RogerBW's Blog

Northrop Flying Wings 27 April 2014

The YB-35 and YB-49 were flying-wing bomber prototypes built during and in the wake of the Second World War.

The same requirement that led to the B-36, a bomber able to strike Germany from a base in the USA, caused Jack Northrop to work on his own design. It was rather more radical: an aircraft with no fuselage or tail, consisting solely of a wing, which could be thick enough to contain the engines, fuel tanks, bomb load and other equipment the plane would need.

Without a tailplane, a double split flap control system was used: for aileron input the top or bottom flaps would open together, causing the aircraft to climb or dive, while for rudder input the top and bottom flaps on the same side would open, causing the aircraft to yaw to that side.

Northrop had been fond of flying wings since the 1920s, but knew they needed a lot of development; the first step was a scaled-down version, the N-9M, with just two engines. This worked reasonably well, but crashed in May 1943, killing its pilot; this was eventually attributed to a control reversal while in a steep nose-down spin, and the problem was corrected.

Pre-production began in 1943. The project was formally cancelled in 1944 when delays made it apparent the plane wouldn't be ready in time for the end of the war, but some private development continued; the XB-35 (experimental aircraft) made its first flight in June 1946. Aero engines belonged to the Army Air Force, and hadn't been tested for suitability for this unusual design; vibration became a big problem after a few flights. It seems pretty clear that the Army didn't want this aircraft; they refused to allow Northrop to modify the testbed to let it carry the Mk. 3 atomic bomb, while declaring that they wouldn't buy any aircraft that didn't have that capability. The YB-35 comfortably outperformed the prototype B-36 that was its competition, but politics continued to dog the project, and only one of the YB-35 airframes flew.

At least in that configuration. Propellers seemed to be obsolete, so two of the YB-35s were converted to jet power: the four radial engines were replaced with eight jets as the YB-49. This was able to fly much higher, but fuel inefficiencies cut its range in half compared with the propeller version, at least at first.

A more serious problem for both models was inherent in the aircraft's radical design: without any sort of vertical stabiliser, it was prone to yaw hunting, oscillating back and forth about a vertical axis in any sort of turbulent air. Not only did this make things uncomfortable for the crew, it meant that bombing runs needed to be longer and straighter than other aircraft required. Early Honeywell autopilots helped with this.

Both the operational YB-49 prototypes were lost: one in a structural failure during a pull-out after stall tests, and the other in a taxi test (with full fuel tanks, a distinctly unusual procedure which no-one admitted to having authorised).

The YB-49's other major problem was that its thick wing impaired its speed; in the high-and-fast era of bomber design, that mattered. But like the TSR-2 a few years later, the YB-49 was mostly a victim of politics. As it turns out, Stuart Symington, Secretary of the Air Force, put pressure on Northrop to merge with Convair on terms hugely favourable to the latter. (Symington became president of Convair on leaving his post, and denied that he had ever done such a thing.) When Northrop wouldn't play, Symington transferred all YB-49 funding to Convair for the B-36, and almost all the prototypes under construction were deliberately broken up and smelted in a fit of governmental pique. The only survivor was the YRB-49 reconnaissance prototype, which was scrapped a few years later.

The Northrop flying wings are obviously ancestors of the B-2 bomber, but their stability problems couldn't really be dealt with until the advent of full fly-by-wire avionics; even with all that, the B-2 is not an agile or efficient aircraft. The B-35 and B-49 would probably never have been great aircraft, but to my mind it's a shame we didn't get to find out; they at least manage to be beautiful, which is more than the B-36 did.

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