Schempp-Hirth Cirrus

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Schempp-Hirth Cirrus

A Cirrus at Pennewitz Airfield, Germany.
Type designation	Cirrus
Competition class	Open
Number built	183
Crew	1
Length	7.20 m
Height	1.7 m
Cockpit width	0.62 m
Cockpit height	0.85 m
Wingspan	17.74 m
Wing area	12.6 m²
Aspect ratio	24.9
Wing profile	FX 66-196 FX 60-126 (tips)
Empty mass	276 kg
Water ballast	98 kg
Maximum mass	400 kg
Wing loading	ca. 28 - 31 kg/m²
Maximum speed	km/h
Rough air speed	km/h
Maneuver speed	km/h
Stall speed	km/h
Minimum sink rate	ca. 0.50 at 80 km/h
Best glide ratio	ca. 44 at 90 km/h

The Schempp-Hirth Cirrus is an Open Class glider built by Schempp-Hirth between 1967 and 1971 and by VTC until 1977.

History

• The Cirrus was designed by Dipl. Ing Klaus Holighaus and was the first glass-fibre glider to be built by Schempp-Hirth.

• The prototype flew in 1967 with a V-tail like the Austria. It won the German Open Class in 1967.

• By 1971 107 had been built in Germany. Production was transferred to Vazduhoplovno Techniki Centar (VTC) at Vrsac in Yugoslavia, who built an additional 63.

• A Cirrus won the World Championship in 1968.

Design description

• Although Holighaus had designed and built the ground-breaking D-36 together with Gerhard Waibel, Wolf Lemke and Walter Schneider, he followed a completely different design philosophy for the Cirrus, preferring a thicker airfoil and the use of PVC foam instead of balsa as a core material.

• The resultant Cirrus has mid-set cantilever wings with a span of 17.74 metres, and a conventional low-set cruciform tailplane. It can carry water-ballast in the wings. There are no flaps. For glidepath control, there are effective top-and-bottom air brakes and a substantial drogue chute built into the bottom of the rudder. The undercarriage is retractable.

Aerodynamics

• Holighaus chose a rather thick flapless Wortmann airfoil (FX 66-196/161) which had low drag (for the time) and very gentle stall characteristics. The span and profile are optimised for the weaker gliding weather of central Europe. The result is excellent thermalling characteristics and a high glide ratio (for 1967).

Construction

• All-fiberglass glider, with foam core sandwiches for the wing skins and fuselage bulkheads.

• Internal tubular-steel frame interconnects the wings, cockpit and landing gear, carrying the flight and landing stresses. This steel frame is bolted to the fiberglass shell.

• The Cirrus was built in female moulds, an innovation that became the standard method for all manufacturers.

Variants

• The first prototype had an all-flying V-tail.
• Cirrus B: a longer span variant, apparently all are later modifications.
• Cirrus VTC: produced in Yugoslavia under license by the Vazduhoplovno Tehnicki Centar in Vrsac.

Sources

• [Cirrus website]
• [Schempp-Hirth website]
• Selinger P, Segelflugzeuge vom Wolf aum Discus, Motorbuch Verlag Stuttgart, 1989
• Ryan J, Cirrus Test Pilot Report, Soaring, July 1967
• Foley W, The Schempp-Hirth Cirrus, Soaring, July 1967
• Simons M, Sailplanes 1965-2000, Equip, 2000

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