Америкалық қанатты бомбалаушы прототипі

American flying wing bomber prototype

{|Infobox aircraft type
|type =Strategic bomber
|manufacturer =Northrop
|designer =Jack Northrop
|first flight =25 June 1946
|introduction =
|retired = 1948 1949
|status = Canceled
|primary user = United States Air Force
|more users =
|produced =
|number built = 14 (Including 1 experimental version)
|program cost=US$66 million or NS 9, were experimental heavy bomber aircraft developed by the Northrop Corporation for the United States Army Air Forces during and shortly after World War II. The airplane used the radical and potentially very efficient flying wing design, in which the tail section and fuselage are eliminated and all payload is carried in a thick wing. Only prototypes and pre production aircraft were built, although interest remained strong enough to warrant further development of the design as a jet bomber, under the designation YB 49.

The B 35 was the brainchild of Jack Northrop, who made the flying wing the focus of his work during the 1930s. In 1941 before the USA entered World War II, Northrop and Consolidated Vultee Corporation had been commissioned to develop a large wing only, long range bomber designated XB 35 and XB 36. Northrop advocated a "flying wing" as a means of reducing parasitic drag and eliminating structural weight not directly responsible for producing lift. Consolidated Vultee proposed a more conventional design with fuselage and tail, which was much larger and heavier. In theory, the B 35 could carry a greater payload faster, farther, and cheaper than a conventional bomber. In December 1941, the Army Air Forces awarded prototype contracts to both Northrop and Consolidated Vultee for a bomber that could carry of bombs to a round trip mission of 10000 mile (16093 km). Requested performance was a maximum speed of , cruise speed of , and service ceiling of 45000 feet (13716 m). This aircraft would be able to bomb Nazi occupied Europe in the event that Britain fell (this was similar to Nazi Germany's own Amerikabomber program design competition through the RLM, itself initiated in the spring of 1942). The original April 1941 USAAC proposal was first submitted to Boeing and Consolidated Aircraft Company and led to the production of the Convair B 36. In May, one month before the USAAF was created, the contract was also extended to include Northrop, inviting it to submit a design along the lines it was already exploring.

On 22 November 1941, the United States Army Air Forces (USAAF, or AAF) signed the development contract for an XB 35; the contract included an option for a second aircraft, which was exercised on 2 January 1942. The first was to be delivered in November 1943, the second in April of the next year. Detailed engineering began in early 1942. A fuselage like crew cabin was to be embedded inside the wing; it included a tail cone protruding from the trailing edge. This tail cone would contain the remote sighting stations for the bomber's gunners and a cluster of rear firing machine guns in the production aircraft. In the midsection of the cabin, there were folding bunks for off duty crew on long missions. The aircraft's bomb load was to be carried in six smaller bomb bays, three in each wing section, fitted with roll away doors; this original design precluded the carrying of large bombs, and the early atomic bombs, without bomb bay redesign and modifications. Production aircraft would have defensive armament of twenty machine guns or 20 mm cannon, carried in six turrets, two turrets along the aircraft's center line, four above and below the outer wings, and four in the "stinger" tail cone. The B 35 would take advantage of a new aluminum alloy devised by Alcoa; it was considerably stronger than any alloy used previously. In June 1946, the XB 35 made its first flight, a 45 minute trip from Hawthorne, California, to Muroc Dry Lake, without incident. The XB 35's engines and propellers were AAF property and had not been tested for engine propeller compatibility by either Pratt & Whitney, Hamilton Standard, or by the AAF which bought them at Wright Field without testing them or assuring reliability, and then shipped them to Northrop. Microfilmed records of reports and correspondence of the XB 35 program relate that after three or four flights, power plant and propeller vibrations increased, and the very efficient contra rotating propellers began failing with frustrating frequency. Meetings were called by Northrop, of the AAF, Pratt & Whitney and Hamilton Standard where no one would take responsibility for correcting the AAF's engines and propellers. In addition, the AAF failed to supply the AC electrical alternator, insisting on Northrop using an onboard auxiliary power unit (APU) unit driven by an automotive engine which limited the high altitude, high speed XB 35 to test flights below 15000 feet (4572 m). The AAF also refused to allow Northrop proposed modification of the bomb bays to carry the standard Mk. 3 atomic bomb, while at the same time declaring the AF would not buy the bomber unless it could carry the A bomb. Northrop reluctantly agreed to try a single rotation propeller, which slightly increased takeoff distance and a reduced rate of climb and maximum speed. Problems with the quartet of contra rotating propellers' shafts comprising each aircraft's drive line system continued until finally Jack Northrop himself grounded the XB 35s until the government fixed their propulsion system. Concurrently, the AAF ordered Northrop to convert two of the YB 35 airframes to YB 49s, essentially substituting eight jet engines for four reciprocating engines. As a result, the airframe promptly flew to more than 40000 feet (12192 m) and topped in flight tests, verifying the XB 35 air frame's aerodynamics, but at the price of range. The prop version had a design range capable of reaching targets 4000 mile (6437 km) away, but the jet engine version's range was cut nearly in half. The new version disqualified it for the Air Force's top priority mission as a strategic bomber, which at that time meant striking at the USSR's industrial and military complexes in the Ural Mountains. The Air Force, itself involved in a confusion of rank and job changes, eventually cancelled the XB 35 project, while continuing testing the B 35 airframe as the YB 49, even ordering 30 of the jet powered bombers after the first YB 49 crashed. The first and second XB 35s were scrapped on 23 and 19 August 1949, respectively.

