Heinkel HD 33

Heinkel HD 33
Type:	Bomb and reconnaissance aircraft
Design country:	German Empire
Manufacturer:	Ernst Heinkel Flugzeugwerke
First flight:	July 1925
Commissioning:	-
Production time:	1925
Number of pieces:	1

The Heinkel HD 33 was a German bomb and reconnaissance aircraft developed by Ernst Heinkel Flugzeugwerke from the 1920s. Due to insufficient flight performance, it was only a one-off. The abbreviation HD stands for "Heinkel Doppeldecker".

history

The HD 33 was built in 1925 on behalf of the Reich Ministry of Transport as a long-range reconnaissance and day bomb aircraft for a secret armament program of the Reichswehr that is currently being planned . As one of the four main types of aircraft intended for this purpose, the military assumed a total required number of 373 aircraft. The production of the prototype with the serial number 237 was carried out at the Heinkel factory in Warnemünde; then it was dismantled and the individual parts were transferred to the Swedish partner company Svenska Aero in Stockholm , where they were assembled by a German group of technicians under the direction of Heinkel's foreman Emil Schneider. It made its maiden flight in July 1925. The HD 33 was transferred to Malmslätt for further tests . In September, Svenska Aero officially declared it as a development intended for the USA and applied for permission for testing, which was granted by the state without restrictions. The HD 33 received Swedish approval with the registration number S-21 and was subjected to extensive tests from September / October 1928 to February 1926. It was then dismantled again and returned to Warnemünde.

In Germany, the type was reported to the Interallied Aviation Guarantee Committee (ILGK) in September 1925 as a postal aircraft with a Puma engine with a takeoff power of only 255 hp . This was intended to circumvent the construction ban on military aircraft that had been in force in Germany since the end of the First World War . In fact, a much more powerful BMW VIa engine with over 600 hp was used as a drive during the entire test phase in Sweden. After this became known to the ILGK, it withdrew its permit in February 1926. Another application by Heinkel, submitted in the same month for approval with a BMW IV drive, was rejected. Nevertheless, the tests were continued in March 1926 with the pilot Eberhardt Mohnicke, which, however, had to be carried out either early in the morning or in the late evening for reasons of disguise. In evaluating the flights in Sweden, the arrangement of the cooler was changed and the HD 33 also received a new engine with higher compression . When all building restrictions were lifted in the course of 1926, the HD 33 could also be officially flown and received its registration for the German Aviation Research Institute (DVL) as D–1205. On April 16, 1926, it was officially demonstrated in flight to representatives of the Reichswehr in Warnemünde. Afterwards, a few more tests were planned in Sweden, but the application submitted by Svenska Aero was withdrawn for unknown reasons. In the meantime, the responsible authorities had come to the conclusion that the aircraft did not meet expectations. As early as September 1926, the initial requirement of 373 HD 33s had been reduced to 24 units. The work program for the period 1927/1928 published in January 1927 by the troop office of the Reichswehr called for replacement of the aircraft that did not meet the requirements of a long-range reconnaissance aircraft. In order to increase performance, the model was equipped with a 755 HP BMW VIIa engine in March 1927 and Heinkel's works pilot Stephan von Prondzynski subjected it to a number of climb performance and speed measurement flights. As a result, some improvements were made in July of that year, but without success. The HD 33 was deleted from the procurement program and initially replaced by the HD 34 and HD 41 , which, however, also failed to establish themselves. After all, the HD 45 took over the tasks of its predecessor.

The only HD 33 can still be found in February 1928 at the DVL; in July 1929 it became part of the Albatros Flugzeugwerke , which acted as the front company of the Reich Association of the German Aviation Industry (RDL), and was withdrawn in February 1932 when its license was withdrawn the aircraft role deleted.

construction

The HD 33 was a staggered , braced double - decker with a single-legged wooden structure . The fuselage was formed by a plywood-clad framework made of four longitudinal spars and rectangular frames with a rectangular cross - section at the front and an oval cross - section in the middle and a curved top that ended in a vertical edge towards the stern. The engine mount, made of welded steel tubes and clad with sheet metal, was located at the bow. It was connected to the fuselage with only four bolts and was therefore quickly dismantled. The brass oil container was housed in it. A firewall made of asbestos-coated sheet steel was installed behind the engine , to which the main fuel tank was connected. This was followed by the open crew cabins behind, which in turn were separated from the tank by a second firewall.

The structure consisted of the two-part upper and lower surfaces with straight outlines and rounded ends. They were staggered positively to one another, with the rear spar of the upper wing at the level of the front spar of the lower wing and the latter having a slight V-shape. The scaffolding consisted of two box spars, spruce bars and plywood frames , mostly covered with fabric and only covered with plywood in the area between the two spars above and below and at the front edge. The surfaces were connected to one another by N-posts made of profile steel and crossed out in one plane with profile steel wire, the fuselage connection of the upper wing was ensured by a tombstone. Both surfaces were equipped with ailerons , which were linked by bumpers. In addition to the main fuel tank in the fuselage, there was an additional tank designed as a drop tank in the upper wing to the right of the tombstone.

The tail unit of the HD 33 consisted of tubular steel structures covered with fabric; only the fin had plywood planking. All rudders were aerodynamically balanced; the braced horizontal fin was in flight, the cantilevered vertical fin was only adjustable on the ground.

The aircraft was equipped with a rear wheel landing gear, with the wheels of the main landing gear having rubber cable springs and not being connected to one another by an axle. At the stern there was a metal-studded, rubber-sprung wooden abrasive spur.

Technical specifications

Parameter	Data
crew	2
span	above 12.8 m, below 11.4 m
length	9.4 m
height	4.0 m
Wing area	43.3 m²
Preparation mass	1600 kg
Payload	1150 kg
payload	220 kg
Takeoff mass	2750 kg
drive	a water-cooled twelve-cylinder - four cycle - V-type engine with a fixed two-blade Holzluftschraube
Type	BMW VIa 7.3
Starting power nominal power continuous power	700 PS (515 kW) at 1650 rpm 620 PS (456 kW) at 1590 rpm 500 PS (368 kW) at 1460 rpm
Fuel volume	900 l
Top speed	246 km / h
Marching speed	200 km / h
Landing speed	90 km / h
Rate of climb	5.4 m / s
Rise time	3.6 min at 1000 m altitude 11.24 min at 3000 m altitude
Service ceiling	6200 m
Range	1200 km
Flight duration	6.0 h
Armament	a rigid 7.9 mm MG Madsen (500 rounds) a movable 7.9 mm MG Madsen (500 rounds) on a turntable

literature

• Volker Koos: Ernst Heinkel Flugzeugwerke 1922–1932. Heel, Königswinter 2006, ISBN 3-89880-502-6 , p. 82/83.
• Volker Koos: Aviation between the Baltic Sea and Breitling. The sea and landing airfield Warnemünde 1914–1945. Transpress, Berlin 1990, ISBN 3-344-00480-8 , pp. 63 and 66.
• Lennart Andersson: German-Swedish secret projects between 1921 and 1935. In: Fliegerrevue Extra No. 18, Möller, Berlin 2007, ISSN 2194-2641, pp. 16/17.

Individual evidence

1. ^ Karl Ries: Research on the German aviation role. Part 1: 1919-1934. Dieter Hoffmann, Mainz 1977, ISBN 3-87341-022-2 , p. 90.