Heinkel He 70

The Heinkel He 70 was a German mail plane and fast passenger aircraft of the 1930s, that also saw use in auxiliary bomber and reconnaissance roles. It had a relatively brief commercial career before it was replaced by types which could carry more passengers. The He 70 was a leading design for its day, setting eight world speed records by the beginning of 1933.

Design and development
The Heinkel He 70 Blitz (lightning) was designed in the early 1930s to serve as a fast mailplane for Deutsche Luft Hansa. The He 70 was developed in response to a Deutsche Luft Hansa request for a faster aircraft than the Lockheed Vega and Orion (as used by Swissair) for employment on short routes.

It was a low-wing monoplane, with the main characteristics of its revolutionary design its elliptical wing, which the Günther brothers had already used in the Bäumer Sausewind sports plane before they joined Heinkel, and its small, rounded control surfaces. In order to meet the demanding speed requirements, the design minimised drag, with countersunk rivets giving a smooth surface finish and a retractable undercarriage, a novel feature for a German aircraft. It was powered by a BMW VI V-12 engine, cooled by ethylene glycol rather than water, allowing a smaller radiator and therefore reducing drag. The pilot and radio operator were seated in tandem, with a cabin housing four passengers on two double seats facing each other.

The first prototype flew on 1 December 1932, and proved to have excellent performance, setting eight world records for speed over distance, and reaching a maximum speed of 377 km/h (222 mph).

Operational history
Luft Hansa operated He 70s between 1934 and 1937 for fast flight service which connected Berlin with Frankfurt, Hamburg and Cologne, as well as on the Cologne/Hamburg route.

He 70s were flown abroad from Stuttgart to Seville between 1934 and 1936. The route was part of the South America mail service provided by Luft Hansa that continued via Bathurst, The Gambia to Natal, Brazil, using Junkers Ju 52/3m and Dornier Wal flying boats.

Remaining aircraft were transferred to the Luftwaffe in 1937.

Military use
Twenty-eight aircraft were sent with the Legion Condor, where they were used during the Spanish Civil War as fast reconnaissance aircraft. Their high speed gave them the nickname Rayo (lightning).

The He 70K (later He 170), a fast reconnaissance airplane variant was used by the Royal Hungarian Air Force in early World War II during 1941-42. The Luftwaffe operated He 70s from 1935, initially as a light bomber and reconnaissance aircraft. As soon as purpose build designs became available, it was relegated as a liaison and courier aircraft.

The main weakness of the He 70 in military use was that crews considered it a fire risk. Elements of the airframe were made out of so-called "Elektron (alloy)", though the majority of the monocoque fuselage was Duralumin. Elektron is a very light, yet strong, alloy of magnesium, which burns readily when ignited, and is difficult to extinguish. Moreover, the wings contained a 47-gallon fuel tank apiece, which may have further added to the aircraft's reputation for being flammable. A single hit from a light machine gun is reputed to have usually set the entire plane ablaze. The Hungarian He 170A (a military version derived from the He-70 with a new WM-K-14 radial engine), fleet was retired for this and other reasons, including poor defensive armament, short range and poor view from the cabin, and replaced with vintage, high-wing He 46 monoplanes, until modern Bf 109 fighter-recce and specialized Fw 189 "Uhu" medium altitude observation aircraft could be introduced.

Influence
While the He 70 saw only limited service in training capacities during World War II, it was the Luftwaffe's first Schnellbomber and served as the antecedent for the majority of bombers involved in both the Battle of Britain and the attack on Pearl Harbor.

Influence on German designs
The He 70 is known mainly as the direct ancestor of the Heinkel He 111 which used its distinctive oval wings and streamlined fuselage in a twin-engine configuration. One can also see the close similarity of the designs in the tail section and cockpit of the early He 111. The He 111, which began service with the Luftwaffe in 1936, went on to become the most numerous bomber type of the Luftwaffe - with just over 5,600 examples produced during the war in total - in the early years of World War II, before the growing numbers of Junkers Ju 88 bomber variants (the -A and -S subtypes) overtook it later in World War II.

Heinkel's pioneering design was also a model for the He 112 fighter which competed unsuccessfully against the Messerschmitt Bf 109 to become the Luftwaffe's first monoplane fighter. The He 112 was nonetheless built in small numbers and its performance proved once again the strength of the He 70's original design. The fighter was basically a scaled down version of the He 70 and shared its all-metal construction and inverted gull-wings.

