The memoirs of Janusz Meissner, the famous Polish pilot and writer, contain the following lines: “Some time ago the stench of castor oil began to drift through the air of the service hangar.
This was where repairs were made to a French SPAD-VII. Its 140-hp geared engine was lubricated by this rare substance, which made one think of a pharmacy. The aircraft was captured from the Austrians and was being restored to flying condition in Polish workshops. After repairs it was to be test-flown by a pilot who had won the Iron Cross while serving with a German fighter squadron. Curious how the fates of men and machines interweave sometimes in most unusual ways”
The author of the passage was recalling an event that occurred at Lewandówka airfield in Lvov. The name Spad was familiar to all pilots who participated in the Great War. It was closely related to the names of two distinguished aviation pioneers, Armand Deperdussin and Louis Blériot.
Armand Deperdussin was fascinated with aviation. In 1911, in the town of Grenelle, he set up a company he named Société des Aéroplanes Deperdussin2. In 1912 the name changed to Société Provisoire des Aéroplanes Deperdussin (SPAD) and the company moved to Bois-Sulain. With the help of talented engineer Louis Béchereau, hired by Armand Deperdussin as technical director, the company produced a variety of successful aircraft designs. They were branded Deperdussin. Béchereau’s design team included André Herbemont and a Dutchman, Frederic Koolhoven. In summer 1913 Armand Deperdussin was arrested on charges of fraud and his company went bankrupt. In August 1914 the company’s assets were bought up by Louis Charles Joseph Blériot, with Béchereau and Herbemont as shareholders. The company was renamed as Societe Pour l’Aviation et ses Derivees (SPAD) and the acronym became the aircraft brand name.
Louis Béchereau’s designs
In the early stage of the war the main design effort focused on arming aircraft with a forward firing machine gun. An alternative to a gun firing through the propeller disc was sought. One such solution was to mount the engine aft of the cockpit in a so-called ‘pusher’ arrangement. Some “pushers”, like the French Farmans, Voisins or the British Airco DH.2 saw combat. The SPAD company took a different approach to the problem, designing a two-seat tractor biplane with the gunner/observer’s nacelle mounted ahead of the propeller. Construction details of this configuration were patented as Brevet d’Invention No. 498.338, with a supplementary 1’ere Addition No. 22.088 to the original patent submitted on 7th June 1915. Thus the Spad S.A1 was created, a biplane of wooden construction, powered by a 59 kW (80 hp) nine-cylinder, air-cooled Le Rhône 9C rotary engine. The fuselage ‘box’ was made of wooden framework and had a rectangular cross-section. The fuselage upper decking was profiled to have a rounded shape. The front section of the fuselage, which included the pilot’s cockpit, was covered with aluminum sheets and plywood, while the section aft of the pilot’s cockpit was covered with fabric. The engine cowling was also made of aluminum sheets. The tailfin and tailplanes were tapered, in a fashion applied to later SPADs3. The nacelle that housed the gunner/observer was of wooden construction. It was supported from below by wooden V-shaped struts and pivoted on lugs at the lower ends of the undercarriage legs.
The wings were of wooden construction, with two rectangular spars and slightly rounded tips. Cutouts were provided in the central leading edge of the upper and lower wings to make room for the propeller blades, while cutouts in the wings’ trailing edge mid-section offered the pilot better visibility over the top of the upper wing and below the aircraft. The wing bay construction used the company’s patented Brevet d’Invention No. 488.191 dated to 4th July 1915. It was designed to eliminate excessive vibration4 in the wing-bay bracing wires. It was discovered that vibrations were generated at the intersection points of the wires (which were steel cables). Hence, a set of interplane struts was fitted, the struts being interconnected fore and aft at their midpoints. An additional benefit of this solution was that it further strengthened the wing bays. The ailerons were attached to the upper wings only and were operated by a rod and bell crank system. Control rods ran from the base of the control column, through the lower wings to external bell cranks located at the base of the rear outboard interplane struts. The bell cranks were connected to vertical push rods, which ran along the rear interplane strut and linked to the actuating levers of the ailerons. The undercarriage comprised two main wheels and a tailskid.
The Spad A.1 made its maiden flight on 21st May 19155. Its performance was notably better than contemporary pusher designs and the French Air Force duly placed an order for the aircraft. Serial-production Spad S.A1s featured additional, mesh-covered intakes, six being mounted on either side of the gunner/observer’s nacelle, in order to provide cooling air for the engine. A new tubular mounting for a flexible machine gun was devised. The upper support struts were detachable allowing the nacelle to be lowered for engine maintenance. The observer was protected from the propeller – spinning right behind his back – by a wire mesh guard. A transparent panel in the floor of the observer’s nacelle was provided. The tailfin was enlarged and tapered. A total of 11 Spad A.1s were manufactured for the Aviation Militaire6.
