The Heinkel He 70 was a mail plane and fast passenger aircraft of the 1930s designed by Germany aeronautics firm Heinkel Flugzeugwerke, which was also used in auxiliary bomber and aerial 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.
The Heinkel He 70 Blitz (Lightning) was designed in the early 1930s to serve as a mailplane for Deutsche Lufthansa in response to a request for an aircraft faster than the Lockheed Model 9 Orion (used by Swissair) to service short routes.
It was a low-wing monoplane, with the main characteristics of its design being an aerodynamically efficient elliptical wing, a two-bladed propeller driven by a single engine.
In order to meet the demanding speed requirements, the design endeavored to minimise drag, with flush rivets giving a smooth surface finish, and retractable main landing gear. The tail wheel was not retractable. It was powered by a BMW VI V12 engine of 630hp cooled by ethylene glycol rather than water. This allowed a smaller radiator which also retracted at high speed to further reduce drag. The pilot and radio operator were seated in tandem, followed by a cabin seating four passengers in pairs facing each other. 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).
Luft Hansa operated He 70s between 1934 and 1937 for a 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.
The Luftwaffe operated He 70s from 1935, initially as a light bomber and reconnaissance aircraft. As soon as purpose built designs became available, it was relegated as a liaison and courier aircraft.
Twenty-eight aircraft were sent in the late 1930s to Spain with the German-manned Legion Condor, where they were used during the Spanish Civil War as fast reconnaissance aircraft. There they were known as the Rayo, Spanish for "lightning".
The He 70K (later He 170) was a fast reconnaissance airplane variant used by the German air force. Fitted with a new WM-K-14 radial engine, it was used by the Hungarian Air Force as the He 170A early in World War II during 1941–42.
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 an extremely flammable magnesium alloy called "Elektron", though the majority of the monocoque fuselage was Duralumin. Elektron is very light yet strong, but burns readily when ignited and is difficult to extinguish. Moreover, each wing contained a non-self-sealing 47-gallon fuel tank, which may have further added to the aircraft's reputation for catching fire. A single hit from a light machine gun is reputed to have often set the entire aircraft ablaze. The Hungarian He 170A 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-reconnaissance and specialized Fw 189 "Uhu" medium altitude observation aircraft could be introduced.
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.
The He 70 is known mainly as the direct ancestor of the Heinkel He 111, which had the distinctive elliptical 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 He 70 was exported to Japan for study and inspired the Aichi D3A ("Val") carrier-launched light bomber. This aircraft shared the He 70's distinctive low-mounted elliptical wing and was one of several collaborations between Heinkel and the Japanese aviation industry.
It has been said that the He 70 was an inspiration or influence for the Supermarine Spitfire's elliptical wing.
In a letter to Heinkel, written after seeing the aircraft perform with the Rolls Royce Kestrel engine fitted, R. J. Mitchell said:
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, Beverley Shenstone, RJ Mitchell's aerodynamic advisor denied that the Spitfire wing was copied from the He 70. Shenstone said:
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.
The Günther brothers had already used an elliptical wing design for the Bäumer Sausewind sports aircraft before they joined Heinkel.
Shenstone said that the He 70's influence on the Spitfire design was limited to use as a benchmark for aerodynamic smoothness.
Data from The Beautiful Blitz