During World War II, the Douglas Aircraft Company manufactured thousands of its A-20 Havoc and A-26 Invader medium bomber/close air support aircraft from its factories in Long Beach, Santa Monica and El Segundo, and the A-20 Havoc became widely used by the US Army Air Force and Royal Air Force (which referred to the A-20 as the Boston), while the A-26 Invader (redesignated B-26 after 1948) saw action in the last years of World War II and most notably in the Korean War, Bay of Pigs invasion, Vietnam War, Biafra conflict, and the war against the Simba rebels in the Congo. In the last two years of World War II, however, Douglas also came with two one-of-a-kind bomber aircraft, an unorthodox pusher-engine long-range medium bomber and one of America's first-ever jet bomber designs. Because the XB-42 and XB-43 shared the same design except in the powerplant, I've opted to dedicate this post to discussing the design, development, and testing of these two prototype bomber aircraft created from the manufacturing halls Santa Monica.
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| Models of the XB-42 Mixmaster and XB-43 Jetmaster at the Lyon Air Museum (photographed by me in November 2021) |
In early 1943, Douglas investigated the feasibility of a twin-engine close air support aircraft able to carry 2,000 lb (907 kg) of bombs over a combat radius of 2,000 miles (3,219 km) at speeds exceeding 400 miles per hour (643 km/h), and its designer, Ed Burton, believed that these goals could be attained by having the engines buried in the fuselage and coming up with a completely clean wing. By late April, the Model 459 design emerged which had a bug-eye canopy configuration created by a pair of bubble canopies, two Allison V-1710 liquid-cooled V-cylinder piston engines buried inside the fuselage behind the pilot's cabin that drove two three-bladed counter-rotating propellers in the extreme tail cone via five lengths of shafting, a ventral vertical stabilizer to prevent the propellers from hitting the ground during nose-high takeoffs and landings, a tricycle undercarriage, and an extremely clean laminar-flow wing at the middle fuselage. Armament comprised six 0.50-caliber machine guns, of which four were housed in two remote-controlled turrets on the trailing edges of the wings between the ailerons and flap, and two were mounted in fixed positions on the sides of the fuselage, but also 8,000 lb (3,628 kg) of bombs. A crew of three was carried, of which the pilot and co-pilot/gunner sat under the twin bubble canopies and the navigator/bombardier sat in a transparent nose. The Model 459 was submitted to the US Army Air Force on June 15, and ten days later two prototypes (serial numbers 43-50224/50225) and a static test airframe were ordered under the designation XA-42. A full-scale mock-up was inspected in September, but by this time the Army Air Force regarded the XA-42 as more of a high-speed long-range bomber than a pure close air support plane, and on November 26 the designation of the Model 459 was changed to XB-42, while the name Mixmaster was applied to the XB-42 because the propellers of the aircraft were reminiscent of the Sunbeam Mixmaster electric kitchen mixer.
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| Top: First XB-42 Mixmaster prototype (43-50224) in flight Bottom left: XB-42A during taxi tests Bottom right: Second XB-42 prototype (43-50225) |
The first XB-42 prototype was completed in early 1944, only several months after the XB-42 prototype contract had been signed. It made its first flight at Palm Springs Army Air Field on May 6, with test pilot Bob Brush at the controls, and the second XB-42 flew for the first time on August 1. Performance of the XB-42 during initial flight testing was judged to be outstanding, with speed within a percent of that predicted, and the range and climb rate surpassing expectations. However, the twin bubble canopies were found to inhibit poor communication between the pilot and co-pilot/gunner, so the second XB-42 was later fitted with a more conventional cockpit canopy. In the meantime, test flights of the XB-42 revealed a number of problems, including excessive yaw, propeller vibration, and poor engine cooling, and cruciform nature of the XB-42's horizontal and vertical stabilizers required careful handling during taxiing, take-off, and landing due to limited ground clearance. In any case, the XB-42 was not ordered into production, largely because the onset of the jet age ensured that the XB-42 would be last wartime American piston-engine bomber to reach the design phase, but the XB-42 prototypes continued to fly after the end of the World War II for a number of test purposes. The second XB-42 prototype set a new transcontinental speed record in early December 1945 when it flew from Long Beach, California, to Bolling Army Air Field (renamed Bolling AFB in 1948) in Washington, D.C., at a speed of 433 mph (698 km/h). However, on December 16, it was destroyed in a crash at Oxon Hill, Maryland, while on a routine test flight out of Bolling Army Air Field due to a landing gear extension problem, failure of the left engine, and cooling problems with the right engine, and the crew bailed out of the aircraft safely. In the meantime, the first XB-42 prototype was fitted with two auxiliary Westinghouse J30 turbojets under the wings in accordance with an earlier proposal by Douglas to use this aircraft as a turbojet testbed and redesignated XB-42A, making its first flight in this iteration on May 27, 1947. All guns were removed during the conversion process and the XB-42A attained a speed of 488 mph (785 km/h) during its flight testing at Muroc Air Force Base (later Edwards AFB), making a total of 22 flights until late 1947, when it suffered damage to the lower vertical and horizontal stabilizers and rudder after a hard landing. The XB-42A was repaired but was never flew again, and the US Air Force officially removed the aircraft from its inventory on June 30, 1949. The XB-42A was transferred to the collection of the National Air and Space Museum in Washington, D.C. shortly afterwards, only to be later donated to the National Air Museum Storage Facility in Park Ridge, Illinois years later. In April 1959, the fuselage of the XB-42A was moved to storage at the Paul Garber restoration facility at Suitland, Maryland, where it languished until 2010 when it was transferred to the USAF Museum at Wright-Patterson Air Force Base in Dayton, Ohio, for eventual restoration.
