The Raab-Katzenstein KL.1 Schwalbe (Swallow) was a German two-seat biplane produced in the 1920s. About fifty were built and the type became well known as an

aerobatic aircraft An aerobatic aircraft is an aerodyne (a heavier-than-air aircraft) used in aerobatics, both for flight exhibitions and aerobatic competitions. Most fall into one of two categories, aircraft used for training and by flight demonstration teams, whic ...

, performing at many displays in the hands of pilots like

Gerhard Fieseler Gerhard Fieseler (15 April 1896 – 1 September 1987) was a German World War I flying ace, aerobatics champion, and aircraft designer and manufacturer. From birth to the 1918 armistice Born in Glesch (near Cologne), Fieseler joined the Air Serv ...

Design and development

In November 1925 test pilot

Antonius Raab The history of AEKKEA (''Anonymos Etaireia Kataskevis Kai Ekmetallefseos Aeroplanon'' - ''Societe Anonyme Pour la Fabrication et l'Exploitation des Avions Raab''), an aircraft maker based in Greece, is connected with the history of a talented Ger ...

and engineer Katzenstein formed the

Kassel Kassel (; in Germany, spelled Cassel until 1926) is a city on the Fulda River in northern Hesse, Germany. It is the administrative seat of the Regierungsbezirk Kassel and the district of the same name and had 201,048 inhabitants in December 2020 ...

-based company that bears their name. They had previously worked at Dietrich Flugzeugwerke, a company which ran into financial problems in 1925. Their first design, known initially as the KL.1 Schwalbe, was a development of the Dietrich-Gobiet DP.XI. Later, in a rationalisation of the company's naming system, it became the RK.1 Schwalbe. The Schwalbe was a single bay biplane with thick section, unequal span wooden wings which were built around twin spars and fabric covered. The wings had marked stagger and were braced between the spars with forward leaning, steel tube, N-form

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. The lower wing was attached directly to the lower fuselage, from which the inner upper wing was braced with an outward leaning pair of parallel struts to the spars and held over the upper fuselage by a pair of inverted V-struts, one on each side, to the forward spar alone. The wings were straight-tapered in plan, with only slight sweep on the

leading edge The leading edge of an airfoil surface such as a wing is its foremost edge and is therefore the part which first meets the oncoming air.Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', page 305. Aviation Supplies & Academics, ...

, out to rounded tips. They also tapered in thickness. The Schwalbe had

ailerons 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 Flight dynamics, roll (or ...

on both wings, externally connected with vertical rods. The upper ailerons had large balances to serve both surfaces. The Schwalbe's rectangular section fuselage had a steel tube structure and was fabric covered. The first examples, designated KL.IA, were powered by a

Siemens-Halske Sh 11 The Siemens-Halske Sh 11 was a seven-cylinder, air-cooled, radial engine for aircraft built in Germany in the 1920s. First run in 1925, it was rated at 75 kW (100 hp). Applications * Albatros L 68 * Bach 3-CT-2 Air Yacht * Bach 3-CT ...

seven cylinder

radial engine The radial engine is a reciprocating type internal combustion engine configuration in which the cylinders "radiate" outward from a central crankcase like the spokes of a wheel. It resembles a stylized star when viewed from the front, and is ca ...

, partially enclosed by a

dural Dural is a suburb of Sydney, in the state of New South Wales, Australia 36 kilometres north-west of the Sydney central business district in the local government areas of Hornsby Shire and The Hills Shire. Dural is part of the Hills District. ...

cowling A cowling is the removable covering of a vehicle's engine, most often found on automobiles, motorcycles, airplanes, and on outboard boat motors. On airplanes, cowlings are used to reduce drag and to cool the engine. On boats, cowlings are a cove ...

which left the cylinders projecting for cooling. Its fuel tank was within the upper wing and the oil tank behind a

firewall Firewall may refer to: * Firewall (computing), a technological barrier designed to prevent unauthorized or unwanted communications between computer networks or hosts * Firewall (construction), a barrier inside a building, designed to limit the spre ...

