| XB-35 | |
|---|---|
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| XB-35 prototype | |
| Role | Strategic bomber |
| Manufacturer | Northrop |
| Designed by | Jack Northrop |
| First flight | June 1946 |
| Status | Cancelled in 1949 |
| Primary user | United States Air Force |
| Program cost | US$66 million[1] |
| Variants | Northrop YB-49 |
The Northrop YB-35 was an experimental heavy bomber aircraft developed for the United States Army Air Forces during and shortly after World War II by the Northrop Corporation. It was the second bomber after the German Ho 229 to use 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 prototype and pre-production machines were built, although interest remained strong enough to warrant further development of the aircraft as a jet bomber, under the designation YB-49.
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Design and development
The B-35 was the brainchild of Jack Northrop, who made the flying wing the focus of his work during the 1930s. During World War II, Northrop had been commissioned to develop a large wing-only, long range bomber designated XB-35. Northrop advocated the "flying wing" as a means of reducing parasitic drag and eliminating structural weight not directly responsible for producing lift. In theory, the B-35 could carry a greater payload faster, farther, and cheaper than a conventional bomber. On 11 April 1941, the United States Army Air Corps sent out a request for a bomber that could carry 10,000 lb (4,536 kg) of bombs to a round-trip mission of 10,000 mi (16,093 km). Requested performance was a maximum speed of 450 mph (740 km/h), cruise speed of 275 mph (443 km/h), and service ceiling of 45,000 ft (13,716 m). This aircraft would be able to bomb Nazi-occupied Europe in the event that Britain fell. This proposal was originally submitted to Boeing and Consolidated Aircraft Company, and led to the Convair B-36. In May, the contract was also extended to include Northrop, inviting them to submit a design along the lines they were already exploring.
Since the radical design would require a significant amount of engineering work in untested waters, the first orders placed were actually for a one-third scale version of the XB-35 dubbed the Northrop N-9M. This aircraft would be used to gather data on the flying wing design, which would be used in designing the XB-35. In early 1942, design work on the XB-35 itself began in earnest. Unlike conventional aircraft, flying wings cannot use a rudder for lateral control, so a set of butterfly-like, double split flaps on the trailing edge of the wingtips were used. When aileron control was input, they were deflected up or down as a single unit, just like an aileron. When rudder input was made, the two surfaces on one side opened, top and bottom, creating drag, and yawing the aircraft. By applying input to both rudder pedals, both sets of surfaces were deployed creating drag so that the airspeed or the glide angle could be manipulated.
Variants
XB-35
On 22 November 1941, the Army Air Corps 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 gunners in the production model. In the rear of the cabin, there were folding bunks for off-duty crew on long missions. The B-35 would take advantage of a new aluminium alloy devised by Alcoa; it was considerably stronger than any alloy used previously.
In June 1946, the XB-35 made her first flight, a 45-minute trip from Hawthorne, California to Dry Lake. The XB-35s were soon grounded after only a handful of flights. When they flew again, problems continued to plague them. Nevertheless, the YB-35 flight test program proceeded until the whole project was cancelled. The first and second XB-35s were scrapped on 23 and 19 August 1949, respectively.[2]
YB-35
On 30 September 1943, 13 pre-production YB-35s were ordered by the Army Air Force. By the time the first one had flown on 15 May 1948, it was clearly made obsolete by the advent of the jet engine.
Only the first YB-35 was ever flown. Testing lasted only a few months. The YB-35 was scrapped 20 July 1949. The unfinished YB-35 #2, was scrapped 19 August 1949.
The other 11 of 13 YB-35 aircraft ordered underwent conversion to other powerplants. Two were converted to use eight Allison J35 jet engines, and designated YB-49. Both aircraft were destroyed in accidents. Seven incomplete airframes began conversion to jet power as YB-35B but were never finished. One was converted to use six jet engines, and was used as an experimental reconnaissance aircraft designated YRB-49A.
The last YB-35B, redesignated EB-35B, was converted to test two 10,000 hp Turbodyne XT-37 turboprop engines. After the Air Force cancelled development of the Turbodyne engine, the EB-35B was scrapped 30 March 1950.
Operational history
The Army Air Force 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 proved to be riddled with design flaws. 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 Force cancelled the production contract, though the Air Technical Services Command continued to run the program for research purposes.
Actual flight tests of the plane revealed several problems. The contra-rotating props caused constant gearbox 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 vibration problems, the new single-rotation props greatly reduced the aircraft's performance. Furthermore, the intricate exhaust system was turning into a fiasco to maintain. After only two years of use, the engines already showed signs of metal fatigue.
