Boulton & Paul Partridge The Boulton & Paul P . 33 Partridge was a single seat single - engined biplane fighter designed to an Air Ministry specification . One prototype was ordered and built for trials in 1928 , but it was not put into production . Design and development . When Air Ministry specification F . 9 / 26 was issued in 1926 , calling for a replacement for the RAF ' s numerous Siskin and Gamecock fighters , many manufacturers responded and nine were rewarded with prototype contracts . Boulton & Paul , who had never built a production fighter aircraft of their own design and had only designed one single - engined fighter before ( the Bobolink ) was one of the successful tenderers with their P . 33 Partridge . The company was an early adopter of metal airframe construction and the Partridge was built this way , with many of its structural components common to the RAF ' s Boulton Paul Sidestrand bomber . The Partridge was a single bay biplane with the unswept constant chord square tipped wings characteristic of Boulton & Paul at this time . 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 ailerons only on the upper wings , but soon they were added to the lower wing with a noticeable vertical interconnecting rigid link . Like the rest of the aircraft the wings were fabric covered . The fuselage had an oval cross section . A large spinner blended smoothly into the engine cowling , though the nine cylinder heads of the 440 hp ( 328 kW ) Bristol Jupiter VII engine protruded without further shrouding ; a Townend ring was discussed but not fitted . Two 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 . The Partridge first flew in early in 1928 and appeared at the Hendon RAF display that July . Competitive trials between the contestants for F . 9 / 26 began in January at RAF Martlesham Heath . The Hawker Hawfinch and the eventual winner , the Bristol Bulldog stood out from the others in terms of handling . These two and the Partridge had similar performance figures , with the Bulldog 7 mph ( 11 km / h ) faster than the Partridge but having a lower service ceiling . The major failure of the Partridge was its poor longitudinal stability and control , which led to heavy stick forces and made aerobatics difficult . No further orders were placed . Some modifications were made to the original machine during the trials , notably an enlarged cockpit to assist a pilot who was baling out , and this variation became known as the Mk II . Boulton & Paul had always intended the Partridge to be powered by the new but unavailable Bristol Mercury and the designation Mk III was reserved for this unbuilt version .