The immediate precursor of the Mistral-C
Club Class glider was the
Strauber Mistral high performance
Standard Class aircraft designed by Manfred Strauber, Alois Fries, Hartmut Frommhold and Horst Gaber. Design works began in January 1970 and the Mistral made its first flight in July 1975. It was not intended to be serially produced. It was a 15.00 m (49 ft 2.5 in) span
shoulder wing monoplane with a
T-tail which made much use of
glass reinforced plastic (GRP) in its structure. The wings had an area of 9.40 m2 (101.2 sq ft), an
aspect ratio of 23.9 and sweepback at one quarter
chord of 0.4°. The
dihedral was also 0.4°. The
airfoil sections used were Wortmann FX-66-S-196 at the root and FX-66-S-161 at the tips. The wings were constructed from GRP/
balsa sandwich with
ailerons of GRP and rigid, closed cell, polymethacrylimide (PMI) foam. Aluminium
Schempp-Hirth airbrakes extended from the upper wing surface only. The tail unit, with an
all-moving tailplane, was also formed from PMI filled GRP. The
fuselage of the Mistral was a pod and boom
monocoque made from GRP/balsa sandwich, with the single seat
cockpit under a single piece, framed
canopy. Its main, single
landing wheel was manually retractable and assisted by a tailskid. The Mistral had a best glide angle of 39:1 and a minimum sink speed of 0.6 m/s (118 ft/mim). In October 1974 the design of a new model was begun by Strauber and Frommhold, now operating as Ingenieur-Büro Strauber - Frommhold Gmbh. This became the
Mistral-C or
model 2 Mistral-C and was one of the first gliders to meet the specifications of the then new
FAI Club Class. It first flew on 21 October 1976. The main changes were to the wings and, overall, to the construction materials. As detailed in the Specification section below, the wing area was increased, though the span was unchanged, reducing the aspect ratio and consequentially the performance. The new wings had different Wortmann sections, quarter chord forward sweep of 1.0° and dihedral 4.30°. GRP/
PVC foam sandwich replaced the earlier balsa sandwich in the wings and the ailerons and fuselage were all GRP. As in the wings, the PMI foam in the tail was replaced by PVC and the all moving tail was changed to a fixed tailplane, fitted with a spring tab. The canopy is side-hinged. The Mistral-Cs produced by Valentin were little different, though the dihedral is reported to be 4.20°. ==Operational history==