User:TSRL/sandbox/Huff-Daland HD.8

The Huff-Daland HD.8A and 9A Petrel were very similar biplanes of simplified construction, built in the US in the early 1920s. The 8A was a three seat passenger aircraft and the 9A a two seat military trainer. They differed chiefly in their engines.

Design and development
They were both unequal span, single bay biplanes with thick section, rectangular plan wings, the lower one having both a smaller span and chord. Both were built around twin spars and were fabric covered and were braced together with outward leaning N-struts formed from streamlined steel tubes. In place of the conventional cabane, the inner part of the upper wing was attached to the lower fuselage longeron with outward leaning pairs of struts on each side, assisted by lighter pairs from mid-fuselage. At its centre, the upper wing was joined to the two upper fuselage longerons. There were wood-framed, overhung (horn balanced) ailerons on he upper wings only.

The commercial HD.8A was powered by a 100 hp water-cooled Curtiss OX-5 V8 engine and the military HD.9A by an Anzani air-cooled engine of the same power. This last was chosen to compete for a military contract for an air-cooled trainer in the TA (trainer, air-cooled} class rather than the water-cooled TW. The Curtiss had a nose mounted radiator. Fuel tanks were in the upper wing centre-section.

Behind the engine, its steel tube mounting and fire wall the fuselage differed from the usual girder construction by having two triangular frames, formed from the longerons, with a major vertical brace from the apex and several light verticals behind. The two frames were then joined together with transverse struts. This method, used earlier on the Huff-Daland HD.4, greatly reduced the number of internal bracing wires. From the rear of the cockpit forward the fuselage was plywood covered below a false longeron on each side, leaving the frames above the cockpit unclad. Details of the trainer's cockpit are lacking but the three seat DH.8A placed the pilot and two passengers in tandem. Cockpit access was by two side doors. The rear fuselage was fabric covered. The biplane's fuselage tapered strongly rearwards, top and bottom meeting at the tail and mounting a wood-framed, adjustable incidence tailplane. The hinge of its one-piece elevator (aeronautics), also wooden was at the fuselage end fuse. In plan the horizontal tail was roughly rectangular but with cropped tips. The fin, braced to the tailplane with a strut on each side, was essentially triangular, though with a cropped apex to clear the horn of its large, rounded balanced rudder. Both the control surfaces were steel-framed.

The fixed landing gear was of the tailskid type. V-struts from the lower fuselage frame were joined by two cross-pieces on which the single axle was mounted by two unusual rubber-cord shock absorbers. To simplify maintenance, these were wound separately and could be replaced as units.

aerofiles - Their photographically nearest types (open frame fuselage, no HD-4 (TA-2) type girder wing strut) are the AT-1 (TW-5) and HD-5. Their HD-8s (no pic) have bigger spans though the (no span, no pics) HD-9A could match Flight.