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| Left: First XB-43 Jetmaster prototype (44-61508) taking off for a test flight at Muroc Army Air Field Right: Color photo of the second XB-43 prototype (44-61509) taking off. The second XB-43 was also called the YB-43 |
Even before the XB-42's first flight, in October 1943 Douglas proposed a jet-powered derivative of the XB-42 Mixmaster with two Allison J35 turbojets in the forward fuselage bays, the XB-43 Jetmaster. Besides jet propulsion, the XB-43 differed from the XB-42 in eliminating the ventral vertical stabilizer, ensuring better ground clearance during taxiing and takeoff, but also a larger upper vertical stabilizer to enable adequate longitudinal stability. Two XB-43 prototypes (serial numbers 44-61508/61509) were ordered on March 31, 1944, and to save time and money Douglas decided to use the sole XB-42 static test airframe on order in the construction of the first XB-43 prototype, while the second XB-43 was manufactured from scratch. However, the slowdown in aircraft manufacturing in southern California following the end of World War II and delays in delivery of the J35s due to teething troubles during bench tests meant that the first XB-43 did not fly until May 17, 1946, when it became the first-ever US jet bomber to fly. Months before the XB-43's first flight Douglas discussed with the US Army Air Force plans for an initial production run of 50 B-43s, and it also submitted a proposal to make preparations for the manufacture of 200 aircraft a month. The production aircraft would have a conventional cockpit canopy and a tail turret with two 0.50-caliber machine guns, and two variants were contemplated, the bomber version with a transparent nose and a 6,000 lb (2,722 kg) bombload, and an attack aircraft variant armed with sixteen forward-firing 0.50-caliber machine guns with an unglazed nose and thirty-five 5-inch rockets. However, production plans were axed on August 18, 1945, because the US Army Air Force was now concentrating on its first generation of multi-engine jet bomber, including the North American B-45 Tornado, Convair XB-46, Boeing B-47 Stratojet, Martin XB-48, and Northrop YB-49. The second XB-43, meanwhile, was completed with a conventional canopy and a plywood nose cover, and first flew on May 15, 1947, by which it bore the designation YB-43. Nearly a year into flight tests, in April 1948 the YB-43 (nicknamed "Versatile II" by US Air Force personnel) became one of several testbeds for the General Electric J47 turbojet when it had one of the J35s replaced by a J47. The first Jetmaster prototype was eventually cannibalized to provide spare parts for the YB-43 after that aircraft was damaged during a flight in February 1951, and it was eventually destroyed during target practice at Edwards Air Force Base. The YB-43 continued to fly until December 1953, when it was retired and put in storage at the Paul Garber facility of the National Air and Space Museum the following year pending restoration work. Like the first XB-42 prototype, the YB-43 was transferred to the USAF Museum at Wright-Patterson Air Force Base in Dayton, Ohio, for eventual restoration in 2010.
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| Artist's conception of the Douglas DC-8 (aka Model 1004) airliner derivative of the XB-42 Mixmaster fast bomber |
As a side note, in late 1945 Douglas proposed an airliner derivative of the XB-42, the DC-8 (not to be confused with the later DC-8 jet airliner), to replace the venerable DC-3 on short- and medium-range routes. Known by the company designation Model 1004, the DC-8 would have been 77 feet 8 in (23.67 meters) long with a wingspan of 110 feet 2 in (33.58 meters), a height of 26 feet 9.75 in (8.17 meters), an empty weight of 24,415 lb (11,074 kg), a gross weight of 40,000 lb (18,144 kg), and seating capacity for 40 to 48 passengers in a pressurized cabin. The V-1710s would be located below and immediately behind the cockpit, driving counter-rotating propellers via driveshafts under the cabin floor (which were also proposed for the Douglas Cloudster II prototype light aircraft). The engine arrangement for this aircraft at first glance would have been an unfamiliar spectacle for airport personnel and passengers alike, but was estimated to reduce drag by 30% and eliminate problems associated with controlling the aircraft with one engine out, while cabin access would have been made through single portside door on the sides of the rear fuselage. Despite its estimated performance being greater than that of conventional twin-engine airliners, the DC-8 project itself was shelved in favor of the less risky Convair Model 240 and Martin 2-0-2 airliners due to high complexity and development costs combined with projected high operating costs.
Although the XB-42 and XB-43 remained at the prototype stage only, the Jetmaster itself provided a wealth of aerodynamic data that would be applied to the development of the first American multi-engine jet bombers, including the B-45 and B-47, effectively making the US the first of the major victorious Allies to get a jet bomber into the sky. Moreover, by a stroke of luck, the first XB-42 and the second XB-43 were spared from the breaker's torch and made their way to museums in preparation for restoration to static display, with the hope that someday visitors to the Air Force Museum in Dayton, Ohio will get a rare glimpse of the first-ever US jet bomber in person.
References:
Boyne, W., 1973. "The First, The Last, And The Only: The Douglas XB-42/42A/43". Airpower 3 (5): 13–14.
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