KC-97 Stratotanker

The Boeing KC-97 Stratotanker was a United States strategic tanker aircraft. For many years, it was the backbone of the United States Air Force's tanker fleet until replaced by the KC-135.

Design and development

The KC-97 Stratotanker was an aerial refueling tanker variant of the C-97 Stratofreighter (which was itself based on the B-29), greatly modified with all the necessary tanks, plumbing, and "flying boom." The cavernous upper deck was capable of accommodating oversize cargo accessed through a very large left-side door, or transferrable jet fuel was contained in tanks on the lower deck. Both decks were heated and pressurized for high altitude operations.

Operational history

The USAF began operating the KC-97 in 1950. It purchased a total of 816 KC-97s from Boeing, as opposed to only 74 of the C-97 cargo version. The KC-97 used piston engines, fueled by aviation gasoline, but it carried jet fuel for its refueling mission. It therefore used independent systems for both types of fuel.

These tankers were vitally important to the world-wide B-47 strategic operations. An example is the support of Arctic reconnaissance flights from Thule Air Base. The struggle to start and operate this complex airplane at temperatures of -40^o F was a triumph. Navigation in the Arctic conditions required great skill.

While it was an effective tanker, the KC-97's slow speed and low operational altitude complicated refueling operations with jet aircraft. B-52s typically lowered their flaps and rear landing gear to slow the aircraft enough to refuel from the KC-97. In addition, a typical B-52 refueling engagement profile would involve a descent that allowed the aircraft pair to maintain a higher airspeed (220-240 knots). In the early 1960s, TAC added J-47 jet pods from retired KB-50 tankers to produce the KC-97L. The jet pods increased performance and made the KC-97 more compatible with jet aircraft.

In 1956, SAC began phasing out the KC-97 in favor of the KC-135. KC-97s continued operating with TAC, the Air Force Reserves, and Air National Guard units. They were finally retired completely in 1978, when the Texas and Utah Air National Guards exchanged their KC-97Ls for C-130s and KC-135s, respectively.

Variants

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XC-97

prototype, 3 built.

YC-97

cargo transport, 6 built.

YC-97A

troop carrier, 3 built.

YC-97B

fitted with 80 airliner-style seats, one in 1954 redesignated VC-97D, retired to MASDC 15 December, 1969.

C-97A

transport, 50 built.

KC-97A

Three C-97As were converted into aerial refueling tankers with rear loading door removed and a flight refueling boom added. After the design was proven, they were converted back into the standard C-97A.

C-97C

medical evacuation transports, 14 C-97As converted during the Korean War (also designated MC-97).

VC-97D

staff transport conversions, 1 YC-97A, 2 C-97As converted, plus the YC-97B. Later designated C-97D.

C-97E

KC-97Es converted to transports.

KC-97E

aerial refueling tankers with rear loading doors permanently closed, 60 built.

C-97F

KC-97Fs converted to transports.

KC-97F

3800hp R-4360-59B engines and minor changes, 159 built.

C-97G

135 KC-97Gs converted to transports.

EC-97G

ELINT conversion of three KC-97Gs. 53-106 was operated by the CIA for covert ELINT operations in the West Berlin Air Corridor.

KC-97G

dual-role aerial refueling tankers/cargo transportation aircraft. KC-97G models carried underwing fuel tanks. 592 built.

GKC-97G

Five KC-97Gs were used as ground instruction airframes.

JKC-97G

One aircraft was modified to test the underwing General Electric J47-GE-23 jet engines, and was later designated KC-97L.

HC-97G

KC-97Gs converted for search and rescue operations, 22 converted.

KC-97H

One KC-97F was experimentally converted into a hose-and-drogue refueling aircraft.

YC-97J

two KC-97G conversion with four 4250 kW Pratt & Whitney YT34-P-5 turboprops, dropped in favour of the Boeing KC-135 Stratotanker.

C-97K

KC-97Gs converted to troop transports.

KC-97L

81 KC-97Gs modified with two J47 turbojet engines on underwing pylons.

Operators

 Spain

• Spanish Air Force

 United States

• United States Air Force

Survivors

A number of KC-97s survive, at least two of which are airworthy: the Angel of Deliverance operated by the Berlin Airlift Historical Foundation, and N1365N known as Tanker 97 and operated until recently as an aerial firefighting airtanker by Hawkins & Powers.

Specifications (KC-97L)

General characteristics

• Crew: five (two pilots, navigator, flight engineer, boom operator)
• Capacity: 9,000 gal (34,000 L) of jet fuel
• Length: 117 ft 5 in (m)
• Wingspan: 141 ft 2 in (m)
• Height: 38 ft 4 in (m)
• Wing area: ft² (m²)
• Empty weight: 82,500 lb (kg)
• Loaded weight: 153,000 lb (kg)
• Max takeoff weight: 175,000 lb (kg)
• Powerplant:
  • 2× General Electric J47-GE-23 turbojets, 5,790 lbf (kN) each
  • 4× Pratt & Whitney R-4360-59 radial engines, 3,500 hp (kW) each

Performance

• Maximum speed: 400 mph (km/h)
• Cruise speed: 230 mph (km/h)
• Range: 2,300 mi (km)
• Service ceiling: 30,000 ft (m)
• Rate of climb: ft/min (m/s)
• Wing loading: lb/ft² (kg/m²)
• Power/mass (prop): hp/lb (kW/kg)