in use
at barnstorming events in the US
and determined to create a
workable system. While posted to
the Middle East he developed and
patented his ‘crossover’ system in
1934, in which the tanker trailed a
large hooked line that would reel
in a similar dropped line from the
receiver, allowing the refueling to
commence. In 1934, Cobham sold
off the airline Cobham Air Routes
Ltd to Olley Air Service and turned
to the development of inflight
refueling, founding the company
Flight Refuelling Ltd. Atcherly’s
system was bought up by Cobham’s
company, and with some
refinement and continuous
improvement through the late ‘30s,
it became the first practical
refueling system. Sir Alan
Cobham’s Grappled-line loopedhose air-to-air refueling system
borrowed from techniques
patented by David Nicolson and
John Lord, and was publicly
demonstrated for the first time in
1935. In the system the receiver
aircraft, at one time an Airspeed
Courier, trailed a steel cable which
was then grappled by a line shot
from the tanker, a Handley Page
Type W10. The line was then
drawn back into the tanker where
the receiver’s cable was connected
to the refueling hose. The receiver
could then haul back in its cable
bringing the hose to it. Once the
hose was connected, the tanker
climbed sufficiently above the
receiver aircraft to allow the fuel to
flow under gravity. When Cobham
was developing his system, he saw
the need as purely for long-range
transoceanic commercial aircraft
flights, but today aerial refueling is
used exclusively by military
aircraft. In 1934, Cobham had
founded Flight Refuelling Ltd and
by 1938 had used FRL’s loopedhose system to refuel aircraft as
large as the Short Empire flying
boat Cambria from an Armstrong
Whitworth AW.23. Handley Page
Harrows were used in the 1939
trials to perform aerial refueling of
the Empire flying boats for regular
transatlantic crossings. From
August 5 to October 1, 1939,
sixteen crossings of the Atlantic
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