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The Martin XB-51 Bomber

Martin's marvelous might-have-been bomber

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If things had worked out differently, the U.S. Air Force might have had a force of B-51 bombers available in the 1950s and during the early Vietnam conflict.

The B-52 may be one of the most famous aircraft of all time, the Stratofortress that handled nuclear alert, dropped conventional bombs in Southeast Asia, and has fought in all of our recent wars. But we’re talking here about the B-51.

No, the name of the aircraft is not a misprint. The B-52 may be one of the most famous aircraft of all time, the Stratofortress that handled nuclear alert, dropped conventional bombs in Southeast Asia, and has fought in all of our recent wars. But we’re talking here about the B-51.

Martin XB-51 (46-685) engine start

XB-51 46-685 during engine start and run-up. The bicycle landing gear, wingtip outrigger oleos, engine locations, and T-tail are all evident in this photo. U.S. Air Force photo

Slap an “X” prefix in front of the “B” for bomber and you have the XB-51, manufactured by the Glenn L. Martin Company in Baltimore, Md. That’s the company founded by and named for one of the nation’s great aviation pioneers. All these years later, after decades of corporate consolidation, the name is the Martin in the now-familiar Lockheed Martin.

For political reasons, not because of any aeronautical flaw, the U.S. Air Force ended up not with the B-51 but with an entirely different aircraft built at the same factory. Experts believe today that failure to put the B-51 into series production was a big mistake.

The XB-51 may have been the best bomber that never entered production and never fought a battle. A somewhat odd-looking aircraft pushed through the sky by three turbojet engines, the XB-51 was fast and effective. It passed every test and met every requirement for which it was designed. For political reasons, not because of any aeronautical flaw, the U.S. Air Force ended up not with the B-51 but with an entirely different aircraft built at the same factory. Experts believe today that failure to put the B-51 into series production was a big mistake.

 

Taking to the Air

Martin XB-51

XB-51 in flight. The third engine was housed internally, with an intake on top of the fuselage. The T-tail kept the horizontal stabilizers away from the jet efflux. The configuration later appeared on airline designs in the United States, United Kingdom, and Soviet Union. U.S. Air Force photo

The B-51 had its origins with the design work performed on an earlier aircraft with an “A” for “attack” appellation. A straight-winged aircraft weighing 70,000 pounds, the Martin XA-45 of the late World War II era was to have been powered by a combination of two TG-110 turboprop engines and two I-40 (service designation J33) turbojets, giving a projected maximum speed of 525 miles per hour. The XA-45 emerged as the winner from a design competition held in February 1946.  The aircraft was proposed to the Army Air Forces’ (AAF) Air Material Command on April 1, 1946, and on May 23 Martin was awarded a $9.5 million fixed-price letter contract for the manufacture of wind-tunnel models, mock-ups, and two prototypes. The AAF evolved into the U.S. Air Force on Sept. 18, 1947, and soon afterward the idea of using turboprop power on Martin’s new aircraft was dropped. On June 5, 1948, still only in the blueprint stage but now looking very different from the original design, the XA-45 was redesignated XB-51.

The physical appearance of the new aircraft was unlike any then seen from a U.S. manufacturer. A mid-wing all-metal monoplane with swept wings and a T-tail, the XB-51 had an overall length of 85 feet 1 inch and wingspan of 53 feet 1 inch. The empty weight of the airframe was 29,584 pounds. Fully loaded, it weighed 59,467 pounds.

After further delays, the first XB-51 (serial number 46-685) was built at the Martin factory at Middle River, Md., and officially rolled out on Sept. 4, 1949. The physical appearance of the new aircraft was unlike any then seen from a U.S. manufacturer. A mid-wing all-metal monoplane with swept wings and a T-tail, the XB-51 had an overall length of 85 feet 1 inch and wingspan of 53 feet 1 inch. The empty weight of the airframe was 29,584 pounds. Fully loaded, it weighed 59,467 pounds.

