The D-D[1] was a mid-wing monoplane with a rectangular plan, blunt tipped, constant thickness wing.
Canvas covered, it was built around a pair of wooden spars that continued through the fuselage with the pilot's seat between them.
The enclosed cabin had, in the four-seater, two rows of side-by-side seats, optional dual control and generous forward, side and upward glazing.
[2] Its tailplane, triangular in plan, was mounted on top of the fuselage and carried separate, parallel chord elevators.
[2] The Invincible's fixed, tailwheel landing gear had mainwheels independently mounted on cranked half-axles hinged at the centre of the fuselage underside.