In 1941 Northrop developed a flying wing design to compete with the Consolidated Model 37. Conceptually more advanced than the B-36, the Northrop XB-35 was a low-drag flying wing with four piston engines in the wings driving contra-rotating pusher propeller units. The type was ordered in prototype form as the XB-35 in November 1941. Powered by four 2237kW Pratt & Whitney R-4360 Wasp Major piston engines driving eight-bladed counter-rotating pusher propellers behind the trailing edges of the 172-ft (52.43m) span wing they could carry a maximum bombload of 56,000 lb (25,402 kg), or a 20,000-lb (9072-kg) bombload over a radius of only 2500 miles (4023 km). The XB-35 was faster than the XB-36 (especially at lower altitude), possessed a usefully higher service ceiling, and was also considerably more agile than the XB-36.
There had been problems with the prototype, but these were concerned with factors such as the propeller gears stripped, blade pitch reversed in flight, propellers 'ran away', uncontrollable fires started, rather than the structure and flight characteristics of the basic airframe.
The first of 15 YB-35 aircraft ordered in early 1943, flew on 25 June 1946, followed by the second in the following year. With the B-36 slated for production, it was then decided to use the design for the evaluation of jet power in a strategic bomber the production contract was cancelled.
The second and third YB-35 pre-production prototypes were converted into YB-35B aircraft: their four 3250-hp (242 3-kW) Pratt & Whitney R-4360 piston engines were replaced by eight 4000-lb (1814-kg) thrust Allison J35-A-5 turbojets, a quartet of the jets being grouped in each trailing edge and aspirated through the same arrangement of leading-edge inlets used to supply carburation and cooling air for the piston engines of the original aircraft.
The YB-35B was redesignated YB-49 while it was being rebuilt, and the first aeroplane flew in October 1947.
Engines: 4 x Pratt & Whitney R-4360 Wasp Major, 2237kW
Max take-off weight: 76340 kg / 168302 lb
Wingspan: 52.4 m / 171 ft 11 in
Length: 16.2 m / 53 ft 2 in
Wing area: 372 sq.m / 4004.17 sq ft
Max. speed: 605 km/h / 376 mph
Range: 10000 km / 6214 miles