Berkshie Concept C-70
The first US all-glassfibre sailplane, known as the Concept 70, did not make its first flight until 1970, some 13 years after the Akaflieg Stuttgart FS-24 Phonix had pioneered this material for sailplane structures. The single-seater Standard Class Concept 70 was the responsibility of Arthur Zimmerman and Wolfgang Schaer.
The cantilever shoulder wings have a constant chord centre section and tapered outer panels, and are of glassfibre/PVC foam sandwich construction, with aluminium flaps lowering to 90°; up to 200lb of water ballast can be carried. The glassfibre monocoque fuselage has a steel tube reinforcing frame connecting the monowheel and wing fittings and continuing into the cockpit for greater strength and rigidity. The pilot sits in a semi-reclining seat, recessed for an American type parachute, under a one-piece flush Plexiglas canopy which is hinged and jettisonable. The manually-retractable Tost monowheel has a drum brake.
Differing in a number of respects from the prototype, the production version emerged with a Wortmann airfoil, full-span flaps, no brakes and a conventional horizontal tail. Production by the Berkshire Manufacturing Corporation got under way in 1973, some 16 Concept 70s having been built by the spring of 1974. Production ceased in 1974 after 21 were built.
Span: 15m / 49 ft 2.5 in
Length: 24 ft 0 in
Height: 6 ft 0 in
Wing area: 12.26 sq.m / 132sq.ft
Aspect ratio: 18.3
Empty Weight: 250kg / 550lb
Gross Weight: 397kg / 875lb
Wing Load: 32.38kg/sq.m / 6.63lb/sq.ft
Water Ballast: 91kg / 200lb
Max speed: 121 mph (in smooth air)
Min sinking speed: 2.03 ft/sec at 50.5 mph
Best glide ratio: 40:1 at 60 mph