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In 1946/1947, the US Army Air Forces (later the US Air Force) was looking for a fast light bomber/attack aircraft to replace its ageing and outdated Douglas A-26 Invaders. Martin was originally building a straight-winged turboprop attacker also designated the XB-51, but after requirements were revised to put a greater emphasis on speed, the aircraft was completely redesigned, resulting in this futuristic-looking jet bomber.
The XB-51 was 25.94 m long, 5.27 m tall, and had a wingspan of 16.18 m. It carried two crew: the pilot and the navigator/systems operator. It was powered by three General Electric J-47 turbojets (sources dispute the specific model, mentioning variants including J-47-GE-3, -7, -13, -17; “Gunston and Gilchrist” and the stats tables in “Libis” are in agreement that the model is the J-47-GE-7 with takeoff thrust of 5820 lbs), two in streamlined pods under the forward fuselage and the third in the tail fed by an S-shaped duct. The highly swept wing was heavily loaded at 100 lbs/sq ft (488 kg/m^2), so to fulfil the short takeoff requirement the wings could vary their incidence between 2˚ and 7˚30’, 69% of the leading edge was fitted with slats, and almost the whole trailing edge had powerful slotted flaps. Additionally, 4 assisted-takeoff rockets with 1000 lbs of thrust each could be attached to the rear fuselage. All control surfaces were hydraulically boosted, and the tailplane was driven by an irreversible screw for trimming. Roll control was provided by small all-speed ailerons at the wingtips and large one-piece spoilers that could also act as lift dumpers by deploying them symmetrically. The variable incidence wing was also necessitated by the bicycle landing gear. Two outrigger wheels were fitted on the wingtips to prevent tipping, and they retracted forward into the wing.
The XB-51 also carried an impressive array of weapons. The nose contained eight 20 mm autocannons with 160 rounds each (no sources mention the model, probably AN/M3 based on the time period). It could carry a maximum of 10400 lbs (4717 kg) of bombs and rockets, ranging from the 4000 lb bomb to HVAR rockets. All of this ordinance is attached to the rotating bomb bay door, and two hardpoints could also be attached to the outside of the door. A special ‘B’ door was needed to mount the 4000 lb or the Mk. 5 nuclear bomb. It was equipped with a SHORAN bombing system, controlled by a dedicated operator, which was said to include a bombing radar and computer (it’s unclear whether this would be considered a CCRP system, or would just be given a regular bombsight in-game).
The XB-51 made its maiden flight on the 27th/28th of October, 1949. Various incidents occurred during flight testing, including an unexpected retraction of the main landing gear that damaged the landing gear doors and a hard landing that destroyed the engine access doors, but all damage was repaired and the two prototypes met almost all of the performance targets. In 1951, the XB-51 participated in a formal flyoff against the North American AJ-1 Savage, Canada’s CF-100, and the English Electric Canberra. While the XB-51 had a higher speed, the Canberra was found to have superior range and low-speed handling. Although many pilots and officers preferred the Martin XB-51, the Air Force ultimately chose the Canberra, which was, somewhat ironically, to be license produced by the Martin Company itself as the B-57. The two prototypes continued to undergo experimental testing, mostly to investigate the rotating bomb door mechanism, but both were eventually lost in accidents.
While officially the XB-51 was not chosen due to it not fitting with Air Force requirements and doctrine, some historians and aviation experts, including Walt Boyne, Erik Simonsen, and Chuck Yeager, believed that the USAF may have deliberately shunned the XB-51 due to their animosity towards the Martin Company. At the time, the Air Force’s B-36 bombers were in fierce competition for funding against the Navy’s aircraft carriers. Not only did Martin continue producing aircraft for the Navy, but its founder Glenn L. Martin publicly backed the Navy and lobbied for support. General Hoyt Vandenburg, Chief of Staff, and Stuart Symington, Secretary of the Air Force, allegedly vowed:
“It would be a cold day in hell before the Air Force bought another airplane from Glenn Martin.”
Specifications
Number produced: 2 prototypes
Crew: 2 (pilot and navigator/systems operator)
Length: 25.94 m
Wingspan: 16.18 m
Height: 5.27 m
Mass: 13419 kg (empty), 28328 kg (maximum)
Wing area: 50.91 m^2
Maximum speed (at standard combat load of 55923 lbs): 1038 km/h at sea level, 930 km/h at 35600 ft (10850 m)
Maximum climb rate: 7130 ft/min (36.22 m/s)
Engines: three General Electric J-47-GE-7
Thrust per engine: 5820 lbs (2640 kg) at takeoff with fuel/water injection, 5000 lbs (2268 kg) military thrust
Assisted takeoff: four rockets providing 1000 lbs of thrust for 14 seconds
Weaponry: Eight 20 mm autocannons with 160 rounds per gun, up to 10400 lbs (4717 kg) of bombs and rockets (known possible loadouts based on images and descriptions in “Libis”: one 4000 lb, two 2000 lb external, four 1000 lb, six 750 lb, eight HVAR)
More pictures
Both XB-51 prototypes in flight
PR shot of XB-51 loadouts
HVAR rockets mounted on the bomb bay door
4000 lb bomb in bomb bay
Nose autocannons viewed through maintenance door
Number 686 in foreground with nose gun ports visible
Two 2000 lb bombs mounted externally
In game
While losing to the Canberra in real life, the XB-51 will almost certainly be superior to it in game. The good bomb load will easily destroy bases or tanks in air and ground battles, and the good speed will allow it to escape in many cases. Thanks to the eight 20 mm autocannons, the XB-51 could also be used as a heavy fighter. The flight characteristics of the XB-51 aren’t very well documented, although pilots have described it as surprisingly agile. In any case, it probably can’t dogfight a single engine fighter, so boom-and-zoom/boom-and-run will be its primary tactic.
Sources
- “The Martin XB-51” by Scott Libis (the main content of the book sometimes contradicts the stats tables in the appendix; I used stats table values whenever discrepancies occurred)
- “Jet Bombers from the Messerschmitt Me 262 to the Stealth B-2” by Bill Gunston and Peter Gilchrist
- First Flight of the XB-51, The Weirdest Plane You’ve Never Heard Of, OTD in 1949
- Martin XB-51
- XB-51 – an American Bomber Beaten by a British Design