Martin XB-48

https://en.wikipedia.org/wiki/Martin_XB-48

The Martin XB-48 was an American medium jet bomber developed in the mid-1940s.
It competed with the Boeing B-47 Stratojet, which proved to be a superior
design, and was largely considered as a backup plan in case the B-47 ran into
development problems. It never saw production or active duty, and only two
prototypes, serial numbers 45-59585 and 45-59586, were built.

In 1944, the U.S. War Department was aware of aviation advances in Germany and
issued a requirement for a range of designs for medium bombers weighing from
80,000 lb (36,287 kg) to more than 200,000 lb (90,718 kg). Other designs
resulting from this competition, sometimes named the class of '45, included the
North American XB-45 and the Convair XB-46. Production orders finally went to
the North American B-45 Tornado, and even this airplane served only for a couple
of years before again being replaced by the much more modern Boeing B-47
Stratojet, although the B-45 had enough "utility" built in to maintain a niche
as a reconnaissance aircraft.

In retrospect, the class of '45 were transitional aircraft, combining the power
of turbojets with the aeronautical knowledge of World War II. The XB-48 was no
exception, as its round fuselage and unswept wings showed a distinct influence
of Martin's B-26 Marauder medium bomber. Still, where the B-26 had enough thrust
with two massive 18-cylinder radial engines, the XB-48 needed no less than six
of the new jet engines.

Although the pictures make it look as if the aircraft had three engine nacelles
under each wing, the jet engines were actually clustered in a pair of flat
three-engined nacelles with an intricate system of air ducts between the
engines, intended to facilitate cooling. At the time of the XB-48's design, jet
propulsion was still in its infancy.

The XB-48 was the first aircraft designed with bicycle-type tandem landing gear,
which had previously been tested on a modified B-26. The wing airfoil was too
thin to house conventional landing gear mechanisms. The main landing gear was in
the fuselage and small outriggers located on each wing were used to balance the
aircraft.


Role
Bomber

Manufacturer
Glenn L. Martin Company

First flight
22 June 1947

Status
Canceled in 1948

Number built
2

Unit cost

US$11.5 million for the program

The XB-48 made its first flight on 22 June 1947, a 37-minute, 73 mi (117 km) hop
from Martin's Baltimore, Maryland plant to NAS Patuxent River, Maryland, but
blew all four tires on its fore-and-aft mounted undercarriage on landing when
pilot Pat Tibbs applied heavy pressure to the specially-designed, but very slow
to respond, insensitive air-braking lever. Tibbs and co-pilot Dutch Gelvin were
uninjured.

Specifications (XB-48)

General characteristics
Crew: three (pilot, co-pilot, and bomber-navigator)
Length: 85 ft 9 in (26.14 m)
Wingspan: 108 ft 4 in (33.02 m)
Height: 26 ft 6 in (8.08 m)
Wing area: 1,330 ft² (123.5 m²)
Empty weight: 58,500 lb (26,535 kg)
Loaded weight: 92,600 lb (42,000 kg)
Max. takeoff weight: 102,600 lb (46,540 kg)
Powerplant: 6 × General Electric J35 axial flow gas-turbine, 3,820 lbf (17 kN)
each

Performance
Maximum speed: 454 kn (523 mph, 841 km/h) at 35,000 ft
Cruise speed: 361 kn (415 mph, 668 km/h)
Range: 1,566 nmi (1,802 mi, 2,900 km)
Combat radius: 795 mi (1,280 km)
Service ceiling: 39,400 ft (12,009 m)
Rate of climb: 4,200 ft/min (21.3 m/s)

Armament

Guns: 2 × .50 in (12.7 mm) M-2 machine guns in tail turret (proposed)
Bombs: 1 × 20,000 lb (9,980 kg) or 36 × 250 lb (113 kg)