An outstanding four-seat cabin touring monoplane of the 1930s with an excellent standard of reliability and comfort, the Caudron C.630 Simoun (Sandstorm) incorporated many technical features developed in designer Marcel Riffard's series of Coupe Deutsche de la Meurthe racers.

The experimental C.500 Simoun IV and C.620 Simoun VI were exhibited at the Paris Salon de l'Aeronautique in 1934. The C.620 was intended for the Challenge Internationale de Tourisme competition and its comfortable individual seats, deep windscreen and three large windows on each side of the cabin found greater favour than the more conventional layout and shallow windscreen and windows of the C.500 Simoun IV. There was clearly a market for the Simoun with its new Renault six-cylinder engine and, apart from the one-off C.520 and two long-range versions of the C.620 with extra fuel tanks in the cabin, the production C.630 was the next version to appear.

The C.630 was an elegant low-wing cantilever monoplane of wooden construction, the wing covered by plywood plus fabric and incorporating flaps that occupied the entire trailing edge inboard of the ailerons. The slab-sided fuselage had light alloy covering for the carefully streamlined curved underside and roof. The non-retractable tailwheel landing gear had cantilever main legs with oleo-pneumatic shock absorbers, the legs, main wheels and castoring tailwheel all enclosed in streamlined fairings. Differential brakes were standard.

The prototype C.620 with a 170 hp (127 kW) Renault Bengali 6Pfi engine was flown for the first time in October 1934. Only a few months later, in mid-1935, deliveries began of the C.630 series with a 180 hp (134 kW) Renault 6Pri (or 6Q-07) driving a Ratier variable-pitch metal propeller. The new type found immediate favour, with orders for some 70 private tourers following. Commercially, 12 C.630s established France's first regular air mail service, each in an elegant light blue finish with a silver arrow along the fuselage side; these belonged to Air Bleu, the air-mail subsidiary of Air France. Air Bleu's first flight from its Le Bourget base was on 10 July 1935. After somewhat erratic early progress, the criss-cross of domestic postal routes resumed in June 1937 and continued until May 1939, establishing a 95 per cent regularity record and carrying over 45 million letters. Other Simouns flew air mail routes in Madagascar.

A number of variants followed the C.630, but only the C.635 with a 220 hp (164 kW) 6Q-09 or 6Q-15 Bengali engine was built in quantity. Five of the type in red livery equipped the French VIP Escadrille Ministerielle, while during 1935-6 the French services placed initial orders for the militarised C.635M version, 110 for the Armée de l'Air and 29 for the Aéronavale. Other military and naval orders followed, the Simoun being used widely for liaison, as a General Staff transport, and as a transition or navigation trainer. At the outbreak of World War II some 60 civil Simouns were requisitioned by the Armée de l'Air for the hastily formed Sections d'Avions Estafettes (air couriers) and Sections d' Avions Sanitaires (air ambulances). During the invasion of France two aircraft were known lost, the remaining captured aircraft were used by Vichy forces. Of 103 Simouns captured by the Germans in November 1942, when they took over the Unoccupied Zone of France from the Vichy regime, 65 were used for training and liaison. Large numbers of Simouns flew with the French in North Africa, although the attrition rate was high. Several examples were reported in the UK during the war.

Many well-known French pilots of the 1930s used the Simoun in long distance attempts. Among those to gain success were Genin and Robert, who flew a C.635 (registered F-ANMA and named Gody Radio) from Le Bourget on 18 December 1935, 57 hours 36 minutes later landing at Antananarivo in Madagascar, having covered a distance of 5,384 miles (8665 km). Marie Bastie flying solo took her C.635 Jean Mermoz from Orly on 12 December 1936, and reached Dakar in West Africa on 19 December and then crossed the South Atlantic to Natal in Brazil, a distance of 1,926 miles (3100 km) averaging 164 mph (264 km/h). This beat the record held previously by Jean Batten of New Zealand. In another solo flight from France, in August 1937, Maryse Hilsz reached Saigon in less than four days.

Other more famous fliers were less fortunate. On a second attempt to reach Tokyo from Paris, Marcel Doret and his partner Micheletti made an emergency landing in Japan and were badly hurt. The great airman-poet Antoine de Saint Exupery, attempting to reach Tierra del Fuego from New York in 1937, crashed on take-off at Guatemala City and was seriously injured. A number of Simouns remained in flying condition post-war. One was used (on the ground, alas) in the film entitled The Little Prince, appropriately enough a story written by Antoine de Saint Exupery. In August 1944, the French Provisional Government began to nationalize the aircraft industry. Caudron, due to its activities during the German occupation, was one of the first companies to be broken up under the new policy. However, some Caudron designs such as the C.449 Goéland and C.800 glider continued to be produced post-war.