In the end, the program was terminated due to its endless technical difficulties, the obsolescence of its reciprocating engines, and the program being far behind schedule and over budget. Another contributing factor to the program's failure was the tendency of Northrop to become engaged in many experimental programs, which spread a small engineering staff far too wide. While the competing B-36 had as many or more problems, the Air Force had more faith that the B-36 problems could be fixed compared to the new radical flying wing. Convair also had more effective lobbyists in Washington DC.
There are long-standing conspiracy theories about the cancellation of the program. Specifically, there is a long-standing accusation that Secretary of the Air Force Stuart Symington attempted to coerce Jack Northrop to merge his company with the Atlas-Corporation-controlled Convair. When Northrop refused, Symington supposedly arranged to cancel the B-35 and B-49 program. In a 1979 taped interview, Jack Northrop claimed the flying wing contract was cancelled because Northrop Aircraft Corporation would not agree to a merger with competitor Convair as Stuart Symington wanted, because according to Jack Northrop Convair's merger demands were "grossly unfair to Northrop". Critics of these allegations note that the B-35 and B-49 designs had well-documented performance and design problems; moreover, the Convair B-36 needed more money.[3] Furthermore, early the same year the B-49 was cancelled, Northrop received a production contract for the F-89 Scorpion.[4][5][6]
At that time, it appeared the B-36 program might be cancelled as well as the B-35. The Air Force and the Texas Congressional delegation desired to have a production program for the Fort Worth factory. Given Northrop's insufficient production capacity, this is probably the source of the 'conspiracy.'
Specifications (YB-35)
General characteristics
- Crew: 9: pilot, copilot, bombardier, navigator, engineer, radio operator, three gunners
- Length: 53 ft 1 in (16.2 m)
- Wingspan: 172 ft (52.2 m)
- Height: 20 ft 3 in (6.2 m)
- Wing area: 4,000 ft² (370 m²
- Fuselage diameter: 9 ft 6 in (2.9 m))
- Empty weight: 89,300 lb (40,590 kg)
- Loaded weight: 180,000 lb (82,000 kg)
- Max takeoff weight: 209,000 lb (95,000 kg)
- Powerplant: 2× Pratt & Whitney R-4360-17 and 2× R-4360-21 radial engines, 3,000 hp (2,200 kW) each
Performance
- Maximum speed: 393 mph (632 km/h)
- Range: 8,150 mi (13,100 km)
- Service ceiling: 39,700 ft (12,100 m)
- Rate of climb: 625 ft/min (3.2 m/s)
- Wing loading: 45 lb/ft² (220 kg/m²)
- Power/mass: 0.07 hp/lb (0.11 kW/kg)
Armament
- Guns: 20 × .50 in (12.7 mm) M2 Browning machine guns
- Bombs: 51,070 lb (23,210 kg)
See also
Related development
Comparable aircraft
Related lists
- List of military aircraft of the United States
- List of bomber aircraft
- List of flying wing aircraft
- List of military aircraft of the United States (naval)
References
- Notes
- ^ Knaack, Marcelle Size. Post-World War II Bombers, 1945-1973. Washington, DC: Office of Air Force History, 1988. ISBN 0-16-002260-6.
- ^ USAF Museum XB-35 fact sheet
- ^ Donald 1997, p. 709.
- ^ Donald 1997, p. 708.
- ^ Jones 1975, p. 238.
- ^ Fitzsimons 1978, p. 2282.
- Bibliography
- Coleman, Ted. Jack Northrop and the Flying Wing: The Real Story Behind the Stealth Bomber. New York: Paragon House, 1988. ISBN 1-55778-079-X.
- Donald, David, ed. "Northrop Flying Wings." Encyclopedia of World Aircraft. Etobicoke, Ontario: Prospero Books, 1997. ISBN 1-85605-375-X.
- Fitzsimons, Bernard, ed. "Scorpion, Northrop F-89." Illustrated Encyclopedia of 20th Century Weapons and Warfare, Volume 21. London: Phoebus, 1978. ISBN 0-83936-175-0.
- Jones, Lloyd S. U.S. Fighters. Fallbrook, California: Aero Publishers, 1975. ISBN 0-8168-9200-8.
- Maloney, Edward T. Northrop Flying Wings. Corona del Mar, California: World War II Publications, 1988. ISBN 0-915464-00-4.
- Pape, Garry and John Campbell. Northrop Flying Wings: A History of Jack Northrop's Visionary Aircraft. Atglen, Pennsylvania: Schiffer Publishing, Ltd., 1995. ISBN 0-88740-689-0.
- Winchester, Jim. "Northrop XB-35/YB-49." Concept Aircraft: Prototypes, X-Planes and Experimental Aircraft. Kent, UK: Grange Books plc., 2005. ISBN 1-84013-309-2.
External links
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