O.Thetford, P.Gray German Aircraft of the First World War (Putnam)
Rumpler C IX (7C 1) (first version)
This experimental two-seater appeared late in 1917. C IV wing panels were used with single 'T'-type interplane struts. The oval, multi-stringered fuselage had pleasing lines, but the pivoted, "all-moving" rudder was a particularly vulnerable component, and was subsequently modified. It was intended the type should be a two-seat fighter, but the machine could not have been successful, as it did not go into production. Engine, 160 h.p Mercedes D III.
Rumpler C IX (second version)
Although the trailing edge of the rudder is unfortunately clipped in this illustration, the general revision of the tail surfaces to include a fin may be seen.
W.Green, G.Swanborough The Complete Book of Fighters
RUMPLER 7C 1 Germany
Late in 1916, the Rumpler team headed by Edmund Rumpler initiated design of both a two-seat and a single-seat fighter embodying a novel, if complex, method of fuselage construction. This, protected by a patent filed early in 1915, sought to combine minimum weight with maximum strength. The fuselage was built up from plywood frames with numerous thin stringers, the whole being covered by two layers of doped fabric strips applied diagonally in opposite directions and intended to provide the necessary torsional stiffness. A close-cowled 160 hp Mercedes D III engine was attached to a fuselage extrusion supporting the upper wing, which embodied an offset flush radiator. The upper wing was of parallel chord, the lower wing being of so-called Libelle (Dragonfly) form featuring a curved trailing edge, the wing cellule being braced by single broad-chord I-section struts with cables running to two fuselage points. This formula, which resulted in what was, aerodynamically, an outstandingly clean aeroplane, was applied to the 7C1 two-seat fighter and the 7D 1 single-seat fighter. The 7C 1 entered flight test in the spring of 1917, initially with vertical tail surfaces confined to a pivoting rudder. The tail was subsequently redesigned to embody a fixed fin, but development was discontinued at a comparatively early stage, presumably as a result of difficulties similar to those experienced with the parallel single-seat 7D 1. No specification for the 7C 1 appears to have survived.