Serial-production Spad S.A2s featured a reduced wingspan and wing area, as well as a redesigned engine cooling system with additional air intakes on either side of the fuselage. A shield to deflect exhaust fumes was also installed. Of the 99 aircraft produced, 42 were delivered to the French Air Force, while 57 were exported to Russia. The Spad S.A4 was a development version, basically the S.A2 airframe coupled to a Le Rhône 9J rotary engine rated at 81 kW (110 hp)7. Ten aircraft were sold to Russia. The Spad S.A4 first flew in February 1916. The Spad S.A3 was a dual-controlled version with a gun fitted to both cockpits. Interestingly, the two crewmembers could switch roles and hence increase the field of fire. Only one prototype of the S.A3 version, designated S.40, was built. The Spad S.A5 was an S.A4 airframe powered by a 75 kW (100 hp) air-cooled, V-shaped Renault 8 engine.
The S.A2 and A4 versions were not popular with French airmen. Pilots claimed that they were difficult to handle, while the observers had serious doubts about the front nacelle they were supposed to fly in, especially the reliability of the hinged mounting points. The unsatisfactory layout of the Spad S.A2 was best summarized by a British report dated to early 1916:
“In this machine the passenger is slung in a small fuselage in front of a tractor propeller. This arrangement is considered to be unnecessarily dangerous and the objects attained as regards arc of fire do not justify it. All the Spad machines are of similar type and are considered to be of no interest in their present form”.
The Spad A2s and A4s were popular in Russia though, where they remained in active service until 1921. One Russian crew – Ju.A. Bratolubov and A.A. Kazakov – even scored an aerial victory in one of them.
In early 1916 the Spad S.A2 was used as the basis of an experimental single-seater design armed with one, or alternatively four, fixed machine guns mounted in a cupola. In April 1916 an official British aircraft review mentioned a single-seat Spad armed with a single Hotchkiss mitrailleuse d’Infanterie machine gun with a belt of 1000 rounds mounted in a gondola in front of the propeller. This was the Spad S.G2, a prototype fighter. It was lighter, had a smaller wingspan, and a wing area of about 18.4 square meters. At 2000 meters it reached the speed of 161 kph and climbed to that altitude in seven minutes and 15 seconds. However, early 1916 saw the rise of the German Fokker Eindekker armed with a synchronized machine gun, while the very manoeuvrable and fast Nieuport 11C1 “Bébé” reigned in the French Air Force. Compared with these, the Spad S.G2 seemed a dead end in the evolution of combat aircraft designs.
Louis Béchereau strove to construct a similar aircraft, a single-seat fighter armed with a single machine gun firing through the propeller arc. Power was to be provided by a 96 kW (130 hp) rotary engine. Three variants8 , the SL and SK biplanes and the SJ monoplane, were envisaged and respective prototypes were built, but none was actually flown. They all used a revolutionary method of constructing fuselages, first used in the Deperdussin Monocoque, a record-breaking racing aircraft – the light and strong ‘monocoque’ fuselage. Still, it took more than a well-constructed airframe to make a successful aircraft design. What Louis Béchereau needed was a new powerplant for his aircraft.
Swiss engineer Marc Birkigt, who in 1904 was contracted by a Spanish automotive and engineering company Hispano-Suiza9, is credited with designing the first ‘cast block’ engine. Instead of machining separate steel cylinders, Birkigt’s design used cast aluminum blocks, into which thin steel liners were fitted. This made the engine more rugged and, at the same time, lighter. Birkigt’s engine had eight cylinders in two banks of four, arranged at a 90° angle in a V-type configuration. In 1914 he began to modify the engine for aircraft use. The new aero engine underwent trials in February 1915. It weighed 150 kg and delivered 103 kW (140 hp) at 1,400 rpm. Birkigt also designed a synchronizer gear driven by the engine camshaft. In May 1915 the French Military Mission got interested in the new product of the Spanish company. Two sample engines were brought from Barcelona to France, and in July 1915 they were tested at Chalais-Meudon. As a result of the tests, an order for 50 engines was placed in Spain and an offer was made to begin their production at the Hispano-Suiza factory in Bois-Colombes. The new engines also caught the attention of the British, who ordered them in August 1915.
