The Douglas XB-19 (XVLR-2) was the largest US military aircraft completed before the US entry into the Second World War and provided valuable data for the development of later heavy bombers such as the Boeing B-29 Superfortress.
The aircraft was one product of a series of USAAC experiments with large aircraft. 'Project D' officially began on 5 February 1935, and the Air Corps entered into talks with Douglas and Sikorsky. By June 1935 a timetable was in place - preliminary design work was to begin on 31 July 1935, detailed design work on 31 January 1936 and the aircraft was to be ready on 31 March 1938. However this failed to take into account the limited funds available and none of these deadlines would be met.
In October 1935 the first contract was issued. This covered the design work, production of a mock-up and testing of the wing centre section, engine nacelles and undercarriage. The aircraft was to be powered by four 1,600hp Allison XV-3420-1 liquid-cooled engines. There was an option to produce a prototype. The contract was approved on either 18 October or 31 October 1935.
Sikorsky and Douglas both submitted mock-ups and the Air Corps chose Douglas as the winner. The new aircraft was designated as the XBLR-2 (eXperimental Bomber Long Range).
Very little progress was made between December 1935 and November 1937, mainly due to a lack of money. The Allison engines were replaced with 2,000hp Wright R-3350 air-cooled radial engines. At the same time the Air Corps lend Douglas a Douglas OA-4A which was used to test a tricycle undercarriage.
On 29 September 1936 the option to have a prototype constructed was taken, but the funding wasn't authorised until 8 March 1938. At about the same time the aircraft was redesignated as the XB-19.
The XB-19 was a low-winged monoplane with a thick wing. The wing was tapered, with a straight trailing edge and swept back leading edge. The four engines were carried in nacelles that were only slightly taller than the wings, and jutted out from the leading edge. The wing was the largest yet built, with a massive span of 212ft and two 45ft ailerons on each side. The main wheels were mounted behind the inner nacelles, the nose wheel below the pilot's cockpit. The 8ft main tires retracted almost flush into the wing. The aircraft had a massive single tail fin.
The XB-19 was heavily armed. It was designed to carry a 37mm and .30in machine gun in a powered nose turret, and the same guns in a powered top upper turret. Single .50in machine guns were placed in a powered rear dome, two waist positions, one belly fairing and the tail, and 0.30in guns were carried on either side of the bombardier and on either side of the fuselage below the tail.
The B-19 could carry 10,350 US gallons of fuel in its built in tanks and another 824 gallons in auxiliary tanks in the bomb bay. It could carry a massive 37,100lb payload, with some bombs carried on ten external bomb ranks under the wings.
The massive aircraft had a normal crew of sixteen, but there was also space for two extra flight mechanics and a six-man relief crew in a compartment given eight seats and six bunks. The aircraft also carried a full galley capable of being used to prepare cooked meals.
On 30 August 1938 Douglas actually recommended that the entire project should be cancelled, on the grounds that the three years of delays had made it obsolete. The Air Corps refused to allow this, and work continued on the aircraft. In 1940 it was removed from the top secret list.
The aircraft was finally completed in the spring of 1941. Taxing tests began on 6 May 1941, and revealed brake problems and problems with engine back fires. The maiden flight was thus delayed until 27 June 1941, when the aircraft finally took to the air, six years after work first began. This was an unusually lengthy maiden flight, lasting for 55 minutes and saw the aircraft fly from Clover Field, Santa Monica to March Field.
The B-19 was the largest aircraft to be completed for the USAAF before the US entry into the war, and that record wasn't lost until 1946. It dwarfed the B-17E, which entered service in the Autumn of 1941. The B-17 had a wingspan of 103ft 9in, a maximum loaded weight of 53,000lb and 4,800hp of power, compared to 212ft and 162,000lb on the B-19!
The Air Force accepted the B-19 in October 1941. Its last four flight tests came after the Japanese attack on Pearl Harbor, and were flow with the guns carried and armed. Early in 1942 the aircraft was moved east to Wright Field, just in case of Japanese attack. Douglas must have been rather pleased to have seen the back of the B-19, as it had cost them $5,400,000 but they had only been paid $1,400,064 by the Air Force!
The B-19 underwent a series of extensive tests during the first eighteen months of its service life. These provided a great deal of information that was used during the construction of the Boeing B-29 and Convair B-36, but eventually newer test aircraft became available. In 1943 the B-19 was given four 2,600hp Allison V-3420-11 liquid cooled engines, which increased its top speed by 40mph and its ceiling to 39,000ft. The modified aircraft was redesignated as the XB-19A and was used as a transport aircraft. The aircraft made its last flight on 16 August 1946 to Davis-Monthan Field and was scrapped in 1949.
The Air Force verdict on the B-19 was that although there were no fundamental flaws with the design, it was too large and too heavy for its engines. This played a part in the decision to make the B-29 a smaller aircraft, despite the availability of more powerful engines. The B-29 ended up with a wingspan of 141ft 2in (down 50ft), a maximum weight of 135,000lb (down from 162,000lb) and 8,800hp power from its four engines, a 10% increase on the 8,000hp of the original B-19.
Engine: Four Wright R-3350-5 Cyclones
Power: 2,000hp each
Length: 132ft 4in
Empty weight: 84,431lb
Loaded weight: 140,000lb
Maximum weight: 162,000lb
Max speed: 224mph
Cruising speed: 135mph
Service ceiling: 23,000ft
Normal Range: 5,200 miles
Range: 7,710 miles with 2,500lb payload
Bomb load: 16,000lb internally plus 20,000lb on external racks