Northrop began to build one flying wing in 1939, designating it N-1M (Northrop model Mock-up). Essentially it was just a 38-foot stressed-skin wing, with a very fat section (and as much camber underneath as on top) and a slightly swept-back shape. The upper surface had very slight dihedral, so that there was quite sharp dihedral on the underside, but the tips sloped sharply downwards so that the ailerons, which were entirely out-board of the kink, could also serve as rudders. On the trailing edge were powerful elevators incorporating trim-ming tabs. The pilot sat close to the centre of gravity, his head projecting above the upper surface under a small canopy and his forward vision being improved by four small windows in the remarkably fat leading edge. Just outboard of these windows were intakes for the cooling air for the two 65 hp Lycoming engines, which were buried in the wing and drove pusher propellers through 10-foot shafts housed in fairings which made no contribu-tion to lift but which Northrop could not avoid. The N-1M rode on a short-wheelbase retractable tricycle landing gear, with a long fixed tailwheel added to, keep the propellers from touching the ground.
Northrop bore most of the costs of building it himself, but in view of its long-term importance he did not invite the press in to have a look at it. Indeed he had already come to the conclusion that the ideal role for an all-wing machine was that of a long-range bomber, and had discussed the possibility with the Army Air Corps and with the top technical staff at Wright Field. They were extremely interested, and it was agreed that the N-1M should be kept under wraps.
In May 1940 the completed machine was painted bright yellow, registered as NX-28311 and trucked by night from the plant at Hawthorne to the very new Army test base at Lake Muroc out in the remote Mojave Desert.
Pilot Vance Breese tried taxying and then, on July 3, cautiously lifted off and held the yellow wing as close to the ground as he could-as someone said, "to make the crash a bit easier". Northrop's comment was "It looks like we have a plane with a twenty-foot ceiling", but of course Breese later made proper flights which on the whole were remarkably successful. There was no catastrophic accident, and the N-1M explored a wide range of configurations with different planform, dihedral, tip shape, c.g. location and, most important of all, control system. Soon it was flying much faster with 117 h.p. Franklin 6AC-264-F2 engines driving three-blade v-p propellers.
The N-1M really flew extremely well, in the hands of several pilots (notably Moye Stephens), and the only persistent difficulty was the cooling of the engines. Ordinary flying had by mid-1941 become a safe and routine operation, with the whole design envelope, including stalls and spins, fully explored in 200 flights. The only control "problem" was that it took a long time to find the best arrangement to control yaw (weathercocking of the nose, for example, due to asymmetric thrust). The original idea of using the ailerons on the down-turned tips to serve as rudders was not wholly adequate, and eventually Northrop considered the best answer was to eliminate the kinked tips and make the ailerons in the form of split upper and lower halves which could be opened to act as a powerful brake. With just one aileron thus opened there would be an extremely potent yawing moment amply capable of holding any asymmetric condition.
The N-1M has survived in the US National Air and Space Museum.
Engine: 2 x Lycoming, 48kW / 65 hp
Max take-off weight: 1360 kg / 2998 lb
Wingspan: 11.6 m / 38 ft 1 in
Length: 5.2 m / 17 ft 1 in
Wing area: 28 sq.m / 301.39 sq ft