03/31/2012. Designed as a catapult-launched light scout and observation aircraft to the French Navy's specification A50, the HD.730 was produced by a team led by Emile Dewoitine at the SNCAM ( Société Nationale de Constructions Aéronautiques du Midi) which, in 1937, had taken over the Societe Aeronautique Française Dewoitine under the Law for the Nationalization of Military Industries.
Two prototypes of the HD.730 were ordered from the Toulouse plant of the SNCAM on March 19, 1938, and these were transported to the SNCASE (Société Nationale de Constructions Aéronautiques du Sud-Est) plant at Marignane for final assembly, the first prototype flying from the Berre Lake in February 1940.
Powered by a 220 hp Renault 6Q-03 six-cylinder air-cooled inverted in-line engine driving a two-bladed Ratier-1759 electric airscrew, the HD.730 was of all-metal construction, the fuselage having a stressed light alloy skin and accommodating the pilot and the observer-gunner, and the single-spar stressed-skin wing being divided into five sections; the centre section built integral with the fuselage and four folding sections, those immediately outboard of the floats folding vertically and the extreme outboard panels folding to meet above the fuselage.
All movable control surfaces were fabric-covered, and the interchangeable floats were attached to the wings by cantilever pylons. All fuel was housed in two tanks in the wing centre section with a total capacity of 63.4 gal (240 l), a vertical camera was mounted in the rear fuselage, and defensive armament comprised one 0.295 in (7.5 mm) Dame machinegun with 300 rounds firing outside the airscrew arc, and a similar gun on a flexible mount for the observer.
The HD.730-01 began evaluation trials at Saint Raphael on April 26, 1940, but it was obvious that the floatplane was underpowered, and it was proposed that the Renault 6Q-03 be replaced by a Beam 6D engine of 350 hp in the production model. In April 1940 it was proposed to order an initial batch of forty machines for the Navy with deliveries commencing in 1941, but in the event the order was not placed owing to France's collapse.
The HD.730-02 flew for the first time from the Berre Lake in May 1940, but its transfer to Saint Raphael was prevented by the capitulation of June 25, 1940, which grounded both prototypes, these subsequently being stored in the SNCASE plant at Mazargues, in the suburbs of Marseilles. Despite France's defeat, development of the basic design continued, and an extensively redesigned third machine, the HD.731-01, was built in Bagneres-de-Bigorre, assembled in the SNCASE plant at Marignane, and flown from the Berre Lake on March 11, 1941.
In order to enable the development of the aircraft to proceed, the HD.731-01 was referred to as a "hydravion colonial de liaison commerciale" (commercial colonial liaison seaplane). Powered by the 350 hp Beam 6D, the HD.731 had smaller overall dimensions than the HD.730, and the method of wing folding was revised, two folding points replacing the original four. The new wing had a shorter span and smaller area, and the entire trailing edge was occupied by slotted flaps and ailerons. All fuel was housed in a single 63.4 gal (240 l) tank located in the port side of the wing centre section, aft of the main spar.
The maiden flight, with Marcel Doret at the controls, lasted forty minutes, after which some modifications were made at the Mazargues plant, including a change in the angle of the float axis from two to four degrees. Flight trials were resumed on April 22, 1941, but seven days later, after 2 hr 20 min had been logged in the air, tests were stopped for further modifications, the tailplane attachment points being reinforced, the elevator chord being increased, and the endplate fins and rudders being enlarged.
Flight tests were once again resumed on June 30, 1941, however, on July 4, the last flight of the HD.731 was made, as it was decided that an increase in wing area was necessary, and as circumstances did not permit such a major modification to be made, the aircraft was disassembled and stored.
The SNCAM had merged with the SNCASE while the HD.731 had been under test, and the two prototypes of the HD.730 had been transferred from Mazargues to Marignane on June 20, 1941, for re-assembly. At the same time the original 220 hp Renault 6Q-03 engine of the HD.730-02 was replaced by a 350 hp Beam 6D. Flight trials with the HD.730-02 were resumed on September 2, 1941, with a 20-minute flight after which the tail fins were enlarged. A second flight was made on September 16, and this was followed by the introduction of a central fin with which five more flights were made between September 24 and 27.
Trials were brought to a standstill when the engine seized. While a replacement engine was awaited, the engine cowling was redesigned to improve cooling, and longer floats were fitted. The installation of a new central fin with a third rudder began on November 24, 1941, but the aircraft was not flown in this configuration as the Italian control commission forbade further trials, and the aircraft was placed in storage at the Vitrolles plant from December 18, 1941. A similar fate overtook the HD.730-01 which, by that time, had been equipped with the Beam 6D engine.
Work on the HD.730-02 was once more resumed after the withdrawal of the German forces. The triple fins were replaced by a single fin and rudder assembly, and Mercier ailerons were fitted to the outer wing panels to permit a greater flap span. The first flight of the HD.730-02 in its new configuration was made on July 21, 1945, after which the aircraft was transferred to the SNCASE plant at Berre where the wing root fairings were enlarged and the span of the tail plane was increased.
Ensuing trials indicated that all teething troubles had been successfully eradicated, and as French warships were no longer equipped with catapults, consideration was given to the possibility of producing the HD.730 as a training and communications floatplane. On June 25, 1946, the HD.730-02 was handed over for official trials, but by this time the SCAN-20 had made its debut and there was no longer any interest in the HD.730.