Ranking second to the Sopwith Camel as the most successful British fighter of World War I, the S.E.5 and improved S.E.5a were the finest warplanes designed at the Royal Aircraft Factory in its period of existence between 1912 and 1918. The primary attributes of the S.E.5 and S.E.5a were their ease of handling in the air combined with adequate if not exceptional agility, good performance especially in terms of speed and climb, structural sturdiness, and excellent stability as gun platforms. This last helped to offset the idiosyncratic armament arrangement of two machine guns, disposed not as what had by this time become the standard arrangement of two 0.303 in (7.7 mm) Vickers fixed forward-firing weapons on the upper part of the forward fuselage with synchronisation equipment (as used in the Camel and most other fighters of the period), but rather as a single synchronised Vickers gun firing through the disc swept by the propeller and one 0.303 in (7.7 mm) Lewis gun on a quadrant mounting above the upper-wing centre section to fire directly forward over the disc swept by the propeller, but also capable of being pulled back to fire obliquely forward and upward into the belly of a higher-flying aeroplane in the fashion devised and made popular by Captain Albert Ball, one of the finest solo rather than patrol aces of World War I.
The stimulus for the design of the S.E.5 can be traced to the emergence in 1915 of the Hispano-Suiza 8 water-cooled V-8 engine designed by an expatriate Swiss engineer, Marc Birkigt. This was a water-cooled unit with monobloc cast aluminium cylinder blocks, and for a weight of 445 lb (202 kg) delivered 150 hp (112 kW) with the promise of considerably more power in its fully developed versions. This was impressive performance by the standards of the day, and in August 1915 the British authorities ordered 50 examples of the engine (deliveries beginning almost exactly one year later) and started negotiations for the licensed manufacture of the engine in the UK. The negotiations were protracted as they involved Hispano-Suiza’s parent company in the neutral Spanish city of Barcelona, and as a result British production of the Hispano-Suiza 8 did not begin until a time early in 1916. At that time, however, the French lent or gave at least one example of the Hispano-Suiza 8 engine to the Royal Flying Corps, and the availability of this unit for test and examination allowed the design team of the Royal Aircraft Factory to start planning two single-seat fighters with this engine as their powerplant.
The first of these was a neat and workmanlike tractor biplane, the S.E.5 (Scout Experimental 5), while the second was the F.E.10 (Fighting Experimental 10), which was an extraordinarily retrograde biplane design with the pilot carried in a ‘pulpit’ ahead of the tractor engine installation in the fashion of the observer’s position in the B.E.9 experimental biplane and SPAD A.2 and A.4 fighters. The F.E.10 was soon dropped from the Royal Aircraft Factory’s plans, allowing work on the S.E.5 to continue in the hands of a design team headed by Henry P. Folland with John Kenworthy and Major Frank W. Goodden as his chief assistants. The intention of the design team from the start of work in the summer of 1916 was the creation of a fighter that could be flown safely by pilots with only limited experience, which is all that trainees of the period were given, and for this reason the S.E.5 was planned with a degree of inherent stability, although nothing like the completely inherent stability of aircraft such as the Royal Aircraft Factory B.E.2 series that had proved so vulnerable to the attentions of German fighters in the period of the ‘Fokker scourge’ from the spring of 1915.
At the time that the S.E.5 was being planned, the British lacked an effective gun synchronisation system, so the armament planned for the S.E.5 was a single 0.303 in (7.7 mm) Lewis machine gun located between the cylinder banks of the Hispano-Suiza 8 engine to fire through the hollow propeller shaft, which was raised well above the line of the crankshaft by gearing.
The resulting aeroplane was an equal-span biplane of wooden construction covered mainly with fabric except on the sides of the forward fuselage and around the engine, where plywood and light alloy respectively were used. The core of the structure was the fuselage, which was of rectangular section with a rounded upper decking and carried, from front to rear, the powerplant, fuel and oil tanks, pilot’s semi-open cockpit with a high windscreen trailed by modest overhead and side glazing, and tail unit. This last comprised single horizontal and vertical surfaces, the former including a wire-braced tailplane that was adjustable in flight and carried plain elevators, and the latter including a wire-braced small ventral fin and wire-braced large upper fin carrying a plain rudder that was hinged at its lower end to the vertical knife-edge in which the fuselage terminated.
The staggered wing cellule was based on essentially similar upper and lower wings that were of constant thickness and chord to their strongly raked tips and carried wire-connected ailerons on the outboard ends of their trailing edges. The dihedralled panels of the lower wing extended from short centre-section stubs that extended from the lower longerons and incorporated a cut-out in the trailing edge of each root, while the dihedralled panels of the upper wing extended from a flat centre section that was carried above the fuselage by four cabane struts, incorporated a substantial cut-out in its trailing edge over the cockpit, and carried the engine’s gravity-feed fuel tank in a fairing above its port side. The upper and lower wings were separated on each side by a single set of parallel interplane struts, and the whole wing cellule was braced with the normal arrangement of twin flying and single landing wires.
