Caudron C.21
The Caudron C.21 was a French twin engine biplane built just after World War I, able to carry three passengers in an open cockpit. Design and development. In 1917 Paul Deville was developing a twin engine observation aircraft when it became clear it would be underpowered and it was therefore not built during World War I. After the war the design, now called the C.21, was completed as a four-seat passenger aircraft. It was a three bay biplane, with fabric covered, constant chord, unswept wings ending at angled tips. The upper wing, which carried the ailerons, had  an 8% greater span and a smaller chord. There was no stagger, so the sets of parallel interplane struts were vertical; flying wires braced each bay. Pairs of V-form engine struts, supporting the two Le Rhône 9C rotary engines above the lower wing, defined the inner two bays. There were short, parallel cabane struts from the upper fuselage. The C.21's fuselage was almost flat sided, with a vertical knife edge at the short nose. It had an open cockpit starting in the extreme nose and seating the three passengers in tandem; the pilot's cockpit was under the  trailing edge, with a deep cut-out for better upward vision. At the rear a straight edged, long and low fin carried a straight edged, balanced rudder that extended down to the keel. An angled tailplane mounted on top of the fuselage had elevators with a cut-out for rudder movement and it had a tailskid undercarriage, with pairs of mainwheels on axles attached to longitudinal bars fixed under the engines on N-form struts. Operational history. The date of the C.21's first flight is uncertain but it was before February 1919. On 10–11 February it gained publicity with  four flights between Paris and Brussels, a distance of covered in about 140 minutes. They were flown by Chanteloup, accompanied by designer Deville, to retrieve the passengers from a Caudron C.23, modified into a passenger transport, which had broken a tailskid at Brussels. The C.21 was advertised in the Caudron catalogue at a price of FF 30,000. It seems only one example was built but its layout was repeated in Caudron's successively larger and more powerful C.22 and C.23 night bombers.