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Early prop tanker had to play catch-up to fuel faster jets

Both planes competing to become the Air Force’s next air refueling tanker use turbofan engines. Early in the Cold War, the Air Force’s KC-97 Stratofreighter tankers were pulled through the sky by old-fashioned propellers.

A KC-97L now displayed at the Air Mobility Command Museum at Dover Air Force Base, Del., is “probably the best display of one of these early tankers that you’ll see anywhere,” according to retired Senior Master Sgt. John Demory, who volunteered thousands of hours to restore it. Thanks to his efforts, museum visitors can go inside the aircraft and observe how it was configured to carry fuel and cargo.

The KC-97 series was developed from the military version of the Boeing Stratocruiser transport. The first tanker versions appeared in 1950.

The Air Force received 60 KC-97E models and, with minor engine changes, 158 KC-97F models. Boeing then built 592 KC-97Gs.

All versions had wings and tails drawn from the B-50 Superfortress bomber and were powered by four 2,800-horsepower Pratt & Whitney R-4360 radial engines. But on the KC-97G, the four main deck air refueling tanks of previous models were replaced by seven upper deck tanks along the left sidewall of the main cabin and four tanks in the lower cargo compartments.

This reduced refueling capacity from 7,200 gallons to 7,131 gallons, so two 691-gallon external fuel tanks were installed, bringing the total to 8,513 gallons.

The Air Force accepted its first KC-97G on May 19, 1953, and the last on Nov. 14, 1956.

The late historian Alwyn Lloyd wrote that the external fuel tanks on the KC-97G made flying more difficult for its pilots. “These tanks altered the airflow around the ailerons and increased the control force inputs required for aircraft maneuvering,” Lloyd wrote.

In later years, 82 KC-97Gs were modified with two 5,200-pound thrust General Electric J47-GE-25 turbojet engines for increased speed, and were redesignated KC-97Ls. But even after the new engines were installed, jet aircraft that received fuel from these aerial filling stations had to slow down to gas up.

The Air Mobility Command Museum’s Web site explains how a prop plane with a slow cruising speed and low altitude refueled faster jets: “It performed a maneuver called ‘tobogganing.’ The refueling connection would be made high up and then the tanker and jet flew ‘downhill’ together enabling the tanker to pick up more speed.”

By the mid-1950s, design work was already beginning — and Boeing was investing its own money — on an all-jet replacement that would become the KC-135 Stratotanker. The last KC-97G and the first KC-135A rolled out of the Boeing factory on the same day. h

Robert F. Dorr, an Air Force veteran, lives in Oakton, Va. He is co-author of “Hell Hawks,” a history of an American fighter group. His e-mail address is robert.f.dorr@cox.net. Army veteran Fred L. Borch is regimental historian for the Army Judge Advocate General’s Corps and the author of “The Silver Star,” a history of America’s third-highest award for combat heroism. His e-mail address is borchfj@aol.com.