The airframe was completed by the landing gear, which was of the fixed tailskid type with a steerable tailskid hinged to the ventral fin and controlled by movement of the rudder, and a main unit of the through-axle type. This latter was based on a two-wheel axle bungee-bound to the aerofoil-faired spreader separating the closed ends of two wire-braced V-type struts extending downward and outward from the lower longerons.
The powerplant was based on one Hispano-Suiza 8A engine rated at 150 hp (112 kW) and driving a two-blade wooden propeller of the tractor type: this engine was installed under a light alloy cowling that left the cylinder heads exposed, discharged its spent gases outward via the single forward exhausts in the two manifolds, and was cooled by a frontal radiator.
One of the first Hispano-Suiza 8Aa engines was installed in the first of three S.E.5 prototypes, which recorded its maiden flight on 22 November 1916. Early trials confirmed that the aeroplane handled well and possessed good performance, but this initial prototype crashed in January 1917 as a result of structural failure in the wings, Goodden being killed. Production of the S.E.5 had already been set in motion, but was now halted as an investigation of the crash revealed the need for less acutely raked tips, improved strut/spar joints and stronger lift bracing. The first aircraft were too far advanced for the revised wing tips to be introduced, so these were completed with reinforced rear spars to support the original type of longer-span tip, but later aircraft were completed with the reduced-span wing cellule and a revised gravity-feed tank incorporated entirely within the contours of the upper-wing centre section. These were the only major changes required to turn the S.E.5 into an extremely strong structure that soon acquired an excellent reputation once the type had entered service.
Production of the S.E.5 by the Royal Aircraft Factory totalled 58 aircraft (an initial batch of 24 followed by a follow-on batch of 34 out of an order for 50 whose other units were completed to S.E.5a standard) to a standard that included the powerplant of one Hispano-Suiza 8Aa engine rated at 150 hp (112 kW) and built by either Hispano-Suiza or Wolseley, span of 27 ft 11 in (8.51 m) with an area of 249.80 sq ft (23.21 m²) in the first aircraft reducing to a span of 26 ft 7.5 in (8.115 m) with area of 245.80 sq ft (22.83 m²) in later aircraft, length of 20 ft 11 in (6.375 m), height of 9 ft 5 in (2.87 m), empty weight of 1,399 lb (635 kg), maximum take-off weight of 1,935 lb (878 kg) in early aircraft reducing to 1,892 lb (858 kg) in later aircraft, maximum speed of 106 kt (122 mph; 196 km/h) at 3,000 ft (915 m) declining to 85 kt (98 mph; 158 km/h) at 15,000 ft (4570 m), climb to 6,500 ft (1830 m) in 8 minutes 0 seconds and to 10,000 ft (3050 m) in 13 minutes 42 seconds, service ceiling of 19,000 ft (5790 m), and endurance of 2 hours 30 minutes.
By the time the S.E.5 was being prepared for service, the Constantinesco synchronisation system had been almost perfected, and the first S.E.5 aircraft were delivered from March 1917 with the armament fit that became standard for the S.E.5 and S.E.5a, namely one 0.303 in (7.7 mm) Vickers machine gun in a synchronised installation in the upper port part of the forward fuselage, and one 0.303 in (7.7 mm) Lewis gun on a Foster mounting over the upper-wing centre section. It was perhaps fortunate that the S.E.5 had the unsynchronised Lewis gun in addition to the synchronised Vickers gun, for the hydraulically operated Constantinesco gear gave considerable trouble before its teething problems were solved and the system became completely reliable.
The S.E.5 entered service with No. 56 Squadron in March 1917, and the unit moved to France early in the following month. No. 56 Squadron was not yet ready for operations, however, for the pilots were decidedly unhappy with the semi-enclosed cockpit glazing that interfered with the forward field of vision and was therefore replaced by a conventional flat windscreen of smaller size, and were also unhappy with the two guns’ parallel lines of fire, which were turned into converging lines of fire by the simple expedient of raising the rear of the Foster mounting so that the fire of the two guns met about 50 yards (46 m) ahead of the fighter. With these changes No. 56 Squadron became operational later in April 1917, and was later joined by Nos 24, 40, 60 and 85 Squadrons. These five units soon began to reveal the formidable nature of the S.E.5 as a front-line type, using the new fighter’s steadiness as a gun platform to tackle and destroy all types of German warplane and using their strength either to survive combat damage or undertake a high-speed escape dive.
