The Berkshire Concept 70, sometimes called simply the C-70, is an American, single seat, high-wing, 15 metre class competition glider that was designed by Arthur Zimmermann and produced by the Berkshire Manufacturing Corporation of Lake Swannanoa, New Jersey between 1971 and 1974.
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 Concept 70 was intended to be a domestic US fiberglass sailplane that would compete with the best European 15 metre aircraft being produced in the late 1960s.
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 (91 kg) of water ballast can be carried with optional water ballast tanks. The prototype has an Eppler airfoil and an all-flying horizontal stabilator. Production aircraft featured a Wortmann airfoil, a more conventional tail, and full-span flaps that deploy to 90° for glidepath control.
The glassfibre monocoque fuselage has a steel tube reinforcing frame connecting the retractable 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, when Zimmermann died in 1974, after 21 were built.
The aircraft was never type certified and all aircraft were registered as experimental aircraft in the Racing/Exhibition category.
The Concept-70 molds and tooling were available for about US $35,000 including 40ft container.
ASC kits appear no longer to be in production.
Concept 70
Wingspan: 49 ft 3 in (15.0 m)
Wing area: 132 sq ft (12.3 sq.m)
Aspect ratio: 18.3
Airfoil: Wortmann
Empty weight: 550 lb (249 kg)
Gross weight: 875 lb (397 kg)
Maximum glide ratio: 39:1
Wing loading: 6.6 lb/sq ft (32 kg/sq.m)
Crew: one
Concept 70
Wing span: 15.0 m (49 ft 2.5 in)
Length: 7.31 m (24 ft 0 in)
Height: 1.83 m (6 ft 0 in)
Wing area: 11.52 sq.m (124 sq ft)
Wing section: Eppler/Wortmann
Aspect ratio: 20.0
Empty weight: 226 kg (500 lb)
Max weight: 396 kg (875 lb)
Water ballast: 91 kg (200 lb)
Max wing loading: 34.38 kg/sq.m (7.04 lb/sq.ft)
Max speed: 105 kt (195 km/h)
Stalling speed: 31 kt (58 km/h)
Min sinking speed at 43.5 kt (81 km/h): 0.62 m (2.03 ft)/sec
Max rough air speed: 105 kt (195 km/h)
Best glide ratio at 52 kt (96.5 km/h): 40
All Aero 