After the second prototype, the RF-02, and the original production version the 3, the German firm of Sporta-via Putzer GmbH took over manufacture of the single seater, and of a two seat development of it, the RF5; Fournier became dissatisfied with “ces Allemands” and struck out on his own.

The RF4 is a short wing aerobatic single seat edition of the Fournier design, the SFS 31 Milan is the same plane but with the long soaring wing. Although very similar in appearance to the Alpavia Avion-Planeur RF3, the RF4 has been completely redesigned and restressed to make it fully acrobatic, with a safety factor of 13 at full loading.

All plywood covering is of Finnish birch, the Frise-type fabric covered ailerons are aerodynamically compensated, the underside of the fuselage is now rounded instead of flat as on the RF3, and the wing/fuselage junction has been improved. Other differences from the RF3 include revised exhaust silencing and capacity of the single fuel tank in the fuselage increased to 8.4 Imp gallons, with a 5.5 Imp gallons auxiliary tank optional.

Three prototype RF4s were built in France by Alpavia SA but in 1966 the letter’s director, Comte Antoine d’Assche, formed Sportavia-Putzer GmbH und Co K.G. with Alfons Putzer to take over manufacture of the Avion-Planeur series form Alpavia, and production of the RF4 started at Dahlemer Binz in Germany. One hundred and sixty were built by Sportavia but production continued of RF-4D fuselages for SF5 31 Milan.

Structurally the RF4D entire tail unit can now be detached for transportation, and the three-section spoilers in each wing upper surface are metal-skinned. The landing gear is very similar, with the addition of a parking brake, and a ski landing gear was offered as an optional installation. The pilot’s canopy opens sideways to starboard, and there is a baggage space aft of his seat; VHF radio and an oxygen system was optional.

By the spring of 1971 a total of 160 RF4Ds had been built and exported to a number of countries, this being the production version with a main spar of laminated pine, giving increased structural strength for aerobatics.

The engine is a 40hp Rectimo 4 AR 1200 converted 1,200cc Volkswagen ‘flat four’ car engine driving a Hoffman two-blade fixed-pitch wooden propeller of 4ft 4in diameter; as on the RF3, this can be stopped and restarted in flight.

A distributor in Ohio, USA, assembled the Fournier RF4 motorgliders, which arrived in crates from Europe; the airplanes then received an experimental category certificate of airworthiness. The airplane was unique: an excellent performer; and, at that time, the closest one could come to an airplane and a sailplane in a single ship. It stimulated a good deal of interest. The RF4’s Volkswagen engine ran well, but the FAA would not grant a standard certificate to an airplane with a single ignition.

A notable flight was made by M. J. Slovak in RF4D N1700, who crossed the Atlantic in May 1969 in 175hr 42min 7.11sec to win the Evening News £1,000 prize for the best performance in that year’s Daily Mail air race by a light aircraft of under 5,000lb weight.

Sportavia Avion-Planeur RF4D
Engine: Rectimo 4 AR 1200, 40hp
Span: 36 ft 11.25 in
Length: 19 ft 1.25 in
Height: 5 ft 1.75 in
Wing area: 121.7 sqft
Aspect ratio: 11.2
Empty weight: 584 lb
Max weight: 859 lb
Max level speed: 122 mph
Max cruising speed: 112 mph
Min sinking speed: 4.27 ft/sec
Best glide ratio: 20:1
Take-off run to 50ft: 875 ft
Range with max fuel: 422 miles

This single-seater low wing motor glider was the first of a series of such types designed by M Rene Fournier to go into production, and to be built by several different companies in France and Germany.

The RF3 was developed from the prototype Avion-Planeur, known as the Fournier RF01, which first flew on 6 July 1960. It proved to be so successful that the French Government helped to finance the building of two RF2 pre-production prototypes, the first of which flew in June 1962, and later ordered six of the production version, the RF3, with 34 hp Rectimo-VW engine, for national flying clubs; the first RF3 made its maiden flight in March 1963 and received its Cof A on7 June that year.

A second prototype of the RF-01 was built, and then Fournier entered into partnership with Antoine d’Assche, who was then producing Jodel two-seaters in a hangar at Gap in the French Alps under the trade name of Alpavia. They produced quite a number of the little airplanes, which were not exactly powered sailplanes but airplanes with an unusually shallow angle of glide; successive improvements brought about the RF4 (the second prototype having been the 2, and the original production version the 3 with Volkswagen engine). The production RF-3 differed only slightly from the prototype RF-01.

The RF-3 is a true airplane-glider and can operate as a conventional airplane, giving very economical flight at low power settings. It can also cruise at higher speeds with very acceptable cross-country performance. The RF-3 also has semi-aerobatic performance both power-on and off.

