M.Goodall, A.Tagg British Aircraft before the Great War (Schiffer)

P.Lewis British Aircraft 1809-1914 (Putnam)

S.E.4

   Following the S.E.2, the S.E.4 was the Royal Aircraft Factory's next essay in Scouting Experimental. The machine was designed by H. P. Folland, whose ideas were to influence the shapes of British fighters for so many years afterwards. The new scout was completed in June, 1914, and was even cleaner in concept than its predecessor. The S.E.4 represented the most advanced aerodynamic thought at the time of its appearance, and the care taken over reduction of drag, coupled with the power from its fourteen-cylinder two-row 160 h.p. Gnome, gave a top speed of 135 m.p.h., making it the world's fastest aircraft in its day.
   Among unusual features were the four wings' full-span ailerons, which could be depressed to act as landing flaps. The fuselage consisted of a circular wooden monocoque, and the engine was fully enclosed in a tight-fitting cowling. Inadequate cooling resulted in scorching of the metal panels and the consequent adoption of a cooling slot and a fan inside the spinner. The original undercarriage was in the form of an inverted triangular pyramid of struts which carried a transverse leaf-spring axle for the wheels. This arrangement led, not surprisingly, to uncontrollable rolling while taxying, and was soon replaced by the more usual pair of vee struts. Another alteration was the discarding of the moulded celluloid cockpit canopy fitted originally, as no pilot would agree to fly beneath it.
   A high-speed section was used for the wings which were connected by single "I" interplane struts and braced with streamlined Raf-wires.
   The S.E.4 was given the number 628, and among its pilots were Lt. Norman Spratt and Major J. M. Salmond, who found the aircraft's speed and climb very good. The 160 h.p. Gnome proved a troublesome and unpopular engine, bringing about the premature end of its production. That installed in the S.E.4 was removed and its place was taken by a 100 h.p. Monosoupape Gnome, the top speed thereby being reduced to 92 m.p.h. After some further flying, damage in a landing accident resulted in the abandonment of the development of the S.E.4.

SPECIFICATION

   Description: Single-seat tractor biplane scout. Wooden structure, fabric covered.
   Manufacturers: Royal Aircraft Factory, Farnborough, Hants.
   Power Plant: 160 h.p. Gnome, 100 h.p. Monosoupape Gnome.
   Dimensions: Span, 27 ft. 6 ins. Length, 21 ft. 4 ins. Height (tripod u/c) 9 ft.; (vee u/c) 9 ft. 10-5 ins. Wing area, 188 sq. ft.
   Performance: Maximum speed (160 h.p. Gnome) 135 m.p.h.; (100 h.p. Monosoupape Gnome) 92 m.p.h. Landing speed, 52 m.p.h. Climb (160 h.p. Gnome) 1,600 ft./min. Endurance, 1 hr.

J.Bruce British Aeroplanes 1914-1918 (Putnam)

