The Lockheed XC-35 'Electra' was an experimental aircraft used for tests with pressurized cabins.
The C-35 was ordered by the War Department in June 1936 for research into pressurised cabins and high altitude flight. Lockheed used the tapered wings and twin horizontal surface tail of the Lockheed 10 Electra, but designed a new fuselage with a circular cross-section (replacing the flat sided fuselage of the standard Electra), internal bracing, heavy doors and much smaller cabin windows (but keeping the standard cockpit windows). Lockheed’s original plan had been to make the pressure cabin air tight using strips of cloth soaked in marine glue between each of the riveted fuselage sections, but this didn’t work. They then used a neoprene sealing tape designed by DuPont, which successfully sealed the cabin.
The XC-35 was powered by two turbosupercharged Pratt & Whitney XR-1340-43 radial engines, which provided power for the cabin pressurization and for the required high altitude flight.
The XC-35 began flight tests at Burbank on 7 May 1937, and was delivered to Wright Field in August 1937. The aircraft was used in extensive experiments that provided valuable information on the use of turbosuperchargers and cabin pressurization. As a result the Air Corps was awarded the US National Aeronautic Association’s Collier Trophy of 1937, given for the greatest achievement in American aeronautics or astronautics in that year.
The XC-35 was also used on a number of long distance flights, including a flight from Chicago to Washington at an average speed of 350mph at 20,000ft. The XC-35 was preserved after the test programme ended, and is now in the collection of the Smithsonian, although not on display.
Engines: Pratt & Whitney XR-1340-43
Power: 550hp each
Wing span: 55ft
Length: 38ft 7in
Height: 10ft 1in
Empty weight: 7,940lb
Loaded weight: 10,500lb
Maximum speed: 236mph at 20,000ft
Cruising speed: 214mph
Rate of climb: 1,125ft/ sec
Service ceiling: 31,500ft