SZD-20X Wampir II

The SZD-20x Wampir II ("Szybowcowy Zakład Doświadczalny" - Glider Experimental Works) was a single-seat tail-less research glider designed and built in Poland from 1959.
Development.
The SZD-20X Wampir II ("vampire II") was designed to compare a flying wing designed to Standard class rules with a more conventional standard class glider. Main designer was Jan Dyrek. Based on experience with the earlier SZD-6X Nietoperz and SZD-13 Wampir tail-less gliders, the SZD-20X was an all wood flying wing, with the pilot sitting in a pod extending aft of the trailing edge on the centreline, and large swept fins & rudders at approx 2/3 span on each wing.
The SZD-20X was associated with the number 15, having a 15m span, aspect ratio of 15 and wing area of 15m², whether this was by design or accident is not known.
Early flight trials commenced with hops towed behind a car to test control responses, followed by an aero-tow launch on 9 September 1959, piloted by Adam Zientek. Flight trials revealed a marked sensitivity to turbulence resulting in flutter, and during trials at stalling speed, the SZD-20X entered a spin, which the rudders were unable to recover the aircraft from, only when the pilot shifted his weight as far forward as he could, did the SZD-20X recover from the spin. Flying in the SZD-20X continued until 6 October 1959, when turbulence-induced flutter tore the aircraft apart, the pilot escaping with parachute.