On June 1, 1945, a contract ordering the conversion of two of the YB-35 flying wings into jet configuration was issued. The four Wasp Major engines of the B-35 were to be replaced by eight 4000 lb.s.t. Allison J35-A-5 turbojets buried inside the wing, four on each side. The engines were to be fed by intakes cut into the leading edges of the wing. The designation given to the jet-powered flying wing bomber was originally supposed to have been YB-35B, but this was changed to YB-49 before the first flight took place.
Since the addition of jet power promised a marked improvement in the performance of the flying wing, work on the YB-35 project was abandoned and plans were made to convert all the YB-35 airframes beyond the first to YB-49 configuration. The airframes for the second and third YB-35 (42-102367 and 42-102368) were selected for modification to YB-49 configuration. The eight 4000 lb.s.t. Allison J35-A-5 turbojets were mounted in banks of four on either side of the wing. The leading edge was reconfigured to provide a low drag intake slot for each of the two sets of jet engines. In order to achieve greater stability a pair of four small vertical fins were added to the wing trailing edge extending both above and below the wing just inboard and outboard of the engines. In addition , a set of wing fences were added to the upper wing surfaces extending all the way from the vertical fins to the wing leading edge. These surfaces were added in order to provide a stabilizing effect that the propellers and propeller shaft housings had given to the YB-35. All guns except the tail cone guns were eliminated. The crew of seven were housed entirely within the wing center section, with the pilot seated underneath a large bubble canopy near the wing leading edge. For long flights, an additional off-duty crew of six members could be carried in quarters in the tail cone just aft of the flight section.
Conversion of the YB-35 to the YB-49 configuration was originally scheduled to be completed by June of 1946. However, this schedule slipped by more than a year because of unforseen problems encountered in adding fins to the wings.
The first YB-49 (42-102367) took off on its maiden flight on October 21, 1947 from the Northrop field at Hawthorne California, piloted by Northrop's chief test pilot, Max Stanley. At the end of the flight, it landed at Muroc Air Force Base where it was to carry out its test program. It was later joined by the second YB-49 (42-102368), which flew for the first time on January 13, 1948.
Over twenty months of flight testing was carried out. Northrop test pilots flew the first YB-49 for almost 200 hours, accumulated in some 120 flights. Air Force pilots completed about 70 hours of flight time in the first YB-49, totaled in some 20 flights. The second YB-49 carried out some 24 flights with Northrop crews for a total of about 50 hours. The Air Force crews flew the second YB-49 five times for about 13 hours. A maximum speed of 520 mph was achieved, and a service ceiling of 42,000 feet was attained. A normal 10,000 pound bombload could be carried for an estimated 4000 miles on 6700 gallons of fuel, less than half the range of the piston-engined B-35. In spite of the added rudders and wing fences, the YB-49 design still encountered some stability problems which were never fully corrected.
On April 26, 1948, the first YB-49 achieved a milestone of sorts, the aircraft staying up in the air for 9 hours, 6 hours of which were above 40,000 feet. This is believed to have set an unofficial record for that period.
On May 28, 1948, the second YB-49 (42-102368) was turned over to the USAF. Only a few days later, tragedy struck. On the morning of June 5, 1948, 42-102368 crashed just north of Muroc Dry Lake. The pilot, Air Force Capt. Glenn Edwards, and all four other members of the crew were killed. What caused the crash is not known, but it was suspected that Capt Edwards managed to surpass the "red line" speed of the aircraft while descending from 40,000 feet, causing the outer wing panels to be shed and the aircraft to disintegrate in midair. Muroc AFB was renamed Edwards AFB on December 5, 1949 in honor of the late Capt. Glenn Edwards.
In spite of the crash, the Air Force still had sufficient confidence in the YB-49 that they continued with plans for the conversion of nine of the remaining eleven YB-35 airframes to a basically similar RB-35B strategic reconnaissance configuration with 8 jet engines, with another airframe to be used as a static test vehicle. In addition, orders were placed for 30 new RB-49s to be built from scratch.
