The Blériot-SPAD S.29 was a two-seat single-bay biplane, with a slightly swept upper wing and a straight lower wing, with the wings connected by a single strut on each side. Ailerons were fitted to the lower wing only. The fuselage was a circular section wooden monocoque structure, with pilot and passenger seated in tandem in a single cockpit. It was powered by a 80hp Le Rhône 9C rotary engine driving a two-bladed propeller fitted with a large hemispherical spinner, mounted on ball-bearings so that it did not rotate with the propeller, possibly a precaution against the spinner disintegrating due to centrifugal force.[1]