XB-51 – an American Bomber Beaten by a British Design
The Martin XB-51, also known as ‘The Flying Cigar’ because of its signature elongated fuselage, was a medium bomber most famous for losing out to the English Electric Canberra during a 1951 fly-off. Despite a brief cameo in a movie, both XB-51 prototypes were unable to maintain their star power and were shelved, rather ironically, after two Hollywood-style crashes.
The XB-51 was an unusual looking aircraft, with two of its three engines being mounted under the cockpit in individual pods. Even though it proved to be a capable machine and, for the most part, did what was asked from it, the XB-51 wouldn’t enter service, as it was beaten by a more capable aircraft.
- The XB-51
- Development and Testing
- Movie Star and the 1951 Fly-off
- XB-51 Crashes
In 1946 the United States Army Air Force (USAAF) organized a competition to find a replacement for the aging Douglas A-26, a piston-propelled medium bomber.
In response Martin proposed the jet-powered model 234, a 70,000 pound unit capable of carrying 8,000 pounds of ordnance over 800 miles. After Martin’s submission was proclaimed the winner, the model 234 was re-designated XA-45 before changing to the XB-51.
Following selection though, USAF officials decided that the A-26 replacement should have a renewed focus on speed, leading to a complete redesign of the XB-51 which had been built without this in mind.
The new model submitted in February 1947 was almost unrecognizable from the original. This rethought 52,000 pound XB-51 was now to be powered by three engines and would include a variable incidence wing and tail, a revolving bomb bay door, and finally bicycle landing gear – a device that Martin had developed as part of their XB-48 program.
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Sufficiently impressed, military officials ordered two XB-51 prototypes as part of a fixed price contact worth $9,417,107 that covered the cost of assembly a well as fees associated with wind tunnel tests, mockups, special tools, spare parts, drawings, technical data and armament reports.
The Martin XB-51 was 25.94 meters in length, 5.26 meters in height, and was typically manned by a crew of two comprising a pilot and a navigator. It was propelled by three General Electric J-47-GE-3 or -17 turbojets that gave it a top speed of 644 mph (1,038 km/h) and a cruise speed of 538 mph (866 km/h).
The engines had a rather unusual arrangement, particularly the front-most pair, which were located externally on both sides of the fuselage, below and slightly behind the cockpit. The third was position inside the fuselage with its exhaust nozzle protruding out the tail.
The XB-51 soared through the skies with the help of a T-tail and a pair of wings sweptback at 35 degrees that had a span of 16.19 meters. Although the wings were unusually thin, they were still able to house multiple mechanisms such as the leading edge anti-ice heating, automatic slats, full-span slotted flaps, and an advanced spoiler aileron which enabled extraordinary roll control.
The XB-51 was equipped with eight 20 mm cannons in the nose with a maximum ammo capacity of 1,280 rounds, and a bomb bay that could accommodate up to 4,717 kilograms worth of bombs or eight 5 inch High Velocity Aerial Rockets (HVAR).
Other notable features included a bicycle-type landing gear balanced by a pair of wingtip outrigger wheels and the inclusion of four JATO bottles rated at 1,000 pounds that assisted in maximum-weight take-offs.
Development and Testing
On February 24th 1948 the first wooden XB-51 mock-up was inspected by an Air Force Contractor review board, after which a young and promising test pilot, Glenn Edwards, was assigned to lead flight evaluations. Two months later however Edwards was killed while testing Northrop’s YB-49 Flying Wing at Muroc Field, with company pilot Pat Tibbs drafted in to replace him.
Afterwards, Muroc Field was renamed ‘Edwards Air Force Base’ in the fallen pilot’s honor.
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The XB-51 took to the skies for the first time on October 27th 1949 with Tibbs at the controls of Ship No.1.
During its maiden voyage the XB-51 ascended to 10,000 feet, where it performed a series of clean and dirty stalls and tested the efficacy of the dive brakes. Afterwards Tibbs climbed to 20,000 feet, operating the plane for 34 minutes before touching down at MAS Patuxent River. Upon hitting the runway a deceleration chute was activated, reducing landing distance to just 3,000 feet.
Following a promising few opening months, the project was dealt its first setback on December 28th 1949 when the aft main landing gear accidentally retracted after a ground run of 2,000 feet, closing because of the sudden application of vertical and forward loads.
With the gear nearly unlocking and collapsing as a result, the aft landing gear doors had to be replaced for $21,000.
Upon the completion of 45 flights with Ship No.1, Phase I testing was officially wrapped up and a couple of modifications were suggested on review. The required changes included the addition of fairing at the tail intersection to prevent vibrations and elevator roughness, hydraulic and mechanical changes to the main landing gear, a redesign of the wing flap control and wing actuating system, and the reconfiguration of the lateral control system from feel aileron and spoiler to all-spoiler.
With most of the issues addressed, Phase II testing with Ship No. 2 commenced on March 31st 1950 at Martin’s facility in Baltimore. After 16 test fights however a distracting lateral trim problem was identified that would keep the design team extremely busy for months, for the issue still hadn’t been resolved 17 flights later.
A fix was finally discovered that involved augmenting the flaps with reinforced control linkages to offset the effects of lateral trim, allowing trials to be resumed by September.
On September 27th 1950 however, disaster struck again when an Air Force pilot forced to make a hard landing completely wrecked the aft engine doors, leading to lengthy repairs. Nevertheless, upon the conclusion of Phase II on November 10th 1950, the XB-51 had reached most of its performance targets over 41 flights and 44 hours of flight time.
