Lioré et Olivier LeO 45
Lioré-et-Olivier LeO 45 was a French medium bomber that was used during and after the Second World War. It had been designed for the new Armée de l'air as a modern medium bomber capable of performing independent strategic operations, unlike the majority of previous French bombers.
The LeO 45 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, which made its maiden flight on 16 January 1937, had been fitted two 1,100 hp Hispano-Suiza engines. The LeO 45 had been developed as a modern and advanced bomber for the new Armée de l'air, which had gained its independence on 1 April 1933. Introduced to operational service in 1938, it was a very effective and capable bomber.
As only a handful of aircraft had been introduced into the French Air Force by the outbreak of the Second World War, the LeO 45 was too late to provide a substantial contribution during the Battle of France in the face of an invasion by Nazi Germany. As a result of the Armistice of 22 June 1940, the type continued to be manufactured and operated by occupied Vichy France as Free France forces operated the aircraft. The LeO 45 participated in combat missions throughout the remainder of the war and continued to be used for some time after its end by the post-war French Air Force. The last examples in active service were retired in September 1957.
Development
Background
On 1 April 1933, the French Air Force was officially recognised as an independent military service. In accordance with this new position, in addition to cooperating with land and naval operations, there was a newfound emphasis on the ability to execute independent strategic-level operations. It was quickly determined that existing aircraft would be incapable of performing the latter role to a sufficient degree, thus a modernisation programme, known as Plan I, was promptly initiated. This plan called for 1,010 modern combat aircraft suitable for first-line service to be provisioned by late 1936; out of these, 350 were to be bombers, further divided into 210 medium bombers, 120 twin-engined heavy bombers, and 20 four-engined heavy bombers.While numerous multi-seat aircraft, such as the Bloch MB.200, Bloch MB.210, Amiot 143, Lioré et Olivier LeO 257, Potez 540 and Farman F.221, were procured between 1933 and 1935, many of these originated from technical programmes which had predated the recognition of the service's independence and thus had not been developed to meet its new strategic ambitions. In addition, several shortcomings was quickly identified with many of these aircraft, including inadequate defensive armaments, being too slow and relatively unmanoeuvrable, and thus too vulnerable for viable sorties over hostile territory. Accordingly, the need for their replacement was apparent. It was out of the Plan I modernisation programme that the requirements for an advanced medium bomber were formulated for the new service.
On 17 November 1934, the Service Technique Aéronautique released the B5 heavy bomber programme and made approaches to all of the main French aircraft manufacturers. Various requirements were specifying a five-seat bomber with a top speed of 400 km/h at 4,000 m and a combat radius of 700 km carrying an internally carried payload of 1,200 kg. The new bombers would have to be capable of operating at day and night, while carrying defensive turrets, the forward unit being fixed to the fuselage while the ventral position was to be flexible. In late 1935, Amiot, Latecoere, Romano, Lioré et Olivier and Bloch presented the mock-ups of their submissions.
During the latter half of 1935, the Service Technique Aéronautique decided to enact several changes to some of the specified requirements; these included the revision of the rearward and lower turret arrangements and the crew reduced from five to four, as it was thought that the co-pilot could also serve as a navigator and bomb-aimer. To reflect the crew change, the programme was re-designated from B5 to B4. In September 1936, the envisioned bomber's requirements were revised to account for development of 1,000 hp -class engines; accordingly, the cruise speed raised to 470 km/h. It was at this point that Plan I was cancelled in favour of Plan II, which called for an even larger and more capable bomber force to be provisioned for the French Air Force; under this plan, it was envisioned that a total of 41 units each equipped with 12 B4-type aircraft would be established.
Amongst the numerous manufacturers to submit proposals for the B4 programme was 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, providing aircraft such as its LeO 20 and other lesser-known biplane bombers. This had earned the company a reputation for reliability, but were had been relatively traditional and conservative in terms of their design. The 1934 programme was put under Pierre Mercier, a younger engineer who had expertise in cantilever airframes. It was out of Mercier's work that a new design emerged, which was soon christened as the LeO 45.