Influence on Japanese designs
The He 70 was exported to Japan for study and inspired the Aichi D3A ("Val") carrier-launched light bomber. This plane too shared the He 70's distinctive low-mounted oval wings and was only one of several collaborations between Heinkel and the Japanese aviation industry.

Influence on British designs
It has been said that the He 70 was an inspiration or influence for the Supermarine Spitfire's elliptical wing planform, although this seems unlikely. The He 70 used as an engine test bed by Rolls Royce did not arrive in the UK until three weeks after the Spitfire's first flight.

Part of a letter that R J Mitchell wrote to Heinkel after seeing the aircraft perform with the Rolls Royce Kestrel engine fitted: "We, at Supermarine Aviation, were particularly impressed, since we have been unable to achieve such smooth lines in the aircraft that we entered for the Schneider Trophy Races.... In addition to this, we recently investigated the effect that installing certain new British fighter engines would have on the He 70, We were dismayed to find that your new aircraft, despite its larger measurements, is appreciably faster than our fighters. It is indeed a triumph."

However, Beverly Shenstone, RJ Mitchell's aerodynamic advisor refuted the idea that the Spitfire wing was copied from the He 70. In Alfred Price's 'Spitfire - A Documentary History' Shenstone is quoted as saying:

"It has been suggested that we at Supermarine had cribbed the wing shape from that of the He 70 transport. This was not so. The elliptical wing had been used on other aircraft and its advantages were well known. Our wing was much thinner than that of the Heinkel and had a quite different section. In any case it would have been simply asking for trouble to have copied a wing shape from an aircraft designed for an entirely different purpose."

Shenstone said that the He 70's influence on the Spitfire design was limited to use as a criterion for aerodynamic smoothness which is to some extent verified by the extract of the letter from Mitchell to Heinkel quoted above.

Versions

 * He 70a
 * First prototype.


 * He 70b
 * Second prototype with the crew of 2 and 4 seats for passengers.


 * He 70c
 * Third prototype armed with machine gun for trials of versions for light bomber, reconnaissance and courier duties.


 * He 70d
 * Fourth prototype built in 1934 for Luft Hansa, powered by BMW VI 7,3 engine.


 * He 70e
 * Fifth prototype built in 1934 for Luftwaffe as light bomber, powered by BMW VI 7,3 engine.


 * He 70A
 * Passenger version for Luft Hansa.


 * He 70D
 * Passenger version for Luft Hansa, 12 examples built.


 * He 70E
 * Light bomber version for Luftwaffe, later converted to F version.


 * He 70F
 * Reconnaissance / courier version for Luftwaffe.


 * He 70F-1
 * Long-range reconnaissance version.


 * He 70F-2
 * Similar to the He 70F-1


 * He 70G
 * Passenger version built for Luft Hansa, after 1937 converted to F version.


 * He 70G-1
 * One aircraft fitted with a 604 kW (810 hp) Rolls-Royce Kestrel piston engine.


 * He 70K (He 170A)
 * License-built Hungarian fast reconnaissance variant equipped with a licence-made 746 kW (1,000 hp) WM-K-14 radial engine.


 * He 270 V1 (W.Nr. 1973, D-OEHF)
 * Prototype with DB-601Aa inline engine.

Civil Operators

 * Nazi Germany
 * Deutsche Luft Hansa received the first two prototypes in 1933 and 1934 as well as three He 70D in 1934 and 10 He 70G in 1935.


 * undefined
 * Imperial Japanese Navy Air Service received one aircraft for test.


 * Rolls Royce acquired one He 70G from the RLM in exchange for 4 Kestrel engines. It was used as an engine test bed.
 * Rolls Royce acquired one He 70G from the RLM in exchange for 4 Kestrel engines. It was used as an engine test bed.


 * 🇨🇭 Switzerland
 * Swissair received a few Heinkel He-70s for express trans-alpine flights between Zurich and Milan in 1934.

Military Operators

 * Nazi Germany
 * Luftwaffe


 * 🇭🇺 Hungary
 * Royal Hungarian Air Force received 18 domestically license-built He 170A aircraft.


 * Spanish State
 * Ejército del Aire received 11 aircraft of the 30 that had served with Legion Condor.