Boeing KC-97 Stratofreighter

KC-97 Stratofreighter
KC-97L in Ohio Air National Guard markings
Role	Strategic tanker
Manufacturer	Boeing
Introduction	July 14, 1951[1][2]
Retired	June 1978[3]
Primary users	United States Air Force Spanish Air Force
Produced	1951–1956[4][5]
Number built	811
Developed from	Boeing C-97 Stratofreighter

The Boeing KC-97 Stratofreighter is a United States strategic tanker aircraft based on the Boeing C-97 Stratofreighter. It was succeeded by the Boeing KC-135 Stratotanker.

Design and development

The KC-97 Stratofreighter was an aerial refueling tanker variant of the C-97 Stratofreighter (which was itself based on the Boeing B-29 Superfortress), 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 right-side door. In addition, transferrable jet fuel was contained in tanks on the lower deck (G-L models). Both decks were heated and pressurized for high altitude operations.

Note: Occasionally the KC-97 has been quoted as "Stratotanker". However, all reputable sources refer to the KC-97 as Stratofreighter, not -tanker. This includes both Boeing and the USAF themselves.^[6][7]

Operational history

Two USAF A-7 Corsair IIs refueling from a KC-97.

The USAF began operating the KC-97 in 1950. It purchased a total of 811 KC-97s from Boeing,^[5][8][9] as opposed to only 74 of the C-97 cargo version.^[10][11][12] The KC-97 used piston engines, fueled by aviation gasoline, but it carried jet fuel for its refueling mission. It therefore used independent (transfer valves) systems for both types of fuel, and was able to transfer its aviation gas to off-load to the receiver in an emergency (known as a "SAVE").

These tankers were vitally important to the world-wide Boeing B-47 Stratojet strategic operations. An example was the support of Arctic reconnaissance flights from Thule Air Base.

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, the Tactical Air Command added General Electric J47 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 Tactical Air Command, the Air Force Reserve, and the Air National Guard. The KC-97 was finally retired completely in 1978, when the Texas Air National Guard and Utah Air National Guard exchanged their KC-97Ls for C-130s and KC-135s, respectively.

Variants

The KC-97's refueling boom

Source: AIRTime^[13]

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.

KC-97E

aerial refueling tankers with rear loading doors permanently closed, 60 built. Some were later converted into transports as the C-97E.

KC-97F

3800hp R-4360-59B engines and minor changes, 159 built. Some were later converted into transport as the C-97F.

KC-97G

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

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.

C-97G

135 KC-97Gs converted to transports.

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

27 KC-97Gs converted to troop transports.^[14]

KC-97L

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

Operators

Spanish Boeing KC-97L Stratofreighter at Albacete (1985)

A KC-97L Stratofreighter (s/n 52-2630 Zeppelinheim) at the National Museum of the United States Air Force

 Spain

• Spanish Air Force

 Israel

• Israel Defense Forces

 United States

• United States Air Force

The following USAF wing organizations flew the various KC-97 models at some time during their existence:^[15]

Active duty

Air National Guard

Accidents and incidents involving the KC-97

• 27 June 1954 – Arriving from Altus Air Force Base, Oklahoma, KC-97G 52-2654 encountered poor weather at its destination, March Air Force Base, California, and attempted to divert to Norton Air Force Base, California, but crashed into Box Springs Mountain north of Riverside, California, killing all 14 people on board.^[16]
• 22 January 1957 - KC-97G 53-0222 Griffiss Air Force Base, Jan. 25. -- The Air Force today sent two squads of investigators in to survey the wreckage of a tanker plane which crashed Tuesday night on a rocky ledge in the Adirondack vastness.
• 9 May 1957 – KC-97F 51-0258 en route from Sidi Slimane Air Base, Morocco, to Lajes AB, Azores, ditched in the Atlantic 550 km (343.8 mls) SE of the Azores Islands following a double engine failure. All seven crew survived. The airplane floated for ten days before being sunk by USS Wisconsin.^[17]
• 18 July 1957 – KC-97G 52-2737 from the 380th Air Refueling Squadron with a crew of eight exploded and crashed into Lake Champlain at 2128 hrs. when two of the four engines failed three minutes after take-off from Plattsburgh AFB, New York.^[18] Three survivors.^[19]
• 29 October 1957 – KC-97G 52-2711 of the 509th Bomb Wing,^[20] out of Walker AFB, New Mexico, crashed 35 miles north of Flagstaff, Arizona, while on a nine-hour low-level survey flight to determine minimum altitude restrictions for B-47 training routes. The aircraft was seen over Gray Mountain, Arizona, at altitude of 60 feet shortly after 0830 hrs., and then heard striking a cloud-shrouded cliff face, killing 16 crew and strewing wreckage for 200 yards along mountainside.^[21][22]
• 14 December 1959 – KC-97G 53-0231 of the 384th Air Refueling Squadron, out of Westover AFB, Massachusetts, collided with a B-52 during a refueling mission at an altitude of ~15,000 feet. The aircraft lost the whole left horizontal stabilizer and elevator, the rudder, and the upper quarter of the vertical stabilizer. The crew made a no-flap, electrical power off landing at night at Dow AFB, Maine; seven crew okay. "Spokesmen at Dow Air Force, Bangor, said the B52 [sic] apparently 'crowded too close' and rammed a fuel boom into the tail of a four-engined KC95 [sic] tanker plane."^[23] Aircraft stricken as beyond economical repair. Two crew on the B-52 ejected, parachuted safely, and were recovered by helicopters in a snow-covered wilderness area. The bomber and remaining eight crew safely landed at Westover AFB.^[24]
• 30 March 1960, off Cape Canaveral a Boeing KC-97 Stratofreighter (USAF Serial Number 51-363, Manufacturer's Serial Number 16430) ditched and sank. This particular aircraft was lost due to engine failure. The crash resulted in 3 fatalities of the 14 crew. The wreck of the aircraft was discovered June 6, 2015 in 365 feet of water by divers.^[25]
• 15 April 1960 – KC-97G 52-0919^[19] of the 307th Air Refueling Squadron, 307th Bomb Wing, crashed on take-off from Lincoln AFB, Nebraska, after the undercarriage collapsed. All 24 on board survived, with two airmen suffering leg fractures and five others with minor cuts and burns.^[26][27]
• 27 June 1960 – KC-97G 52-2728 of the 380th Air Refueling Squadron, Plattsburgh AFB, New York, suffered failure of lubrication on an engine impeller shaft during an evening four-hour training mission to refuel a Boeing B-47 Stratojet. During rendezvous at 15,500 feet, the tanker's number one (port outer) powerplant caught fire. As the bomber moved away from the burning tanker, the crew tried unsuccessfully to put out the blaze. The plane went into a spin as the wing failed outboard of the engine; the aircraft crashed on Jonathan Smith Mountain, a hill east of Puzzle Mountain in Newry, Maine. The flash of the fire was seen from as far away as Lewiston and Bridgton. All five crew were killed. Wreckage covering five acres was still there as of 2010.^[28][29][30]
• 17 September 1971 – KC-97G 4X-FPR/033 of the Israeli Air Force, was shot down by Egyptian missiles over Suez, Egypt; seven of eight-man crew were killed.^[31]