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Despite having a worrying tendency to haphazardly enter into Dutch Rolls, USAF officials were satisfied that the incorporation of wing incidence and flap unloading modifications would prevent the same from happening to the production version.
Movie Star and the 1951 Fly-off
The XB-51 project now entered into a pre-production stage referred to as the ‘production prototype program’, in which Martin was expected to be responsible for further studies, investigations, design evaluations, design changes, and flight testing.
Key among the objectives was to transform the XB-51 into a modern-day bomber capable of jet propulsion, resulting in a series of tests to Ship No.1 taking place over 39 flights that looked into wing, tail, nacelle, and nacelle pylon airloads as well as high-speed and forced tail vibrations.
However only a few months into investigations on May 7th 1951, Ship No.1 was briefly engulfed in flames when one of its engines caught fire. The ignition was caused by an expansion of fuel into the tank vent line that occurred after the tanks had been fed too much fuel during a routine top-up.
Consequently, when the pilot braked during taxiing the fuel had spilled onto the hot No.3 engine which burst into flames, damaging the nacelle, nacelle pylon, the engine itself and related wiring. The incident was significant because it forced to the design team totally re-examine the placement of the No.1 and No.2 fuel tanks before the XB-51 was rolled out.
Shortly after Ship No.1 was patched up it was ruined again during another landing accident at Wright-Patterson Air Force Base, Ohio, which resulted in the destruction of the front landing gear wheels and the damaging of the lower-foreword segment of the airframe.
After being mended for $408,000, Ship No.1 was transported to Edwards Air Force Base where, alongside Ship No.2, it was to undergo high-speed bombing tests.
It was during this battery of operational examinations that the XB-51 was filmed for the 1955 sci-fi movie ‘Towards the Unknown’ where it starred as the XF-10 Gilbert fighter flown by intrepid test pilot Lincoln Bond, played by actor William Holden.
For the flying scene, Air Force Major Pete Everest became Holden’s stunt double, performing an impressive showcase of snap rolls and climb for the cameras. Everest, who was also known as ‘The Fastest Man Alive’, would also fly the X-2 flights from the movie and was one of its main technical advisors.
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At the same time as Ship No. 1 was becoming an unexpected movie star, performance and armament evaluations for Ship No.2 were already underway. During its first flight on April 17th 1950, Ship No.2 was flown for 10 minutes by test pilot F. E. ‘Chris’ Christofferson without incident, but it was later damaged in another landing mishap that took $96,000 in repairs to make right.
By January 26th 1951 after extensive weapons testing, the XB-51 No.2 had dropped a total of five hundred 2,000 and 4,000 pound explosives, proving itself a capable bomber and an ideal candidate for the upcoming fly-off organized by the US Army in response to the Korean War.
In March 1951 the XB-51 faced off against North American’s AJ-1 Savage, Canada’s CF-100 and English Electric’s Canberra for a production contract of 300 units.
Despite being slower than the XB-51, the Canberra’s lower wing loading gave it the range and superior low altitude maneuvering characteristics the judges were on the lookout for.
Moreover in comparison to the XB-51, which could only loiter for one hour over a target 400 miles away, the Canberra could do it for two and a half hours over a target that was 900 miles from base. With the Canberra emerging triumphant any hopes for a production version of the XB-51 were promptly defenestrated.
For the rest of the developmental cycle, the XB-51 was treated as a testbed aircraft and was mainly used to outline the pros and cons of an innovative rotary weapons bay door that would ultimately make its way onto the English Electric Canberra.
At Edwards Air Force Base from December 14th 1951 the characteristics of the bomb release at high speeds became the earliest investigatory focus.
This culminated in another emergency on March 21st that occurred after the right hand aft door opened mid-flight at 15,000 feet, causing excessive air pressure to build up and dislodge a key component, which fragmented into the engine No.2 exhaust.
The XB-51 also evaluated how Jet Assisted Take Off (JATO) rockets worked with new liquid fuel motor engines, an arrangement that was found to reduce take-off roll from 5,200 feet to 4,175 feet.
On May 9th 1952 however the program was irreparably damaged after Ship No.2 crashed while making low-altitude high speed flybys at Edwards. Pilot Major Neale Lathrop was killed instantly when an aileron roll caused the plane to suddenly become inverted, at which point it struck the ground with its left wing and exploded.
A few years later Ship No.1 was also destroyed after crashing on a ferry flight between Edwards and Eglin Air Force Base on March 26th 1956 because of a stall attributed to premature take-off rotation.
Taking off from El Paso Municipal Airport en-route, eyewitnesses reported that the XB-51 had accelerated around 7,000 feet down the airstrip and had entered into a slight nose-high position when the calamity had befallen.
When the landing gear retracted the XB-51 failed to climb, and before long it had passed over the right side of the runway abut 500 feet from the end. The airplane then struck the boundary fence, coming to a halt after sliding 750 more feet and disintegrating to pieces.
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Tragically, the airplane’s crew chief was killed while the test pilot Major James Rudolph died from severe burns in hospital a few days later.
- Crew: 2
- Length: 25.6 m (85 ft 1 in)
- Wingspan: 16.2 m (53 ft 1 in)
- Height: 5.28 m (17 ft 4 in)
- Max takeoff weight: 25,400 kg (56,000 lbs)
- Powerplant: 3 x General Electric J47
- Maximum speed: 645 mph (1,038 km/h)
- Range: 1,600 miles (2,575 km)
- Service ceiling: 12,350 m (45,000 ft)