Boeing KC-97

Double Bubble

By

SandNSky

     Although the Boeing B-29 Superfortress had been phased out of USAF service by 1956, one of its descendants served well into the late 20^th century.      

      It was an attempt to incorporate the B-29’s speed and range into a large transport that led to the construction of the XC-97 Stratofreighter (Boeing Model 367).  First flown in 1944, the XC-97 utilized the wings, empennage, and Wright R-3350 engines of the B-29.  The lower fuselage was structurally similar to that of the B-29.  However, a cargo deck was added which was wider than the lower fuselage.  This gave the airplane its “double-bubble” look, when viewed head-on.   Three XC-97’s and ten YC-97’s were built.

     The airplane clearly had potential.  In 1945, one of the XC-97’s set a speed record for transports, when it flew from Seattle to Washington D.C.  During the flight, the aircraft hit 383mph while carrying 20,000 pounds of cargo.  The XC-97 also served as the prototype of the Model 377 Stratocruiser airliner. 

     While this flight testing was going on, Boeing was developing its B-50 Superfortress, which was powered by four huge Pratt & Whitney R-4360 28 cylinder engines.  Each of these engines produced more than three thousand horsepower.  The B-50, itself a B-29 derivative, had stronger wings and a slightly taller vertical stabilizer.  It stood to reason that the new C-97 transport would benefit from these improvements.  Accordingly, the first production C-97, the C-97A, used the B-50’s wings, tail, and engines, as did all subsequent C-97 variants. 

Deliveries of the C-97A began in 1949, and by 1951, the C-97C was in service with the USAF.  The C-97, with its 41,000 pound payload, rear loading ramp, and internal cargo hoist was used during the Korean War to carry supplies and to evacuate wounded soldiers.  A few served as airborne command posts for the Strategic Air Command. 

The C-97 served admirably as a transport aircraft.  However, the USAF was in dire need of aerial refueling tankers for its fleet of thirsty jet bombers and fighters.  Of the 888 C-97’s that were produced between 1951 and 1956, 814 of them were converted to KC-97 tankers.  Fitted with the “flying boom” refueling equipment designed by Boeing, the KC-97 greatly extended the operating range of strategic aircraft, such as the B-47.  With the advent of the KC-97, the art of air to air refueling was nearly perfected. 

Despite finding its niche as a tanker, the KC-97 retained much of its cargo-carrying capacity.  The upper and lower decks were pressurized, and the refueling boom could be removed by ground personnel, thus allowing use of the airplane’s rear loading doors. 

     The KC-97 had an “official” top speed of 375mph.  But when laden with nearly 10,000 pounds of jet fuel, the airplane’s cruising speed was barely higher than the stall speed of its jet “customers”.  Thus, a technique known as “tobogganing” was used.  “Tobogganing” meant that the KC-97 and the airplane receiving fuel descended while the refueling operation was taking place.  This enabled the KC-97 to fly fast enough for the jet aircraft being refueled.  In the early 1960’s, some KC-97’s were fitted with two General Electric J-47 jet engines.  One jet engine was mounted under each wing.  These modified KC-97’s were designated KC-97L’s, and the addition of the jet engines eliminated the need to “toboggan”. 

     The last KC-97 emerged from Boeing’s Renton plant on July 18, 1956.  Ironically, this was also the day that the first jet powered tanker, the KC-135 left the plant.  This did not mark the end of the KC-97’s career, though. Gradually replaced by the KC-135, the Air Force used the KC-97 until 1973.  After that, the airplane continued to serve in Air Force Reserve and National Guard units until 1977. 

     Besides its extremely long career with the U.S. Air Force, the KC-97 is notable in several other respects.  For one thing, it was the last piston engine airplane produced by Boeing.  The KC-97 was also the last active military aircraft in the U.S. inventory that had any direct connection to the B-29 Superfortress.  In addition, the final retirement of the KC-97 marked the end of the U.S. Air Force’s use of large piston engine aircraft, and the end of that service’s use of aircraft equipped with turbo-superchargers.

    Several KC-97’s survive to this day.  One of them is flyable.  This airplane is named The Angel Of Deliverance and is flown by the Berlin Airlift Historical Foundation.  A few others are on display at various museums around the country.  

     

    

This is the KC-97's flight deck.  Photo by Scott Schwartz.

Boom operator's position- KC-97.  Photo by Scott Schwartz.