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 C-97 was the cargo/transport version of the B-29. Fatten the B-29's fuselage, use the same wings, tail and engines and you have a cargo plane. The prototype first flew in 1944 with the first production C-97A in 1949. Boeing also developed a practical in-flight refueling boom about the same time. Previously, the Air Force had experimented with a trailing hose technique with some success, but Boeing's boom changed the state of the art overnight.
Very soon the basic C-97 Stratofreighter became a KC-97 Stratotanker refueling bomber aircraft, usually a B-47 Stratojet. 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. The tanker version (KC-97) was introduced in 1950 using the "flying boom" refueling system and all subsequent USAF contracts were for tankers, having the capability of serving as a heavy cargo aircraft without removing the refueling gear.
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.
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.
The KC-97L had an extra jet engine mounted under both wings which gave it the added speed required for flight and takeoff. This enabled it to refuel jet bombers without tobogganing. The KC-97 carried both AVGAS and jet fuel. The AVGAS was used to power its radial Piston engines while the jet fuel was carried to power its two jet engines and to be off loaded to its receivers.
In 1964, selected aircraft were returned to tanker configuration (KC-97L) primarily for the Air National Guard. Two jet engines were added to increase speed and altitude, making the tankers more compatible with high performance jet aircraft. Although the last USAF C/KC-97 was retired in 1973, it remained in use in the AFRes and ANG until the late 70s.
After 1956, USAF KC-97s were gradually replaced by KC-135 jet tankers, but some were modified for continued use in other roles. The KC-135 jet powered aircraft, with a greater capacity, took over the tanker role along with its name, Stratotanker. The KC-97 did all the pioneering work.
|Join the GlobalSecurity.org mailing list|