The Lockheed R7O/ R7V was a US navy transport aircraft based on the Lockheed Super Constellation airliner, a stretched version of the earlier Constellation.
The Super Constellation was designed to use the Wright R-3350-91 Turbo-Compound engine, which used a turbine to extract the unused energy from the exhaust gases from the radial engine, and feed it back to produce more power for the same level of fuel consumption, or decrease fuel consumption for a particular level of power.
The Navy's first order for the Super Constellation was for six PO-2W airborne early warning aircraft, and was placed in July 1950. It was followed in August 1950 by an order for sixty-five R7O-1 cargo and personnel transports (Lockheed Model 1049B). The designation was soon changed to the R7V-1. Deliveries began in November 1952, but the Navy only received fifty of the original 65 aircraft as R7V-1s. Ten went to the USAF where they became the RC-121C. One went to the USAF to become the Presidential aircraft VC-121E. Four were completed as turbo-prop powered R7V-2s. The fifty that were delivered were powered by four 3,250hp Wright R-3350-91 Turbo Compound engines, had a reinforced floor in the cargo bay and a large cargo loading door on the port side.
Of the 50 aircraft, 32 were later transferred to the USAF where they became the C-121G, while those still in Naval service in 1962 became the C-121J. Both types generally operated alongside USAF aircraft as part of the Military Air Transport Service, so the transfer made sense.
One R7V-1 was given cameras for service with the Antarctic Development Squadron Six (VXE-6) and was used to investigate the polar ice-pack as part of Project Birdseye. It was redesignated as the R7V-1P.
The R7V-2 (Model 1249) was the designation given to four aircraft that were completed with turbo-prop engines. They were built with four 5,550 eshp Pratt & Whitney YT34-P-12A engines driving three blade propellers, giving more power than the turbo-compound engines and with much less complexity. Work on the R7V-2 began in August 1951 and the first made its maiden flight on 1 September 1954. The last of the four was later used by Lockheed to test out the Allison 501 turbo-prop engine, before going to the USAF as the YC-121F-LO.
Engine: Four Wright R-3350-91s
Wing span: 123ft
Length: 116ft 2in
Height: 24ft 8in
Empty weight: 72,815lb
Maximum weight: 143,600lb
Maximum speed: 368mph at 20,000ft
Cruising speed: 259mph at 10,000ft
Service ceiling: 22,300ft
Normal range: 2,100 miles