11/30/2008. Remarks by Johan Visschedijk: "The Hurel-Dubois company was formed to develop Maurice Hurel's theories on high-aspect ratio wings. The concept was tested in the experimental single-engined HD.10 (F-WFAN, later F-BFAN) that was built at the Etablissements P. Levasseur.
(NOTE. A French registration starting with a 'W' indicates the aircraft is used for tests, experiments, CoA-qualifying, etc. After the aircraft gains its CoA the 'W' is altered in a different character.)
Trials showed a high fineness coefficient while is remained controllable at low incidences, it also showed excellent lateral stability and a surprising roll-rate. The success of these trials resulted in a contract from the French Government for two twin-engined cargo-aircraft of the same general configuration, the HD.31 (F-WFKU, later F-BFKU) powered by 800 hp Pratt & Whitney C7BA1 seven-cylinder radials, and the identical HD.32 (F-WGVG, later F-BGVG) powered by 1,200 hp Pratt & Whitney R-1830-92 radials. The former was flown on January 27, 1953, the latter on December 29, 1953.
A second HD.32 (F-WHHA) was produced, the twin-fins being replaced by a single one with a pair of auxiliary fins, the first (F-WGVG) was also fitted with a single fin. The two HD.32s were fitted with 1,525 hp Wright 982-C9-HE2 Cyclone engines and redesignated HD.321, these led to the slightly larger HD.34 of which eight were produced as photographic survey aircraft for the l'Institut Géographique National. The first HD.34 (F-WHOO, later F-BHOO) was flown February 26, 1957."