Heinkel HD 21

Heinkel HD 21
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Type:	Trainer aircraft
Design country:	German Empire
Manufacturer:	Heinkel Arado
First flight:	1924
Production time:	1924/1925
Number of pieces:	18th

The Heinkel HD 21 was a German training aircraft produced by the Ernst Heinkel Flugzeugwerke . The abbreviation HD stands for "Heinkel Doppeldecker".

development

The HD 21 was developed in 1924 at the Heinkel factory in Warnemünde, and three copies with the serial numbers 218–220 were built there that same year. A possible conversion from a land plane to a seaplane by replacing the wheel chassis with double floats was also in the planning stage , but this was ultimately not realized. 15 more HD 21s were produced under license in 1925 as the first aircraft of the newly founded Hamburg Arado Handelsgesellschaft mbH , which was entered in the commercial register on June 18, with the serial numbers 1–15 in its Warnemünde branch. Most of the HD 21 was taken over by Sportflug GmbH , whose flying schools were officially civil in character, but were secretly used for the training of future military pilots and which was incorporated into the German Commercial Aviation School at the turn of the year 1926/1927 . For the same reason, at least one HD 21 was handed over to the Secret Aviation School of the Reichswehr in the Soviet Union and one was flown from April 1928 at the Albatros Flugzeugwerke . This example with the Arado work number 7 was sold to Sweden in September 1929 and finally came to Ethiopia in December 1935 on behalf of the Red Cross, where its trace was lost in the turmoil of the Abyssinian War. Six HD 21 took part in the German round flight of 1925 and occupied several front seats.

A public presentation of the HD 21 took place together with the models HD 29 , HD 32 and HD 35 also developed by Heinkel on December 16, 1925 at the Berlin-Tempelhof airfield . In addition to the press, domestic and foreign representatives of state authorities were invited, and the pilots who were present were given the opportunity to test the models on site in flight. Nevertheless, and although a total requirement of 165 HD 21 and its successor HD 32 was estimated for the planned armaments program of the Reichswehr in December 1925, there was ultimately no further series production: the 18 units built remained.

construction

The HD 21 is a single-legged, tensioned and strongly positively staggered double-decker in timber construction with a tail landing gear .

Fuselage: The fuselage consists of wooden longitudinal spars and transverse frames and is planked with plywood except for the front part, which is clad with sheet steel up to the fire bulkhead. The cross-section is square with a curvature in the upper area and tapering towards the rear in a vertical cutting edge. The engine is mounted in a tubular steel support and clad with removable aluminum sheets for maintenance work. The storage space behind the fire bulkhead can either be used as a luggage rack or an additional third cabin for a passenger. During training, the flight instructor usually sits in the furthest crew compartment and the student in front of it; the foremost seat is covered and not used. A double control is available.

Structure : The wings are in two parts and consist of two box spars and spruce belts made of wood. The lower wing has a slight V-position, while the upper wing is straight. The wing nose and the undersides between the individual spars are made of or with plywood and planked, the remaining surfaces are covered with fabric. The wings are connected to each other with N-shaped sections made of steel tubes and braced in one plane. Ailerons are only in the upper wing, which also houses the fuel tanks with a capacity of 160 liters.

Tail unit: The tail unit is of normal construction, the vertical fin is made of wood, the horizontal fin is braced towards the fuselage. The elevator has a horn compensation, rudder and ailerons are not balanced. All oars are covered with fabric.

Landing gear: The HD 21 has a rigid main landing gear with a continuous axle, rubber rope suspension and two auxiliary axles. There is also a rubber-sprung grinding spur at the rear .

Technical specifications

Parameter	HD 21 with engine D I	HD 21 with motor D II
crew	2-3	2-3
span	above 10.60 m below 10.0 m	above 10.0 m below 9.4 m
length	7.25 m	7.2 m
height	2.95 m	k. A.
Wing area	27.8 m²	27.4 m²
Preparation mass	710 kg	680 kg
Payload	270 kg	300 kg
Takeoff mass	980 kg	980 kg
drive	a liquid-cooled six - cylinder four-stroke in - line engine
Type	Mercedes DI	Mercedes D II
fuel	160 l	160 l
Starting power	110 hp (81 kW)	129 hp (95 kW)
rated capacity	100 hp (74 kW)	120 hp (88 kW)
Top speed	145 km / h	142 km / h
Landing speed	k. A.	73 km / h
Rise time	5.0 min at 1000 m altitude 13.0 min at 2000 m altitude	6.0 min at 1000 m altitude 13 min, 30 s at 2000 m altitude 28.0 min at 3000 m altitude
Range	k. A.	570 km
Service ceiling	k. A.	4000 m

literature

• Volker Koos: Ernst Heinkel Flugzeugwerke 1922–1932 . Heel, Königswinter 2006, ISBN 3-89880-502-6 , p. 55/56 .
• Volker Koos: Aviation between the Baltic Sea and Breitling . Warnemünde sea and land airfield 1914–1945. Transpress, Berlin 1990, ISBN 3-344-00480-8 , pp. 57 ff .
• Helmut Stützer: The German military aircraft 1919–1934 . E. S. Mittler & Sohn, Herford 1984, ISBN 3-8132-0184-8 , p. 34, 137 and 180 .

Individual evidence

1. ^ Volker Koos: Ernst Heinkel . From the biplane to the jet engine. Delius Klasing, Bielefeld 2007, ISBN 978-3-7688-1906-0 , p. 64/65 .