The Caudron C.21 was a French twin engine

biplane A biplane is a fixed-wing aircraft with two main wings stacked one above the other. The first powered, controlled aeroplane to fly, the Wright Flyer, used a biplane wing arrangement, as did many aircraft in the early years of aviation. While ...

built just after

World War I World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, the United States, and the Ottoman Empire, with fightin ...

, able to carry three passengers in an open

cockpit A cockpit or flight deck is the area, usually near the front of an aircraft or spacecraft, from which a Pilot in command, pilot controls the aircraft. The cockpit of an aircraft contains flight instruments on an instrument panel, and the ...

Design and development

In 1917 Paul Deville was developing a twin engine

observation aircraft A surveillance aircraft is an aircraft used for surveillance. They are operated by military forces and other government agencies in roles such as intelligence gathering This is a list of intelligence gathering disciplines. HUMINT Human ...

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

aileron An aileron (French for "little wing" or "fin") is a hinged flight control surface usually forming part of the trailing edge of each wing of a fixed-wing aircraft. Ailerons are used in pairs to control the aircraft in roll (or movement around ...

s, had an 8% greater span and a smaller chord. There was no stagger, so the sets of parallel

interplane strut In aeronautics, bracing comprises additional structural members which stiffen the functional airframe to give it rigidity and strength under load. Bracing may be applied both internally and externally, and may take the form of strut, which act in ...

s were vertical;

flying wire In aeronautics, bracing comprises additional structural members which stiffen the functional airframe to give it rigidity and strength under load. Bracing may be applied both internally and externally, and may take the form of strut, which act in ...

s braced each bay. Pairs of V-form engine struts, supporting the two

Le Rhône 9C The Le Rhône 9C is a nine-cylinder rotary aircraft engine produced in France by '' Société des Moteurs Le Rhône'' / Gnome et Rhône. Also known as the Le Rhône 80 hp in a reference to its nominal power rating, the engine was ...

rotary engines The rotary engine is an early type of internal combustion engine, usually designed with an odd number of cylinders per row in a radial configuration. The engine's crankshaft remained stationary in operation, while the entire crankcase and its ...

above the lower wing, defined the inner two bays. There were short, parallel

cabane strut In aeronautics, bracing comprises additional structural members which stiffen the functional airframe to give it rigidity and strength under load. Bracing may be applied both internally and externally, and may take the form of strut, which act in ...

s from the upper

fuselage The fuselage (; from the French ''fuselé'' "spindle-shaped") is an aircraft's main body section. It holds crew, passengers, or cargo. In single-engine aircraft, it will usually contain an engine as well, although in some amphibious aircraft t ...

. The C.21's

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 Tandem, or in tandem, is an arrangement in which a team of machines, animals or people are lined up one behind another, all facing in the same direction. The original use of the term in English was in ''tandem harness'', which is used for two ...

; the pilot's cockpit was under the

trailing edge The trailing edge of an aerodynamic surface such as a wing is its rear edge, where the airflow separated by the leading edge meets.Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', page 521. Aviation Supplies & Academics, 1997. ...

, with a deep cut-out for better upward vision. At the rear a straight edged, long and low

fin A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift or thrust, or provide the ability to steer or stabilize motion while traveling in water, air, or other fluids. Fin ...

carried a straight edged,

balanced rudder Balanced rudders are used by both ships and aircraft. Both may indicate a portion of the rudder surface ahead of the hinge, placed to lower the control loads needed to turn the rudder. For aircraft the method can also be applied to elevators and ...

that extended down to the keel. An angled

tailplane A tailplane, also known as a horizontal stabiliser, is a small lifting surface located on the tail (empennage) behind the main lifting surfaces of a fixed-wing aircraft as well as other non-fixed-wing aircraft such as helicopters and gyroplane ...

mounted on top of the fuselage had

elevator An elevator or lift is a wire rope, cable-assisted, hydraulic cylinder-assisted, or roller-track assisted machine that vertically transports people or freight between floors, levels, or deck (building), decks of a building, watercraft, ...

s 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 Paris () is the capital and most populous city of France, with an estimated population of 2,165,423 residents in 2019 in an area of more than 105 km² (41 sq mi), making it the 30th most densely populated city in the world in 2020. S ...

and

Brussels Brussels (french: Bruxelles or ; nl, Brussel ), officially the Brussels-Capital Region (All text and all but one graphic show the English name as Brussels-Capital Region.) (french: link=no, Région de Bruxelles-Capitale; nl, link=no, Bruss ...

, 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 The Caudron C.23 was a French long range twin engine night bomber, flown in the last year of World War I. Post-war some machines were modified to carry passengers. Design and development The C.23 BN.2 was designed to be a night bomber able to ...

, 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.

Specifications

References

{{Caudron aircraft C.021 1910s French civil aircraft Biplanes Rotary-engined aircraft Aircraft first flown in 1919