In November 1925 test pilot
Antonius Raab and engineer Katzenstein formed the
Kassel-based company that bears their name. They had previously worked at Dietrich Flugzeugwerke, a company which ran into financial problems in 1925. Their first design, known initially as the KL.1 Schwalbe, was a development of the
Dietrich-Gobiet DP.XI. Later, in a rationalisation of the company's naming system, it became the
RK.1 Schwalbe. The Schwalbe was a
single bay biplane with thick sections, unequal span wooden wings which were built around twin
spars and
fabric covered. The wings had marked
stagger and were braced between the spars with forward leaning, steel tube, N-form
interplane struts. The lower wing was attached directly to the lower
fuselage, from which the inner upper wing was braced with an outward leaning pair of parallel struts to the spars and held over the upper fuselage by a pair of inverted V-struts, one on each side, to the forward spar alone. The wings were straight-tapered in plan, with only a slight sweep on the
leading edge, out to rounded tips. They also tapered in thickness. The Schwalbe had
ailerons on both wings, externally connected with vertical rods. The upper ailerons had large balances to serve both surfaces. The Schwalbe's rectangular section fuselage had a steel tube structure and was fabric covered. The first examples, designated KL.IA, were powered by a
Siemens-Halske Sh 11 seven cylinder
radial engine, partially enclosed by a
dural cowling which left the cylinders projecting for cooling. Its fuel tank was within the upper wing and the oil tank behind a
firewall. Two later versions of the Schwalbe, designated KL.1B and KL.IC, were powered by an
Siemens-Halske Sh 12 nine cylinder radial. The forward open
cockpit was under the wing but it was flown solo from the rear cockpit which was over the
trailing edge of the lower wing and behind that of the upper wing, where there was a cut-out to increase the pilot's field of view. A large, almost triangular
tailplane was mounted on top of the fuselage and carried generous, curved and
balanced elevators. Its
fin was small but the
rudder large and balanced, reaching down to the keel and working in an elevator cut-out. The Schwalbe had fixed, conventional
landing gear, with its mainwheels on a split axle sprung by rubber cords to V-struts from the lower fuselage and stabilized centrally by a transverse V-strut. There was a short, steel tailskid. ==Operational history==