Arcus M overran runway after self-launch was not aborted at briefed point

Two pilots self-launched an Arcus M from Bellechasse RWY 26 (520 m grass), near the 800 kg max mass, in 25 °C heat (~ISA+13), on slightly damp 20 cm grass with 80 cm corn beyond. The engine ran normally but acceleration was sluggish; at the briefed abort point the required speed had not been reached, yet the takeoff continued. The glider overran, briefly flew over a terrain depression, brushed the corn, and ground-looped ~100 m into the field. Both pilots were experienced but with limited time on type; the cumulative penalty was underestimated and the briefed abort point was not honored. Minor winglet damage; no injuries.

1. Self-launch takeoff roll: Self-launch takeoff run on Bellechasse RWY 26 (520 m grass) with two pilots near 800 kg max takeoff mass and ~10 L of fin ballast.
2. Adverse runway conditions: The grass along the runway was about 20 cm tall and still slightly damp from recent rain, with possibly softer ground than normal, raising rolling resistance and takeoff distance.
3. High weight and density altitude: At a mass of about 785 kg and a density altitude of ISA+13°C, the takeoff distance over a 15 m obstacle reached about 660 m, beyond the 520 m runway with no wind margin.
4. Limited time on type: Limited experience on the aircraft type likely explained the underestimation of the cumulative performance penalty.
5. Briefed abort point not honored: At the briefed abort point the required speed had not been reached and no further acceleration was felt, but the pilots decided to continue the takeoff rather than abort.
6. Runway overrun and low flight: The glider rolled past the end of RWY 26, lifted briefly over a terrain dip, brushed the corn beyond, and stayed partly airborne and partly rolling for about 100 m.
7. Outlanding - damage: Settled into the cornfield ~100 m beyond the runway end with a ~180° ground-loop. Minor winglet damage; both pilots uninjured.