Sportavia Pützer RF4D
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.
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; VHP 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