Faced with the distinct possibility of a British defeat in the war in Europe, America's most pressing need in 1941 was for a bomber with intercontinental range which could strike Germany and return home. The US Army gave the go-ahead for an aircraft which spanned 52.4 m (172 ft), had a gross weight of 78,845 kg (165,000 lb) and could carry a 23,225-kg (51,200-lb) bombload. Four 3000-hp Pratt & Whitney Wasp Major engines driving contra-rotating pusher propellers powered the aircraft which had a crew of 15 and was to have been defended by 20 remotely-controlled 12.7-mm (0.5-in) machine-guns.
By mid-1941 Northrop was well advanced with a far more ambitious design based on the encouraging results obtained with the N-1M. This design was for a flying-wing bomber.
The scale model of the bomber was designated N-9M. This was approximately a one-third linear scale of the great bomber, and thus weighed about 1/27th as much, the actual weight being of the order of 7,100 lb. The first two aircraft, and the third (designated N-9M-A), had two 275 hp Menasco Buccaneer engines driving pusher propellers positioned midway between the thrust lines of the four propellers of the bomber; the fourth aircraft, designated N-9M-B, had two 300 h.p. Franklins. The fact that four aircraft were needed is explained by the sheer volume of work that had to be accomplished. Not only was the definitive form of surface system-controls and flaps-far from settled, but there were also extensive development programmes for autopilot and other systems, while concurrently exposing the aircraft to the hands of the greatest possible number of Army test pilots in order both to acquire critical feedback from the customer and also allay a whole string of fears about how all-wing aircraft behaved.
The first N-9M was flown on December 27, 1942. After about 30 encouraging hours it crashed, killing the pilot. Nobody had the slightest indication of what happened. Northrop could not find evidence of in-flight failure and decided the pilot must have got into a spin at low level. The other three N-9Ms gave no trouble at all, and in the course of many hundreds of hours were stalled and spun even with c.g. at the aft limit.
A three-year test programme was flown from Muroc Army Air Base, providing much data and giving pilots experience in the handling and performance of flying wings, and the autopilot for the XB-35 was developed in an N-9M. All N-9Ms had retractable landing gear and varying colour schemes; the first two were all yellow, the third (N-9MA) was blue on top and yellow underneath, while the fourth (N-9MB) had the colour reversed. The colours identified the top or bottom of the aircraft during observations of the flight programme.
Engines: two 205kW / 275 hp Menasco Buccaneer
Engines: 2 x Franklin 224kW / 300 hp
Max take-off weight: 3200 kg / 7055 lb
Wingspan: 18.3 m / 60 ft 0 in
Length: 5.3 m / 17 ft 5 in
Wing area: 46 sq.m / 495.14 sq ft