It was one of many designs from several countries aiming to provide low cost flying and was quite successful, with about twenty built.

The Grasmücke was a single bay biplane with thick-section wings of equal chord but unequal span, mounted with strong stagger and without dihedral.

Only the upper wing carried broad-chord ailerons, which filled about half the span and had conspicuous horn balances.

[1] The RK.9 was powered by a 26 kW (35 hp) three-cylinder Anzani radial engine mounted, uncowled, on the nose.

[1] The tail surfaces were largely wooden structures, though with curved dural tube edges, and were fabric covered.

The tailplane, strut braced from below, was mounted on top of the fuselage and carried large, almost semi-circular plan elevators.