Boulton Paul Low Volume Production

Single seat biplane fighter to Specification A.1A. It was a two-bay design with equal-span wings with 2 ft 31/2 in stagger. They featured N struts, their advantage being that they simplified rigging. The structure was a conventional wooden one, with fabric covering. To begin with ailerons were only fitted on the upper wings, but a lack of manoeuvrability shown in early trials at Mousehold caused strut-linked ailerons to be fitted to the lower wings. There was a large rectangular cut-out in the upper wing to give the pilot excellent upper hemisphere vision. The front fuselage was of circular section to accommodate the rotary engine, but the aft fuselage was flat-sided, made up of a simple wire-braced box-girder, with a curved upper section behind the pilot's head. The two fuel tanks, of 34 and 6 imp. gal, were placed behind the pilot, with an armour plate between them, so that one bullet would have little chance of damaging both. In case they caught fire, both tanks could be jettisoned in flight so that the pilot could glide safely to a landing, saving the rest of his aircraft. The tail had a sharply-swept leading edge running to a curved fin. Two .303-in Vickers machine-guns were fitted on the forward fuselage, firing through the arc of the two-blade propeller, and provision was made for a Lewis gun on a rail on the upper wing. One 230 h.p. Bentley B.R.2 rotary powerplant.
The Bobolink was later fitted with a larger horn-balanced rudder to try to cure the ground-handling difficulties. The strut connection of the ailerons was also changed, being replaced by cable links.

P.3 Bobolink Specification
Span	Length	Height	Wing Area	Empty Wt	Max AUW	Cruise Speed	Maximum Speed	Endurance	Service Ceiling
29 ft	20 ft	8 ft 4 in	266 sq ft	1226 lb	1992 lb		125 mph/ 109 kn	3hr 15min	19500 ft
8.84 m	6.1 m	2.54 m	24.71 m2	556 kg	904 kg		201 km/h		5944 m

Single seat biplane fighter to Specification A.1A. One 230 h.p. Bentley BR2 rotary powerplant?

7 passenger, three-bay twin-engined biplane airliner, though the first prototype was built as a 3 seat trans-Atlantic competition machine. Derived from P.7 Bourges Mk.IB, the aircraft was built from wood, albeit with many metal fittings and joints. Although the main visual difference between the P.8 and the Bourges was that the fuselage filled the interplane space, the fuselage actually retained the basic design of the Bourges. The upper part was simply a fairing of formers and stringers. The fuselage had four longerons with wire bracing; the nose gunners position was replaced by a rounded structure covered with plywood and fabric. The wings were neither staggered nor swept and were of parallel chord, though the lower wing was narrower than the upper. Ailerons were fitted on both wings and as on the Bourges their horn balances projected beyond the wingtips. The two engines were mounted on top of the lower wings just inside the innermost interplane struts, cooled with a retractable radiator mounted under the fuselage between the undercarriage legs. The fin and horn balanced rudder had a near-circular profile, but the tailplane was quite rectangular, carrying unbalanced elevators. The tailplane incidence was adjustable from the cockpit for trim and there was a pair of ancillary fins mounted on the tailplane to hold the aircraft straight when flying on one engine. The fins could be rotated from the cockpit and locked to cope with the asymmetry. A split axle undercarriage was fitted: on each side the short main leg extended from below the forward and innermost interplane strut. There was a second member back to below the aft interplane strut and an axle from the large single wheel upwards and inwards, hinged to the lower fuselage longeron. Shocks were absorbed by a combination of oleo-pneumatic and bungee elastic components. Two 450 h.p. Napier Lion W-12 powerplants.

P.8 Atlantic Specification
Span	Length	Height	Wing Area	Empty Wt	Max AUW	Cruise Speed	Maximum Speed	Range	Service Ceiling
60 ft 4 in	40 ft	12 ft 4 in	770 sq ft	5710 lb	7880 lb	116 mph/ 101 kn	149 mph/ 129 kn		25000 ft
18.39 m	12.19 m	3.76 m	71.54 m2	2590 kg	3574 kg	187 km/h	240 km/h		7620 m