500-lb. bombs in XB-51 rotary bay

The rotary bomb bay of the XB-51, armed with 8 500-pound bombs. HVAR rockets as well as a mixture of other munitions could be carried internally. Two 2,000-pound bombs could also be carried on external hardpoints on the outside of the rotating bay door. A single conventional 4,000-pound bomb or a single nuclear free fall bomb could also be carried internally. U.S. Air Force photo

The previous month, on Aug. 29, 1949, at Semipalatinsk in Kazakhstan (then the Kazakh SSR), the Soviet Union had detonated its first atomic device. Tensions were increasing with the former Soviet ally, and the term Cold War had entered the lexicon. The United States was on the verge of building a massive bomber force able to deter or win an atomic war.

The XB-51 was officially a “light” bomber – albeit a beefy and very heavy light bomber – but it might have had a role in the growing strategic standoff between superpowers.

The XB-51 was officially a “light” bomber – albeit a beefy and very heavy light bomber – but it might have had a role in the growing strategic standoff between superpowers. The aircraft, also known in manufacturer’s parlance as the Martin Model 234, made its first flight on Oct. 28, 1949 at Middle River, with Martin’s O. E. “Pat” Tibbs at the controls.

Martin XB-51

An XB-51 pulls up hard during a high performance take off. Note the deployed wing slats and the fuselage shape that earned it the nickname “Flying Cigar.” U.S. Air Force photo

The engine configuration was unorthodox. The XB-51 may have been the world’s first tri-jet, long before the Boeing 727 and other three-engined jetliners. Two of the XB-51′s three General Electric J47 turbojet engines, each rated at 5,200 pounds of thrust, were mounted on pylons under the fuselage, with the third in the rear fuselage.

The bomber had a crew of two. The pilot sat beneath a fighter-style “bubble” canopy. The second crewmember, a navigator/radio operator, sat below and behind the pilot and had only a small observation window on the starboard side of the aircraft. Both men sat in pressurized, air-conditioned comfort, equipped with upward ejection seats.

The bomber had a crew of two. The pilot sat beneath a fighter-style “bubble” canopy. The second crewmember, a navigator/radio operator, sat below and behind the pilot and had only a small observation window on the starboard side of the aircraft. Both men sat in pressurized, air-conditioned comfort, equipped with upward ejection seats.

 

Bicycle Landing Gear

Martin XB-51 landing

An XB-51 on landing approach, flaps, bicycle landing gear and wingtip outriggers deployed. U.S. Air Force photo

The bomber employed a bicycle-type landing gear, which had earlier been evaluated on a Martin XB-26H Marauder, nicknamed “Middle River Stump Jumper.” The XB-51 incorporated a rotary weapons bay that enabled it to deliver bombs while flying at high speed. Capable of 645 mph at sea level in level flight, the XB-51 would have been able to run away from most fighters of its era.

The XB-51 incorporated a rotary weapons bay that enabled it to deliver bombs while flying at high speed. Capable of 645 mph at sea level in level flight, the XB-51 would have been able to run away from most fighters of its era.

The XB-51 combined a radically thin wing with a bulky, muscular fuselage almost entirely lacking in aerodynamic grace and propelled virtually by the sheer force of its three powerplants. The wing was the first variable-incidence wing fitted on a bomber, enabling the pilot to adjust the angle at which the leading edge met the air. The XB-51 was radical, but practical. Maintenance people liked it. Pilots loved it. Designers saw so much versatility in the XB-51 they even proposed a seaplane version, which was never built – not such an unlikely idea considering that Martin was working on a planned family of jet-powered flying boats.

XB-51 cockpit and coal hole

The XB-51 pilot had great visibility through a fighter-type cockpit canopy, but the bombardier less so, with only a small window on the right side of the fuselage, where he sat below and behind the pilot. U.S. Air Force photo

The U.S. Air Force developed many experimental warplanes in the 1940s and 1950s, but the service was dead serious about the XB-51 and wanted it to make up several Tactical Air Command bomber squadrons. The second of the two prototypes (46-686) flew on April 17, 1950. Tests were carried out at Muroc airfield in California, re-named Edwards Air Force Base (AFB) in 1951.

The second aircraft was used in gunnery, rocket, and bombing trials and in successful “live” tests of the rotary bomb dispensing mechanism. Test pilot Maj. Charles E. “Chuck” Yeager once flew five realistic bombing missions in the XB-51 in under three hours while Tibbs, Yeager, Russell E. “Russ” Schleeh and other pilots reported that every feature of the XB-51 – from its T-tail to its eight 20 mm cannon in the nose – proved easy to operate and effective under simulated combat conditions.