S.E.4

  THE S.E.3 was a projected development of the S.E.2a which was never built. It is possible that the design was abandoned in view of the great promise of the S.E.4, for the later machine was certainly a remarkable aeroplane.
  The S.E.4 was designed by H. P. Folland, and was built in 1914. Its derivation from the S.E.2 and S.E.2a was reflected in the shape of the fuselage and the vertical tail surfaces, but very great care was taken to minimise drag throughout the design. The engine was a 160 h.p. fourteen-cylinder two-row Gnome rotary which was completely cowled in, and a large spinner was fitted to the airscrew. The combination of a complete cowling and large spinner led to overheating, so an opening was made in the nose of the spinner and a fan was fitted inside it between the roots of the four blades of the airscrew.
  The fuselage was of circular cross-section and was covered entirely with plywood. A streamlined transparent cockpit-cover was designed and, after some experiment, was moulded in celluloid. However, no pilot of the time could be induced to fly the S.E.4 with the canopy on, for it was considered too dangerous. The wings were of equal span, and were rigged without stagger. The interplane bracing was unconventional: there was only a single I-strut on each side, with fairly long transverse members at each end connecting with the two spars of each mainplane. The centre-section struts were of similar form, and through their hollow interiors were led the control cables for the ailerons. Control surfaces ran along the entire trailing edge of both upper and lower mainplanes: they acted both as ailerons and as camber-changing flaps. In flight, the flaps could be reflexed slightly in order to reduce drag; and they could be lowered for landing. All gaps between moving and fixed surfaces on the mainplanes and tail-unit were faired over with elastic netting.
  The original undercarriage consisted of an inverted tripod which had at its apex a faired leaf spring: a wheel was mounted at each end of this spring. It was found that the S.E.4 rolled too much when taxying, however, so a vee-type of undercarriage was fitted, and once again great care was taken to fair the axle and its junctions with the vee-struts.
  When the S.E.4 was designed, the intention was to produce the fastest aeroplane in the world, and this aim was unquestionably achieved. The maximum speed of the machine was over 135 m.p.h., and its initial rate of climb was better than 1,600 feet per minute. The test flying was carried out by Norman Spratt, and Major J. M. Salmond also flew the S.E.4. Both reported favourably on it.
  Unfortunately, the landing speed of 52 m.p.h. was considered at that time to be too high for Service use, and production was not undertaken. The big Gnome engine gave a good deal of trouble, and was ultimately replaced by the 100 h.p. Gnome Monosoupape. The reduction in power inevitably had an adverse effect upon the S.E.4’s performance; the maximum speed dropped to 92 m.p.h. Development of the S.E.4 ceased when it was badly damaged by turning over after a wheel collapsed on landing. It saw no operational service.


SPECIFICATION
  Manufacturers: The Royal Aircraft Factory, Farnborough, Hants.
  Power: 160 h.p. Gnome, later 100 h.p. Gnome Monosoupape.
  Dimensions: Span: 27 ft 6 in. Length: 21 ft 4 in. Height: 9 ft with tripod undercarriage, 9 ft 10 1/2 in. with vee undercarriage. Chord: 3 ft 9 1/2 in. Gap: 5 ft 1 in. Stagger: nil. Dihedral: 1° 30'. Incidence: 2°. Span of tail: 10 ft 9 in. Wheel track (tripod undercarriage): 3 ft.
  Areas: Wings: upper 98 sq ft, lower 90 sq ft, total 188 sq ft. Tailplane: 18 sq ft. Elevators: 12 sq ft. Fin: 6-5 sq ft. Rudder: 8 sq ft.
  Performance: With 160 h.p. Gnome: maximum speed at ground level, 135 m.p.h. With Monosoupape: maximum speed at ground level, 92 m.p.h.; at 7,500 ft: 82-5 m.p.h. Endurance: 1 hour.
  Armament: Nil.
  Production: One S.E.4 was built in 1914.
  Serial Number: 628.



