Boulton and Paul P.6 and P.9

Two seat biplane full-scale experimental aircraft to examine different aerofoil sections. It was a wood and fabric single-bay biplane, its wings being without stagger or sweep, with a constant chord of 5 ft on both wings. The wings were built of spruce spars and ribs, with a spruce leading edge and an ash trailing edge. The ailerons were identical on upper and lower wings. The fuselage was flat sided with a rounded top, rather similar in construction to that of the Camel and using many Camel parts. The fin and horn balanced rudder together were almost circular and the tailplane was braced to the fin. The large interplane gap put the upper wing well above the fuselage with the centre section braced to front and rear spars by outward sloping struts from the upper longerons. The pilot's cockpit was under the trailing edge, where there was a cut-out for visibility and the passenger sat in a separate cockpit under the wing. The engine was partly enclosed in a metal cowling, with the cylinder heads protruding as it was air-cooled. There was a simple single axle undercarriage and tail skid. One 90 h.p. RAF 1a powerplant driving a four-blade propeller.

P.6 Specification
Span	Length	Height	Wing Area	Empty Wt	Max AUW	Cruise Speed	Maximum Speed	Endurance	Service Ceiling
25 ft	19 ft	8 ft	235 sq ft	1100 lb	1725 lb	85 mph/ 74 kn	103 mph/ 90 kn	2hr 20min
7.62 m	5.79 m	2.44 m	21.83 m2	499 kg	782 kg	137 km/h	166 km/h

Two seat touring biplane, a larger version of the P.6, 6ft longer with a 2ft 6in increase in span, though the wings remained single-bay. They were built in five sections, three for the upper and two for the lower which were attached directly to the lower fuselage longerons. The upper wing was carried on wooden N interplane struts and the centre section was supported above the fuselage by two struts each side. Ailerons were fitted on both top and bottom wings. The undercarriage was a conventional V-type with an elastic-sprung tubular axle. The same tail unit and centre fuselage section were used, but both the wing chord and gap were increased by 6 inches to 5 ft 6 in each. The fuselage was a simple wire-braced box-girder but the top longerons were not horizontal. They sloped up 10 deg so that the tailplane was above the line of thrust. The fuel tankage was increased by nearly 4 gal to 24 imp gal. The engine was mounted directly on the upper longerons, and was partially enclosed by a cowling cum air-scoop. Long exhaust pipes discharged behind the rear cockpit.
After the first aircraft, the definitive production P.9s had slight changes. The rudder horn-balance and the tail incidence gear were both altered. The tailplane incidence could be altered by means of a lug with three holes, one or other of which received a bolt attaching it to a bracket on the rear spar. Extra centre-section struts were installed, the centre section being supported above the fuselage on metal tube N struts, the vertical members having streamlined fairings. A luggage space was created behind the two seats, and two hemispherical suitcases were specially made to fit the resulting compartment, which was covered by a metal cowling with quick release catches. The fabric covering of the fuselage could easily be removed by undoing the lacing by which it was fixed. The cockpit decking and engine section were covered in three-ply. Full dual controls were fitted so that the aircraft could be used as a trainer, the control column in the front cockpit being removable. Instruments and engine controls were provided in both cockpits, except for the engine revolution indicator which was mounted in a streamlined casing outside the forward fuselage on the port side where it was visible from both cockpits. Wicker-work seats were provided in both cockpits, which were comfortable and roomy. One 90 h.p. RAF 1a powerplant driving a 9 ft 3 in diameter four-blade propeller.

P.9 Specification
Span	Length	Height	Wing Area	Empty Wt	Max AUW	Cruise Speed	Maximum Speed	Range	Service Ceiling
27 ft 6 in	25 ft	10 ft	323 sq ft	1244 lb	1770 lb	85 mph/ 74 kn	104 mph/ 90 kn	300 mi	14000 ft
8.38 m	7.62 m	3.05 m	30.01 m2	564 kg	803 kg	137 km/h	167 km/h	483 km	4267 m