Knights of the Air: Experimental Quadruplanes:

This was a quadruplane of most unusual layout, in which the fuselage filled the gap between the two middle wings, with the upper and lower main planes carried above and below it on struts. At first, single wide-chord struts were used for the cabane and for the single wing bays between the upper, mid-upper and mid-lower wings, all of which had ailerons. The bottom wing, of shorter span, was carried on pairs of struts under the fuselage, and from the mid lower wing. The main wheels were carried on single struts each side and were notched into the bottom wing, with which the axle was in line. Construction was of wood, with mixed fabric and plywood covering. (More detail in Mr. Boucher’s blog).

In Germany, the Euler Vierdecker of 1917 unusually featured a standard triplane arrangement of fixed wings with a fourth uppermost wing comprising left and right hand articulated surfaces which acted as full-span ailerons. Two examples were built, with different engines.

Also in 1917, Friedrichshafen created the even more unusual Friedrichshafen FF54 scout fighter, which featured narrow-chord second and third wings, with struts connecting only the upper pair and lower pair of planes. The prototype proved unacceptable in the air and was later modified as an equally unsuccessful triplane, again with a short-chord intermediate plane.

The Naglo D.II quadruplane fighter of 1918 featured a standard triplane arrangement with a smaller fourth wing attached below the main assembly, somewhat analogous to a sesquiplane. It participated in Germany’s second D-type contest in 1918, and was praised for its construction and workmanship.

In Russia, V.F.Saveljev and Vladislav Zalevskij built this experimental 2-seat reconnaisence aircraft. It used fuselage from the “Morane-G” and single strut Quadruplane wing box tilted forward.

(Artwork & Info by W.I. Boucher)

The Russian quadruplane was powered by an 80hp engine when it was flown on April 15, 1916. According to the test pilot Ungmejster, “The aircraft is very responsive and may compete with the 165hp Albatros, But it needs a 100hp Monosaupape engine.” Later this engine was fitted with minor modifications, and aircraft performed numerous flights.

Sources: Wikipedia, WWI Aviation Pictorial History, WWI Aviation blog