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Siren D 77 Iris
Issorie-Aviation D 77 Iris



Design of the D 77 Iris single-seat training sailplane was started in 1973 by Siren SA. Of glassfibre/plastic foam sandwich construction, the Iris was also available in kit form for homebuilders, and has cantilever mid-set wings of Bertin E55-166 aerofoil section and glassfibre/polyester/PMC sandwich construction, with glassfibre ailerons and metal Schempp-Hirth air brakes in the upper surfaces. The fuselage is a glassfibre/polyester monocoque built in two halves and reinforced at the wing attachment points. As originally designed, the Iris had a cantilever T-tail but this was changed to one with a low-set fixed incidence tailplane and a spring tab in each elevator; the tail is of similar construction to the wings. There is a non-retractable unsprung monowheel with a Siren hydraulic brake, and a tailskid. The pilot sits in an adjustable semi-reclining seat under a one-piece flush-fitting cockpit canopy which opens sideways to starbaord.
The prototype first flew on 26 February 1977 and made its public debut at that year's Paris Salon Aeronautique; after the manufacturer's tests were completed, tests by the CEV (Centre d'Essais en Vol) followed early in 1978, after which certification got under way.
Production of the Iris and of the E 75 Silene became the responsibility of Societe Issorie-Aviation, which was formed late in 1977 by the President of Siren SA following the bankruptcy of Wassmer-Aviation; approximately 50 D 77s had been ordered by February 1979 when production was due to begin.
Issoire D 77 Iris
Span: 13.5 m / 44 ft 3.5 in
Length: 6.37 m / 20 ft 10.75 in
Height: 0.9 m / 3 ft 11.25 in
Wing area: 11.4 sq.m / 122.7 sq.ft
Wing section: Berlin E-55-166
Aspect ratio: 16.0
Empty weight: 220 kg / 485 lb
Max weight: 330 kg / 727 lb
Water ballast: None
Max wing loading: 27.2 kg/sq.m / 5.57 lb/sq ft
Max speed: 145 mph / 126 kt / 234 km/h (in smooth air)
Max aero-tow speed: 105 mph
Stalling speed: 32.5 kt / 60 km/h
Min sinking speed: 2.23 ft/sec / 0.68 m/sec at 50 mph / 39.5 kt / 73 km/h
Best glide ratio: 33:1 at 48.5 kt / 90 km/h
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