Many deficiencies turned up in the second series of tests. The J35 turbojets of the YB-49 were extremely thirsty for fuel, and the jet-powered YB-49 had only half the range of the YB-35 that preceded it. The test pilots complained that the aircraft was extremely unstable and difficult to fly. They also maintained that the YB-49 was completely unsuitable as a bombing platform-- it could not hold a steady course or a constant airspeed and altitude, and that here was a persistent rocking motion in yaw, which tended to upset the bomb sights. In comparison with the B-29, the YB-49 had a much poorer circular average error and range error during bombing trials. In retrospect, many of the stability problems with the flying wing may have been insoluble with the technology available in the late 1940s, requiring the fly-by-wire technology that was developed much later for their solution.
By 1948, progress in range extension by other projects had reached the level that the YB-49 was now considered as being a medium bomber rather than a heavy bomber. This put it in competition with the XB-46, XB-47, and XB-48 projects, where the XB-35 had been considered as a B-36 competitor.
On January 4, 1949, the Air Force ordered Northrop to fly 42-102367 from Muroc AFB to Washington DC for a military air display at Andrews AFB. It departed Muroc on February 9, 1949, and when it landed at Andrews it had set a new transcontinental speed record of 4 hours and 20 minutes for the 2258-mile flight, averaging 511.2 mph. The pilot was Major Robert Cardenas, who had replaced the late Capt Glen Edwards as chief of flight test on the Northrop flying wing test program. Northrop test pilot Max Stanley was also on board. During the display at Andrews AFB, President Harry Truman inspected the YB-49 and was impressed.
On the way back to California, 42-102367 stopped off at Wright Field in Dayton so that the Air Force could take a look at the new plane. On February 23, the YB-49 took off to return to Muroc, but during the flight three of the J35 engines on the left and one on the right side caught fire, forcing an emergency landing at Winslow, Arizona. There were hints of sabotage, since it was later determined that the cause of the engine fires was that the turbine oil reserves had not been filled in any of the J35 engines during refuelling at Wright Field. The FBI was called in to investigate, but a blanket of security was thrown over the entire affair and the incident was all but forgotten.
By October of 1948, the YB-49 was clearly a doomed program. Nevertheless, testing continued, and there was always a remote possibility that its problems might be cured. However, the accidents and stability problems continued. On April 26, 1949, a fire occurred in one of the aircraft's engine bays, forcing $19,000 worth of repairs. The handwriting was now on the wall-- the contract for 30 new RB-49A aircraft was canceled in April of 1949. In November of 1949, the conversion of existing YB-35 airframes to YB-35B configuration was also cancelled.
On March 15, 1950, the cancellation of the entire YB-49 program became official. On that very same day, the first YB-49 (42-102367) got itself involved in a ground taxiing accident at Edwards AFB. There were no fatalities, but crewmen were injured and the aircraft was totally destroyed by fire. Excessive shimmy of the nosewheel followed by total gear collapse were blamed for the mishap.
The movie *War of the Worlds* filmed between 1952 and 1953 used stock footage of one of the YB-49s. In the movie, it was the plane which delivered a nuclear bomb onto the attacking Martian force. Many people confuse this plane with the B-2 stealth comber, which was designed much later.
Engines: Eight 3750 lb.s.t. Allison J35-A-15 turbojets. Performance: Maximum speed 493 mph at 20,800 feet, 464 mph at 35,000 feet. Cruising speed 429 mph. Stalling speed 90 mph. Service ceiling 45,700 feet, combat ceiling 40,700 feet. Initial climb rate 3785 feet per minute. Combat radius 1615 miles with 10,000 pound bomb load. Ferry range 3575 miles. A normal 10,000 pound bombload could be carried for 4000 miles on 6700 gallons of fuel. A load of 36,760 pounds of bombs could be carried 1150 miles. Dimensions: Wingspan 172 feet, length 53 feet 1 inches, height 15 feet 2 inches, wing area 4000 square feet. Weights: 88,442 pounds empty, 133,559 pounds combat, 193,938 pounds gross.