The SPAD S.VII was the first of a series of highly successful biplane fighter aircraft produced by Société Pour L'Aviation et ses Dérivés (SPAD) during the First World War. Like its successors, the S.VII was renowned as a sturdy and rugged aircraft with good climbing and diving characteristics. It was also a stable gun platform, although pilots used to the more manoeuvrable Nieuport fighters found it heavy on the controls. It was flown by a number of the famous aces, such as France's Georges Guynemer, Italy's Francesco Baracca and Australia's Alexander Pentland.
Design and development
Performance in early aircraft designs was largely dependent on engines. In February 1915, Swiss designer Marc Birkigt had created an overhead cam aviation powerplant based on his Hispano-Suiza V8 automobile engine, resulting in a 330 lb engine capable of producing 140 hp at 1,400 rpm. Further refinement of the engine brought the power to 150 hp by July 1915. Given the engine's potential, French officials ordered that production be set up as soon as possible and called upon aircraft designers to create a new high-performance fighter around the engine, called the Hispano-Suiza 8A.
Louis Béchereau, chief designer of the SPAD company, quickly produced drawings for a prototype fighter equipped with the new engine. The SPAD V was basically a smaller version of the SPAD S.A two-seat "pulpit fighter", although as a single seater it dispensed with the so-called "pulpit" which carried the observer in front of the propeller.
One of many common design feature between the new SPAD V and the S.A-2 was the use of a single-bay biplane wing with additional light struts mounted mid-bay at the point of junction of the flying and landing wires. This design simplified rigging and reduced flying wire vibration, reducing drag. The fuselage was of the standard construction for the time, consisting of a wooden frame covered with fabric, while the forward part was covered with metal sheeting. A .303 Vickers machine gun was installed above the engine, synchronized to fire through the propeller arc. The prototype was also fitted with a large spinner, to be abandoned later.
SPAD test pilot Bequet flew the SPAD V for the first time in April 1916. Flight testing revealed excellent maximum speed (192 km/h, 119 mph) and climb rate (4.5 min to 2,000 m or 6,500 ft). The airframe's sound construction also enabled remarkable diving performance. In comparison, the Nieuport sesquiplane fighters that equipped a large part of the fighter units could occasionally shed their lower wings in a steep power-on dive, a result of the single-spar lower wing design. The combination of high speed and good diving ability promised to give Allied pilots the initiative to engage or leave combat. If the new fighter was a rugged and stable shooting platform, some pilots regretted its lack of maneuverability, especially when compared to lighter types such as the Nieuport 17.
In the face of such performance, an initial production contract was made on 10 May 1916, calling for 268 machines, to be designated SPAD VII C.1 (C.1, from avion de chasse in French, indicating the aircraft was a fighter, while the 1 indicated it was a single seater).
Early production aircraft suffered from a number of defects which took some time to solve and limited the delivery rate to units. While a few SPADs arrived to frontline units as early as August 1916, large numbers only began to appear in the first months of 1917. In hot weather, the engine was prone to overheating. In cold weather, the engine would not warm up. Various field modifications were used to counter the problem, including cutting extra holes in the metal sheeting to provide more air flow over the engine. On the production lines, the cowling opening was first enlarged and eventually redesigned with vertical shutters to solve both problems. The engine mount also proved too weak and reinforcements were designed to counter that. Early production aircraft also had two ammunition drums: one for normal rounds and the other for empty ones. This system was prone to jamming and was only solved when Prideaux disintegrating ammo links were introduced.
With the initial teething problems solved, several subcontractors began producing the SPAD VII under license in order to supply frontline units with the fighter. The subcontractors were the firms Grémont, Janoir, Kellner et Fils, de Marçay, Société d'Etudes Aéronautiques, Régy and Sommer. It was not, however, until February 1917 that the initial batch of 268 aircraft was delivered. In early 1917, an improved version of the engine developing 180 hp, the Hispano-Suiza 8Ab, was made available. This new powerplant provided the SPAD VII with even better performance, the top speed increasing from 192 km/h (119 mph) to 208 km/h (129 mph). The new engine gradually became the standard powerplant for the SPAD VII and by April 1917, all newly produced aircraft were equipped with it.
Variants and experiments
Numerous experiments were made with new equipment or engines in the hope of further improving the SPAD VII's performance. A Renault V8 150 hp powerplant was tested but required some major redesign and the resulting performance was not considered worthwhile. A supercharged Hispano-Suiza engine was also tested, and also failed to improve performance by any significant degree. Different wing profiles appear to have been tested but were not incorporated in production models. One field modification was applied in Czechoslovakia after the war when the undercarriage struts of one S.VII were faired over in an attempt to reduce drag to increase maximum speed.
Very early in the development of the S.VII, the British RFC and RNAS had shown an interest in the new fighter. An initial order for 30 aircraft was made but difficulties in early production were such that the delivery rate was very low, production being barely enough for French units alone. As the RFC was encountering an increasing opposition over the Front, measures were taken to set up production of the S.VII in the United Kingdom. Blériot & SPAD Aircraft Works and Mann, Egerton & Co. Ltd. were supplied with plans and sample aircraft and ordered to initiate production as soon as possible.
The first British-built S.VII was flown and tested in April 1917, and the first aircraft was reported to have performance equal to that of French models. There were however differences between the two types. The British were worried about the light armament of the S.VII: most German fighters were now carrying two guns and experiments were made to fit an extra machine gun on the S.VII. One aircraft was fitted with a Lewis machine gun on the top wing and tested at Martlesham Heath in May 1917, while front line units also made field modifications with Foster mounts as used on the S.E.5. The resulting drop in performance was considered too drastic for the installation to become standard, and most SPAD S.VIIs continued to fly with a single Vickers.
Other distinguishing features of the British-built S.VIIs included a gun fairing and a solid cowling access panel. The gun fairing partially covered the gun and extended rearwards, replacing the windshield. This, however, seriously limited pilot vision to the front and, although retained on training aircraft, it was ordered removed on aircraft destined for front line units in France. The bulged engine access panel located under the exhaust pipe on British models was made of a solid sheet of metal, in place of the louvered panel fitted on French production models. Some British SPADs were also fitted with small spinners on the prop hub.
It quickly became apparent that the British production lines of the S.VII had lower quality standards than their French counterparts, resulting in aircraft with degraded performances and handling. Poor fabric sewing, fragile tailskids and radiators of insufficient effectiveness plagued the British SPADs. Photographic evidence shows that a number of British SPADs had the cylinder banks fairings, or even the entire upper engine cowling, cut out to compensate for the ill-functioning radiators. Most British S.VIIs were used for training purposes, front line units being equipped with French-built models. After some 220 aircraft had been produced, British production of the S.VII was halted in favour of better British types that were becoming available.
In a similar fashion, Russia produced approximately 100 S.VIIs under license in 1917 at the Dux factory in Moscow, with engines supplied by France. It would appear the engines were often used and/or of lower quality, and that Dux used lower-grade material in building the airframes. This combination of extra weight and weaker powerplant resulted in aircraft with significantly reduced performance.
The total number of aircraft produced seems uncertain, sources varying from 3,825 to some 5,600 SPAD S.VIIs built in France, 220 in the United Kingdom and approximately 100 in Russia.
The SPAD XII began as a development of the S.VII, equipped with a 37 mm cannon. However, it underwent a major redesign and was a distinct type rather than a variant of the S.VII. the S.VII can be distinguished from both the S.XII and the later and larger S.XIII by having unraked cabane struts, connecting the top wing to the fuselage, as well as differences in armament.