Two seat biplane built to develop techniques for the construction of all steel aircraft. It is also notable for its first use of plastic as a structural material. It was a single-engined two-seat biplane with an airframe of high tensile steel, zinc treated and varnished against corrosion. It had single bay wings with no stagger or sweep. Both wings had the same span and the same constant chord. The interwing gap was large and equal to the chord, putting the upper wing high above the fuselage. Either side of the centre section were a pair of vee struts to front and rear spars, assisted by another strut from front spar to the engine bulkhead The wings were built around two I section spars, each a box section constructed from rolled steel strips. The forward spar had four of these strips, the rear two. The ribs also were made of steel. There were interconnected ailerons on both wings. The P.10 had a small fin, which with its horn balanced rudder formed a teardrop shape. The tail, with unbalanced elevators was strut braced to the fin. The front fuselage was built on four tubular longerons, but from leading edge rearwards it was a monocoque of oval formers of channel section placed back to back with double S-section longitudinal stringers, featuring a load-bearing Bakelite-Dilecto skin, a hard, synthetic cellulose-formaldehyde product devised by Boulton and Paul, riveted between the formers and stringers. This was the first use of structural plastic in an airframe. The front cockpit was at the wing leading edge with a rather distant second cockpit under the trailing edge. Dual control was fitted. It had a tall single axle undercarriage mounted on a pair of vee-struts on either side. These were bungee sprung, though there were plans for oleo dampers. One 100 h.p. Cosmos Lucifer powerplant, so arranged that by removing the vertical hinge-pin on one side the whole engine and its mounting may be swung about the opposite vertical hinge, thus allowing easy access to the back of the engine for inspection and adjustments. The piping, controls, etc., are so arranged that they do not require disconnecting when the engine is swung out.

P.10 Specification
Span	Length	Height	Wing Area	Empty Wt	Max AUW	Cruise Speed	Maximum Speed*	Endurance	Service Ceiling
30 ft	26 ft	12 ft	309 sq ft	1104 lb	1700 lb		104 mph/ 90 kn	5 hr	14000 ft
9.14 m	7.92 m	3.66 m	28.71 m2	501 kg	771 kg		167 km/h		4267 m

3/4 seat biplane designed to Specifications 9/20 (originally DofR Type 3) for a medium range postal aircraft, and Specification 11/20 for medium range bomber/reconnaissance conversion of the postal aircraft. A large three bay biplane, the airframe was made entirely of high-strength steel sheet, drawn or stamped, and used the locked joint system, a new system of connections developed by Boulton and Paul, which involved steel tubes made by rolling long steel strips, which could be produced to finer tolerances than metal tubes. The wings were unswept and unstaggered with square tips, of equal span and constant chord, with balanced ailerons on upper and lower planes. The rectangular fin and tailplane carried similarly balanced control surfaces, the rudder extending below the fuselage underside. The fuselage centre section contained the "engine room" with its two 450 hp Napier Lion powerplants in tandem. One was ahead of the wing leading edge and the other at the wing centreline, with an enclosed, illuminated space between them where the engineer could stand upright and monitor them. The engines were mounted on the upper fuselage longerons, leaving a crawl space beneath.The engines were orientated with their gearboxes away from the engineer's room and the power from each was taken to the airscrews by two drive shafts at right angles to the fuselage. The two from the front engine drove a pair of two-bladed tractor propellers ahead of the leading edge via a pair of gearboxes halfway between the wings, just beyond the first interplane struts. Their mountings extended rearwards to carry a pair of four-bladed pusher propellers driven by the rear engine. Port and starboard airscrews rotated in opposite directions and the fore and aft pairs did likewise, so that either engine could be shut down without any power asymmetry. The centre section, engine drive shafts and propeller mountings were built as a unit independent of the wings, the drives having their own struts and bracing. The space between each fore and aft pair of propellers was occupied by a cylindrical petrol tank and thin radiators extended between these tanks and the fuselage. Radiators and driveshafts were enclosed by a streamlined fairing on either side. The rest of the fuselage was conventional and of square cross section with rounded decking. The pilot sat well forward, behind a front gunner's position. There was also provision for a dorsal gunner just behind the wings. The main wide tracked single axle undercarriage had pneumatic springing and damping; a pair of smaller wheels further ahead and closer together served to prevent nose-overs and a standard tail skid extended below the rudder.