In autumn 1915 Louis Béchereau, with only a mock-up of the Hispano-Suiza V8 engine at hand, began to design his new fighter around it. It was to be a tractor biplane with its wing bay construction taken from the Spad S.A2 and a wingspan of 7.62 m. Initially it received the company designation Biplan-SH110 . The wings had neither dihedral, sweep nor stagger. The ailerons were attached to the upper wing and were operated by the same system that had functioned successfully on the Spad S.A2. The lower wing had a slightly reduced span. In order to improve visibility from the cockpit, the customary cutout was provided in the mid-section of the upper wing, and parts of the lower wing at the trailing edge adjacent to the fuselage were also cut out in similar fashion. The front section of the carefully streamlined fuselage housed the engine, mounted behind an octagonal radiator. The engine cylinder banks protruded out of the otherwise smooth outline of the fuselage, and were covered with teardrop-shaped fairings. The Biplan-SH1 featured a large conical spinner with a central opening to allow cooling air into the engine, and the radiator and its cowling were circular to blend with it. The control surfaces and the landing gear were also modelled after the Spad S.A2.
In April 1916, when a Hispano-Suiza 8Aa engine rated at 111 kW (150 hp) was obtained, a prototype Spa. V was built and first flown11. It was armed with a single synchronized Vickers machine gun. The propeller spinner was discarded. Exhaust fumes were ejected from the engine cylinders via short exhaust stubs. During factory tests the Spa. V attained a top speed of 200 kph. Official trials, carried out in April and May at Villacoublay, proved the overall sturdiness of the construction, which allowed diving speeds of up to 300 kph to be reached. Although the level flight speed and climb rate were inferior to those of the Nieuport XVIIC1 or the German Halberstadt D.II, 268 aircraft were ordered to be built. The SFA12 designated them Spa. VIIC1 (Spad S.VII.C113 ). In case deliveries of Hispano-Suiza engines failed an alternative powerplant was sought, and to this end one Spad was experimentally fitted with a Renault engine rated at 109 kW (150 hp). The engine was also a V-8, but had its cylinder banks angled at 60° (as opposed to 90° on the Hispano-Suiza). Its installation required considerable modification to the aircraft’s nose and cowling.
Serial-production machines were slightly different from the prototype Spad V14 . Long exhaust pipes ran along either side of the fuselage and terminated just to the rear of the pilot’s cockpit. By the end of September 1916 the SPAD company had delivered only 24 aircraft (instead of the expected 50) to the French Air Force. This delay was caused by the relatively small production capacity of the plant, as well as an inadequate supply of raw materials, an issue not taken into consideration when the order was placed. In August 1916, the first three Spad S.VII.C1s were allotted to: Lt. Armand Pinsard of Escadrille N26 (s/n S.122), Sgt. Paul Sauvage (s/n S.112) and Lt. Georges Guynemer (s/n S.113), the latter two of Escadrille N315.
Problems continued with the delivery of radiators, which proved a major ‘bottleneck’ during the production of Spads. Initially, the radiators weren’t even standardized. The plants producing them experienced shortages of raw materials (mainly copper and brass), which hindered production and caused maintenance problems with the aircraft already in service. In March 1917 the radiator was finally standardized: the octagonal Bonfils et Laval radiator was chosen, having been found most resistant to engine vibration.
In frontline service the Spads’ cooling system demonstrated two major shortcomings. At high ambient temperatures they quickly overheated; when subjected to low temperatures, they tended to get excessively cold. The overheating problem was tackled ‘in the field’ by drilling extra cooling holes in the cowling and removing the engine side panels. The overcooling problem was, in turn, addressed by limiting the active surface of the radiators, various solutions being tried (even a solid metal cover). Eventually, regulating the cooling airflow by means of radiator shutters proved to be the most efficient solution. After experimenting with many different arrangements, a set of seven vertical shutter bars became standard.
In November 1916 the STAé16 suggested the Spad VII’s wings should be modified by reducing their span and increasing their chord, to give a bigger wing area of 19 m². However, since the performance of the modified aircraft was only slightly improved17, further tests were discontinued in December 1916. Another modification ordered by the STAé was a ‘flatter’ wing, which used the standard geometry. The ‘flat wing’ was tested in February 1917 but there are no indications that it ever made it to serial production.
By March 1917 several modifications were introduced in response to operational service experience. The most important were the replacement of the aluminum fuselage bracing components with steel alternatives, some strengthening of the engine bearers and the internal strengthening of the fuselage framework by means of steel cables. In summer 1917 Spad S.VII.C1 was modified for the ground-attack role. Some aircraft were fitted with racks for carrying 10 kg (22 lb) Anilite bombs. The racks were mounted on the rear undercarriage legs.
