O.Thetford, P.Gray German Aircraft of the First World War (Putnam)

Aviatik C IX
   Three prototypes were constructed during 1918 (6306/18-6308/18) and differed mainly in the shape of the tail surfaces. One aircraft had ailerons on the top wing only; the other had ailerons at all four wingtips. Airframe 6307/18 was tested to destruction at Adlershof over the period 13th to 18th June 1918. Engine, 200 h.p. Benz IV. Weights: Empty, 980 kg. (2.156 lb.). Loaded, 1,340 kg. (2,948 lb.). Speed, 160 km.hr. (100 m.p.h.). Ceiling, 4,500 m. (14.760 ft.). Armament, one Spandau and one Parabellum machine-gun.

J.Herris Aviatik Aircraft of WWI (A Centennial Perspective on Great War Airplanes 10)

Aviatik C.IX
  
   The C.IX was the final Aviatik two-seater design built. During 1918 three prototypes, 6306-6308/18, were constructed. Powered by the 200 hp Benz Bz.IV and mounting a nose radiator, the prototypes explored different tail surfaces and aileron configurations in an attempt to optimize maneuverability and flying qualities. The lower wing was suspended below the fuselage on struts for greater wing gap. The second airframe was tested to destruction at Adlershof in mid-June 1918. Armament was the then-standard fixed, synchronized Spandau for the pilot and flexible Parabellum for the observer. The Aviatik C.IX was not chosen for production.

Журнал Flight

Flight, September 11, 1919.

AVIATIK "MILESTONES"

The Aviatik, Type C IX
   In 1918 a somewhat different type, the C IX, was produced. This had a 200 h.p. Benz engine, and the radiator was placed in the nose of the fuselage, motor car fashion. The lower plane, which was of smaller chord than the top one, ran underneath the fuselage, much after the manner of the Bristol Fighter, which may quite possibly have inspired the Aviatik designer to adopt this feature. The fin and tail planes, three-ply covered, "grow" out of the body, while the rudder is fabric covered. There is a small fin underneath the fuselage, containing the tail skid.