When Hollywood came to Edwards AFB to shoot the movie Toward the Unknown with Holden and Lloyd Bridges, the XB-51 was dressed up to portray the fictitious “Gilbert XF-120” fighter and even had the fictitious name painted on its nose.

An early photo of the XB-51 shows the bomber not with Yeager (who seems never to have been photographed with it) but with film actor William Holden. When Hollywood came to Edwards AFB to shoot the movie Toward the Unknown with Holden and Lloyd Bridges, the XB-51 was dressed up to portray the fictitious “Gilbert XF-120” fighter and even had the fictitious name painted on its nose.

The XB-51 was unmistakably a prime candidate for a production order, but it never happened. Author Walter J. Boyne, former director of the National Air and Space Museum, once set forth to find out why. Boyne learned that a significant number of the U.S. government’s records on the XB-51 had gone missing. Boyne believes that there existed an irrational U.S. Air Force prejudice against Martin-designed aircraft, although not Martin-built products.

XB-51 showing wing incidence marks, JATO

A view of an XB-51 from the rear quarter shows the JATO bottles mounted to the rear fuselage as well as the incidence markings on the fuselage just behind the trailing edge of the variable incidence wing. U.S. Air Force photo

Test pilot Tibbs claims that thinking was “too conservative” in an era when every operational bomber was driven by propellers. The Korean War likely had a major influence, with range and loiter time becoming major considerations. The XB-51 was inferior in both categories to the aircraft the Air Force ultimately chose.

Sadly, neither of the two XB-51 airframes has survived to be enjoyed by museum goers today, with both lost in crashes attributed to pilot error. It is not unreasonable to suppose that there might have been hundreds of these fine aircraft, had the U.S. Air Force not rejected it for reasons never made clear. After all, the aircraft that was chosen in place of the XB-51 fared well in service indeed. Instead of manufacturing its own design, Martin found itself license-building a light bomber of foreign design that was less innovative but no less effective.

That “foreign” machine was the B-57 Canberra.

 

Martin XB-51 Specifications

  • Armament: Eight 20mm cannon in the nose and up to 10,400 pounds of bombs (or eight 5-inch High Velocity Aerial Rockets carried internally)
  • Engines: Three General Electric J47-GE-13 turbojets of 5,200 pounds thrust each
  • Maximum speed: 645 mph
  • Cruising speed: 532 mph
  • Range: 1,600 miles
  • Service ceiling: 40,500 ft
  • Span: 53 ft 1 in
  • Length: 85 ft 1 in
  • Height: 17 ft 4 in
  • Weight: 59,467 pounds gross
  • Crew: Two
  • Serial numbers: 46-685 and 46-686

By

Robert F. Dorr is an author, U.S. Air Force veteran, and retired American diplomat who...

  • Hi Robert,

    The XB-51 certainly should have been built, but given the Air Force deliberate campaign to vilify the Martin B-26, it wasn’t too surprising.
    The USAF bomber mafia dominated USAF generally ignored the tactical end of things when ever it could, as demonstrated by how few B-45′s it built.
    The XB-51′s swept wings weren’t that unusual, given the B-47, F-86, etc.

    Rather than admit it was the Air Force’s mistaken policy of sending B-26′s produced ahead of schedule to pilots with no training in twin engine aircraft, then refusing to admit it had killed them not the B-26, because the pilots who manned 2 bomber groups before the USAAF did that had no problems (book is available at Amazon) before SOMEBODY (no one’s ever found out who) made the regulation that all twin engine trainers were reserved only for the 4 engined bombers, not twin engined aircraft on December 8, 1941 that Hap Arnold signed.
    Flight Journal has the USAAF regulation order and number in an old article several years ago on the B-26 and it’s bad reputation.

    I suspect the Canberra/B-57 was more amenable to modification than the XB-51, but we’ll never know.

    Lyonking

  • Kenneth Kavula

    Definitely one of the best pieces I have ever read respecting the XB-51, and a resounding “AMEN” to Lyonking’s comment about the USAF-Martin brouhaha. Does anyone have any data regarding the internal arrangement of the -51? I’ve been looking with no joy for a number of years. K Kavula