Of all-wood construction, the RF3 has a single spar one-piece wing with D-section leading edge, with 4° dihedral and plywood and fabric covering, attached to the fuselage by four bolts. The ailerons are fabric-covered and there are no flaps, but instead a three-section air brake in the upper surface of each wing inboard of the ailerons. The wooden fuselage, having typical strip longerons, cross-members, spars, ribs, is plywood-covered, fabric covering is used on the rear portion of the wing behind the main spar. Airfoil is NACA 23015 section and aspect ratio is 11:1. The pilot sitting under a moulded one-piece canopy; radio and oxygen equipment are among the optional ‘extras’.

The monowheel has rubber chord shock absorption and retracts forward manually into a glassfibre cowling; it has a manually-operated brake and is supplemented by a hoop-shaped balancer skid of 6mm steel wire under each wing. The mono-wheel gear gives no problems in maneuvering with ground turning radius about half the wingspan. There is also a steerable tailwheel. Retracting the wheel is by pulling the lever full back and up-lock is automatic.

The cantilever wooden tail unit has a trim tab in the rudder. The RF-3 vertical tail has gentle sweep back not employed on previous aircraft in the series. Sailplane type retractable spoilers (speed brakes) are fitted to upper wing surfaces.

Rene Fournier has designed a comfortable, well laid-out cockpit with excellent pilot visibility. The large Plexiglas canopy is one-piece bubble type with ample head and shoulder-room forward and to the sides. Canopy making was entrusted to a molding specialist able to produce distortion-free surfaces. A sliding window-vent is fitted in canopy left side. The right canopy side is hinged along the top longeron for opening. A strap prevents canopy from flopping completely over against fuselage side.

The pilot’s seat has a thick comfortable cushion. Seat back cushions are removable and two back cushions of different thicknesses are available to suit the size and leg reach of any pilot. A small baggage compartment is located behind the seat in the fuselage bulkhead and is accessible from the cockpit.

The cockpit floor has wheel well housing extending upward between the pilot’s legs. Wheel retraction lever is along right cockpit side. Fournier has provided a recess in the left cockpit side for the brake handle when released. This keeps it out of the pilot’s way during flight. Elevator trim tab control is also on right side just below top longeron.

Turning to left cockpit side the wing spoiler (speed-brake) actuating lever is located beside the seat and the push-pull throttle is under longeron and panel.

The unperforated speed brakes extend 5.75 inches above the upper wing surface and retracts flush with the wing surface.

Wheel braking is by hand lever in floor. Hand brake is of same type used in small French cars. The control stick appears rather short but top is at convenient height so that pilot’s arm rests easily on the leg. Rudder pedals are two wooden bars on which the whole foot rests.

The instrument panel, though simple, has all the essentials. Blind flying gyro instruments are not included. A red stall warning light is flashlight battery powered (has test switch) since the RF-3 has neither battery nor generator. Starter and fuel cut-off knobs are at right lower panel edge. Production aircraft have engine cut-off and restarter system installed. This consists of a simple de-compression device which pushes on the exhaust valve rocker arms. With prop windmilling, the engine re-starts easily, even at very low airspeeds. A prop brake is also provided which stops the blades horizontally, covering the cowl air inlets, thus reducing drag to nearly that of a feathered prop.

Rene Fournier entered into partnership with Comte Antoine d’Assche of Alpavia SA, which had been building Jodel D117s, and this firm took on the production of the RF3, building a total of 95 in all; deliveries started in November 1963. Alpavia was turning out one RF-3 per week with delivery time of about 8 months in 1964. The RF-3 export price was $4,300 (21,500 Fr.) in 1964. Alpavia produced 95 in total before production ended.

Although the engine can be stopped and restarted in flight and the RF3 is capable of prolonged soaring flights – many such flights of up to five hours have been made – the type should not be regarded as just a powered sailplane, as it has a high performance and is capable of all simple aerobatic manoeuvres such as stall turns, loops, half-rolls, slow rolls and spins.

Starting at 97 Knots the RF-3 goes up smoothly for a loop to inverted position at 43 Knots, and gently completes the downward curve to level flight. A hammerhead stall is done at the same starting speed, with near stall speed at the top turn downward. The spilt “S” requires higher starting speed, 113 Knots, for the half-roll. Pull out is at 118 Knots. The slow roll in the RF-3 somewhat difficult to perform well, probably because of the long wing span. The snap roll is easy by comparison. The RF-3 spins with no bad habits. The turning rate is rather slow, but spin recovery is easily achieved. Rudder response is very sensitive and the ailerons produce practically no inverse yaw.

The stall characteristics, with stick full back, the stall warning light comes on at about 40 Knots, then at 36 knots the nose drops downward cleanly with a slight left wing low tendency. By simply releasing the stick at the stall, the RF-3 noses down and recovers from the stall on its own.

