Nimbus 4M loses its tail on a flutter test flight; pilot bails out

A Nimbus 4M lost its tail in flight and was destroyed near Lenningen; the pilot bailed out and landed unhurt. The self-launcher was on a maker's flutter test for a 50 kg weight increase, pulsing the controls up to the design dive speed, 308 km/h. About an hour in, at around 1,600 m and 160 km/h, the pilot felt the rudder go soft and saw the tail tilting; a colleague alongside watched the tilt reach about 45° before the whole tail broke off. Investigators traced it to a fuselage weakened over the aircraft's unusual life — repeated overloads and an earlier repair after a ground collision — which left a frame loose, so the tail finally tore off.

1. Certification flutter test: A Nimbus 4M self-launcher aerotow-launched from Hahnweide for a manufacturer's flutter test to certify a 50 kg increase in maximum weight, pulsing the controls at speeds up to the design dive speed of 308 km/h.
2. Airframe weakened over its life: The 1991 aircraft, an ex-engine-testbed and demo glider, had taken repeated beyond-limit loads and a repair after a ground collision, leaving a fuselage frame loose.
3. Rudder goes soft near 160 km/h: About an hour in, at around 1,600 m and 160 km/h, the rudder felt soft and the pilot saw the tail begin to tilt.
4. Colleague sees the tail tilt to 45 deg: A colleague flying alongside watched the whole tail rock and tilt, the angle growing to about 45 degrees, and advised bailing out.
5. Tail breaks off the fuselage: The entire empennage broke from the fuselage tube in torsion — briefly held by the rudder cables — and the glider pitched over the nose into inverted flight.
6. Pilot bails out, lands unhurt: The pilot jettisoned the canopy and got out; the automatic parachute opened and he landed unhurt on a field. The glider was destroyed.