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Akaflieg Braunschweig SB-9 Stratus
The SB-9 Stratus high-performance single-seater was developed by Akaflieg Braunschweig from the 18m (59ft 0in) span SB-8, and first flew in prototype form on 23 January 1969, making its debut at the German National championships that year. The SB-9 featured a higher aspect ratio (31.3) wing of 22m (72ft 2.5in) span, this giving a best glide ratio of 48:1 compared to 42:1 for the SB-8, a lower minimum sinking speed and otherwise improved performance.
But some problems were encountered with the wing geometry, especially aileron length, load distribution over the wing and rudder action, and as a result the maximum speed had to be limited to only 107mph. Later, wing span was reduced to 21m (68ft 11 in), this giving an improvement of 12mph in the maximum speed. The SB-9's wing is of PVC foam construction for lightness, and has a glassfibre roving spar; the HKS type flaps are of elastic glassfibre construction with no hinge or gap.



The fuselage is of glassfibre construction with balsawood support, and the landing gear is an unsprung retractable monowheel with a drum-type brake. A T-tail is featured, the tail unit being of glassfibre and balsa construction.
Wing span: 22 m / 72 ft 2.5 in
Length: 7.5 m / 24 ft 7 in
Height: 1.4 m / 4 ft 7 in
Wing area: 15.48 sq.m / 166.6 sq.ft
Aspect ratio: 31.27
Airfoil: Wortmann FX 62-K-153/131
Empty weight: 321 kg / 692 1b
Max weight: 412 kg / 917 lb
Water ballast: None
Wing Load: 26.6 kg/sq.m / 5.53 lb/sq ft
Max speed: 107 mph / 97 kt / 180 km/h
Stalling speed: 32 kt / 59 km/h
Max rough air speed: 97 kt / 180 km/h
Min sinking speed: 1.5 ft/sec at 45 mph / 39 kt / 72 km/h
MinSink: 0.51 m/s / 1.5ft/sec @ 81 kph
Best glide ratio: 48:1 at 53mph / 46 kt / 85 km/h
L/DMax: 46 @ 81 kph
No. of Seats: 1
No. Built: 1

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