This single-seater motor glider was developed from the earlier SF-29 and is intended especially for training and powered cross-country flying, and for use by clubs as well as private owners.
It made its first flight in 1977, and although it did not go into production it was aimed at filling the gap between the two-seater SF-25 Falke variants and the higher performance single-seat powered gliders such as the PIK-20E and Nimbus 2M; it was also designed for ease of handling by the less experienced pilot. Like the earlier SF-25 Falke variants which it resembles, the SF-33 is a cantilever low-wing monoplane of basically wooden construction; the fuselage is a steel tube framework covered with plywood and fabric, and the engine cowling panels are of glassfibre reinforced plastic. The two-piece wings have plywood leading edges and wooden ailerons, and there are spoilers in the wing upper surfaces. The wooden tail unit has a trim tab in the starboard elevator. The landing gear consists of a fixed monowheel, a steerable tailwheel linked to the rudder for taxying, and two detachable outrigger wheels under the wings. The pilot sits under a large blown canopy that opens sideways to starboard and gives excellent all-round visibility. Powerplant is a 900cc BMW two-cylinder motorcycle engine derated to 35hp and driving a Hoffman two-blade variable pitch propeller; total fuel capacity is 4.8 Imp gallons.
The SF-33 is self-launching, and its gliding performance is claimed to be comparable to that of the Schleicher Ka 8.
Span: 49 ft 2.5 in
Length: 22 ft 1.75 in
Height: 4 ft 9 in
Wing area: 134.5 sqft
Aspect ratio: 18.0
Empty weight: 661 lb
Max weight: 904 lb
Max speed: 106 mph (in smooth air, power off)
Max cruising speed: 93 mph (power on)
Min sinking speed: 2.79 ft/sec at 50 mph
Best glide ratio: 29:1 at47 mph
Take-off run : 490-655 ft
Range with max fuel: 186 miles