S.E.4a

  DESPITE its designation of S.E.4a, the next aeroplane in the S.E. series bore little resemblance to the S.E.4. The S.E.4a appeared in 1915, and was a pretty little single-seat biplane powered by an 80 h.p. Gnome rotary engine. The engine installation resembled that of the later Bristol M.1A monoplane scout, but the large spinner of the S.E.4a incorporated a fan to assist the cooling of the engine.
  The fuselage was a conventional structure. The basic wire-braced wooden box-girder was faired by stringers and formers, and the covering was of fabric, with the exception of the metal panels behind the engine. The vertical tail unit is of considerable interest, for in outline and construction it foreshadowed that of the S.E.5.
  The single-bay wings were of equal span, and embodied the same full-length ailerons-cum-flaps that had been used on the S.E.4. Structurally the wings were conventional: they had wooden spars, ribs and riblets, and were internally cross-braced. Single-bay interplane bracing was used, with auxiliary flying wires running to a mid-bay position on the upper wing. The wing cellule was remarkable for the absence of an upper centre-section: the upper mainplanes met at a central trestle-shaped cabane formed of two inverted vee-struts. By contrast, there was a wide lower centre-section, with transverse steel tubes to interconnect the lower wing spars.
  The S.E.4a proved to be a delight to fly, and provided an excellent mount for Frank Goodden, that great pilot who went to Farnborough as chief test pilot. He frequently displayed his aerobatic prowess on an S.E.4a, and incidentally provided a useful store of experience in his test reports.
  The engine cowling proved to be too enclosed, and the 80 h.p. Gnome overheated despite the fan installation. The spinner was removed and a new cowling was fitted; the performance suffered very little from this modification. An alternative installation of the 80 h.p. Le Rhone engine was made, and at least one of the S.E.4a’s had the covering removed from the lower centre-section in order to improve the pilot’s downward view.
  Although structurally more suitable for production than the S.E.4, the S.E.4a was not built in quantity. Four were built in 1915, and at the end of that year one of them was at Joyce Green for Home Defence duties.


SPECIFICATION
  Manufacturers: The Royal Aircraft Factory, Farnborough, Hants.
  Power: 80 h.p. Gnome; 80 h.p. Le Rhone.
  Dimensions: Span: 27 ft 5-2 in. Length: 20 ft io| in. Height: 9 ft 5 in. Chord: 4 ft 2 in. Gap: 4 ft 9-06 in. Stagger: 1 ft 6-54 in. Incidence: 40. Span of tail: 10 ft 7 1/2 in. Wheel track: 5 ft 2 in. Airscrew diameter: 8 ft 6 in.
  Armament: One rifle; or one Lewis machine-gun mounted centrally above the upper wing, firing forwards above the airscrew.
  Service Use: Home Defence: Joyce Green aerodrome.
  Production: Four S.E.4a’s were built at the Royal Aircraft Factory in 1915.

P.Lewis The British Fighter since 1912 (Putnam)

