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

The D 17 is undoubtedly based on the Nieuport formula. It is said to have been built for Lt. Voss and was powered with 100 h.p. Hansen engine.

W.Green, G.Swanborough The Complete Book of Fighters

REX D 7

   Designed by Dipl-Ing Friedrich Hansen and built as a private venture in the summer of 1917, allegedly to the specific requirements of Lt Werner Voss, the D 7 was a small sesquiplane of wooden construction and powered by a 100 hp Hansen seven-cylinder single-valve rotary engine. Featuring a slab-sided, plywood-skinned fuselage with fabric-covered wings and horizontal tail surfaces, the D 7 was novel in that the lower wing halves pivoted about the bases of the V-type interplane struts, either collectively or differentially, thus serving as flaps or ailerons, a scheme that was the subject of a patent. No record of the flight testing of the D 7 has survived, but the arrangement would seem to have been of dubious practicality as the prototype appears to have been abandoned after the death of Voss, on 23 September 1917.

J.Herris German Aircraft of Minor Manufacturers in WW1. Vol II (A Centennial Perspective on Great War Airplanes 50)

Rex

The Flugmaschinen Rex-Gesellschaft mbH company was established on 14 December 1914 by Walter Gutbire. The company intended to build a Morane-type monoplane and a biplane, similar to the Bristol Scout, but nothing came of this. The first trials of a small biplane were held on the Manne-Herten airfield which, due to rising costs, were curtailed. The same fate befell the design of a rotary engine that was proposed to power the biplane. During these trials a repair facility for military aircraft was established. The company then concerned itself with the repair of aircraft, but also experimented in 1917, by building a fighter the "D17" that was described as an almost exact copy of the Albatros and was never accepted.

Журнал Flight

Flight, July 12, 1917.

SOME 1917 TYPE GERMAN AEROPLANES.

The "Rex" Chaser.

   A small, single-seater biplane, built by the Rex Co., of Cologne, has been observed at the front, but little is known regarding it except that it is apparently somewhat similar to the Nieuport, in that the lower wing is of smaller span and chord than the upper. Also, the inter-plane struts - of which there is only one pair on each side - are placed in the shape of a V. It differs from the Nieuport, in that the upper plane has no sweepback, and the lower neither sweepback nor dihedral. The centre section of the top plane is attached to struts sloping outwards, as in the Sopwiths.
   The body is of the monocoque type, built of three-ply wood, with projections for the attachment of the lower planes. In front view this machine appears approximately as shown in the accompanying silhouette.