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The aircraft was completed in prototype form in June 1915 and, for its time, was a remarkably clean and smooth-contoured aircraft. While the brothers Caudron had collaborated closely in aircraft design up to this point, the G.3 and G.4 had been credited largely to Gaston Caudron, while the R.4 was mostly the work of René Caudron. The R.4 was a radical departure from its predecessors, with an attractive full-length fuselage and single fin and rudder. The unequal-span wings had three bays on each side, and there were ailerons on the upper wing only. As well as the twin-wheel main landing gear units and tailskid, there was a single nose-wheel intended to protect the propellers in rough landings.
The R.4 performed well in combat conditions, not only maintaining defensive capabilities whilst in reconnaissance mode but also achieving success in shooting-down a considerable number of enemy aircraft. Intended originally as a bomber, it served mainly as a three-seat reconnaissance aircraft, frequently engaged in photographic work. Its climb rate was not impressive, and a few aircraft were built with more-powerful 112 kW Hispano-Suiza 8Aa engines in an attempt at improvement. The problem which emerged was that production aircraft began to reveal a certain structural weakness. In developing the aircraft, a number of crashes occurred; the most disastrous for the Caudron firm occurred on 12 December 1915, when a series aircraft under test was destroyed and Gaston Caudron, who was piloting the aircraft, was killed. In early use Escadrille C.46 had claimed 34 German aircraft brought down with its R.4s in an eight-week period, but it was soon clear that in addition to structural redesign, improved ceiling and greater manoeuvrability were highly desirable. The new Caudron chief designer, Paul Deville, accordingly set to work on an improved development which was to emerge as the Caudron R.11. Production of the R.4 was terminated after 249 had been built. In the reconnaissance escadrilles it was replaced by the more-powerful Letord 1 in 1917.
- Crew: Three
- Length: 11.80 m (38 ft 9 in)
- Wingspan: 21.10 m (69 ft 3 in)
- Height: 3.20 m (10 ft 6 in)
- Wing area: 70.0 m2 (754 ft2)
- Empty weight: 1,710 kg (3,770 lb)
- Gross weight: 2,330 kg (5,137 lb)
- Powerplant: 2 × Renault 12Db, 97 kW (130 hp) each
- Maximum speed: 136 km/h (85 mph)
- Endurance: 3 hours 0 min
- Service ceiling: 4,600 m (15,090 ft)
- Rate of climb: 1.9 m/s (374 ft/min)
- 2 × .303 Lewis guns in flexible mount in nose
- 2 × .303 Lewis guns in flexible mount in dorsal position
- Up to 100 kg (220 lb) of bombs
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- Taylor, Michael J. H. (1989). Jane's Encyclopedia of Aviation. London: Studio Editions. p. 241.
- World Aircraft Information Files. London: Bright Star Publishing. pp. File 891 Sheet 17.