Boulton and Paul P.64 and P.71

3 crew all-metal two-bay equi-span, slightly staggered biplane transport aircraft to Specification 21/28. The fuselage was a rectangular rigidly braced steel and duralumin framework, the more highly stressed members of which were of solid-drawn steel tube, but the remainder of the structure was primarily composed of Boulton and Paul's locked joint system of steel tube construction, with duralumin for the bracing members. The fuselage was fabric covered with the exception of the nose section, which was a streamline plywood structure. The upper center section was carried above fuselage on short struts and faired into fuselage, while the lower center section wings attached to bottom fuselage longerons. The high-tensile steel wing spars, of different depths, used standard sections. The front spar was made up of two drawn-tube booms with a corrugated web. The rear spar was of the figure 8 section formed of two strips with closed, joints top and bottom. The wing featured duralumin ribs, built up of beaded channel-section booms with tubular bracing, steel compression ribs and tie-rod bracing, the whole being fabric covered. Frise ailerons were fitted on all four mainplanes and Handley Page slots on upper wings. The streamlined outer interplane struts were closed-joint tubes and within the rear portions of the rear struts passed the aileron interconnecting rods so that these were out of the airstream. The whole control system used rods rather than cables. Unlike the wing, the horizontal tail unit was tapered in shape with rounded ends, the large rudder had a pointed shape. The design of the empennage was different from the wing design. The tail unit was a monoplane metal structure with a structure similar to wings, with metal covering for stabilizer, and fabric for the rest. Unlike the wing, the horizontal tail unit was tapered in shape with rounded ends. The elevators and rudder were both controlled by servo-flaps hinged to the trailing edges of these surfaces, and the rudder featured a large horn balance.
The engines were mounted in hexagonal nacelles under the upper wings at the innermost interplane struts. Directly below the innermost interplane struts, the undercarriage consisted of mainwheels enclosed in streamline fairings under the lower wings, each wheel being carried in an oleo fork and a pair of backwardly sloping radius rods, with all but the lower portion of each wheel enclosed in the fairing. The tailwheel was faired into the rear end of fuselage.
The two pilots sat under an enclosed canopy, with the navigator/radio operator's compartment behind. Aft of the navigators compartment was the main mail compartment. The specified mail load of 1,000 pounds was stowed in standard mail bags carried on hooks on the sides of the net-lined compartment. For loading and unloading the mail, there was a wide door aft on the port side, and doors in the bulkhead between the mail and navigators compartments allowed members of the crew to enter the mail compartment when the airplane is in the air. Two Bristol 555 h.p. Pegasus I.M2 powerplants fitted within an hexagonal Townend ring and driving two-bladed fixed pitch propellers.

P.64 Specification
Span	Length	Height	Wing Area	Empty Wt	Max AUW	Cruise Speed	Maximum Speed	Range	Service Ceiling
54 ft	42 ft 6 in	13 ft	756 sq ft	7008 lb	11267 lb	150 mph/ 130 kn	185 mph/ 161 kn	1000 mi	22500 ft
16.46 m	12.95 m	3.96 m	70.23 m2	3179 kg	5111 kg	241 km/h	298 km/h	1609 km	6858 m

3 crew all-metal biplane transport aircraft developed from the P.64. In general, the design was similar to the P.64 with the exception of the central section of the fuselage, which included a passenger compartment. This part of the fuselage with four square windows on each side was made of elements made of light alloy and covered with a corrugated coating of light alloy. The fuselage was slightly thinner, but also slightly longer, and the tail unit was completely redesigned with triple fins and twin rudders on the outer pair. The wings now featured rounded tips. Side-by-side seating was was provided in the cockpit, but dual control was not installed, the radio operator/navigator normally occupying the right hand seat. Above the pilots' seats was a sliding hatch.
The passenger compartment was equipped by L A Rumbold and Co, which specialized in such work. The interior walls were luxuriously trimmed with blue leather, walnut veneer and beige fabric with considerable heat and noise insulation distance between the inner and outer walls. In the passenger salon there were six fixed seats with a frame of tubular frames of three on each side in a staggered pattern, rather than side by side. In addition, there was a seventh place, which was folded in the recess in the center of the rear bulkhead. Each seat had a controlled outlet for fresh air. Hot air was taken from the engine exhaust pipe and mixed in a chamber at the rear of the fuselage with cold air from the scoop-type air intake, the mixed air used was ejected from the front of the cabin. Each passenger was provided with a spring-loaded hanger which could be turned to the side when not in use. At the front of the cabin on the right side was a toilet, which was provided with a small round window. Next to the toilet, on the port side was a door to the cockpit. The aircraft was equipped with two luggage compartments with external doors in the nose and tail. Two 490 h.p. Armstrong Siddeley Jaguar VIA powerplants.

P.71A Specification
Span	Length	Height	Wing Area	Empty Wt	Max AUW	Cruise Speed	Maximum Speed	Range	Service Ceiling
54 ft	44 ft 2 in	15 ft 2 in	718.5 sq ft	6100 lb	9500 lb	150 mph/ 130 kn	195 mph/ 169 kn	600 mi	21000 ft
16.46 m	13.46 m	4.62 m	66.75 m2	2767 kg	4309 kg	241 km/h	314 km/h	966 km	6401 m