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Zahn Spectre
The Specter was designed during 1994-96, to build a glider that delivers much better performance than delta wings in fall and finesse rates, with good performance in the high-speed (up to 100 km / h) range.
The D-tubes cover 20% of the profile. They were made of carbon / kevlar 200 gr / sq.m, directly on core of foamed 30kg / cu.m hollow, cut with hot wire. Unidirectional carbon beams have been inserted, as well as aluminum plates for riveting / screwing the various fixings: root, ribbed and cable ties.
The wingspan was set at 12.4 m, with a length of 12.4 m. The Worthmann FX 63-137 was designed to take advantage of take-off and low-speed behavior, and for the simplicity of the flaps. This profile has a maximum Cz of 1.7, and good stall characteristics. It equipped pedal-powered planes, but also motor-gliders. The wing tip of 3 degrees is obtained by modifying the back of the profile from half the wingspan of the wing.
To maintain the unique feel of the delta wing, as well as transport and simple assembly, the pilot is installed in a harness. Therefore, a trapezoid and the minimum of aerodynamic controls are required: only spoilers to turn, the rest will be done by displacement of the weight.
Spoilers: Axis is at 50% of the wing. They deploy almost vertically.
The trapeze will be used as an attachment to the lateral structural cables and will not be able, like on the rigid wings, to actuate the spoilers. Handles sliding on the speedbar will control them, using cords passing inside the uprights.
The ribs were also built with a foam-carbon / kevlar sandwich. They are connected to the D-tubes by aluminum fasteners, which also serve to fix the main cables for the median rib. Incident-maintaining cables are attached to the back of the rib by stainless steel fasteners. The ribs are extended with an aluminum tube for the tension of the sail.
Sail work is dacron 160 gr / sq.m, more than 1km of polyester yarn. The empennage was manufactured in a very classic way, in wood covered with a heat-shrinking filament (Oracover). It is very solid and was a bit heavy: 3.6 kg. The drift consists of fabrics stretched over an aluminum frame and carbon.
The calculations (unfortunately inevitably somewhat imprecise) give a fineness of 18 to 48 km / h and a drop rate of 0.65 m / s to 40 km / h.
In 2002, the prototype was ready for its first tests.
There were various revisions, and the big flight came on October 12th. The rolling behavior was very pleasant, but there is too much stability in pitch.
Zahn renounced the formula of the flying wing, despite its great advantage in free flight: allow an easy takeoff. The formula, which subjects an aerodynamic element (the wing) to perform two distinct functions (ensuring the stability of the aircraft and lift with minimum drag) is a delicate compromise to design and calculate. It imposes profiles with little variation of moments, unsuitable for gliding, and an important twist which makes them work at unfavorable impacts at the tip of the wing.
Wing area: 12.4 m²
Wing span: 12.4 m
Wing profile: Worthmann FX 63-137
Tail surface: 1.5 m²
Hang glider weight: 45 kg
Minimum pilot weight: 60 kg
Maximum pilot weight: 80 kg
Minimum speed: 36 km/h
Maximum speed: 90 km/h
Max glide ratio (L/H): 18
Max glide ratio speed: 48 km/h
Minimum sink rate: 0.75 m/s
Packed length: 6.2 m
Nose angle: 180°

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