Heinkel He 111
The Heinkel He 111 is a German airliner and medium bomber designed by Siegfried and Walter Günter at Heinkel Flugzeugwerke in 1934. Through development, it was described as a wolf in sheep's clothing. Due to restrictions placed on Germany after the First World War prohibiting bombers, it was presented solely as a civil airliner, although from conception the design was intended to provide the nascent Luftwaffe with a heavy bomber.
Perhaps the best-recognised German bomber of World War II due to the distinctive, extensively glazed "greenhouse" nose of the later versions, the Heinkel He 111 was the most numerous Luftwaffe bomber during the early stages of the war. It fared well until it met serious fighter opposition during the Battle of Britain, when its defensive armament was found to be inadequate. As the war progressed, the He 111 was used in a wide variety of roles on every front in the European theatre. It was used as a strategic bomber during the Battle of Britain, a torpedo bomber in the Atlantic and Arctic, and a medium bomber and a transport aircraft on the Western, Eastern, Mediterranean, Middle Eastern, and North African Front theatres.
The He 111 was constantly upgraded and modified, but had nonetheless become obsolete by the latter part of the war. The failure of the German Bomber B project forced the Luftwaffe to continue operating the He 111 in combat roles until the end of the war. Manufacture of the He 111 ceased in September 1944, at which point piston-engine bomber production was largely halted in favour of fighter aircraft. With the German bomber force virtually defunct, the He 111 was used for logistics.
Production of the Heinkel continued after the war as the Spanish-built CASA 2.111. Spain received a batch of He 111H-16s in 1943 along with an agreement to licence-build Spanish versions. Its airframe was produced in Spain under licence by Construcciones Aeronáuticas SA. The design differed significantly only in the powerplant used, eventually being equipped with Rolls-Royce Merlin engines. These remained in service until 1973.
Development
Conception
After its defeat in World War I, Germany was banned from operating an air force by the Treaty of Versailles. German re-armament began earnestly in the 1930s and was initially kept secret because the project violated the treaty. Early development work on bombers was disguised as a development program for civilian transport aircraft.Among the designers seeking to benefit from German re-armament was Ernst Heinkel. Heinkel decided to create the world's fastest passenger aircraft, a goal met with scepticism by Germany's aircraft industry and political leadership. Heinkel entrusted development to Siegfried and Walter Günter, both fairly new to the company and untested.
In June 1933, Albert Kesselring visited Heinkel's offices. Kesselring was head of the Luftwaffe Administration Office: at that point Germany did not have a State Aviation Ministry but only an aviation commissariat, the Luftfahrtkommissariat. Kesselring was hoping to build a new air force out of the Flying Corps being constructed in the Reichswehr, and required modern aircraft. Kesselring convinced Heinkel to move his factory from Warnemünde to Rostock – with its factory airfield in the coastal "Marienehe" region of Rostock and bring in mass production, with a force of 3,000 employees. Heinkel began work on the new design, which garnered urgency as the American Lockheed 12, Boeing 247 and Douglas DC-2 began to appear.
Features of the He 111 were apparent in the Heinkel He 70. The first single-engined He 70 Blitz rolled off the line in 1932 and immediately started breaking records. In the normal four-passenger version, its speed reached when powered by a BMW VI engine. The He 70 had an elliptical wing, which the Günther brothers had already used in the Bäumer Sausewind before joining Heinkel. This wing design became a feature in this and many subsequent designs they developed. The He 70 drew the interest of the Luftwaffe, which was looking for an aircraft with both bomber and transport capabilities.
The He 111 was a twin-engine version of the Blitz, preserving the elliptical inverted gull wing, small rounded control surfaces and BMW engines, so that the new design was often called the Doppel-Blitz. When the Dornier Do 17 displaced the He 70, Heinkel needed a twin-engine design to match its competitors. Heinkel spent 200,000-man hours designing the He 111. The fuselage was lengthened to from and wingspan increased to from.
First flight
The first He 111 flew on 24 February 1935, piloted by chief test pilot Gerhard Nitschke, who was ordered not to land at the company's factory airfield at Rostock-Marienehe, as this was considered too short, but at the central Erprobungstelle Rechlin test facility. He ignored these orders and landed back at Marienehe. He said that the He 111 performed slow manoeuvres well and that there was no danger of overshooting the runway. Nitschke also praised its high speed "for the period" and "very good-natured flight and landing characteristics", stable during cruising, gradual descent and single-engined flight and having no nose-drop when the undercarriage was operated. During the second test flight Nitschke revealed there was insufficient longitudinal stability during climb and flight at full power and the aileron controls required an unsatisfactory amount of force.By the end of 1935, prototypes V2 and V4 had been produced under civilian registrations D-ALIX, D-ALES and D-AHAO. D-ALES became the first prototype of the He 111A-1 on 10 January 1936 and received recognition as the "fastest passenger aircraft in the world", as its speed exceeded. The design would have achieved a greater total speed had the DB 600 inverted-V12 engine that powered the Messerschmitt Bf 109s tenth through thirteenth prototypes been available. Heinkel was forced initially to use the BMW VI "upright" V12 liquid-cooled engine.
During the war, British test pilot Eric Brown evaluated many Luftwaffe aircraft. Among them was an He 111H-1 of Kampfgeschwader 26 Löwengeschwader which was forced to land at the Firth of Forth on 9 February 1940. Brown described his impression of the He 111s unique greenhouse nose,
The overall impression of space within the cockpit area and the great degree of visual sighting afforded by the Plexiglas panelling were regarded as positive factors, with one important provision in relation to weather conditions. Should either bright sunshine or rainstorms be encountered, the pilot's visibility could be dangerously compromised either by glare throwback or lack of good sighting.
