Consolidated B-24 Liberator XB-24

The XB-24 grew out of a 1938 request by the US Army Air Corps for Consolidated to set up a second production line building Boeing's B-17 under licence. After touring the Seattle plant, company president Reuben H. Fleet replied that Consolidated could build a better, more modern bomber of its own. In January 1939, under Specification C-212 and with General Henry "Hap" Arnold behind the invitation, the Air Corps formally asked Consolidated for a design study for a bomber with more range, more speed and a higher ceiling than the B-17. The effort sat under "Project A", the Air Corps' ambition for an intercontinental bomber, and the specification was worded so that Consolidated's design would win.

The design team, led by Isaac Laddon, put range first. The Model 32 paired David R. Davis's high-aspect-ratio wing, already proven on the Model 31 flying boat, with that aircraft's twin-fin tail and an all-new fuselage built around two bomb bays, each the size of the B-17's. It also introduced a tricycle undercarriage, still unusual on a bomber. Compared with the B-17, the wing spanned six feet more yet had 25% less area, cutting drag at the price of a wing loading 35% higher.

On 30 March 1939 the Air Corps contracted for an additional wooden mock-up, a wind-tunnel model and a single aircraft, the XB-24, on condition that it be ready before the end of the year. Orders arrived before the prototype had flown: on 27 April 1939, less than thirty days later, seven pre-production YB-24s were ordered, and in all the Air Corps asked for 36 aircraft, France for 120 and Britain for 164.

Consolidated beat the deadline by two days. On 29 December 1939 the company's chief test pilot, William Ballantine "Bill" Wheatley, took the XB-24, Army serial 39-556, off from Lindbergh Field, San Diego's municipal airport. George Newman flew as co-pilot, with Jack Kline and Bob Keith as flight engineers, and the flight lasted just seventeen minutes. Photographs from January 1940 show the prototype still without the Air Corps' red, white and blue fin flash and with a partial civil registration, "NX2–", on the right rudder.

The aircraft was laid out for a crew of seven. It was 19.43 m long, with a span of 33.53 m, a height of 5.69 m and a wing area of 97.36 m². Empty weight was about 12,473 kg; maximum weight is given as 20,910 kg by one source and 21,047 kg by another. Power came from four mechanically supercharged Pratt & Whitney R-1830-33 Twin Wasp fourteen-cylinder radials, rated at 1,200 hp for take-off and 1,000 hp at 4,400 m, driving three-bladed Curtiss Electric variable-pitch propellers inside round cowlings. Sources describe a design load of eight 1,000 lb bombs and defensive armament of 12.7 mm and 7.62 mm machine guns, while another mentions only provision for a few hand-held 7.62 mm guns on the prototype.

Testing confirmed the range, about 4,586 km with 1,133 kg of bombs and 7,563 km on a ferry flight, but not the speed: the XB-24 reached 439 km/h at 4,572 m, well short of the contract figure, with a service ceiling of 9,601 m and a cruising speed of 299 km/h. The pre-production YB-24s differed only in their de-icing boots, a higher gross weight and propeller spinners that were later removed.

A newly funded conversion of the prototype itself addressed the shortfall. The R-1830-33s gave way to turbo-supercharged R-1830-41s able to hold 1,200 hp up to 7,620 m; the round cowlings were replaced by the elliptical ones that became a Liberator hallmark; the engine slots were deleted, the tailplane span was widened by 61 cm, the pitot-static probes moved from the wings to the fuselage, and self-sealing tanks and armour were added. Redesignated XB-24B and re-serialled 39-680, it reached 499 km/h. These changes became standard from the B-24C onwards.

Consolidated kept the aircraft, which passed to Consolidated-Vultee after the merger of 17 March 1943. In 1944 it was converted into a company transport, with large cabin windows fitted with Venetian blinds. It was scrapped at Brookley Field, Mobile, Alabama, on 20 June 1946. The Liberator name, given by the Royal Air Force and later adopted by the US Army, ended up covering more than eighteen thousand aircraft, more than any other American type of the Second World War.