Convair XB-46

https://en.wikipedia.org/wiki/Convair_XB-46

The Convair XB-46 was a single example of an experimental medium jet bomber
which was developed in the mid-1940s but which never saw production or active
duty. It competed with similar designs, the North American XB-45 and Martin
XB-48, all of which saw little use after the successful development of the
Boeing XB-47.

In the fall of 1945, Convair found it was competing with itself when the USAAF
became interested in an unorthodox forward-swept wing jet attack design, the
XA-44-CO that the company had also been working on. With the end of World War II
severely curtailing budgets, the company considered canceling the XB-46 in favor
of the other project as there was insufficient funding for both. Company
officials argued that it made more sense to allow them to complete the XB-46
prototype as a stripped-down testbed omitting armament and other equipment and
for the AAF to allow them to proceed with two XA-44 airframes in lieu of the
other two XB-46s on contract. In June 1946, the AAF agreed to the substitution
but that project was ultimately cancelled in December 1946 before the prototypes
were completed. The B-46 would be completed with only the equipment necessary to
prove its airworthiness and handling characteristics.

The XB-46 was a graceful design and had a long streamlined oval torpedo-shaped
fuselage, long narrow straight shoulder-mounted wings with four Chevrolet-built
J35-C3 axial-flow eleven stage turbojets of 3,820 pounds-force (17.0 kN) static
thrust paired in an integral nacelle under each wing. The fuselage turned out to
be a problem, as it distorted under flight loads. The pilots sat in tandem in a
pressurized fighter-style cockpit under a single Plexiglas teardrop canopy with
the bombardier-navigator-radio operator in a transparent Plexiglas nose section.

The straight wing had an aspect ratio of 11.6, and was equipped with Fowler
flaps which extended over 90 percent of the span, in four sections. The flaps
extended via electrical actuators, and had very small ailerons. Each wing had
five spoilers made of perforated magnesium alloy. The engine air intakes were
flat oval inlets, with a duct curving downward in a flat “S” to the engines,
which were mounted behind the leading edge of the wing. The unusual flight
control system utilized a system of pneumatic piping to transmit the pilots
control inputs and actuate various systems, rather than the more typical
hydraulic, manual or electrical control lines and systems of most aircraft of
the era.

Production versions were to be equipped with a pair of .50 caliber Browning M2
machine guns in a tail turret designed by Emerson Electric Company and provision
was made for an APG-27 remote control optics and sighting system, but no
weaponry was fitted into the prototype. Likewise, production aircraft were
intended to be built with the General Electric J47 engines with 5,200 lbf (23
kN) static thrust rather than the J35s used on the prototype.


Role
Medium bomber

Manufacturer
Convair

First flight
2 April 1947

Retired
1947

Status
Cancelled

Primary user
United States Air Force

Number built
1

Unit cost

US$4.9 million for the program

The XB-46's first flight occurred 2 April 1947 after a month of taxi testing,
and lasted ninety minutes as the bomber departed the Convair plant in San Diego,
California for Muroc Army Airfield in the high desert. The pilot praised its
handling qualities. Basic flight testing took place for five months, and by
September 1947 it was concluded after 127 hours aloft on 64 flights by both the
Convair company and AAF test pilots. Stability and control were excellent but
there were engineering problems with engine de-icing, the cabin air system, and
vertical oscillations caused by harmonic resonance between the wing and
spoilers. There was also concern regarding the ability of the three man crew to
exit the aircraft in case of an emergency, since the exit plan relied on the
pneumatic system to hold the main door open against the airstream. The aircraft
was accepted on 7 November and delivered on 12 November 1947.

The B-46 program was cancelled in August 1947, even before flight testing had
been completed, because it was already obsolete. The North American B-45 Tornado
already had production orders, and even it would be eclipsed by the Boeing B-47
Stratojet's superior performance. Furthermore, the bulky radar fire-control
system which was not installed in the XB-46 prototype would have undoubtedly
forced an expensive redesign of the slender fuselage. Subsequent testing
investigated excessive noise, tail vibration, and stability and control issues,
and was conducted at Palm Beach Air Force Base, Florida between August 1948 and
August 1949. After 44 additional flight hours, the XB-46 was taken out of
service, since the cost of support and maintenance, coupled with a lack of spare
parts, had become prohibitive.

Specifications (XB-46)

General characteristics
Crew: three
Length: 105 ft 9 in (32.24 m)
Wingspan: 113 ft 0 in (34.45 m)
Height: 27 ft 11 in (8.51 m)
Wing area: 1,285 ft² (119.4 m²)
Empty weight: 48,018 lb (21,826 kg)
Loaded weight: 91,000 lb (41,364 kg)
Max. takeoff weight: 95,600 lb (43,455 kg)
Powerplant: 4 × Allison J35-A-3 turbojets, 4,000 lbf (17.8 kN) each

Performance
Maximum speed: 545 mph (474 knots, 877 km/h) at 15,000 ft (4,580 m)
Cruise speed: 439 mph (382 knots, 707 km/h) at 35,000 ft (10,700 m)
Range: 2,870 mi (2,496 nm, 4,621 km)
Service ceiling: 40,000 ft (12,200 m)
Climb to 35,000 ft (10,700 m): 19 min

Armament

Guns: 2× .50 in (12.7 mm) M2 Browning machine guns
Bombs: 22,000 lb (10,000 kg)




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