Development and Design
René Fournier conceived the RF-4 following a fatal aerobatic accident involving its predecessor, the RF-3, over his factory. Determined to create an "unbreakable" aerobatic motor glider, Fournier designed the RF-4 with substantially strengthened construction, featuring wing spars rated for +12/-6g loads compared to typical light aircraft limits. The design incorporated pushrod controls with sealed bearings replacing the cable controls of earlier models, along with a rounded belly profile, enlarged wing-root fairings, and a broader vertical stabilizer.
The RF-4's most revolutionary feature was its powerplant: a Rectimo-converted Volkswagen Beetle engine producing 39 horsepower from 1,179 cubic centimeters. This marked the first certified use of a converted automotive engine in a certified aircraft, pioneering what would later be recognized as "green aviation" technology during the oil crises of the 1970s.
Production History
Initial production began in 1966 at Gap-Tallard, France, where Alpavia constructed three pre-production aircraft in collaboration with René Fournier. However, Alpavia faced significant operational challenges including unfavorable exchange rates, unreliable electricity supply, and intermittent telephone service. These difficulties forced the closure of French production in 1966, with manufacturing rights transferred to Germany.
Sportavia-Pützer GmbH, established specifically for Fournier aircraft production, took over series manufacturing of the RF-4D variant at Dahlemer-Binz, West Germany. Operating at a rate of six aircraft per month from 1966 to 1970, Sportavia-Pützer built 155 to 156 RF-4D aircraft with construction numbers ranging from 4004 to 4158. Total RF-4 production reached 173 aircraft, including the French pre-production examples.
The Manufacturer
Alpavia operated during the early 1960s, previously manufacturing 89 RF-3 aircraft between 1963 and 1966 before encountering the operational difficulties that led to its closure. Sportavia-Pützer, founded by Alfons Pützer, was created specifically to continue Fournier aircraft production after the French manufacturing challenges.
Sportavia-Pützer later became part of the VFW-Fokker Group, though this conglomerate eventually dissolved with its assets absorbed into larger aerospace companies. Neither Alpavia nor the original Sportavia-Pützer exists as an independent entity today, representing the consolidation typical of the general aviation industry during the late 20th century.
Technical Innovation
The RF-4's all-wood construction combined traditional craftsmanship with innovative design solutions. The aircraft featured a forward-retracting monowheel landing gear system that retracted into a fiberglass cowling, equipped with wheel brakes and supplemented by a small steerable tailwheel and wing-mounted outrigger wheels for ground stability.
Balanced Frise ailerons provided enhanced control response during aerobatic maneuvers, while an enlarged fuel tank supported extended cross-country flights. The design enabled high-altitude performance capabilities, with related Fournier aircraft demonstrating the ability to reach altitudes exceeding 36,750 feet in unpowered flight.
Operational Service
The RF-4 found its primary market among private pilots, gliding clubs, and sport aviation enthusiasts across approximately 30 countries including throughout Europe, the United States, and Japan. Its single-seat configuration and dual-purpose design as both a powered aircraft and glider made it particularly attractive to pilots seeking economical cross-country touring combined with aerobatic capability.
The aircraft's efficient operation and low fuel consumption aligned with emerging environmental consciousness in aviation, particularly relevant during the energy crises of the 1970s. However, later Fournier designs encountered certification difficulties when aviation authorities began requiring dual ignition systems, which complicated the use of converted automotive engines.
Legacy and Survivors
At least three RF-4 aircraft are known to survive today. The first prototype remains believed airworthy in France, while the second aircraft is preserved on static display at the Musée de l'Air in Paris. These survivors represent the pioneering spirit of René Fournier's approach to efficient, environmentally conscious aircraft design.
The RF-4's significance extends beyond its production numbers, establishing important precedents for automotive engine conversions in certified aircraft and demonstrating the viability of wood construction in modern aerobatic designs. Its influence can be traced through subsequent Fournier designs and the broader acceptance of alternative powerplant solutions in general aviation, making it a notable milestone in the evolution of sport and touring aircraft.