On 30 September 1943, 13 pre production YB 35s were ordered by the Army Air Force. The first one did not fly until 15 May 1948. While some Air Force generals felt the piston engines made the B 35 obsolete, it remained superior in overall performance and range to its competitor, the Convair B 36, and General Hoyt Vandenberg wrote that only the B 35 and the B 36 had adequate range for the Air Force's primary mission, and nothing comparable would be available until the mid 1950s.

In order to test the advanced Northrop T37 Turbodyne turboprop engine, produced by a Northrop subsidiary, the ultimate YB 35A was to be converted to a single EB 35B test aircraft (in this case the prefix "E" for the designation meant "Exempt," not the later Electronic). The test aircraft would use two of the powerful T37 engines, each driving a pair of contra rotating, paddle blade propellers; the first planned ground tests were to be made using a single T37 engine. When the EB 35B project was canceled, the Air Force had Northrop's Turbodyne engine name, all its patents, and technical data reassigned to General Electric.

The XB2T 1 was a U. S. Navy designation for one YB 35 airframe to be used for development trials; the project was canceled while still in the planning stage.

The U. S. Army Air Forces had originally ordered 200 production model B 35s. Since Northrop's facilities were not up to the task of producing them, the Glenn L. Martin Company agreed to undertake mass production. This proved irrelevant when the aircraft had too many development problems. Even disregarding these, so many of Martin's engineers had been drafted by 1944 that Martin pushed the first delivery date back to 1947. Seeing that it would almost certainly never be ready in time for the war, the Army Air Forces canceled the production contract, though the Air Technical Services Command continued to run the program for research purposes. Actual flight tests of the aircraft revealed several problems: the contra rotating props caused constant heavy drive shaft vibration and the government supplied gearboxes had frequent malfunctions and reduced the effectiveness of propeller control. After only 19 flights, Northrop grounded the first XB 35; the second aircraft was grounded after eight test flights. During this time, the contra rotating propellers were removed and replaced with four blade single rotation propellers. In addition to having continued drive shaft vibration problems, the new single rotation props greatly reduced the aircraft's speed and performance. Furthermore, the intricate exhaust system turned into a fiasco to maintain. After only two years of use, the engines already showed signs of metal fatigue. Other observers note that the B 35 and B 49 designs had well documented performance and design issues while the Convair B 36 needed more development money. At that time, it appeared the B 36 program might be cancelled as well as the B 35. The USAF and the Texas Congressional delegation desired to have a production program for the large Fort Worth aircraft production factory, and Convair had much more effective lobbyists in Washington, DC. The Northrop Corporation was always a technological trailblazer, but the independent nature of Jack Northrop often collided with the political wheeling and dealing in Washington that tended to run huge military allocations. Consequently, the B 36 prevailed, with just over 380 aircraft built. Furthermore, earlier the same year, when the YB 49 jet bomber was cancelled, Northrop received a smaller production contract for its F 89 Scorpion fighter as compensation for the lost Flying Wing contract.