Lacking a fuselage and tail, a Flying Wing can rotate easily around its lateral axis--the imaginary line running spanwise through the wings--and even Jack Northrop fretted that his design might be inherently unstable. While he was experimenting with moving the N-9M's center of gravity forward and aft, the test pilot apparently let the nose point so high that the wing stalled.
Now, if you stall a Cessna, you can release back pressure on the control stick and the airplane will drop its nose naturally and resume flying. A Flying Wing is not so polite. In the N-9M and other all-wing aircraft of the time, the airflow separation at the stall rendered the trailing-edge control surfaces ineffective (see "Go With the Flow," June/July 1995). Or worse, the forces on the controls reversed, slamming the control stick into the pilot. The Wing might go into a tail slide, flip over backwards, or fall off to one side in a spin.
In time, the team of Northrop, von Karman, and Sears tamed the N-9M, but the Army was losing patience with the development problems at Northrop and Consolidated. Development of the B-36 was behind schedule, and the XB-35, which was even more of an engineering challenge, had yet to fly. So the production contract was canceled, leaving only two X (experimental) and 13 Y (service test) B-35s on order.
The XB-35 finally took to the air in June 1946, almost a year after Japan had surrendered. Company pilot Max Stanley flew it to Muroc Army Air Base. "No trouble," he reported. The same couldn't be said of the XB-35 thereafter: Its engines overheated, its propeller shafts vibrated, its propeller gearbox broke down, and its auxiliary power unit (a gasoline-powered electrical generator) failed. In the end, the X models would manage to fly for a total of 36 hours, for an amortized cost of $1.8 million per hour.
It didn't matter, because the Army had already decided to adapt its super-bombers to jet propulsion. Consolidated (now called Convair) would hang four turbojets on its B-36, outboard of its piston engines. Northrop's Flying Wing would get an even more radical makeover, its engines replaced by eight turbojets, along with a new designation: the B-49. Because the airframe had proved airworthy, it could go straight into flight test, and with little delay: The first YB-49 was rolled out in October 1947. "Spewing a twin trail of black smoke, the sky monster swept into the air before the awed thousands gathered to witness the historic take-off," gushed a company press release. Max Stanley was again at the controls, and again it was a delivery flight to Muroc--now the property of the newly independent United States Air Force.
In theory, company pilots performed the initial flight tests on new airplanes to prove their airworthiness, then military pilots put them through acceptance tests. In fact, the Air Force's Bomber Test Branch was involved from the first day. When the second YB-49 was ready, Major Robert Cardenas flew it from the factory to Muroc. Cardenas was also the pilot on February 23, 1948, when the nosewheel door blew off the "Two" (the test pilots coined a shorthand to refer to the first two airplanes--the One and the Two). With jet engines, the Wing simply took off too fast. Thereafter, Cardenas lifted the nose as soon as the wheels left the ground, bleeding off speed until the wheels retracted. "Then you leveled off," he recalls, "and you'd sit there rocking in your seat, back and forth, in unison with the slosh of the fuel." The B-49 had no fuel-cell baffles.
Perhaps more serious, the turbojet lacked the stabilizing effect of the B-35's propellers and prop-shaft fairings. To compensate, the airplane had been equipped with four tall vertical fins, which were carried forward as "fences" to prevent the air from flowing toward the wingtips, a tendency that marred the performance of early swept-wing aircraft. So in some respects, the YB-49 really was a new airplane and could not be counted upon to behave exactly like the XB-35, never mind the relatively docile N-9M.
On April 26, a Northrop crew kept the Two aloft for nine and a half hours, and the flight set a record for jet endurance at altitude, though they had to shut down one engine, and the electrical generator failed. Nobody seemed concerned that the distance was only 3,500 miles--not much better than hundreds of Boeing B-29s had done in the Pacific. Even more astonishing, the old B-29 could carry a larger bomb load, including the large and heavy atomic bomb. Rarely mentioned in the Flying Wing saga is the fact that the YB-49 bomb bays were too small for "Fat Man," the plutonium bomb dropped on Nagasaki and still the U.S. standard in 1948.
Shortly after this modest success, the Air Force sent Cardenas to the University of Southern California to get an engineering degree. Back at Wright Field, Glen Edwards wrote in his diary: "Then this evening all heck broke loose. Seems like I'm bound for Muroc tomorrow by fastest means possible. Plan to run stability [tests] on the YB-49. . .what fun! Sounds like I'll be there for awhile. Packing like mad tonight."
The Air Force had two series of acceptance tests, one for performance measures like speed, altitude, and rate of climb, the other for stability and control--the qualities that make an airplane either easy, comfortable, and safe to fly or tiring, uncomfortable, and risky. Accordingly, the two YB-49s each had a different set of instruments. The first was meant to test stability and control; this was Glen Edwards' specialty, so the One would be assigned to him.