However, the Royal Aircraft Factory’s staff had not been idle and in June, 1914, revealed a successor to the S.E.2a. A projected modification of the S.E.2a, the S.E.3, was dropped and the Factory went ahead to construct the S.E.4 designed by H. P. Folland, a man destined to play an ever-increasingly important part in British fighter design for many years afterwards.
   In the S.E.4 he produced a fast, unarmed scout embodying the very latest advances in aerodynamic practice. To reduce drag to the absolute minimum the fourteen-cylinder, two-row 160 h.p. Gnome was closely cowled and faired into the circular section, wooden monocoque fuselage. Single centre-section and interplane struts were used and both upper and lower wings had full-span ailerons which could be brought into play as landing flaps. The undercarriage was reduced to three struts and a leaf-spring axle, but uncontrollable swaying on the ground brought a reversion to the conventional vee-type structure. Another very advanced feature was the moulded celluloid cockpit canopy which was so distrusted by the pilots that it was soon discarded. With its original engine the S.E.4 No. 628 achieved a top speed of 135 m.p.h., making it the World’s fastest aircraft of its time. The 160 h.p. Gnome gave trouble with cooling, however, and was replaced by a 100 h.p. Monosoupape Gnome with an attendant drop in speed to 92 m.p.h.
   Although it was a brilliantly-conceived design, and was liked by its test pilots Norman Spratt and Major J. M. Salmond, the S.E.4’s landing speed of 52 m.p.h. was thought excessive for general use and, after damage in a landing accident, it faded from the scene. During its brief career, the S.E.4 had shown just what could be achieved at such an early stage in scout and fighter development and the machine remains a masterpiece of early aeroplane design.
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   During 1915 designers were still faced with the two main alternatives of either the pusher or tractor layout for the armed scout. Steady evolution of the tractor type in general had endowed it with every advantage but one over the untidy pusher. The exception was still the installation and effective aiming of a forward-firing gun. In time a solution is found for every problem but, pending one for this particular obstacle, the Royal Aircraft Factory went ahead in 1915 with the design of another single-seat tractor scout.
   Although little connected with the S.E.4 - general overall layout and duty being about all that they had in common - the new machine was designated S.E.4a. H. P. Folland’s talents as a designer were responsible for the creation of the elegant and trim little newcomer, which exhibited simpler construction than that of its predecessor. The streamlined form of the S.E.4a’s fuselage was achieved by the addition of formers and stringers to the main rectangular-section, wire-braced framework of longerons and spacers. The 80 h.p. Gnome’s propeller was faired into the cowling ring with a large shallow spinner, inside which a fan cooled the engine with air drawn through the front orifice. Metal panels covered the nose as far back as the cockpit, the remainder of the airframe receiving the usual doped fabric covering. The staggered, equal-span wings were of single-bay cellule; the lower planes were joined to a centre-section, while the upper pair met at the centre-line to be joined to the fuselage by a pair of inverted V struts. The S.E.4a incorporated the idea, carried out on the S.E.4, of full-span ailerons which acted also as flaps. The machine’s fin and rudder profile was notable as that which stamped it and many succeeding fighters as Folland designs. The S.E.4a was an excellent example of the axiom that an aeroplane which looks right should fly well, a truth which was amply demonstrated by Frank Goodden with aerobatic displays at Farnborough.
   Overheating of the engine, even though the fan had been incorporated, brought about the discarding of the large spinner and the modification of the cowling to remedy the defective cooling. In all, four S.E.4as were produced by the Factory during 1915 and the 80 h.p. le Rhone was fitted as an alternative to the Gnome. To overcome the difficulty of firing straight ahead, a mounting for a Lewis gun was fitted above the upper wings at the apices of the centre-section struts so that the line of fire passed over the propeller, alternative armament being a rifle mounted at an angle on the fuselage side. Although it was a successful design and eminently suited to production, the S.E.4a constitutes yet another promising type which was unlucky enough to be passed over as a service machine. The only known military use made of it was that one was available at Joyce Green for Home Defence in the closing days of 1915.

F.Mason The British Fighter since 1912 (Putnam)

R.A.F. S.E.4 and 4A

   Designed by Henry Folland, the S.E.4 was intended quite simply to be the fastest aeroplane in the world. First flown by Norman Spratt in June 1914 - only two months after the Sopwith Tabloid seaplane had won the Schneider Trophy at 86 mph and demonstrated a top speed of around 100 - the S.E.4 achieved a speed of 135 mph, faster by a considerable margin than any other aeroplane then flying.
   Power was provided by the 160hp Gnome fourteen-cylinder two-row rotary, totally enclosed in a smooth-contoured cowling fronted by a large spinner which, after trouble due to engine overheating, had an intake cut in the nose to allow more airflow to pass through to the engine. The fuselage was reminiscent of the S.E.2A but was covered overall with ply. The wings were similar to those of the earlier aircraft but rigged without stagger, and featured single cabane and interplane struts on each side; full-span ailerons-cum-flaps replaced the former wing warping.
   The most unusual feature was the undercarriage which initially comprised a transverse half-elliptic leaf spring attached to the apex of an inverted tripod, the landing wheels being attached to the extremities of the spring. This proved unsatisfactory owing to a tendency of the aircraft to roll while taxying and, after initial flight trials, it was replaced by a conventional pair of V-struts.
   Although no armament was ever fitted, there is no doubt but that the aircraft attracted interest as a potential fighting scout, and it was flown on occasion by Maj J M Salmond (later Marshal of the Royal Air Force Sir John, gcb, cmg, cvo, dso), who reported favourably on it.
   The big Gnome, however, continued to give trouble, and the landing speed (at 52 mph) was considered too high for Service pilots. The engine was replaced by a 100hp Gnome monosoupape and, not surprisingly, the speed performance decreased to mediocrity. Development of the S.E.4 was finally abandoned when it was badly damaged following a wheel collapse while landing.

