In the summer of 1936, the Air Corps contracted for a single Lockheed Electra Model 10-A with extensive modifications. The plane, designated XC-35 by the Army, was intended for use as a high-altitude research and pressurized cabin test plane. As a result, the basic Electra fuselage was redesigned with a near circular cross section to better withstand the stresses of pressurization. Next, the large passenger windows were replaced with much smaller slit windows. The interior was split into two sections: the forward pressurized section had room for three crewmen and two passengers. The aft section, behind the pressure bulkhead had room for one additional passenger but could only be used at lower altitudes (below 12,000 feet). Besides the pilot and copilot, the XC-35 carried an engineer who controlled the pressurization and high altitude research equipment. The XC-35 was the world's first airplane specifically constructed with a pressure cabin.
The XC-35 was fitted with a pair of Pratt & Whitney XR-1340 radial engines. These 550-hp engines were turbo-supercharged to deliver the necessary high-altitude performance. The plane was designed to fly at altitudes above 30,000 feet.
The aircraft was delivered to Wright Field, Ohio, in May 1937. It was used in an extensive flight test program, and as a result, the Air Corps was awarded the 1937 Collier Trophy for the most significant aircraft development of the year.
Pressurized research plane; mod. Electra Model 10-A
TECHNICAL NOTES: Engines: Two Pratt & Whitney XR-1340-43 radials of 550 hp each Maximum speed: 236 mph Cruising speed: 214 mph Range: 800 miles Service ceiling: 31,500 ft. Span: 55 ft. 0 in. Length: 38 ft. 7 in. Height: 10 ft. 1 in. Weight: 10,500 lbs. maximum gross weight Crew: Three (pilot, co-pilot and engineer) Passenger capacity: Three Serial number: 36-353