The SB-13 looks like the balancing toys where a bird-shaped toy balances on its beak

It was apparently was more like the drinking bird toys.

[the 1/3 scale model] stalled readily when [c.g.] was too far aft. Recovery from the spin that followed was difficult. With the centre of gravity too far forward, a rapid longitudinal "pecking" oscillation set in, which was difficult to control due to its short duration.

Sounds bad. But at least they found this in the model and then fixed it in the full size right?

the full-scale SB-13 still "pecked" and spun readily; when the standard spin correction procedure was applied, a new spin started in the opposite direction.

Ah.

one longer-lasting outcome from the project was the start of an investigation into whole aircraft rescue parachutes.

Oof.

https://en.wikipedia.org/wiki/Akaflieg_Braunschweig_SB-13_Arcus