Fuel consumption is an economical low 1.98 gal/hr with cruising speed of 105-mph (91 Knots). This gives 4-hour endurance, without reserve, and a maximum no-wind range of 420 statute miles (364 nautical miles). Allowance for wind would reduce this range to a practical 315 s.mi. (270 n.m.). With economy cruise throttle setting, consumption drops to low-low .77 gal/hr. at 56-mph. If one cared to chug along at this speed, range would be over500 miles—48.6 Knots and over 400 n.m.

Airborne at 48.5 knots after a takeoff roll of a bit over 400-ft. In the pattern at 59 Knots, using the speedbrakes and throttle, unlocking the gear release, the wheel extends under its own weight. Simply push the gear full forward at the end of its travel to lock the gear down. With an approach at 48.5 Knots and, after rounding out, the RF-3 touches down gently with no difficulty at 37.7 Knots. The roll-out is about 300-ft.

This performance was soon being proved in service, one notable flight in the winter of 1963-64 being made by an RF3 pilot over St Auban in the Basses-Alpes region, who climbed to 19,700ft after stopping his engine at 6,500ft. Another RF3 was successfully operated in the French Alps with a mono-ski landing gear replacing the retractable monowheel. The engine is a 39hp modified version of the Volkswagen 1,200cc ‘flat four’ car engine, converted by the Rectimo Co of Chambery. The only modifications are the fitting of a special Zenith carburettor, a propeller shaft and a Bendix magneto of the type used on the 65hp Continental engine. For restarting in flight, an optional mechanical system pushes the four exhaust valves in simultaneously, enabling the propeller to start the engine during a dive at 90mph; a two-blade wooden prop made by Evra or Helice Legere is fitted, and there is a single 6.5 Imp gallon fuel tank in the fuselage. The fuel tank is located between instrument panel and firewall with a Cub-style internal float gauge has graduated wire rod protruding through the filler cap. Pilot has a clear view of this fuel gauge on cowl top.

Gallery

Alpavia RF-3
Engine: Rectimo, 39-hp
Prop: Fixed pitch 4’5.5” diameter
Span: 36 ft 9 in
Length: 19 ft 8 in
Wing area: 118.0 sqft
Aspect ratio: 11.0
Airfoil: NACA 23015 section
Empty weight: 529 lb
Max weight: 772 lb
Fuel capacity: 7.9 USG / 30 lt
Max level speed: 118 mph
Max cruising speed: 112 mph
Min sinking speed: 3.94 ft/sec
Service ceiling: 15,000-ft
Rate of climb: 689 fpm at 53.9 kt
Glide ratio: 18:1
Take-off run to 50ft: 875 ft
Range with max fuel: 310 miles

A second prototype of the RF-01 was built, and then Four¬nier entered into partnership with Antoine d’Assche, who was then producing Jodel two-seaters in a hangar at Gap in the French Alps under the trade name of Alpavia. They produced quite a number of the little airplanes, which were not exactly powered sailplanes but airplanes with an unusually shallow angle of glide; successive improvements brought about the RF4 (the second prototype having been the 2, with 34 hp Rectimo-VW engine, and the original production version the 3).
Government assistance was provided for development of the improved RF-2, subsequently produced by Alpavia as RF-3, with slightly uprated engine, first flown March 1963.

The RF-2 had perforated wing spoilers that extended from both upper and lower surfaces of the wing. They retracted vertically flush with the wing surface.

The Centennial 100 was developed as an improved version of the Found FBA-2. Design work started in October 1966 and the prototype first flew on 7 April 1967.

The aircraft is powered by a 290 hp (216 kW) Avco Lycoming IO-540-G1D5 engine.

Three prototypes and two production aircraft were built and were used to gain certification for the type in July 1968. No further aircraft were built as the company went out of business.

Engine: 1 × Avco Lycoming IO-540-G1D5, 290 hp (220 kW)
Propeller: 2-bladed Hatzell metal constant speed propeller, 7 ft 4 in (2.24 m) diameter
Wingspan: 39 ft 0 in (11.89 m)
Wing area: 196.6 sq ft (18.26 sq.m)
Aspect ratio: 7.2:1
Airfoil: NACA 23016 at root, NACA 23012 at tip
Length: 26 ft 6 in (8.08 m)
Height: 8 ft 4 in (2.54 m)
Empty weight: 2,000 lb (907 kg)
Max takeoff weight: 3,500 lb (1,588 kg)
Fuel capacity: 50.5 imp gal (60.6 US gal; 230 L)
Maximum speed: 162 mph (261 km/h, 141 kn) at sea level
Cruise speed: 140 mph (230 km/h, 120 kn) (Econ. cruise, 65% power)
Stall speed: 55 mph (89 km/h, 48 kn) (flaps down)
Range: 700 mi (1,100 km, 610 nmi)
Service ceiling: 18,000 ft (5,500 m)
Rate of climb: 1,250 ft/min (6.4 m/s)
Takeoff run to 50 ft (15 m): 1,020 ft (310 m)
Landing run from 50 ft (15 m): 950 ft (290 m)
Crew: 1
Capacity: 5 passengers