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The SPAD S.A (also called S.A.L.) was a French two seat tractor biplane of 1915 that saw some service with France and Russia in the early stages of the First World War in the fighter and reconnaissance roles. It was somewhat unusual in having a buried engine, mounted between the pilot and observer. ==Design and development== The SPAD A.1 prototype was the first aircraft produced by SPAD following its reorganization from the pre-war Deperdussin company. The chief designer, Louis Béchereau had been involved in designing that firm's successful monocoque racing monoplanes, and many design details were carried over from the Deperdussins. In addition to its pilot, the aircraft was designed to carry an observer in a streamlined nacelle ahead of the propeller. This configuration attempted to combine the advantages of the tractor and the pusher types, giving the observer had a clear field of view to the front and sides without the drag penalty of the typical pusher. However, this made communication between the pilot and the observer nearly impossible, the pulpit (as it was known in English) or basket (as it was known in Russian) vibrated badly and in multiple cases, parted company from the rest of the aircraft while in flight. Like many pushers, it also put the observer at risk of being crushed in even a relatively mild crash or "nose-over". A British evaluation of the type suggested "it would be expensive in observers if flown by indifferent pilots".〔Bruce, 1996, p.2〕 While not originally designed explicitly as a gunner's position,〔Bruce, 1996, p.1〕 early combat experience had shown a need for forward-firing machine guns yet mechanisms to allow a gun to fire through the propeller were not yet available and the observer's nacelle on the S.A-1 represented a temporary solution. On all but the earliest prototypes and the SPAD S.G, the nacelle was fitted with a light machine gun on a flexible tubular mount, and incorporated air intakes on its sides and underside to redirect air towards the Le Rhône rotary engine which was otherwise masked by the nacelle. Starting the engine required the prop being swung from alongside the fuselage. The nacelle was hinged at the bottom to provide some access to the engine for maintenance but this was insufficient and additional sliding panels were added to the sides of the fuselage. A mesh screen behind the observer was intended to prevent propeller strikes. Aside from the unorthodox configuration, the aircraft was of standard wood and fabric construction for the period. The wings had a single bay but to prevent the long flying and landing wires from vibrating in flight, light vertical struts were added mid-bay to brace the wires, giving the aircraft the appearance of a two-bay biplane. The SPAD S.A.2 was an improved version of the S.A.1 which first flew on 21 May 1915. The S.A-2's 110 hp engine frequently suffered from overheating so the design reverted back to the S.A-1s 80 hp Le Rhone in the S.A-4, with the same engine being retrofitted to some S.A-2s.〔Somer, 1990, p.18〕 Other changes included dispensing with the lower ailerons on the narrower chord lower wings and a larger tailplane to eliminate the need for a bungee to help with trimming.〔Bruce, 1996, p.4〕 Russian examples had minor structural differences to the top wing, incorporating a separate center section rather than each wing panel being joined along the centerline.〔Bruce, 1996, p.4〕 In spite of its lack of success, the design brought valuable experience to Béchereau and his team. The successful S.VII fighter had a lot in common with the A series and aside from the pulpit being dispensed with, the rotary was replaced with a V8, the tailplane reverted to the delta shape used on the prototype, stringers were added to the fuselage, the rigid trailing edges of the A series was replaced with wire, rib spacing was reduced and proportions adjusted slightly. Most other design details were retained. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「The SPAD S.A (also called S.A.L.) was a French two seat tractor biplane of 1915 that saw some service with France and Russia in the early stages of the First World War in the fighter and reconnaissance roles. It was somewhat unusual in having a buried engine, mounted between the pilot and observer.==Design and development==The SPAD A.1 prototype was the first aircraft produced by SPAD following its reorganization from the pre-war Deperdussin company. The chief designer, Louis Béchereau had been involved in designing that firm's successful monocoque racing monoplanes, and many design details were carried over from the Deperdussins. In addition to its pilot, the aircraft was designed to carry an observer in a streamlined nacelle ahead of the propeller. This configuration attempted to combine the advantages of the tractor and the pusher types, giving the observer had a clear field of view to the front and sides without the drag penalty of the typical pusher. However, this made communication between the pilot and the observer nearly impossible, the pulpit (as it was known in English) or basket (as it was known in Russian) vibrated badly and in multiple cases, parted company from the rest of the aircraft while in flight. Like many pushers, it also put the observer at risk of being crushed in even a relatively mild crash or "nose-over". A British evaluation of the type suggested "it would be expensive in observers if flown by indifferent pilots".Bruce, 1996, p.2While not originally designed explicitly as a gunner's position,Bruce, 1996, p.1 early combat experience had shown a need for forward-firing machine guns yet mechanisms to allow a gun to fire through the propeller were not yet available and the observer's nacelle on the S.A-1 represented a temporary solution. On all but the earliest prototypes and the SPAD S.G, the nacelle was fitted with a light machine gun on a flexible tubular mount, and incorporated air intakes on its sides and underside to redirect air towards the Le Rhône rotary engine which was otherwise masked by the nacelle. Starting the engine required the prop being swung from alongside the fuselage. The nacelle was hinged at the bottom to provide some access to the engine for maintenance but this was insufficient and additional sliding panels were added to the sides of the fuselage. A mesh screen behind the observer was intended to prevent propeller strikes.Aside from the unorthodox configuration, the aircraft was of standard wood and fabric construction for the period. The wings had a single bay but to prevent the long flying and landing wires from vibrating in flight, light vertical struts were added mid-bay to brace the wires, giving the aircraft the appearance of a two-bay biplane.The SPAD S.A.2 was an improved version of the S.A.1 which first flew on 21 May 1915. The S.A-2's 110 hp engine frequently suffered from overheating so the design reverted back to the S.A-1s 80 hp Le Rhone in the S.A-4, with the same engine being retrofitted to some S.A-2s.Somer, 1990, p.18 Other changes included dispensing with the lower ailerons on the narrower chord lower wings and a larger tailplane to eliminate the need for a bungee to help with trimming.Bruce, 1996, p.4 Russian examples had minor structural differences to the top wing, incorporating a separate center section rather than each wing panel being joined along the centerline.Bruce, 1996, p.4In spite of its lack of success, the design brought valuable experience to Béchereau and his team.The successful S.VII fighter had a lot in common with the A series and aside from the pulpit being dispensed with, the rotary was replaced with a V8, the tailplane reverted to the delta shape used on the prototype, stringers were added to the fuselage, the rigid trailing edges of the A series was replaced with wire, rib spacing was reduced and proportions adjusted slightly. Most other design details were retained.」の詳細全文を読む スポンサード リンク
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