Survivors

KC-97G/L at the Barksdale Global Power Museum

A number of KC-97s survive, at least two of which are potentially airworthy: 52-2718 / N117GA Angel of Deliverance operated by the Berlin Airlift Historical Foundation.,^[32] and N1365N known as Tanker 97 and operated until recently as an aerial firefighting airtanker by Hawkins & Powers.

Static displays include:

• 52-0895–Rogue Valley International-Medford Airport in Central Point, Oregon, registered as N1365D.^[33]
• 52-0905– Wisconsin National Guard Museum at Volk Field Air National Guard Base in Camp Douglas, Wisconsin.^[34]
• 52-2624– At the now-closed Florence Air & Missile Museum, Florence Regional Airport, Florence, South Carolina.
  • Following museum closure, parts were used complete the KC-97, 53-0335, on display at the Carolinas Aviation Museum
• 52-2630– National Museum of the United States Air Force at Wright-Patterson Air Force Base near Dayton, Ohio.^[35]
• 52-2694– Located at Grant County International Airport, Moses Lake, Washington. Seen wearing civil registration N31338.^[34]
• 52-2697– Grissom Air Museum at Grissom Air Reserve Base (former Grissom AFB) in Peru, Indiana.^[36]
• 52-2961– Located in Greybull, Wyoming, registered as N29862.^[34]
• 53-0151– Pima Air and Space Museum adjacent to Davis-Monthan Air Force Base in Tucson, Arizona.^[37]
• 53-0198– Strategic Air and Space Museum in Ashland, Nebraska.^[38]
• 53-0218– Minnesota Air National Guard Museum, St. Paul, Minnesota. Displayed in C-97G configuration.^[39]
• 53-0230– Air Mobility Command Museum at Dover Air Force Base, Delaware.^[40]
• 53-0240– Barksdale Global Power Museum at Barksdale Air Force Base, Louisiana.^[41]
• 53-0280– Tail section preserved in Zruč nad Sázavou, Czech Republic, registered as N49548.^[41]
• 53-0282– Dyess Air Force Base in Abilene, TX.^[42]
• 53-0283– The Airplane Restaurant adjacent to Peterson Air Force Base and Colorado Springs Municipal Airport in Colorado Springs, Colorado.^[41]
• 53-0298– Museum of Aviation at Robins Air Force Base in Georgia.^[43]
• 53-0327– Whiteman Air Force Base in Knob Noster, Missouri.^[41]
• 53-0335– Carolinas Aviation Museum at Charlotte-Douglas International Airport in Charlotte, North Carolina.^[44]
• 53-0354– Castle Air Museum at the former Castle Air Force Base in Atwater, California.^[41]
• 53-0363– March Field Air Museum at March Air Reserve Base (former March AFB) in Riverside, California.^[45]
• 53-0360– Malmstrom Museum, Malmstrom Air Force Base, Montana. Displayed as 52-2638.^[46]
• TK1-3– Museo del Aire (Spain) at Cuatro Vientos Airport in Madrid, Spain. Former USAF aircraft, AF Ser. No. 53-0189.^[41]

In popular culture

The KC-97 Stratofreighter is shown in the 1955 film Strategic Air Command, refueling a B-47 in flight, and in the 1957 film Bombers B-52, refueling B-52s.

Specifications (KC-97L)

Data from USAF Museum^[47] and FAS.^[48]

General characteristics

• Crew: six (aircraft commander, copilot, navigator, flight engineer, radio operator, 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 (644 km/h)
• Cruise speed: 230 mph (370 km/h)
• Range: 2,300 mi (3700 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)

See also

Related development

• Boeing C-97 Stratofreighter
• Boeing B-50 Superfortress
• Boeing 377 Stratocruiser
• Aero Spacelines Pregnant Guppy
• Aero Spacelines Super Guppy

Aircraft of comparable role, configuration and era

• Douglas C-124 Globemaster II
• Lockheed C-121 Constellation
• Lockheed L-1249 Super Constellation (R7V-2/YC-121F)

Related lists

• List of military aircraft of the United States
• List of United States military aerial refueling aircraft

References

Citations

Bibliography

External links

Wikimedia Commons has media related to KC-97 Stratotanker.

• KC-97 page at the National Museum of the United States Air Force
• Airworthy KC-97 Angel of Deliverance