P.12 Bodmin Specification
Span	Length	Height	Wing Area	Empty Wt	Max AUW	Cruise Speed	Maximum Speed	Range	Service Ceiling
70 ft	53 ft 4.5 in		1204 sq ft	7920 lb	11000 lb		116 mph/ 101 kn		16000 ft
21.34 m	16.27 m		111.86 m2	3592 kg	4990 kg		187 km/h		4877 m

3 seat reconnaissance biplane to Specification 4/20, effectively a steel framed version of the P.7 Bourges. A twin-engined, three bay biplanes with equal span, constant chord wings with no sweep or stagger, it carried ailerons on upper and lower wings; the wingtips were cut off square. The wings had two spars, each made up of four corrugated steel strips formed into a box. The wide chord interplane struts were made of two linked triangular sections covered in fabric. The structure used the locked joint system, first introduced on the P.12 Bodmin. The fuselage had flat sides, with a triangular top, designed to allow the rear gunner to fire downwards on both sides of the aircraft. There were supporting sloping struts from the midpoints of the wing midsection to the upper fuselage longerons. The fuselage was built around tubular longerons built in two parts to improve their strength. It was square sided except behind the wings where an extra central member made the upper section triangular, to enhance the downward field of fire from the dorsal gunners position. The pilot's cockpit was forward of the wings and in the nose there was another gunner's position, which, like the dorsal gunners position, was fitted with a single .303-in Lewis machine gun. This crew member doubled as bomb-aimer from a windowed position slightly further forward in the lower fuselage. The tailplane was mounted at the top of the fuselage, with a fin and rudder that projected below the fuselage, protected by a tailskid. The rudder had a large horn balance that overhung the fin and its unusual forward extension that acted as a trimming surface. The single axle undercarriage was mounted just inboard of the engines on pneumatically sprung and damped legs. A pair of members converged from the legs to a single forward wheel, there to prevent nose-overs. The engines were mounted just inboard of the inner interplane struts, on pedestals carried on the lower wing. Each pedestal carried the radiators at the front, and the top of the engines were uncovered, to allow for air cooling. The engines were carried on anti-vibration mountings. The main fuel tanks were installed in the centre of the fuselage, between the wings. Windmill driven pumps moved fuel from the main tanks to a high mounted feeder tank, which was used to gravity feed the engines. Two 450 h.p. Napier Lion W-12 powerplants driving four-bladed propellers.

P.15 Bolton Specification
Span	Length	Height	Wing Area	Empty Wt	Max AUW	Cruise Speed	Maximum Speed	Range	Service Ceiling
62 ft 6 in	48 ft				9500 lb		130 mph/ 113 kn
19.05 m	14.63 m				4309 kg		209 km/h

Single-seat cantilever wing night fighter to Specification 27/24. Two significantly different prototypes were produced. Both had some features in common. They had the same flat sided fuselage, with a flat base, curved top, and streamlined appearance when seen from the side. Both had fixed landing gear, with the main wheels under the engines. The pilot sat in an open cockpit over the nose. The wings had square ends.
On the first prototype the engines were carried in the middle of the wings, and used engine cowlings but with cylinder heads exposed in the slipstream for cooling. The wings had a narrow profile close to the fuselage and at the tips, swelling at the engines. The wings were shoulder mounted. The wheels were supported by struts that connected the wheel to the engine above, and to the base of the fuselage, with another strut connecting the engine to the base of the fuselage. It was armed with two fixed forward firing .303 in Vickers machine guns, carried in the sides of the forward fuselage.
On the second prototype, the engines were mounted in nacelles carried below the wing. Wingspan increased by 5ft, and the wings were about the same thickness all along. The system of struts was similar, although an extra strut was added connecting the main wheels to the outer wing. The engines were given Townend rings instead of close cowling. The wings had Handley Page leading-edge slots. The biggest change was in the armament. The second prototype was armed with two .303 in Lewis machine guns, one on each side of the nose. These were carried in barbettes that could change their elevation from 0 degrees (level) up to 45 degrees above horizontal. The ring-and-bead gun sight moved to match. The idea was to make it easier to attack bombers that were above the aircraft. Two 230 h.p. Armstrong Siddeley Lynx powerplants.