. Two later versions of the Schwalbe, designated KL.1B and KL.IC, were powered by a

Siemens-Halske Sh 12 The Siemens-Halske Sh 12 was a nine-cylinder, air-cooled, radial engine for aircraft built in Germany in the 1920s. First run in 1925, it was rated at 80 kW (110 hp). The Sh 12 was also produced in the United States by Ryan Aeronautic ...

nine cylinder radial. The forward 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 ...

was under the wing but it was flown solo from the rear cockpit which was over 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. ...

of the lower wing and behind that of the upper wing, where there was a cut-out to increase the pilot's field of view. A large, almost triangular

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 ...

was mounted on top of the fuselage and carried generous, curved and

balanced In telecommunications and professional audio, a balanced line or balanced signal pair is a circuit consisting of two conductors of the same type, both of which have equal impedances along their lengths and equal impedances to ground and to other ...

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. Its

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 ...

was small but the

rudder A rudder is a primary control surface used to steer a ship, boat, submarine, hovercraft, aircraft, or other vehicle that moves through a fluid medium (generally aircraft, air or watercraft, water). On an aircraft the rudder is used primarily to ...

large and balanced, reaching down to the keel and working in an elevator cut-out. The Schwalbe had fixed, conventional

landing gear Landing gear is the undercarriage of an aircraft or spacecraft that is used for takeoff or landing. For aircraft it is generally needed for both. It was also formerly called ''alighting gear'' by some manufacturers, such as the Glenn L. Martin ...

, with its mainwheels on a split axle sprung by rubber cords to V-struts from the lower fuselage and stabilized centrally by a transverse V-strut. There was a short, steel tailskid.

Operational history

Piloted by Raab, the Schwalbe first flew on 16 January 1926. Numbers built are uncertain but have been estimated at forty-two or about fifty-eight. Engines apart, the unknown differences between the variants were small enough to allow several airframes to have been IAs, IBs and ICs over their lifetime. Several well known pilots used them as aerobatic aircraft, including

who was regarded as the best and most innovative aerobatic pilot of his day. In September 1927 he claimed a world duration record for inverted flight in his Schwalbe KL.IC. at a Zurich meeting, then bettered it later in the month with a fifteen minute flight. He gave aerobatic demonstrations in his Schwalbe during 1927-8 at several other European meetings including

Blackpool Blackpool is a seaside resort in Lancashire, England. Located on the North West England, northwest coast of England, it is the main settlement within the Borough of Blackpool, borough also called Blackpool. The town is by the Irish Sea, betw ...

and

Waalhaven Waalhaven Airport in 1932, with the Graf Zeppelin in the background. The Waalhaven is a harbour in Rotterdam, the Netherlands. It used to be home to an airport, Vliegveld Waalhaven (Waalhaven Airport). It was the second civilian airport in the ...

. One Schwalbe was on display at the 1928

Berlin Berlin ( , ) is the capital and largest city of Germany by both area and population. Its 3.7 million inhabitants make it the European Union's most populous city, according to population within city limits. One of Germany's sixteen constitue ...

International Aero Show.

Variants

;KL.IA: Original design with

engine. ;KL.IB: More powerful

. ;KL.IC: Siemens-Halske Sh 12. ;Schwalbe II: Version of KL.IC built in

Greece Greece,, or , romanized: ', officially the Hellenic Republic, is a country in Southeast Europe. It is situated on the southern tip of the Balkans, and is located at the crossroads of Europe, Asia, and Africa. Greece shares land borders with ...

AEKKEA-RAAB The history of AEKKEA (''Anonymos Etaireia Kataskevis Kai Ekmetallefseos Aeroplanon'' - ''Societe Anonyme Pour la Fabrication et l'Exploitation des Avions Raab''), an aircraft maker based in Greece, is connected with the history of a talented Ger ...

, which was established in 1935. ;Pintsch Schwalbe II: derivative by Pintsch ;Rheinische FR-2 Schwalbe :Derivative by ''Flugzeugbau Rheinische''

Specifications (KL. 1A)

Raab-Katzenstein_RK_1a_Schwalbe_3-view_L'Air_January_1,1927

References

Bibliography

* Gerdessen, Frederik. "Estonian Air Power 1918 – 1945". ''

Air Enthusiast ''Air Enthusiast'' was a British, bi-monthly, aviation magazine, published by the Key Publishing group. Initially begun in 1974 as ''Air Enthusiast Quarterly'', the magazine was conceived as a historical adjunct to '' Air International'' maga ...

'', No. 18, April – July 1982. pp. 61–76. . {{Raab-Katzenstein aircraft Raab-Katzenstein aircraft Aerobatic aircraft 1920s German civil trainer aircraft Single-engined tractor aircraft Biplanes Aircraft first flown in 1926