Warplanes of France: SNCAC NC.3021 Belphégor

SNCAC NC.3021  Belphégor

(SNCAC Photo)

The SNCAC NC.3021 Belphégor was a French high altitude research aircraft designed and built at the end of the Second World War. Only one was completed and it was not a success, in part because of problems with its unusual engine.

The Belphégor had its origins during World War II in Marcel Roca's SNCAC NC.3020 design, an ultimately unbuilt aircraft powered by a coupled pair of Hispano-Suiza HS.12Z engines mounted side by side in the nose driving coaxial propellers. When work on the design resumed at the war's end these engines were replaced with a similarly arranged Daimler-Benz pair, resulting in a revised type, the NC.3021. The Belphégor was intended to provide a high altitude laboratory for studies of the meteorology of the upper atmosphere, high altitude aerodynamics and also of incoming cosmic rays. The measurements were to be made at altitudes between 10,000 m (32,800 ft) and 14,000 m (45,900 ft). The pressurization system was fed from a large scoop intake below the engine into engine driven compressors. The pressurized cabin, slightly wider than high had an average diameter of about 2.45 m (8 ft 0 in) allowing the two observers comfortable working room and a total cabin volume of 11 m3 (390 cu ft). They had observation windows in the cabin roof and in its floor. The crew positions were also in the pressurized region: the pilot's cockpit placed his head above the upper fuselage under a clear canopy. Two other crew, navigator and radio operator sat wholly within the cabin.

Museum-preserved DB 610 "power system" twin-crankcase "coupled engine", similar to the Belphegor's powerplant.The Belphégor was a cantilever mid-wing monoplane. The three part, high aspect ratio wing was strongly tapered in plan, mid-positioned and built around a single steel main spar with two auxiliary spars which were wooden in the outer sections.[3] The broad chord wing roots were carefully faired into a near circular fuselage. The ailerons, fitted with tabs, were metal framed but fabric covered. Two part, hydraulically operated camber changing metal slotted flaps were fitted. Its semi-monocoque fuselage was in three sections; the metal forward part contained the German-designed 2,200 kW (2,950 hp) Daimler-Benz DB 610A twin-crankcased "power system" engine unit weighing some 1.5 tonnes by itself, with its circular radiator in the nose and driving a single four blade propeller as well as the pressurization system. Behind it a tubular Dural structure supported the double skinned cabin and a final, wooden tail section. The tail unit was conventional, with a single tall straight edged, round topped fin and rudder. All the flight controls, whether on the wings or the tail, were both dynamically and aerodynamically balanced. The tail wheel undercarriage had inward retracting main legs.

Its first flight was on 6 June 1946 from Toussus-le-Noble Airport. Flight tests were made difficult, if not dangerous, by the DB 610's tendency to overheat and they were abandoned either in 1947 in the absence of financial support or in 1949, after only forty flying hours, because of the continuing mechanical problems. (Wikipedia)

(SNCAC Photos)

The NC 3021 before the dorsal fairing was added forward of the vertical stabilizer. Note the glazing on the lower fuselage. Between the panels was the lower pressure cabin bulge with observation ports.

The NC 3021 was completed at the end of May and registered as F-WBBL. Taxi tests were initiated at the beginning of June, and the aircraft made its first flight on 6 June 1946 with Joanny Burtin as the pilot. The aircraft suffered from directional instability, and a dorsal fairing was soon added in front of the tail to increase its lateral surface area. Testing was brought to a halt later that summer when the right main gear collapsed. The landing gear manufacturer was slow to provide a new main gear leg, and SNCAC resumed flight tests as best as it could with a temporarily repaired main gear fixed in the down position.

The landing gear was eventually repaired, but the DB 610 engine proved to be difficult to service and maintain. To make matters worse, SNCAC was having financial issues and did not have the funds to spend on an experimental project that offered little in return. When SNCAC delivered the NC 3021 to the Centre d’essais en vol (CEV, Flight Test Center) at Brétigny-sur-Orge on 12 October 1948, the aircraft had only made 45 flights for a total of 40 hours of flight time.

The CEV worked to maintain and test the NC 3021. By April 1949, the CEV had put in 1,500 hours of work on the NC 3021 but had only flown the aircraft for 2 hours and 45 minutes. The CEV did not want to continue to operate the aircraft, and SNCAC declared bankruptcy in July 1949. There were no other parties interested in funding the expensive and difficult to maintain experimental aircraft, and the NC 3021 was most likely scrapped in late 1950.

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