Lioré et Olivier LeO 451
| Lioré et Olivier LeO 451 | |
|---|---|
 |
|
| Role | Medium bomber |
| Manufacturer | SNCASE, SNCAO |
| First flight | 15 January 1937 |
| Introduction | 1938 |
| Retired | 1957 |
| Primary user | French Air Force |
| Produced | 1938–1942 |
| Number built | 561 |
Lioré-et-Olivier LeO 45 was a French medium bomber used during World War II. It was a low-wing monoplane, all-metal in construction, equipped with a retractable undercarriage and powered by two 1,060 hp Gnome-Rhône 14N engines. The prototype had two 1,100 hp Hispano-Suiza engines. It was a very effective bomber but it appeared too late to give any substantial contribution to the war effort. Although designed before World War II, it remained in service until September 1957.
The LeO 451 was conceived as an advanced medium bomber for the new French Air Force. In contrast to its predecessors, which relied on machine guns for protection, the emphasis was placed on high-speed high-altitude cruise. The expectation was that high speed would force enemy fighters into tail-chase attacks and to that effect the aircraft was designed with a rear-firing cannon with an unobstructed rear arc of fire thanks to the twin rudders.
The Service Technique Aéronautique released the initial requirements on 17 November 1934, specifying a five-seat bomber with a top speed of 400 km/h (215 knots, 250 mph) at 4,000 m (13,125 ft) and a combat radius of 700 km (435 mi) carrying a payload of 1,200 kg (2,650 lb). In September 1936, the requirements were revised to account for development of 1,000 hp (746 kW)-class engines, with cruise speed raised to 470 km/h (255 knots, 290 mph) and crew reduced to four. Plan II called for 984 of the resulting B4-class bombers and numerous manufacturers submitted a proposal, including Latécoère, Amiot with its Amiot 351 and Lioré et Olivier, which was to be soon nationalized as part of the SNCASE.
Lioré et Olivier was a long-time supplier to the Armée de l'air with its LeO 20 and other lesser-known biplane bombers, which had earned a reputation for reliability but were traditional in design. The 1934 programme was put under Pierre Mercier, a younger engineer with expertise in cantilever airframes. Mercier's work resulted in a design christened LeO 45, which was a twin-engined aircraft of all-metal construction, with a monocoque fuselage. Because of the speed requirements of the programme, a lot of effort was spent in reducing parasitic drag. Wings were equipped with slotted flaps and small bomb bays in the wing roots in addition to the main fuselage bomb bay, to minimise the fuselage cross-section. The wing structure was designed and patented by Mercier, in which the inner part used two spars, with enough room between them for a 200 kg-class bomb and large self-sealing fuel tanks; the spars did not continue to the wing-tip but made way for a box-type structure.
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