The Spad S.VII.C1 powered by the Hispano-Suiza 8Aa proved to be slower than its main adversaries, the German Albatrosses and Fokkers. Hence, in the spring 1917 Birkigt modified the Hispano-Suiza 8Aa engine, increasing its compression ratio from 4.7:1 to 5.3:1. This increased power output to 133 kW (180 hp) at 1,800 rpm. The upgraded engine was rushed into production under the designation ‘Hispano-Suiza 8Ab’. The increase in revolutions required a decrease in propeller pitch. By April 1917, the Hispano-Suiza 8Ab had become the standard engine on all production Spad VIIs. The first pilot to fly the re-engined Spad S.VII.C1 in combat was Georges Guynemer, who scored 19 aerial victories in it.
The production of Spad S.VII.C1s increased only slowly. Instead of the expected 800, only 268 examples were delivered to the French Air Force by 25th February 1917. Since it was planned to withdraw all the sesquiplane Nieuports (leaving only the Nieuport 28C1) from frontline units by the end of 1917, something had to be done about the poor production output of Spads. They were in urgent demand not only by the French, but also by other Allies (Great Britain, Italy, Russia and Belgium). There were two solutions: expand the already existing factories and start license production. In France, several companies were contracted to produce Spads: Bleriot Aeronautique, Les Ateliers d’Aviation L. Janoir, Kellner et ses Fils, Construction Aeronautique Edmond de Marçay, L’Atelier de Construction d’Apareils d’Aviation Roger Sommer, Les Ateliers de Construction Regy Freres, Societe d’Etudes Aeronautiques (SEA) and Gremont. Abroad, license manufacture was started in Russia by the Duks (Aktsionyernoye Obschestovo Duks) company in Moscow, and in Great Britain by Mann, Egerton & Co. Ltd from Norwich and L. Blériot (Aeronautics) Ltd Brooklands (later renamed Blériot & Spad Aircraft Works). Modifications and improvements incorporated into the basic design during the subsequent production included enlarged ailerons and wing area. Some Spad VIIs were equipped with a photographic camera of 26 cm focal length for reconnaissance duties. The camera was mounted on the port side of the fuselage aft of the pilot’s cockpit in a specially designed recess. It was accessible through a removable plywood panel. The ‘recce’ Spads were marked with PHOTO lettering on either side of their fuselages.
Like Nieuports, Spad VIIs were modified to combat enemy airships and observation balloons. For this purpose they were armed with Le Prieur unguided rocket missiles, fired from tubular launchers attached to the mid-bay struts. To prevent damage from the rocket exhaust gases, metal sheathing was used to protect part of the lower wing area under the strut. Spads produced in Great Britain were slightly different from their counterparts manufactured in France. Noteworthy differences included the installation of un-louvered engine cowling panels (in place of the original design’s louvered side panels) and a hood-like fairing over the breech of the Vickers machine gun in front of the pilot’s cockpit (in Spads produced by Blériot & Spad at Addlestone). The cumbersome fairing was expected to make it easier for the pilot to clear jams, as it was intended to serve as a windshield. However, the fairing was not transparent and significantly impaired the pilot’s view forward; it was therefore usually removed. The Addlestone plant attempted to re-engine the Spad with a 147 kW (200 hp) Hispano-Suiza engine, and to augment its onboard armament by installing twin machine guns. Nevertheless, tests were abandoned in June 1917, most probably due to the fact that the Spad S.XIII.C1 was already coming down the pipeline. Another British initiative was to mate a Spad S.VII to a 147 kW (200 hp) Wolseley Viper engine. In general, the performance of British-built Spads was found inferior to that of the French-built aircraft. Many aspects contributed to this situation, mainly related to production technology and the materials used. For example, the Spads produced by Mann, Egerton & Co. Ltd were 20 kph slower than the French Spads.
Pilots who flew the Spad S.VII.C1 in combat generally considered it a good aircraft, very rugged, with decent manoeuvrability, but flawed in its weak armament. By summer 1916 a single machine gun was a serious drawback. Two machine guns, which at that time were becoming standard on German fighters, offered substantially greater firepower. The British mounted an additional Lewis machine gun on top of the upper wings of their Spads (slightly offset to starboard) firing over the propeller arc. This modification augmented the firepower, but at the cost of increased drag. The total production output of Spad VIIs is estimated at 3820 aircraft, including approximately 3500 built in France, 220 in Great Britain and 100 more in Russia.