The S.E.4A

   Only superficially related to the S.E.4, the S.E.4A was said to be an attempt to suit the former aircraft to quantity production and, in so doing, almost all the S.E.4’s novel features disappeared, other than the ailerons-cum-flaps. It is true that the S.E.4A flew initially with a huge open-nosed spinner, but engine overheating ensued nonetheless and a conventional cowling without spinner was substituted. It may be of interest to remark that the outline and structure of the S.E.4’s tail unit was to reappear almost unaltered in the design of the much more illustrious S.E.5 which started in 1916.
   Four examples were produced in 1915, being flown frequently by Maj Frank Goodden, who by then had been appointed the Factory’s Chief Test Pilot. Provision was made to mount a Lewis gun above the upper wing, and at least one S.E.4 was based at Joyce Green on Home Defence duties at the end of that year. However, the aeroplane’s performance was not outstanding and failed to arouse further official interest.


   Type: Single-engine, single-seat, single-bay tractor biplane.
   Manufacturer: The Royal Aircraft Factory, Farnborough, Hants.
   Powerplant: S.E.4. 160hp Gnome; 100hp Gnome monosoupape. S.E.4A. 80hp Gnome; 80hp Le Rhone.
   Structure: Composite wood and steel construction with ply and fabric covering. S.E.4 with single interplane and cabane struts; twin interplane and cabane struts on S.E.4A.
   Dimensions: S.E.4. Span, 27ft 6in; length, 21ft 4in; height, 9ft 0in (with tripod undercarriage); wing area, 188 sq ft. S.E.4A. Span, 27ft 5 1/10in; length, 20ft 10in; height, 9ft 5in.
   Performance: S.E.4 (160hp Gnome). Max speed, 135 mph at sea level; initial rate of climb, over 1,600 ft/min. (100hp Gnome). Max speed, 92 mph at sea level. S.E.4A. Max speed, approx 90 mph at sea level.
   Armament: S.E.4. None. S.E.4A. Provision for single Lewis gun on upper wing.
   Prototype and Production: One S.E.4, No. 628. Four S.E.4As.

W.Green, G.Swanborough The Complete Book of Fighters

ROYAL AIRCRAFT FACTORY S.E.4A UK

   Designed at Farnborough by H P Folland at the end of 1914, the S.E.4a was one of a series of “Scouting Experimentals" used to study the interplay of stability and manoeuvrability. Unrelated, except in configuration and design authorship, to the high performance S.E.4 of mid-1914, the S.E.4a was a sturdy little single-bay biplane with equi-span wings incorporating 3.5 deg of dihedral and having no centre section. The square-section fuselage was of conventional spruce construction with steel tubes to accept the loads from the lower wings, and, like the wooden wings and tail unit, was fabric-covered. Full-span ailerons were fitted to both sets of wings, and power was provided by an 80 hp Gnome seven-cylinder rotary in a fully circular short - chord cowling. The first of four S.E.4a's built at the RAF flew there on 25 June 1915, and differed from its successors in having faired fuselage sides and an outsize spinner. The fourth and last S.E.4a flew on 13 August that year. The third, flown on 27 July, was at first fitted with an 80 hp Le Rhone engine, the Gnome being substituted later, and in October 1916 this same S.E.4a was provided with an 80 hp Clerget. In the hands of the RFC, at least one of the S.E.4a’s was armed with a 0.303-in (7,7-mm) Lewis gun mounted on the centre line above the upper wing to clear the propeller disc.

Span, 27 ft 6 in (8,38 m).
Length, 20 ft 10 1/2 in (6,37 m).
Height, 9 ft 5 in (2,87 m).

H.King Armament of British Aircraft (Putnam)

S.E.4a. On at least one single-seater of this type (built 1915) there were brackets for a gun, probably of Lewis type, well above the top wing on the centre line. The gun fired above the airscrew.