Flight testing
On 16 January 1937, the LeO 45-01 prototype, powered by a pair of Hispano-Suiza 14AA-6 / Hispano-Suiza 14AA-7 radial engines producing 1,120 hp each, flew for the first time. Despite problems experienced with longitudinal instability, engine reliability and overheating, the aircraft demonstrated excellent overall performance. During flight testing, the prototype was capable of reaching 480 km/h at 4000 m and of attaining 624 km/h in a shallow dive.In September 1937, the prototype was delivered to the Centre d'Essais de Matériels Aériens at Villacoublay for the type's official evaluation. On 6 December 1937, it was involved in a forced landing incident as a result of both engines having failed simultaneously in mid-flight; the pilot, Jean Doumerc, was able to land without sustaining any damage. The prototype was promptly returned to the manufacturer for adjustments prior to the resumption of evaluation flights. In July 1938, the prototype, fitted with the new Mercier-designed cowlings, attained 500 km/h. The earlier instability issues were partially addressed via the adoption of redesigned twin fins and rudders on the tail unit.
Various issues with the troublesome Hispano-Suiza engines had been experienced and this resulted in several changes being made to the prototype, such as the adoption of broader, more efficient air intakes for the oil coolers, which in turn reduced instances of engine overheating. On 29 August 1938, it was decided to replace the existing Hispano-Suiza engines by Gnome-Rhône 14N 20/21 engines, which were capable of producing 1,030 hp each; as a result of these changes, the aircraft was re-designated as LeO 451-01. Following the completion of the re-engining, the flight test programme was resumed, running from 21 October 1938 to February 1939. In spite of the new engines being slightly less powerful, the speed and general performance of the prototype remained relatively unchanged.
Production
In May 1937, the Armée de l'Air placed an initial pre-production order for a pair of LeO 450 aircraft, one being fitted with Hispano-Suiza AA 06/07 engines and the other with Hispano-Suiza 14 AA 12/13 engines. On 29 November 1937, an order for 20 production machines was received, the first being specified for delivery in May 1938. On 26 March 1938, a further 20 LeO 450 was ordered in line with the French Air Ministry's newly adopted Plan V, which called for the reequipping of 22 bomber units. In order to meet French ambitions, which was viewed as requiring 449 frontline aircraft and 185 reserve aircraft, by April 1940, official contracts were also issued for Bloch 131 and Amiot 350 aircraft as stop gap measures, along with another 100 LeO 45 aircraft being ordered on 15 June 1938.On 21 October 1938, it was specified that all production LeO 45 aircraft were to be equipped with Gnome-Rhône engines in place of the originally envisioned Hispano-Suiza powerplants. However, as a result of this demand, there was considerable delays in the delivery of the first production aircraft. During late November 1938, the first LeO 45 was on static display at the Paris Air Show; it performed its maiden flight on 24 March 1939. On 28 April 1939, the second production aircraft conducted its first flight. Further production issues were encountered as a result of supply issues with Gnome-Rhone engines and associated propellers; as a result, it was decided to fit the type with Ratier-built propellers instead, which reduced the maximum speed from 500 km/h to 470 km/h.
During early 1939, as it was becoming apparent that the international situation was worsening and that the European powers were increasingly likely to be involved in a major war, the Armée de l'Air explicitly requested of SNCASE that the company would not delay production by enacting any further improvements; the mandate was issued in spite of known teething troubles with the type that were far from cleared. At the same time, the requirements of Plan V were elevated to 1188 B4 bombers, 396 of these being first line aircraft. Accordingly, on 20 February 1939, a tentative order for 100 aircraft was confirmed; on 18 April 1939, a large order for a further 480 LeO 45 bombers was received.
By September 1939, the eve of the outbreak of the Second World War, there were a total of 749 LeO 45 aircraft on order; this included several different variants of the type, such as an envisioned high altitude model, aircraft outfitted with American-built Wright GR-2600-A5B engines, and 12 aircraft which had been ordered for the Greek Air Force. At the same point, there were only 10 LeO 451 bombers in French Air Force service, while another 22 were in the process of being delivered. It was at this point that a flurry of additional wartime production orders were issued, calling for hundreds more aircraft to be manufactured, amounting to around 1,549 LeO 45 aircraft of various models. While additional productions lines were established in order to produce more aircraft, much of this extra capacity did not arrive until mere months prior to the catastrophic Battle of France, thus making their contribution to the course of the war minimal.