Through the 1960s Paul Siebert's company had built
Kaiser Ka 6 gliders under licence. Anticipating the end of this agreement, they began to design a successor with a relatively low cost and simple wooden structure but with performance enhanced by a more modern
Wortmann wing profile. The outcome was the Sie 3, which first flew in September 1968. The Sie-3 has a wooden structure and is largely
plywood covered. The
high set single spar wings have the same aerodynamic profile throughout, with an unswept centre section of parallel
chord and constant thickness over 60% of the span and strongly straight tapered panels outboard. There are aluminium
Schempp-Hirth airbrakes near mid-chord on the outer centre section, just behind the spar, and
ailerons on the outer panels. The only
fabric covering on the wing is over the centre section aft of the spar. The
fuselage is a ply covered
semi-monocoque with a short
glass fibre nose fairing; aft of the wing it gently tapers towards the tail. The single piece
canopy blends into the fuselage profile. The narrow chord swept
fin is an integral ply covered part of the fuselage carrying a broad, fabric covered
rudder with a near vertical
trailing edge that extends to the fuselage keel. A straight tapered, largely fabric covered
all moving tailplane with a cut-out for rudder movement is mounted at the base of the fin. The Sie 3 lands on a
monowheel well embedded within the fuselage, aided by a sprung tailskid. The Sie-3 flew for the first time in September 1968, piloted by its designer. Its performance was similar to contemporary wooden gliders. ==Operational history==