By William Pearce

In January 1937, the Ministère de l’Air (French Air Ministry) gave Arsenal de l’Aéronautique a contract to develop a twin-engine heavy interceptor fighter built from wood and powered by two 690 hp (515 kW) Hispano-Suiza 12X engines. The engines were to be mounted in tandem inside the fuselage driving coaxial propellers in the nose. Through the course of several changes, the aircraft’s design was developed into the all-aluminum VB 10 fighter. The VB 10 was designed in 1938 by Michel Vernisse and Robert Badie; the initials of their last names formed the ‘VB’ of the aircraft’s designation.

The Arsenal VB 10-01 prototype powered by two 860 hp (641 kW) Hispano-Suiza 12Y-31 V-12 engines. Note the obstructed rear view from the flush canopy.

The VB 10 was a low-wing monoplane in a standard taildragger configuration with retractable undercarriage and a single-seat. It was a large aircraft with a span of 50 ft 10 in (15.49 m), length of 42 ft 7 in (12.98 m), height of 17 ft 3/4 in (5.2 m), and an empty weight of 15,190 lb (6,890 kg).

While the aircraft was of a standard configuration, the engine arrangement was not. One engine occupied the standard position in the nose of the aircraft and a second engine was included behind the cockpit. Each engine drove a set of propeller blades that, together, made up a coaxial contra-rotating unit in the nose. The front engine drove the rear propeller, and the rear engine drove the front propeller. The drive shaft from the rear engine ran through the Vee of the front engine and to the front propeller. A Vernisse or homocinetic coupling was used in which flexibly-mounted ball joints join sections of the rear engine’s propeller shaft to accommodate deflection and vibration of the shaft.

The Latécoère 299A that served as an engine testbed for the Arsenal VB 10. The 229A was powered by two 860 hp (641 kW) Hispano-Suiza 12Y V-12 engines, same as the VB 10-01 prototype. Note the front propeller is not turning and the German markings.

Before the prototype was built, a contract for 40 aircraft was placed in May 1940. However, construction was suspended with the capitulation of France in June 1940. In April 1942, the Vichy government was able to persuade the RLM (Reichsluftfahrtministerium or German Ministry of Air) to allow construction to resume on the twin-engine propulsion system. To thoroughly evaluate the unusual engine arrangement, a Latécoère 299 was made into a flying testbed and renamed 299A. Completed in July 1943, the Latécoère 299A was destroyed in an Allied bombing raid on 30 April 1944.

With the tide of the war changing, the French restarted construction of the first prototype, VB 10-01, in July 1944. The unarmed prototype was powered by two 860 hp (641 kW) Hispano-Suiza 12Y-31 12-cylinder, liquid-cooled engines and had a flush, sliding canopy with an obstructed rear view. This aircraft was first flown on 7 July 1945 by Modeste Vonner. During initial flight tests, the VB 10-01 achieved a sea-level speed of 304 mph (490 km/h). An order for 200 aircraft was placed on 22 December 1945.

The second prototype VB 10-02 under construction. Note the two 20 mm cannons and three .50-cal machine guns in each wing.

The second prototype, VB 10-02, had a bubble canopy for improved visibility and was powered by two 1,150 hp (858 kW) Hispano-Suiza 12Z engines. The aircraft was also armed with four 20 mm Hispano-Suiza cannons (with 600 rounds total) and six .50-cal Browning machine guns (with 2,400 rounds total), all mounted in the wings. The VB 10-02 first flew on 21 September 1946. Mechanical issues and engine overheating plagued both prototypes; these challenges, combined with the availability of cheap surplus allied aircraft and the jet age on the horizon, led to a revised order of just 50 aircraft.

Another image of the Arsenal VB 10-02 with the side panels removed. Note the bubble canopy.

The first production VB 10 made its maiden flight on 3 November 1947. The aircraft was powered by two Hispano-Suiza 12Z-15/16 engines that were rated at 1,300 hp (969 kW) max and 1,150 hp (858 kW) continuous. It was armored with only four 20mm cannons but had provisions to carry one 1,100 lb (500 kg) bomb under each wing. Additional fuel took the place of the removed machine guns. The production aircraft went on to achieve a max speed of 323 mph (517 km/h) at sea-level and 435 mph (700 km/h) at 24,600 ft (7,500 m).

For the VB 10, the beginning of the end occurred on 10 January 1948 when the second prototype, VB 10-02, caught fire while over southern Paris. An uncommanded propeller pitch change over-reved the rear engine, destroying it and starting the fire. The pilot, Pierre Decroo, was forced to bail out. He survived but suffered burns. On 15 September 1948, the third (some say first) production machine crashed in much the same fashion, killing the pilot, Henri Koechlin. Six days later on 21 September 1948, the Arsenal VB 10 contract was cancelled. At the time of cancellation, four production VB 10 aircraft (including the one that crashed) had flown, six additional airframes had been completed, and a number of airframes were under construction. All remaining VB 10s (including the first prototype) were scrapped.

The size of the VB 10 is illustrated here by the crowd in front of the first production VB 10. The aircraft was powered by two Hispano-Suiza 12Z-15/16 engines. Note the 20 mm cannons and no machine guns.

Sources:
– The Complete Book of Fighters by Green and Swanborough (1994)
– Hispano Suiza in Aeronautics by Manuel Lage (2004)
– Jane’s All the World’s Aircraft 1948 by Leonard Bridgman (1948)
– “Behind the Lines: French Development” Flight (3 February 1944)
– http://fr.wikipedia.org/wiki/Arsenal_VB-10
– http://en.wikipedia.org/wiki/Arsenal_VB_10
– L’ Arsenal de l’Aéronautique by Gérard Hartmann (pdf in French)