The Boeing KC-97 is the refueling tanker version of the C-97 Stratofreighter, a 74-ton multi-purpose airplane combining both transport and aerial refueling tanker capabilities. The Strategic Air Command, the Military Air Transport Service, and the Air National Guard flew this aircraft during the 1950s through the 1970s.
In June 1942, three months before the first B-29 bomber was test flown, Boeing proposed to the Army Air Forces a freight-carrying airplane able to match the B-29 in speed, range and ruggedness, and utilizing as many as possible of the identical components used in the B-29. These included wings, empennage, engines, landing gear, and many minor accessories.
The key to the success of the B-29 was its wing (type-117). Designed entirely by Boeing engineers, the wing had lower drag characteristics per pound of lift than any other airfoil. It also enjoyed better stall warning and had the biggest and most efficient flaps then devised. The wing was also stronger and had greater volume for gasoline storage than any other at the time. With utilization of the B-29 wing for the C-97, use of the same four engines was a natural choice-the 2000-h.p. Wright Cyclone.
However, adaptation of the B-29 fuselage for cargo carrying was a more challenging task. The cross-section of the fuselage was not practical for the proposed missions. Thus, the inverted "figure 8" fuselage design was born. The lower lobe was designed with the same diameter as the fuselage of the B-29. The wing and landing gear also remained the same. The larger fuselage upper section was streamlined into the lower lobe.
The interior of the new double-decked transport optimized the use of space with provisions for cargo-handling simplicity. The upper deck cargo compartment was made 74 feet long, with huge rear "clam shell" loading doors designed to permit rapid loading of objects up to 61 feet long. In all, the C-97 contained 6,140 cubic feet of usable cargo space, more than twice the volume of that of any transport then flying.
Meanwhile, additional contracts had been issued, and on June 16, 1949, the first of 44 C-97A production models took to the air. September of the following year saw delivery of the first of three SAC Command transports, known as C-97Ds; and five months later the C-97C production models took to the air, featuring flush-mounted antennae and a strengthened fuselage. Fourteen of these were built. Then came three KC-97As, prototypes of the versatile multi-purpose tanker/troop transport/cargo carrier/hospital ship. The XC-97 also served as the prototype for the commercial Boeing 377 Stratocruiser airliner.
Quick convertibility from basic freighter to aerial tanker was made possible by unique packaging of the tanker equipment. The flying boom, plus the controls and operator station, were assembled as a single pod, attached beneath the Stratofreighter's fuselage in the same space normally occupied by the loading doors. The first of 60 production tankers, designated the KC97E, was delivered in July 1951, to be followed by 159 KC-97Fs, which featured Pratt & Whitney engines. Then came the last of the production models, the KC97G, of which 592 were built. This airplane was fitted with external wing tanks and a new arrangement of internal refueling tanks that permitted the carrying of troops or cargo without removing the refueling equipment.
Nearly 900 double-decked C-97s were built at the Boeing plant in Renton, Washington, near Seattle. The first of three XC-97 prototypes made its maiden flight on 9 November 1944 and the last production KC-97G was delivered to SAC on Nov. 16, 1956. This marked the end of a 12-year production program.
Used as a personnel carrier, the C-97 accommodated 96 fully-equipped combat troops. As a flying ambulance, its capacity was 69 litter patients, their medical attendants, and supplies. With refueling equipment installed, these loads were reduced to 65 troops or 49 litter patients. The C-97 could also carry light tanks, artillery pieces (up to 155-mm howitzers), ambulances, and 2 1/2-ton trucks.
As the last of the C-97s left the plant in July 1956, Boeing's production people at Renton proudly pointed to their record in delivering the big airplanes on time. Since C-97As started to come off the line in 1949, they had, with one exception, been on schedule, missing their production quota only on one occasion in December 1950. While on-schedule production was maintained, production costs were continually reduced. The C-97A, for instance, called for approximately 6.0 man-hours of work per pound of airframe. The 888th airplane (the last built) required less than one man-hour per pound.
The advent of refuelable jet aircraft became problematic. How did a piston engine tanker refuel a faster jet bomber? It "tobogganed." The refueling connection was made at high altitudes and then the bomber and tanker flew "downhill" together enabling the tanker to pick up speed. The KC-97L had an extra jet engine mounted under both wings that gave it the added speed required for flight and takeoff. This addition increased the KC-97L's capabilities for refueling jet aircraft. 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, they remained in use in the AFRes and ANG until the late 70s.
Unlike most of the aircraft in the Museum's collection, KC-97G Serial Number 243 is not a complete aircraft. Storage of such a large aircraft is a problem, and therefore only those parts considered to be technically significant were transferred from Davis-Monthan AFB in July 1979. The nose section is a representative C-97 cockpit and at the same time is typical of a cockpit of any conventionally powered aircraft of this size, and the aft section, containing the boom operators position and the inflight-refueling boom were acquired to preserve an example of that technology.
The Museum aircraft, KC-97G serial number 53-243, was manufactured by the Boeing Airplane Co., Renton, Washington, and was delivered to the 90th Strategic Reconnaissance Wing (SAC), Forbes AFB, Kansas, on August 12, 1955. After a short time at an Air Base located in French Morocco (May-July 1956), the aircraft began an extended stay at Forbes.
From September 1962 to January 1963, the aircraft was attached to the 4108th Air Refueling Wing (SAC) at Plattsburg AFB, New York, and then the 497th Air Refueling Wing, still at Plattsburg, until October 1964, with the 136th Air Transport Group (ANG). The aircraft remained there until its last assignment in August 1972 with the 161st Air Refueling Group (ANG) in Phoenix, Arizona (with periodic assignments to Rhein-Main AB, Germany). After arriving at Davis-Monthan AFB, Arizona, for storage in February 1977, it was removed from the USAF inventory in July of that year. There are no records of day-to-day activity or special missions for this aircraft.
Wingspan: 141 ft. 2 in.
Length: 117 ft. 5 in. (with boom retracted)
Height: 38 ft. 4 in.
Weight: 153,000 lbs. normal max.
Armament: None
Engines: Four Pratt & Whitney R-4360s of 3,500 hp. ea. and Two General Electric J47s of 5,970 lbs. thrust ea.
Reference and Further Reading:
KC-97G Curatorial Files, Aeronautics Division, National Air and Space Museum.
DAD, 11-11-01