Developed as a low-level bomber and ground attack platform for the then-United States Army Air Forces (USAAF), the Martin XB-51 proved itself a failed development, producing just a pair of prototypes. First flight was recorded on October 28th, 1949 and the program ran until 1952 when it was officially cancelled and then formally retired in March of 1956 with a price tag of $12.6 million USD. Both prototypes were eventually lost in crashes which ended any notion of them ending as museum showpieces. The renamed United States Air Force (1947 onwards) eventually selected the British English Electric Canberra bomber in its place.
The XB-51 was intended to fulfill a USAAF requirement in replacing its aging line of Douglas A-26 Invaders in the light bombing / ground attack role. Martin engineers returned with a unique turbojet-powered design in which the aircraft utilized three engines - the primary pair set along nacelles held away from the forward lower fuselage with the third engine buried in the tail section. The fuselage also took on a unique appearance with its slab sides. The finish was of all silver, consistent with American aircraft of the period. The main wing elements were mid-mounted and swept at 35-degree angles for aerodynamic efficiency. Each element showcased variable incidence for take-off and landing actions and an anti-icing capability was built-in. Dive brakes were added for glide controlling during combat diving actions envisioned for the aircraft. The empennage was made up of a "T-style" tail unit which utilized the vertical fin as the support for the high-mounted horizontal planes. The third engine was aspirated at the fuselage spine at the base of the tail system and exhausted through a port at rear. The cockpit was held well-forward in the design, aft of the nose cone assembly which sloped downwards to provide the necessary out-of-the-cockpit vision for the pilot. The crew included the primary pilot and a systems officer in a pressurized, air conditioned cockpit that featuring ejection seats and a bulletproof windshield. However, only the pilot sat under the provided canopy for the systems officer was hidden away in his shrouded position nearby. The undercarriage was of a "bicycle" arrangement which utilized two main, double-tired landing gear legs in line with small, single-wheeled supporting legs at the wingtips - the latter for controlling lateral stability. When at rest, the aircraft exhibited a noticeable "nose-up" appearance. Landing was aided by release of a drag chute at rear.
The XB-51 was completed with 3 x General Electric J47-GE-13 turbojet engines of 5,200lbs thrust each. These included a water-alcohol thrust quality which was used to support short/quick take-off actions beyond the normal thrust power output of the turbojets. Also, 4 x rocket pods could be installed at the rear of the fuselage for 14-seconds of take-off assistance (Rocket-Assisted Take-Off = "RATO"), each canister producing 954lbs of additional thrust each. The engines were protected in armor against ground-based artillery fire (FlaK type) and their combined output power gave the airframe a maximum speed of 645 miles per hour with a cruising speed of around 530 miles per hour. Ferry range was out to 1,600 miles with an operational service ceiling of 40,500 feet (hence the cockpit pressurization for the crew).
Dimensions included a wingspan of 53 feet, a length of 85 feet and a height of 17.3 feet. Empty weight was listed at 29,590lb with a Maximum Take-Off Weight of 62,560lb.
Proposed armament for the XB-51 line was to include 8 x 20mm cannons with a total of 1,280 x 20mm projectiles carried. All of the cannon were to be fitted in the nose assembly and used for strafing runs against land-based or naval targets. An internal bomb bay was nestled in the fuselage complete with a rotary-style delivery system and cleared to carry up to 10,400lbs of internal stores. This would have included conventional drop bombs or 8 x 5" High-Velocity Aerial Rockets (HVAR). Aiming systems for the aircraft included an A-1-B gun-bomb rocket sighting device with radar ranging capability. All gun actions would be recorded on an onboard camera and a rear-facing camera would record the ground for damage assessment during strafing/bombing rungs. Still another camera was installed for high-altitude attack work or general reconnaissance. The XB-51made use of the SHORAN (SHOrt RAnge Navigation) bombing system already proven in the Korean War (1950-1953) through the Douglas A-26/B-26 Invader light bombers and Boeing B-29 Superfortress heavy bombers. The SHORAN system used the AN/APN-3 radar set and K-1A bombing computer in conjunction with a pair of AN/CPN-2/2A ground stations for improved bombing effectiveness over that seen in World War 2 (1939-1945).
The prototype XB-51 aircraft were assigned serial numbers 46-685 and 46-686. Its original attack-minded approach begat the little-known, short-lived "XA-45" designation before the bomber-minded classification was introduced to produce the "XB-51" designation. The original USAAF requirement was met by submissions from Martin as well as Avro Canada (the CF-100) and English Electric (the Canberra). While the XB-51 proposal was favored ahead of the two competing types for its inherent speed and agility, it eventually lost out to the British Canberra for its vastly superior operational range which was highly coveted. The Canberra was procured by the now-renamed USAF as the "B-57" and was, ironically, produced in 250 examples by Glenn L. Martin Company facilities.
Despite the XB-51 program setback, the prototypes continued in flight testing after their formal, potential USAF run had ended. Both prototypes were then lost in separate crashes - the second during maneuvers in May of 1952 and the first on a flight to Elgin AFB during March of 1956. Such ended the short-lived tenure of the Martin XB-51.
[ 2 Units ] : Glenn L. Martin Company (Martin) - USA
United States (cancelled)
- Ground Attack
- X-Plane / Developmental
84.97 ft (25.9 m)
53.15 ft (16.2 m)
17.39 ft (5.3 m)
(Showcased structural dimension values pertain to the Martin XB-51 production model)
29,586 lb (13,420 kg)
62,457 lb (28,330 kg)
(Showcased weight values pertain to the Martin XB-51 production model)
3 x General Electric J47-GE-13 turbojet engines.
(Showcased powerplant information pertains to the Martin XB-51 production model)
646 mph (1,040 kph; 562 kts)
40,354 feet (12,300 m; 7.64 miles)
1,075 miles (1,730 km; 934 nm)
6,980 ft/min (2,128 m/min)
(Showcased performance values pertain to the Martin XB-51 production model; Compare this aircraft entry against any other in our database)
8 x 20mm cannons in nose assembly
OPTIONAL (internal rotary launcher):
Up to 10,400lb of conventional drop ordnance OR 8 x High-Velocity Aerial Rocket (HVAR) rockets.
(Showcased armament details pertain to the Martin XB-51 production model)
XB-51 - Base Project Designation
XA-45 - USAAF designation for attack requirement
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