P.31 Bittern Specification
Span	Length	Height	Wing Area	Empty Wt	Max AUW	Cruise Speed	Maximum Speed	Endurance	Service Ceiling
41 ft	32 ft 4 in			3215 lb	4500 lb		145 mph/ 126 kn	3.75 hr
12.5 m	9.86 m			1458 kg	2041 kg		233 km/h

3/4 seat long range night bomber to Specification B.22/27. It was a metal framed aircraft, using steel for the main members and duralumin elsewhere. Its unstaggered, foldable wings were straight edged with constant chord and rectangular tips. Both wings carried ailerons, but only the lower one had dihedral. Two of the engines were mounted on the top of the lower wing just within the inner bay, the third engine was similarly mounted on the upper wing, above the fuselage. The square section, slab sided fuselage held either four or five crew, and an additional sixth crew member could be an instructor or co-pilot to perform long-range flights. The nose gunner was also a bombardier and navigator; the position was equipped with a single .303-in Lewis machine gun on a Scarff ring mount and had a swivel seat, where he could use the bombsight when sitting facing forward and, by rotating his seat, take up his third role as navigator at a chart table. There was a walkway aft, which passed in turn the pilot's open cockpits in tandem on the port side, the wireless/camera operator's internal position near the leading edge, the dorsal gunner's cockpit and the tail gunner's station in the extreme, slightly drooped tail. The dorsal gun could be manned either by the wireless operator or the tail gunner, both positions having a .303 in Lewis gun on a Scarff ring. Offensive armament included 4× 550 lb or 520 lb bombs or 6× 250 lb bombs in semi-recessed bomb bay and 6× 120 lb bombs under wings. The monoplane horizontal stabiliser carried servo assisted elevators and a pair of fins with horn balanced rudders. These were also servo assisted, with the servo surfaces mounted well behind the rudders' trailing edges on outriggers. The main undercarriage was unusual in that on either side pairs of wheels were fitted on a long axle so that the inner one was close to the fuselage and the outer one beyond the engine and inner bay. The P.32 was initially fitted with a pair of tailskids, soon replaced with a tailwheel with a little faired leg. Initially fitted with three uncowled 550 h.p. Bristol Jupiter XF powerplants fitted with three-bladed propellers, these were replaced with 575 h.p. Bristol Jupiter XFBM powerplants enclosed in Townend rings and driving four bladed airscrews as soon as these medium supercharged models became available.

P.32 Specification
Span	Length	Height	Wing Area	Empty Wt	Max AUW	Cruise Speed	Maximum Speed	Range	Service Ceiling
100 ft	69 ft	21 ft	2090 sq ft		22700 lb
30.48 m	21.03 m	6.4 m	194.17 m2		10297 kg

Single seat biplane fighter to Specification F.9/26. It was a single bay biplane with the unswept constant chord square tipped wings. There was slight stagger and only the lower wing, smaller in span and chord, had dihedral. The interplane struts leaned outwards markedly and the centre section struts more so. Initially there were Frise ailerons only on the upper wings, but soon they were added to the lower wing with an interconnecting rigid link. Like the rest of the aircraft the wings were fabric covered. The fuselage had an oval cross-section. The forward fuselage, made of high-strength solid steel tube, was the engine mount, fuel tank, wing mounts and cockpit. Behind the pilot's seat, the fuselage was made of steel tube longerons with steel and duralumin struts, with wooden auxiliary frames that formed an oval cross-section. For crash resistance, the section around the cockpit was made of large-diameter tubes. The fairing behind the pilot's head was made of three-layer plywood mounted on wooden auxiliary frames. A large spinner blended smoothly into the engine cowling. Two .303 in Vickers machine guns were mounted on the fuselage immediately behind the engine and firing through the propeller and between the cylinder heads. The maximum fuselage diameter was just behind the wing at the single cockpit, giving the aircraft a slightly humped appearance. The pilot had a clear forward view under the upper wing and a trailing edge cut-out helped his upward view. The fin and the strut braced tailplanes were both rather rectangular and low aspect ratio. Both the rudder and elevators were horn balanced, the latter with balance surfaces extending beyond the tailplane. The undercarriage had a single axle and was mounted on vee struts. There was a faired tail skid. One 440 h.p. Bristol Jupiter VII powerplant.

P.33 Partridge Specification
Span	Length	Height	Wing Area	Empty Wt	Max AUW	Cruise Speed	Maximum Speed	Range	Service Ceiling
35 ft	23 ft 1 in	11 ft	311 sq ft	2021 lb	3097 lb		167 mph/ 145 kn		28950 ft
10.67 m	7.04 m	3.35 m	28.89 m2	917 kg	1405 kg		269 km/h		8824 m