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U.S. military aerial refueling: extending ‘the reach’

by Mark Morgan
Hq. AMC History Office

This is the third article in a series of articles highlighting the history of aerial refueling and the important role aerial refueling has played in American military history.

On Aug. 6, 1946, the world’s largest bomber took to the air from the Consolidated-Vultee plant on the south side of Lake Worth, west of Fort Worth, Texas. The huge, six-engine B-36 was a wartime design, built for non-stop round-trip flights from the United States to Germany in the event of the loss of bases in England.

The first B-36 production models entered service with Strategic Air Command in late 1948. The B-36 was big enough to carry the large nuclear weapons of the time and carried enough fuel – more than 183,000 pounds — to make the 10,000-mile round-trip flight to Europe and back.

However, the B-36 lacked speed and maneuverability and, during the early 1950s, the aircraft became highly vulnerable to enemy jet fighter aircraft. Fortunately, the Boeing Airplane Company had the B-36’s replacements in development: the jet-propelled B-47 and B-52. However, these new aircraft — unlike the B-36 — needed air refueling to hit targets in the Soviet Union. At the time of their development, no aerial refueling aircraft existed.

In January 1948, former bomber commander and the first U.S. Air Force chief of staff, Gen. Carl A. “Tooey” Spaatz, identified in-flight refueling as the young service’s highest initial priority. Two months later, Air Force personnel from Wright-Patterson AFB, Ohio, visited Britain’s Flight Refueling Limited, evaluated the company’s loop-hose air refueling system design, and bought two examples. The Air Force also ordered 40 additional sets and acquired manufacturing rights for the system.

Upon arrival in the states, the two refueling systems went to Boeing’s Wichita, Kan., plant for installation in B-29s. The subsequent conversion program resulted in the production of 40 KB-29M tankers and 40 B-29MR receivers. On June 30, 1948, SAC activated its first two KB-29M squadrons: the 43rd Air Refueling Squadron at Davis-Monthan AFB, Az., and the 509th Air Refueling Squadron at Walker AFB, New Mexico.

The introduction of dedicated tanker aircraft and crews allowed SAC to extend the range of its B-29 and B-50A bombers. Concurrently, SAC and the Air Force made the decision to equip all future bombers with an in-flight refueling capability. However, the loop-hose system proved unwieldy and difficult, particularly in bad weather. With a two-and-a-half-inch diameter refueling hose, the FRL-developed system transferred fuel at a rate of only 110 gallons per minute. With new high-speed, high-altitude jet bombers coming on line, capable of operating at night and in bad weather, it quickly became apparent something better was needed.

Interestingly enough, Boeing already had a better system in mind. The company developed a “flying boom,” which featured a telescoping pipe with fins at the nozzle end. The fins were termed “ruddervators” because they functioned as both rudders and elevators. The boom operator, sitting in the B-29’s converted tail turret, literally flew the boom into a receptacle on the upper fuselage of the receiver aircraft. This design allowed more positive control of the air-to-air refueling operation and, with the boom’s four-inch diameter, it offered much faster fuel transfer.

The Air Force responded by ordering more than 100 B-29s fitted with the flying boom system, designated the KB-29P. The first KB-29Ps went into service with the 97th Air Refueling Squadron at Biggs AFB, Texas, on Sept. 1, 1950.

In the meantime, training continued with the KB-29Ms, including periodic attempts at record-breaking flights. For example, in 1948, from Dec. 7 through Dec. 9, a 43rd Bombardment Group B-50A, commanded by Lt. Col. Michael N. W. McCoy, flew from Carswell AFB, Texas, to Hawaii, dropped a practice bomb, and then returned to Carswell. The flight was made possible by KB-29Ms assigned to the 43rd and 509th Air Refueling Squadrons.

The Air Force followed up with a non-stop, around-the-world flight. Again, the 43rd Bombardment Group got the call, although the first attempt on Feb. 25, 1949, came to a quick end when the B-50A “Global Queen” sustained engine problems and landed at Lajes Air Base, Azores.

The next day, the back-up plane, the “Lucky Lady II,” commanded by Capt. James Gallagher, launched from Carswell. The aircraft returned to Texas on March 2, having completed a 94-hour-1-minute flight of 23,452 miles with four in-flight refuelings.

Afterwards, Gen. Curtis E. LeMay, SAC commander, told the news media the obvious: SAC could now deliver an atomic bomb anywhere in the world, and tankers made it possible.

Subsequently, SAC converted its KB-29Ms to a probe and drogue system, using another design pioneered by Flight Refueling International. It featured a refueling hose mounted on an electrically-driven reel inside the tanker, with the receiver aircraft taking on fuel through a fixed refueling probe. While initially tested with bombers, the design later proved particularly useful with fighter aircraft.

However, the B-29’s aging airframe and limited fuel offload capability definitely made it an interim tanker (although the last B-29s didn’t retire from SAC until November 1957). In the meantime, Boeing came up with an improved tanker aircraft, the KC-97.

Based on the Model 377 “Stratocruiser” trans-oceanic airliner, the KC-97 featured a unique double-bubble fuselage with plenty of space available inside for fuel, cargo and passengers, combined with the wings and engines of the Boeing B-50.

The first prototype YC-97A transport served with the Military Air Transport Service during the Berlin Airlift in 1949 and went into full production that same year. In 1950, Boeing introduced the KC-97 variant, equipped with the flying boom system.

Dubbed the “Stratotanker,” the KC-97 quickly became the most numerous SAC tanker, with more than 800 built. The first aircraft went into service with the 306th Air Refueling Squadron at MacDill AFB, Fla., in 1951. By 1953, SAC operated almost 30 air refueling squadrons with 502 tankers, with the majority of the squadrons flying KC-97s. Nearly every B-47 wing had a KC-97 air refueling squadron assigned to it. When B-47s deployed overseas, their tankers went with them, enabling the mass deployment of entire wings of bombers to bases in Europe and the Far East under Operation Reflex.

However, even the new KC-97 operated with several limitations. While a single KC-97 could adequately refuel a B-47, it took two or more to refuel a B-52. Additionally, it took a long time for a fully laden KC-97 to get to its cruising altitude. This forced SAC to deploy its tankers for extended periods to locations in Alaska and Canada, strategically located along the routes the bombers would use to get to their targets. With adequate warning, the KC-97s would get to altitude in time to service the bombers coming from the United States.

However, speed disparity between the KC-97 and its receivers provided the biggest problem. During aerial refueling, the bomber had to slow down and drop to the KC-97’s altitude. Once the aircraft connected, the tanker went into a dive, allowing the bomber to maintain enough speed to stay in the air. As the receiver took on more fuel, it grew heavier, which made the maneuver — known as “tobogganing” — even more difficult. When done in poor or marginal weather, the experience proved even less enjoyable for the aircrews. Once the two aircraft completed the refueling, the jet bomber had to climb back up to its cruise altitude, which burned a lot of the fuel it had just taken on.

Fortunately, a suitable replacement for the KC-97 was already on the way. And this aircraft, still in operation to this day, would feature jet propulsion.

Source:

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May 10, 2009 - Posted by | History |

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