Even as the S.E.5 was being readied for production, Hispano-Suiza was finalising an improved variant of the basic engine as the Hispano-Suiza 8B rated at 200 hp (149 kW) and driving its propeller via reduction gearing that also raised the thrust line and made the propeller turn in the opposite direction to that of the Hispano-Suiza 8A. The new engine was tested in the third prototype, which recorded its maiden flight on 12 January 1917 and in its evaluation revealed a considerable improvement in performance over that of the standard S.E.5 with the 150 hp (112 kW) engine. The uprated engine was therefore adopted for the S.E.5a main production model, which thus differed from the S.E.5 primarily in its revised powerplant in a deeper nose installation with a shutter-controlled radiator and two long pipes exhausting the engine’s spent gases to the rear of the cockpit, but secondarily in a slightly revised structure including shortened rear spars that reduced the rake of the wing tips in a fashion that also appeared on the last production examples of the S.E.5. The pilot’s comfort was enhanced by the addition of a head rest that was often removed by service pilots. Many pilots did not like the long exhausts and therefore had them trimmed to a point just to the rear of the engine, where short angled-out sections were welded.
The first S.E.5a fighters were delivered to No. 56 Squadron in June 1917, and the type then replaced the S.E.5 over the following months as the improved model entered service with an increasing number of units on the Western Front: these eventually comprised Nos 1, 24, 29, 32, 40, 41, 56, 60, 68 (later No. 2 Squadron of the Australian Flying Corps), 74, 84, 85, 92 and 94 Squadrons. The S.E.5a was also operated by Nos 37, 50, 61 and 143 Squadrons for home defence, Nos 111 and 145 Squadrons in Palestine, Nos 17, 47 and 150 Squadrons in Macedonia, and A Flight of No. 72 Squadron in Mesopotamia. The other operational user of the S.E.5a was the US Air Service, whose 25th and 148th Aero Squadrons flew 38 examples of the type in France. The S.E.5a was additionally operated by the Schools of Aerial Fighting at Freiston, Marske, Sedgeford and Turnberry, and by the Australian Flying Corps Depot at Minchinhampton.
Production of the S.E.5a lasted to the end of World War I and totalled 5,302 aircraft delivered by the Royal Aircraft Factory (177 machines), the Austin Motor (1914) Co. Ltd. (1,550), the Air Navigation Co. Ltd. (Blériot and Spad) (560), Martinsyde Ltd. (400), Vickers Ltd. (Aviation Department) (2,215), and Wolseley Motors Ltd. (400). Of these aircraft, 1,999 were sent to France for the use of the Royal Flying Corps (from April 1918 the Royal Air Force), 172 to the Middle East, 74 to home-defence units, and 728 to training units, with the rest placed in store.
The greatest problem in the acceleration of S.E.5a deliveries was the slow pace of engine deliveries, for the high power/weight ratio of the Hispano-Suiza 8 engine, especially in its Hispano-Suiza 8B form, had led to its adoption for many different types of Allied warplane. This demanded production on the largest possible scale (ultimately 28,977 such engines were produced in World War I ) by companies in France, Italy, Japan, Russia, Spain, UK and USA. In the last two countries the main licensees were respectively Wright, with the so-called Wright-Hispano, and Wolseley, with the W.4A Viper that was a high-compression unit of the direct-drive type initially delivered at a rating of 200 hp (149 kW) but later at the increased rating of 220 hp (164 kW). Thus deliveries of the S.E.5a totalled 767 aircraft in 1917 and 4,377 aircraft in 1918 as the efforts of various airframe and engine manufacturers began to bear fruit.
The use of engines from a variety of sources resulted in a number of slightly differing standards. The specification above details the S.E.5a with the Wolseley W.4A Viper, and the differences in standard are revealed by comparison of the S.E.5a with the Hispano-Suiza 8B and the Wolseley-built Hispano-Suiza 8B, in each case rated at a nominal 200 hp (149 kW): the two variants were dimensionally identical, but whereas the aircraft with the engine of Hispano-Suiza manufacture had an empty weight of 1,400 lb (635 kg), maximum take-off weight of 1,953 lb (886 kg), maximum speed of 105 kt (121 mph; 195 km/h) at 15,000 ft (4570 m), climb to 10,000 ft (3050 m) in 10 minutes 20 seconds, service ceiling of 22,000 ft (6705 m) and endurance of 3 hours 0 minutes, the equivalent performance data for the S.E.5a with the engine of Wolseley manufacture included a maximum take-off weight of 2,034 lb (923 kg), maximum speed of 114.5 kt (132 mph; 212.5 km/h) at 6,500 ft (1980 m) declining to 100 kt (115.5 mph; 186 km/h) at 15,000 ft (4570 m), climb to 10,000 ft (3050 m) in 11 minutes 20 seconds, service ceiling of 19,000 ft (5790 m), and endurance of 2 hours 15 minutes.
