Northrop YB-35

The Northrop YB-35 (Northrop NS-9) was an experimental heavy bomber aircraft. Developed for the United States Army Air Force during and shortly after World War II. It was the first bomber to use the radical and potentially very efficient flying wing design, in which the tail section is eliminated and the fuselage is embedded in a thick wing. Only prototype and pre-production machines were built, although interest remained strong enough to further test the aircraft as a jet bomber, under the designation YB-49; though this project failed also, the B-2 Spirit stealth bomber would vindicate Northrop's approach many years later.

XB-35 in flight

Contents

4 Specifications (YB-35)

4.1 General Characteristics
4.2 Performance
4.3 Armament

5 References

6 External links

7 Related content

Development

The B-35 was the brainchild of Jack Northrop, who made the flying wing the focus of his work during the 1930s. He considered it the next major step forward in aircraft design, since it had the theoretical promise of both less drag and more lift. Thus, in theory, the B-35 could carry a greater payload faster, farther, and cheaper than a conventional bomber. On April 11 1941, the United States Army Air Corps sent out a request for a bomber that could carry 10,000 lb of bombs to a combat radius of 10,000 miles. Requested performance was a maximum speed of 450 mph, cruise speed of 275 mph, and service ceiling of 45,000 ft. This plane 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 ¹/₃-scale version of the XB-35 dubbed the Northrop N-9M. This plane 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 a single flap was opened, it caused braking on one side, turning the aircraft. By opening both, the airspeed or the glide angle could be manipulated; they could also serve as longitudinal 'trim flaps'.

Variants

XB-35

On November 22 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 January 2 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. Difficulties on this flight foreshadowed problems to come. Both XB-35s were grounded after only a handful of flights. When they flew again, problems continued to plague them. Nevertheless, the YB-35 programme proceeded as planned until the whole project was cancelled.

YB-35

On September 30 1943, 13 pre-production YB-35s were ordered by the Army Air Force. By the time the first one had flown on May 15 1948, it was clearly made obsolete by the advent of the jet engine. However, the newly formed United States Air Force was unwilling to drop the expensive programme without any tactical return, so they considered using it as a reconnaissance aircraft or tanker. Unfortunately, it was unable to have any utility: it was too unstable to be a useful bombing or camera platform, and continuing problems made other uses unlikely also.

Only the first YB-35 was ever flown. Testing lasted only a few months. In August 1949, the first two YB-35s were scrapped. Two were converted to use eight jet engines, and redesignated YB-49. Another four were converted to spare parts aircraft, designated the YB-35B. The final five of the YB-35s were built to improved specifications, where the previous eight used the same designation as the XB-35; these were designated YB-35A. One was converted to use six jet engines, and was used as an experimental reconnaissance aircraft designated YRB-49A. The last YB-35A, designated EB-35B, was converted to test two turboprop XT-37 Turbodyne; it was disassembled in March 1950. The other three YB-35As were also converted to YB-35Bs.

Setbacks

The Army Air Force had originally ordered two-hundred 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 programme for research purposes.

The obvious setbacks began when the testing of the N-9M showed that the range of the B-35 would probably by 1,600 miles less than the 10,000 miles requested by the Army Air Force. The estimated maximum speed was also less than had originally been anticipated. The actual flight of the plane made matters worse. The contra-rotating props caused constant gearbox malfunctions and reduced the effectiveness of propeller control. After only nineteen flights Northrop grounded the first XB-35; the second aeroplane was grounded after eight. During this time, the contra-rotating propellers were removed and replaced with single ones. In addition to having vibration problems, the new single props greatly reduced the plane'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 programme was doomed due to its endless technical difficulties, the obsolescence of its prop engines, and its unstable flight (reducing its effectiveness as a bombing platform). Nevertheless, there are long-standing conspiracy theories about the cancellation of the programme. Specifically, there is a long-standing theory that Secretary of the Air Force Stuart Symington attempted to coerce Jack Northrop to merge his company with the government-controlled Convair. When Northrop refused, Symington supposedly arranged to cancel the B-35 and B-49 programme. Critics of these allegations note that the B-35 and B-49 designs had well-documented performance and design problems, and were incapable of carrying nuclear weapons. Furthermore, around the same time the B-49 was cancelled, Northrop received a production contract for the F-89 Scorpion fighter.

Specifications (YB-35)

General Characteristics

Crew: nine - 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: 180,000 lb (82,000 kg)
Loaded: 120,000 lb (54,432 kg)
Maximum takeoff: 209,000 lb (95,000 kg)
Powerplant: 2× Pratt & Whitney R-4360-17 and 2× R-4360-21, 3,000 hp (2,200 kW) each

Performance

Maximum speed: 391 mph (629 km/h)
Range: 8,150 miles (13,100 km)
Service ceiling: 39,700 ft (12,100 m)
Rate of climb: 625 ft/min (190 m/min)
Wing loading: 45 lb/ft² (220 kg/m²)
Power/Mass: 0.07 hp/lb||0.11 kW/kg

Armament

20× .50 M2 machine guns
Up to 51,070 lb (23,213 kg) of bombs

References

Knaac, Marcelle Size (1988). Post-World War II bombers. Office of Air Force History. ISBN 0160022606.
Maloney, Edward T. (1988). Northrop Flying Wings. World War II Publications. ISBN 0915464004.
Wagner, Ray (1982). American Combat Planes. New York, New York: Doubleday. ISBN 0930083172.

External links

Encyclpedia of American Aircraft (http://home.att.net/~jbaugher2/b35.html)
USAF Museum XB-35 (http://www.wpafb.af.mil/museum/research/bombers/b3-66.htm)
USAF Museum YB-35 (http://www.wpafb.af.mil/museum/research/bombers/b3-67.htm)