Dupuy D-40

The D-40 was designed and built by Roger Dupuy, with the assistance of the Provençal Aero Club, to be a robust aircraft fit for flights over large bodies of water and unfamiliar lands. It had a mostly wooden structure and was plywood covered.^[1]

It was a monoplane with a thick section, three part wing. Its inner section was rectangular in plan, only occupying 20% of the span and without dihedral. The outer sections were trapezoidal out to briefly blunted tips and initially had 11.24° of dihedral. There were plans for further optimization of the dihedral angle during flight testing, though it is not known if it was changed. Ailerons occupied about 35% of the trailing edges. There were six span-wise members on both the tops and bottoms of the wings, the forward pair forming the rear of a ply covered leading edge box spar and the third and fourth pairs defining a second box spar around mid-wing. A layer of fabric, easily doped and smoothed was stretched over the ply skin, a technique widely used at the time. Each wing was braced from the upper fuselage longerons by V-struts rooted on the two wing spars at about 30% span.^[1]

The fuselage of the D-40 was built around four longerons and divided into eight sections; the forward section was aluminium framed and covered as it housed the small diameter, 30 kW (40 hp) nine cylinder Salmson 9AD radial engine. In photographs the engine was uncowled though early plans show a Townend ring-type cowling; it was mounted as high as possible to provide propeller clearance on rough landing sites. Behind it the underside fell away rapidly to maximum depth at the wing; overall it was deep, flat sided and bottomed, with rounded decking. The longerons were ash in the more highly stressed forward and tail sections, with spruce elsewhere. Its single seat, open cockpit was over the wing trailing edge, with a small windscreen and long, faired headrest.^[1]

The D-40 had a triangular fin and trapezoidal rudder, the latter hinged forward of the one-piece, blunt tipped, rectangular tailplane and with the rectangular elevator hinged behind its trailing edge.^[1]

Its fixed undercarriage had its main wheels mounted without axles, with a track of 1,600 mm (63 in). On each side a V-strut, with the hub at its vertex, was hinged at about 45° to the vertical from the lower fuselage longerons. A vertical bungee strut acted as a shock absorber, placing the wheel below the joint between centre and outer wing panels. Its tailskid was of the steel leaf spring type.^[1]