Schempp-Hirth Cirrus

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

Development

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.

Haro Wodl won the 1968 World Gliding Championships in the open class with a Cirrus.

Design

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 drag 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.
*The original Cirrus has a span of 17,74m. Sometimes it is called Open Cirrus. Cirrus VTC were produced in Yugoslavia under license by the Vazduhoplovno Tehnicki Centar in Vrsac.
*Standard Cirrus, Standard Cirrus VTC and Standard Cirrus 75 have a span of 15m an a T-tail. Standard Cirrus VTC were produced in Yugoslavia under license by the Vazduhoplovno Tehnicki Centar in Vrsac.
*Cirrus 75B base on the Standard Cirrus 75 but have a span of 16m.
*The two Cirrus K are modified Standard Cirrus. They have a reduced span (12.6m), larger ailerons, a cross tail with larger elevator, and a strengthened fuselage which make them suitable for aerobatics. This modification was initiated by Wilhelm Düerkop in the late 1980s. [http://www.sagach.ch/Deutsch/Flugzeuge/Cirrus-K.htm Swiss Glider Aerobatics Association's Cirrus K website (in German)] ] [http://toyteam.fox07.de/flugzeuge.html List of planes and gliders of the "Toy Team" (in German)] ] Wolfgang Seitz took part in the 1995 World Glider Aerobatic Championships with a Cirrus K. [http://events.fai.org/aerobatics/pilot.asp?id=11582&chron=0&champ=0&full=147 FAI pilot profile of Wolfgang Seitz] ]

pecifications

aerospecs
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crew=One
capacity=98 kg (215 lb) water ballast
length m=7.20
length ft=23
length in=8
span m=17.74
span ft=58
span in=2
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width m=
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height m=1.70
height ft=5
height in=7
wing area sqm=12.6
wing area sqft=136
swept area sqm=
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rot area sqm=
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volume m3=
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aspect ratio= 24.9
wing profile= FX 66-196, FX 60-126 (tips)
empty weight kg=276
empty weight lb=607
gross weight kg=400
gross weight lb=880
lift kg=
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glide ratio= 44
climb rate ms=
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sink rate ms= 0.5
sink rate ftmin= 98

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References

* 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

External links

* [http://classicsailplane.org/Cirrus/ Cirrus website]
* [http://www.schempp-hirth.com/ Schempp-Hirth website]