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Rhein-Flugzeugbau Sirius
The Sirius 1 single-seat high performance motor glider was developed primarily to investigate the efficiency of the ducted fan as a powerplant for sailplanes, and its use of a new integrated power system enabled a sailplane's aerodynamic qualities to be retained virtually uncompromised by the drag of a conventional tractor or pusher engine installation, at the same time making powered take-offs from small airfields possible. The Sirius 1 was developed from the basically all-metal VFW-Fokker FK-3, but was of combined metal and glassfibre construction, and in its initial form was powered by a 48hp Nelson 'flat four' air-cooled two-stroke driving an eight-bladed ducted metal fan coupled directly to the engine. The powerplant is a fixed low drag installation fitted at the eg, the fan exhausting down the length of the tail boom; fuel capacity is 7 Imp gallons and an electrical starter enabled the engine to be restarted in flight easily. The Sirius 1 was later fitted with two Yamaha motorcycle engines, and finally with two 20hp Finkel & Sachs Wankel rotary engines. It had cantilever mid-set wings with flaps variable in movement from -10° to +15°, and conventional air brakes just ahead of the flaps. There was a retactable monowheel with brake shoes, and a tailwheel, and the Sirius 1 could be landed with the wheel retracted. The tail unit resembled that of the VFW-Fokker FK-3, and the pilot sat on a glassfibre seat under a large sideways-hinged Perspex canopy; he could be provided with radio, oxygen equipment and a barograph.
The Sirius II is a side-by-side two-seater development of the Sirius 1 which utilised the wings, constructail unit and landing gear of the Caproni Vizzola Calif A-21S; this version made its first flight in January 1972 and the wing span was now 66ft 10.25in and aspect ratio 25.8 compared to the Sirius 1's 57ft 6.5 in and 22.0, while length was increased by 2ft 3in.
Powerplant consists of two 30hp Wankel rotary engines coupled to drive a ducted fan in an installation similar to that of the Sirius 1, one engine being mounted in front of the fan and the other behind it. The fan shroud has an annular slat-type intake around the wing leading edge to keep the airflow attached to the duct and prevent its breakaway; suck-in doors shut to fair off this intake when the powerplant is not operating, so as to enable the soaring performance to be maintained unaffected by drag. Fuel capacity is 6.6 Imp gallons.
Sirius II
Span: 66ft 10.25 in
Length: 26ft 4.5 in
Height: 5ft 11 in
Wing area: 173sq ft
Aspect ratio: 25.8
Empty weight: 1,124lb
Max weight: 1,521lb
Max speed: 168mph (power on)
Min sinking speed: 1.97ft/sec
Best glide ratio: 38:1
Take-off run: 656ft
Range: 168 miles

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