Taxiing was easy and was only complicated by rain, when the pilot needed to slide back the window panel and look out to establish direction. On take off, Brown reported very little "swing" and the aircraft was well balanced. On landing, Brown noted that approach speed should be above and should be held until touchdown. This was to avoid a tendency by the He 111 to drop a wing, especially on the port side.
Competition
In the mid-1930s, Dornier Flugzeugwerke and Junkers competed with Heinkel for Ministry of Aviation contracts. The main competitor to the Heinkel was the Junkers Ju 86. In 1935, comparison trials were undertaken with the He 111. At this point, the Heinkel was equipped with two BMW VI engines while Ju 86A was equipped with two Jumo 205Cs, both of which had. The He 111 had a slightly heavier takeoff weight of compared to the Ju 86's and the maximum speed of both aircraft was. The Ju 86 had a higher cruising speed of, faster than the He 111. This stalemate was altered drastically by the appearance of the DB 600C, which increased the He 111's power by per engine. The Ministry of Aviation awarded both contracts. Junkers sped up development and production at a breathtaking pace, but their financial expenditure was huge. In 1934–1935, 3,800,000 RM was spent. The Ju 86 appeared at many flight displays all over the world which helped sales to the Ministry of Aviation and abroad. Dornier, which was also competing with their Do 17, and Heinkel were not as successful. In production terms, the He 111 was more prominent with 8,000 examples produced against just 846 Ju 86s, and was therefore the Luftwaffe's most numerous type at the beginning of the Second World War.Design
The design of the He 111 A-L initially had a conventional stepped cockpit, with a pair of windscreen-like panels for the pilot and co-pilot. The He 111P and subsequent production variants were fitted with fully glazed cockpits and a laterally asymmetric nose, with the port side having the greater curvature for the pilot, offsetting the bombardier to starboard. The resulting stepless cockpit, which was a feature on a number of German bomber designs during the war years in varying shapes and formats, no longer had the separate windscreen panels for the pilot. Pilots had to look outside through the same bullet-like glazing that was used by the bombardier and navigator. The pilot was seated on the left and the navigator/bomb aimer on the right. The navigator went forward to the prone bomb-aiming position or could tilt his chair to one side, to move into the rear of the aircraft. There was no cockpit floor below the pilot's feet—the rudder pedals being on arms—giving very good visibility below. Sliding and removable panels were manufactured into the nose glazing to allow the pilot, navigator and or bomb aimer to exit the aircraft quickly, without a time-consuming retreat into the fuselage.File:Heinkel He 111 interior.JPG|thumb|Inside Wk Nr 701152 He 111 H-20. Looking forward to the first bulkhead from the ventral gunner's position. The control column and cockpit glazing is visible in the central background.
The fuselage contained two major bulkheads, with the cockpit at the front of the first bulkhead. The nose was fitted with a rotating machine gun mount, offset to allow the pilot a better field of forward vision. The cockpit was fully glazed, with the exception of the lower right section, which acted as a platform for the bombardier-gunner. The commonly used Lotfernrohr-series bombsight penetrated through the cockpit floor into a protective housing on the outside of the cockpit.
Between the forward and rear bulkhead was the bomb bay, which was constructed with a double-frame to strengthen it for carrying the bomb load. The space between the bomb bay and rear bulkhead was used up by Funkgerät radio equipment and contained the dorsal and flexible casemate ventral gunner positions. The rear bulkhead contained a hatch which allowed access into the rest of the fuselage which was held together by a series of stringers. The wing was a two spar design. The fuselage was formed of stringers to which the fuselage skin was riveted. Internally the frames were fixed only to the stringers, which made for simpler construction at the cost of some rigidity.
The wing leading edges were swept back to a point inline with the engine nacelles, while the trailing edges were angled forward slightly. The wing contained two fuel tanks between the inner wing main spars, while at the head of the main spar the oil coolers were fitted. Between the outer spars, a second pair of reserve fuel tanks were located, carrying an individual capacity of of fuel. The outer trailing edges were formed by the ailerons and flaps, which were met by smooth wing tips which curved forward into the leading edge. The outer leading edge sections were installed in the shape of a curved "strip nosed" rib, which was positioned ahead of the main spar. Most of the interior ribs were not solid, with the exception of the ribs located between the rear main spar and the flaps and ailerons. These were of solid construction, though even they had lightening holes.
The control systems also had some innovations. The control column was centrally placed and the pilot sat on the port side of the cockpit. The column had an extension arm fitted and had the ability to be swung over to the starboard side in case the pilot was incapacitated. The control instruments were located above the pilot's head in the ceiling, which allowed viewing and did not block the pilot's vision. The fuel instruments were electrical. The He 111 used the inner fuel tanks, closest to the wing root, first. The outer tanks acted as reserve tanks. The pilot was alerted to the fuel level when there was left. A manual pump was available in case of electrical or power failure but the delivery rate of just per minute demanded that the pilot fly at the lowest possible speed and just below. The He 111 handled well at low speeds.
The defensive machine gun positions were located in the glass nose and in the flexible ventral, dorsal and lateral positions in the fuselage, and all offered a significant field of fire. The machine gun in the nose could be moved 10° upwards from the horizontal and 15° downwards. It could traverse some 30° laterally. Both the dorsal and ventral machine guns could move up and downwards by 65°. The dorsal position could move the MG 131 machine gun 40° laterally, but the ventral Bola-mount twinned MG 81Z machine guns could be moved 45° laterally. Each MG 81 single machine gun mounted in the side of the fuselage in "waist" positions, could move laterally by 40° and could move upwards from the horizontal by 30° and downwards by 40°.