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Boeing KC-97 Stratofreighter


Strategic Air Tanker / Aerial Refueling Aircraft


Produced in over 800 examples from 1951 to 1956, the versatile Boeing KC-97 served the air branches of the United States, Israel and Spain for its time in the air.
Authored By: Staff Writer | Edited: 4/13/2019
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Specifications


Year: 1951
Status: Retired, Out-of-Service
Manufacturer(s): Boeing Company - USA
Production: 811
Capabilities: Electronic Warfare (EW); Aerial Refueling; Transport; Search and Rescue (SAR); Reconnaissance (RECCE); X-Plane; Training;
Crew: 6
Length: 117.45 ft (35.8 m)
Width: 141.08 ft (43 m)
Height: 38.39 ft (11.7 m)
Weight (Empty): 82,497 lb (37,420 kg)
Weight (MTOW): 175,003 lb (79,380 kg)
Power: 4 x Pratt & Whitney R-4360-59 radial piston engines developing 3,500 horsepower (OPIONAL): 2 x General Electric J47-GE-23 podded turbojet engines underwing developing 5,790 lb of thrust each.
Speed: 401 mph (645 kph; 348 kts)
Ceiling: 30,003 feet (9,145 m; 5.68 miles)
Range: 2,299 miles (3,700 km; 1,998 nm)
Operators: Israel; Spain; United States
Events of World War 2 (1939-1945) pressed upon American warplanners the value of heavy-lift aircraft when attempting to keep pace in a conflict with many fluid fronts. As such, it fell to large-aircraft developers like Boeing to meet the growing demand for "upsized" transports - these typically based off of existing heavy bombers. As early as 1942, Boeing engineers were working on such an aircraft based on their experience in developing what eventually became the famous B-29 "Superfortress" and B-50 "Superfortress" four-engine heavy bombers (both detailed elsewhere on this site). In November of 1944, an all new four-engined type - with transport at the heart of its design - flew for the first time based heavily in the B-29/B-50 series. It was eventually taken into service, though only after the war had concluded, in 1947 as the KC-97 "Stratofreighter".

The success of the Stratofreighter warranted further variants of the line and additional work spawned the KC-97 Stratofrieghter which was purposely-developed as an aerial refueling tanker aircraft for the newly-minded USAF. As many early-form, fuel-thirsty jet-powered fighters and bombers burned through their supplies in a short amount of time, it became essential to provide these combat platforms with an in-air delivery system to meet the demand in stride.

The new aircraft essentially reused much of the form and function of the C-97 (including the deep fuselage) but also introduced all of the requisite components to carry and deliver fuel to in-air aircraft - namely the fuel stores, a boom arm, and the facilities to pump fuel to awaiting aircraft. Now USAF fighters and bombers would not be limited by their internal fuel alone and have to return to base to refuel - their combat ranges could, essentially, become doubled or tripled under certain circumstances.

First-deliveries of what became the KC-97 were being made to the USAF as soon as 1950 and the series was formally introduced on July 14th, 1951. A total of 811 KC-97 aircraft were procured by the service from Boeing who produced it from 1951 until 1956. Once in service, the design proved a success for the role it was intended for though some higher-flying platforms, like the soon-to-be Boeing B-52 Stratofortress heavy bomber, had to make special accommodations to reach this "low-and-slow" fuel delivery aircraft (which was still powered by its original 4x Pratt & Whitney air-cooled, propeller-spinning radial engines). This design limitation was somewhat offset by the later introduction of podded General Electric J47 turbojets attached under each wing of the KC-97 to produce the "KC-97L" mark - the jets were used to supply the large aircraft with short bursts of power to meet its target aircraft in stride.

KC-97s were used by several sub-branches of the USAF including Strategic Air Command (SAC), the Air Force Reserve, and the Air National Guard. Some examples were being retired from frontline service as soon as 1956 as more efficient solutions for the USAF came online but the series soldiered on into the middle part of 1978 for its time in the air. The Israeli Air Force (IAF) and Spanish Air Force counted themselves as the only other operators of the series.






Variants began with the original KC-97A transport which numbered three examples modified to an aerial tanker standard. They lost their rear loading ramps in the conversion process but received a refueling boom arm for testing the validity of the overall aircraft design. Once the proving phase was complete, the trio were converted back into their original transport guises.

The KC-97E were true tanker forms and sixty were produced, some ultimately reconverted to transport roles under the "C-97E" designation. The KC-97F introduced 4 x R-4360-59B engines of 3,800 horsepower each and were produced to the tune of 159 examples. Again, some of this lot were reconverted to transport forms, these designated as "C-97F".

The KC-97G was the definitive mark with 592 built in all. They were purpose-designed "combination" airframes able to take on the aerial tanker role or serve in the cargo transport role as needed. Underwing fuel tanks were fitted to these aircraft.

The EC-97G was an ELectronics INTelligence (ELINT) conversion applied to three KC-97G models and outfitted with specialized equipment. The C-97G were transport conversions numbering 135 aircraft from the KC-97G stock. The GKC-97G became five KC-97G models set aside to serve as ground instruction classrooms. The JKC-97G was a "one-off" model used to test General Electric J47-GE-23 turbojet engines in underwing pods - this work eventually led to the aforementioned KC-97L of which 81 were produced from the existing KC-97G stock.

The HC-97G, another G-model offshoot, designated twenty-two aircraft converted to the Search And Rescue (SAR) role. The KC-97H was another one-off used to test a specific hose-and-drogue fuel delivery system. The YC-97J designated a pair of KC-97G models outfitted with experimental 4 x Pratt & Whitney YT34-P-5 turboprop engines but the design was not furthered. The C-97K became twenty-seven KC-97G aircraft reworked as dedicated troop transports.

A sole KC-97 example was modified for super-heavy-lift duties (as the "Super Guppy") in support of the famous American Apollo (Saturn) space program. The example eventually fell under NASA ownership in 1993 and remains in flyable condition today (2018) - one of just two such aircraft of the series to claim that status.

Despite its service role as an aerial "tanker", the KC-97 was not given the "Stratotanker" name but retained the original C-97's "Stratofreighter" name by both the United States Air Force and Boeing.








Armament



None.

Variants / Models



• KC-97 - Base Series Designation
• KC-97A - Three proof-of-concept aircraft from C-97A stock; reconverted to original form post-testing.
• KC-97E - Tanker form; sixty examples; some converted to C-97E transport standard..
• KC-97F - Taker form with PW R4360-59B engines of 3,800 horsepower; some converted to C-97F transport standard.
• KC-97G - Definitive production model; combination airframes for tanker and transport roles; underwing fuel tanks fitted; 592 examples.
• EC-97G - Conversion of three KC-97G models to ELINT platforms.
• C-79G - KC-97G models converted to dedictaed transports.
• GKC-97G - KC-97G aircraft reserved for ground instruction; 5 examples.
• JKC-97G - Test article for GE J47 turbojets.
• HC-97G - KC-97G converted to SAR platform; 2 examples.
• KC-97H - One-off conversion of KC-97F to testing hose-and-drogue fuel delivery system.
• YC-97J - Conversions of KC-97G to test out PW YT34-P-5 turboprop engines; 2 examples.
• C-97K - Conversions of KC-97G models to dedicated troop transports.
• KC-97L - KC-97G models outfitted with underwing GE J47 turbojet engines; 81 examples.
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