Aces who flew the S.E.5 and S.E.5a to good effect included Major Edward Mannock, the highest-scoring British ace with 73 victories, Major James T. B. McCudden with 57 victories, Captain Andre W. Beauchamp-Proctor with 54 victories, Captain Albert Ball who scored the last of his 44 victories in the S.E.5 after initially characterising the type to Major General H .M. Trenchard with the words ‘It’s a bloody awful machine’, Captain Percy J. Clayson with 29 victories, Major Gerald J. C. Maxwell with 26 victories, and Captain William E. Shields with 24 victories.
The S.E.5a was phased out of British service shortly after the end of World War I, and a few of the aircraft were sold to Poland, where they saw some service into the early 1920s. Other aircraft remained in service with the air forces of Australia (50 machines), Canada (12+ machines), Ireland and South Africa.
The S.E.5b was an experimental sesquiplane development of the S.E.5a of which only a single prototype was completed out of the last airframe ordered from the Royal Aircraft Factory as an S.E.5a. Evaluated in 1918 with the Hispano-Suiza 8B engine, the standard two-gun armament, and the rear fuselage and tail unit of the S.E.5a, the S.E.5b had its engine cooled by a retractable radiator under the revised forward fuselage carrying the engine driving the two-blade propeller with a large spinner that completed a fine nose entry, and was carried by a new wing cellule in which the upper wing (fitted with ailerons on the outboard ends of its trailing edges) was of greater span and chord than the lower wing, from which it was separated on each side by a single pair of parallel interplane struts that were angled out from bottom to top.
Trials revealed that the handling was essentially unaltered from that of the S.E.5a, and that performance was also substantially similar as the greater drag of the revised wing cellule offset the lower drag of the engine installation. In 1918 the S.E.5b was fitted with a standard S.E.5a wing cellule and used for trials of a modified tail unit. The known data for the S.E.5b in its sesquiplane form include a span of 30 ft 7 in (9.32 m) with area of 278.00 sq ft (25.83 m²), length of 20 ft 10 in (6.35 m), height of 9 ft 6 in (2.89 m), and maximum take-off weight of 1,950 lb (885 kg).
The USA ordered 1,000 examples of the S.E.5a from Curtiss with the powerplant of one Wright-Hispano E V-8 engine rated at 180 hp (134 kW), but only 57 of these aircraft had been completed (56 machines assembled from British-supplied components and one wholly American-built aeroplane) before the Armistice of November 1918 led to the cancellation of the order. The American-built version of the S.E.5a was dimensionally identical to the British-built model, but than its powerplant differed in details such as its maximum take-off weight of 2,060 lb (934 kg), maximum speed of 106.5 kt (122.5 mph; 197 km/h) at sea level declining to 101.5 kt (117 mph; 188 km/h) at 10,000 ft (3050 m), and climb to 10,000 ft (3050 m) in 13 minutes 0 seconds.
In 1922/23 the Eberhart Steel Products Company used spare parts to complete an additional 50 more aircraft to the revised S.E.5E standard as advanced trainers with a plywood-covered fuselage.
Accommodation: pilot in the open cockpit
Powerplant: one Wolseley W.4A Viper liquid-cooled V-8 piston engine rated at 200 hp (149 kW) for take-off
Performance: maximum level speed 120 kt (138 mph; 222 km/h) at sea level declining to 107 kt (123 mph; 198 km/h) at 15,000 ft (4570 m); climb to 10,000 ft (3050 m) in 11 minutes 0 seconds; service ceiling 19,000 ft (5790 m); range 260 nm (300 miles (485 km); endurance 2 hours 30 minutes
Weights: empty 1,406 lb (638 kg); maximum take-off 1,940 lb (880 kg)
Dimensions: span 26 ft 7.5 in (8.115 m); length 20 ft 11 in (6.375 m); height 9 ft 6 in (2.90 m); tailplane span 11 ft 0 in (3.35 m); wheel track 5 ft 0 in (1.52 m); wing area 245.80 sq ft (22.83 m²)
Armament: one 0.303 in (7.7 mm) Vickers fixed forward-firing machine gun with 400 rounds on the port upper side of the forward fuselage with synchronisation equipment to fire through the propeller disc, and one 0.303 in (7.7 mm) Lewis fixed forward-firing machine gun with 388 rounds above the upper-wing centre section; there was also provision for up to 100 lb (45 kg) of disposable stores carried on two hardpoints under the lower wing and each rated at 50 lb (27 kg), and generally comprising four 25 lb (11.3 kg) Cooper bombs