Northrop YB-35

https://en.wikipedia.org/wiki/Northrop_YB-35

The Northrop XB-35 and YB-35 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 prototype 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. During World War II, Northrop had been
commissioned to develop a large wing-only, long-range bomber designated XB-35.
Northrop advocated a "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 4,500 kg (10,000 lb) of bombs to a
round-trip mission of 16,000 km (10,000 mi). Requested performance was a maximum
speed of 720 km/h (450 mph), cruise speed of 443 km/h (275 mph), and service
ceiling of 14,000 m (45,000 ft). This aircraft would be able to bomb
Nazi-occupied Europe in the event that Britain fell. (This was similar to Nazi
Germany's own Amerika Bomber program design competition through 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 the contract was also extended to include
Northrop, inviting them to submit a design along the lines they were already
exploring.

Since the new aircraft would require a significant amount of engineering work in
untested waters, the first order placed was actually for a one-third scale
version of the XB-35 dubbed the Northrop N-9M (M standing for model). This
aircraft would be used to gather flight test data on the Flying Wing design,
which would then be used in designing the big XB-35. It would also be used as a
flight trainer, to familiarize pilots with the radical, all-wing concept. Early
in 1942, design work on the XB-35 itself began in earnest. Unlike conventional
aircraft, truly "tailless" flying wings cannot use a rudder for lateral control
as it was absent, so a set of clamshell-like, double split flaps (so called
flaperon, a portmanteau of flap and aileron) 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.


Role
Strategic bomber

Manufacturer
Northrop

Designer
Jack Northrop

First flight
25 June 1946

Status
Cancelled in 1949

Primary user
United States Air Force

Program cost
US$66 million

Variants
Northrop YB-49

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.

In the end, the program was terminated due to its technical difficulties, the
obsolescence of its reciprocating propeller 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 its small engineering staff far too wide. While the
competing propeller-driven B-36 was obsolete by that time and had just as many
or even more development problems, the Air Force needed a very long-range,
post-war atomic bomber to counter the perceived Soviet threat. It had more faith
that the B-36's "teething" problems could be overcome, compared to those of the
new and radical "Flying Wing", the unofficial name that was later associated
with all the Northrop "all-wing" designs.

There are long-standing conspiracy theories about the cancellation of the Flying
Wing program; specifically, an accusation from Jack Northrop that Secretary of
the Air Force Stuart Symington attempted to coerce him to merge his company with
the Atlas Corporation-controlled Convair. In a 1979 taped interview, Jack
Northrop claimed the Flying Wing contract was cancelled because he would not
agree to a merger because Convair's merger demands were "grossly unfair to
Northrop." When Northrop refused, Symington supposedly arranged to cancel the
B-35 and B-49 program. Symington became president of Convair after he left
government service a short time later.

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 (371.6 m²)
Aspect ratio: 7.4

Fuselage diameter: 9 ft 6 in (2.9 m)
Empty weight: 89,300 lb (40,590 kg)
Loaded weight: 180,000 lb (81,647 kg)
Max. takeoff weight: 209,000 lb (94,802 kg)
Powerplant: 2 × Pratt & Whitney R-4360-17 and 2× R-4360-21 radial engines, 3,000
hp (2,237 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) M3 Browning machine guns
Bombs: 51,070 lb (23,210 kg)





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