Variants

Caudron C.500 Simoun IV - The experimental C.500 Simoun IV was exhibited at the Paris Salon de l'Aeronautique in 1934.

Caudron C.520 Simoun - Another single aircraft similar to the C.500 but intended as a pre-production aircraft for the C.630 series.

Caudron C.620 Simoun VI - This experimental C.500 Simoun IV was also exhibited at the Paris Salon de l'Aeronautique in 1934. The C.620 was intended for the Challenge Internationale de Tourisme competition and its comfortable individual seats, deep windscreen and three large windows on each side of the cabin found greater favour than the more conventional layout and shallow windscreen and windows of the C.500 Simoun IV. Powered by 170 hp (127 kW) Renault Bengali 6Pfi engine it was flown for the first time in October 1934.

Caudron C.620 Simoun Long Range - Two aircraft were produced and fitted with extra fuel tanks in the cabin in order to extend the range.

Caudron C.630 Simoun - Deliveries began of the C.630 Simoun series in mid-1935 powered by a 180 hp (134 kW) Renault 6Pri (or 6Q-07) engine driving a Ratier variable-pitch metal propeller. The new type was an immediate success, with private orders for some 70 aircraft soon following. Only 20 aircraft were eventually built.

Caudron C.631 Simoun - Three aircraft powered by a 220 hp (164 kW) Renault Bengali 6Q-01 6-cylinder engine.

Caudron C.632 Simoun - A single aircraft powered by a 220 hp (164 kW) Renault Bengali 6Q-01 6-cylinder engine with only minor detail changes.

Caudron C.633 Simoun - Six aircraft produced with a modified fuselage and powered by a 180 hp (134 kW) Renault Bengali 6Q-07 6-cylinder inline engine.

Caudron C.634 Simoun - Three aircraft produced with a modified wing, increased take-off weight and a 220 hp (164 kW) Renault Bengali 6Q-01 or 6Q-09 6-cylinder inline piston engine.

Caudron C.635 Simoun - Main production type incorporating an improved cabin layout and powered by a 220 hp (164 kW) Renault Bengali 6Q-01 or 6Q-09 6-cylinder inline piston engine. 46 aircraft were built, but some earlier aircraft were converted to this standard.

Caudron C.635M Simoun - This was a version of the C.635 built to military specifications (detailed modifications based on the service) and with standard military equipment installed. Powered by a 220 hp (164 kW) Renault Bengali 6Q-09 or 6Q-15 6-cylinder inline piston engine. 436 aircraft were built for the Armée de l'Air and another 52 aircraft were built for the Aéronavale. A single aircraft was also produced for the US Naval attaché in Paris.

Specifications (Caudron C.635M Simoun "Sandstorm")

Type: Four Seat Trainer, Liaison, Air Ambulance, Staff Transport & Civil Touring/Mail Airplane

Accommodation/Crew: Pilot & Co-Pilot/passenger and two more seats for passengers plus up to 330.75 lbs (150 kg) of baggage and/or cargo.

Design: Designer Marcel Riffard of the Société Anonyme des Avions Caudron

Manufacturer: Société Anonyme des Avions Caudron in Issy-les-Moulineaux and Billancourt (Renault engines). In 1933 the Caudron and Renault companies were amalgamated. In 1936 the french aircraft industry was nationalised, but the Société Anonyme des Avions Caudron managed to survive as an independent company. During the German occupation, the Caudron and Renault companies were closely linked with a portion of the Renault factory in Billancourt being devoted to Caudron aircraft production.

Powerplant: One 220 hp (164 kW) Renault Bengali 6Q-09 6-cylinder inline piston engine.

Performance: Maximum speed 186 mph (300 km/h) at sea level; economical cruising speed 162 mph (260 km/h); service ceiling 19,685 ft (6000 m).

Range: 932 miles (1500 km) on internal fuel.

Weight: Empty equipped 1,664 lbs (755 kg) with a maximum take-off weight of 3,042 lbs (1380 kg).

Dimensions: Span 34 ft 1 1/2 in (10.40 m); length 29 ft 10 1/4 in (9.10 m); height 7 ft 6 1/2 in (2.30 m); wing area 172.23 sq ft (16.0 sq m).

Armament: None.

Variants: C.500 Simoun IV (experimental), C.520, C.620 Simoun VI (experimental), C.620 Simoun Long Range, C.630 Simoun, C.631, C.632, C.633, C.634, C.635, C.635M (military).

Equipment/Avionics: None.

History: First flight (C.500/C.620) early 1934; first flight (C.620) October 1934; first commerical flight (C.630) on 10 July 1935.