Heinkel HD 20 on:
[Wikipedia]
[Google]
[Amazon]
The Heinkel HD 20 was a twin engine, three seat German biplane built in 1926 for civil survey work.
Design and development
The Heinkel HD 20 was one of the early products of post-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 ...
aircraft companies after the Allies aviation ban was lifted. HD stood for german: Heinkel Doppeldecker or Heinkel biplane.
The HD.20 had unswept wings of mixed construction with wooden spars, two in the upper wing and one in the lower, and steel ribs; they were fabric covered. Both wings had constant chord over the inner section and semi-elliptical outer panels. The upper wing was considerably the larger, with 45% greater overall span and 17% greater chord over the inner panels. The wings were mounted with slight and equal dihedral and considerable stagger. Only the upper wings carried the long span, narrow chord ailerons. The lower wings were mounted directly onto the lower 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 aircraf ...
structure and the upper wing centre-section was joined to the upper fuselage with a pair of steel inverted V-strut
A strut is a structural component commonly found in engineering, aeronautics, architecture and anatomy. Struts generally work by resisting longitudinal compression, but they may also serve in tension.
Human anatomy
Part of the functionality o ...
s on each side and a central parallel pair arranged transversely. It was a single bay biplane with V-form interplane struts
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 ...
leaning outward strongly from the lower wing below the engines to the upper wings at about 55% span.
It was powered by two Wright R-790 Whirlwind
The Wright R-790 Whirlwind was a series of nine-cylinder air-cooled radial aircraft engines built by Wright Aeronautical Corporation, with a total displacement of about and around . These engines were the earliest members of the Wright Whirl ...
nine 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 ...
s, mounted in streamlined cowlings with the cylinder heads protruding for cooling. They were fed from fuel tanks in the upper wing; oil tanks were in the cowlings. Each engine was bolted to a frame formed of the interplane struts, a nearly horizontal V-strut to the upper fuselage and an N-form strut from the lower wing to the upper fuselage.
The square cross-section fuselage was formed with steel tubes and covered with fabric
Textile is an umbrella term that includes various fiber-based materials, including fibers, yarns, filaments, threads, different fabric types, etc. At first, the word "textiles" only referred to woven fabrics. However, weaving is not th ...
, with a light, rounded, wooden upper decking. There were three open cockpits: one in the nose, another under the upper wing and the last, from which it was flown, just behind the upper trailing edge which had a shallow, rounded cut-out to aid the pilot's forward view. The tail surfaces were conventional and straight-edged, with angled leading edges and unswept trailing edges. The 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 gyropla ...
, mounted on the upper fuselage, was braced from below to the fuselage with a single strut on each side. Both 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 air or water). On an aircraft the rudder is used primarily to counter adve ...
and elevator
An elevator or lift is a cable-assisted, hydraulic cylinder-assisted, or roller-track assisted machine that vertically transports people or freight between floors, levels, or decks of a building, vessel, or other structure. They a ...
s were 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 ci ...
; the latter were separate, their inner corners cut away for deflections of the deep rudder.
The HD.20 had a conventional tailskid undercarriage. Each mainwheel was mounted on a group of three struts, two to the lower fuselage longeron at points on the wing leading edge and at mid-chord and the third to the upper longeron. There was a solid rubber shock absorber in each hub. The wheels could be replaced with floats.
Operational history
Rather little is known about the history of the HD 20. From the January 1927 date of the Les Ailles article the first flight was probably in later 1926. The number built is also not known. One (D-1157), which appears on a reconstructed civil register, was owned by the Epro advertising agency and was destroyed on 21 November 1929. The HD.20 is also mentioned as a photographic survey aircraft in a 1930 review of the topic, though it does not show the camera positions.Specifications
References
{{Heinkel aircraft 1920s German civil aircraft HD 20 Aircraft first flown in 1926