The Heinkel 70 (Blitz) was originally born out of a need for a speedy aeroplane charged with "fast" mail delivery for the Deutsche Lufthansa company. Lufthansa was in the market for such a platform to best performance of the six-passenger monoplane Lockheed Vegas and Model 9 Orions over short distances. In the end, the Heinkel engineers delivered an excellent product that would quickly set eight world speed records, covering speed-over-distance. Some He 70s would later see combat actions in the Spanish Civil War with the fabled German "Condor Legion". Regardless, the type was quickly overtaken by more impressive breeds worldwide by the time of World War 2.
Heinkel delivered a proposal to Lufthansa that ultimately became the firm's He 70 design. The aircraft utilized a wing concept as brought about by the Gunther brothers, the pair now having joined the Heinkel bureau. As speed was the call of the day, landing gears would be made wholly retractable, rivets would be countersunk to leave a smooth aerodynamic finish and the design would be highly streamlined complete with rounded wing edges. First flight was recorded on December 1st, 1932, and its general responsiveness was highly promising while performance proved excellent. Standard operating crew for the aircraft were two personnel (pilot and navigator seated in tandem). Cabin space was such that cargo or up to four passengers could be ferried about. In the latter role, luggage could be stored safely in an aft compartment and seating for the four was arranged in two pairs of seats - the seat rows to face one another. Power was derived from a single BMW VI series V12 liquid-cooled engine. Of note to this powerplant was that it was cooled by ethylene glycol as opposed to water or other means - this being a design decision by Heinkel engineers and required a smaller radiator, further relieving the airframe of excess weight. The He 70a became the first prototype followed by the He 70b passenger prototype. The He 70c served as a gunnery trial platform while the fourth was produced for Lufthansa with the BMW engine. Likewise, the fifth prototype went to the Luftwaffe as a light bomber with the BMW engine.
The He 70 sported a clean design, consistent with Heinkel standards. The engine was fitted to the extreme forward end of slim duralumin monocoque fuselage and mounted low. When viewed head on, the forward fuselage displayed a rectangular shape, culminating in a rounded body and rounded empennage. The crew compartment was fitted ahead of amidships under a framed contoured canopy and was interestingly offset to the portside ever so slightly. The low cantilever wings, constructed of spruce and plywood, were elliptical in shape and arranged in a low-wing monoplane format also ahead of amidships. The empennage tapered off to a point to which a round-edge vertical fin sat. Stabilizers were affixed to the empennage sides at the extreme rear. While the He 70 maintained two retractable main landing gear legs, there was no tail wheel - just a tail skid. In all, the Heinkel He 70 was a pleasing design full of streamlining and contours.
Production of the civilian airliner model reached 28 examples with 14 delivered to Lufthansa. The initial passenger model became the He 70A followed by the He 70D and He 70G. At its inception, the He 70 was an impressive aircraft, essentially modern by early 1930s standards - fast and adaptable to multiple roles. Lufthansa managed its fleetfrom 1934 to 1937 with several routes across Germany opened. Despite its impressiveness, the He 70 would lead a relatively short civilian-minded life before being replaced by larger aircraft that could ferry more passengers, luggage and associated goods from place to place. Additionally, the Luftwaffe found a need for the fast monoplane by 1935 and its military value soon grew.
The Heinkel He 70 caught the eye of the rebuilding German Luftwaffe, they themselves ordering and receiving deliveries of a communications-minded He 70D model. From there, the type was evolved into a three-man light bomber (He 70E) and a three-man reconnaissance/courier model (He 70F). A long-range reconnaissance model existed under the He 70F-1 and He 70F-2 marks. At least 28 He 70s served with the Condor Legion in the Spanish Civil War, this conflict essentially a test-bed for such German war machines as the Panzer tank, the Messerschmitt Bf 109 fighter (Heinkel's own He 112 fighter competed unsuccessfully for this fighter contract) and the Dornier Do 17 medium bomber. After Germany's involvement there ended, some eleven Condor Legion aircraft were passed on to the Ejercito del Aire of Spain.
While the He 70 proved a solid aircraft in her own right, the system was not without some major flaws. Dominant of these was the aircraft's tendency to burst into flames when hit, this owing to its magnesium airframe which combusted when heated in the air. Crews were generally quite unlucky if their aircraft were to catch fire, the blaze quickly engulfing crew and aircraft alike. Additionally, as impressive as the He 70 was by early 1930s standards, it became clearly outclassed by the middle of the decade and the type was relegated to secondary roles or retired altogether, replaced by the newer breed of aircraft coming online in time for World War.
By the time of World War 2, the heydays of the He 70 were behind her. She was used by the German Luftwaffe primarily as a trainer by then. It is of note that the He 70 was also delivered to the Empire of Japan for evaluation, resulting in the Aichi D3A "Val" light bomber of the IJN. Heinkel and the Empire would meet on such common ground on several more occasions before the war negated such exchange of ideas and technology.
In the end, over 320 examples were produced in all, both in military and civilian forms and included license production of the type in Hungary as the He 70K/He 170A. Eighteen German He 70s were also delivered to Hungary between 1937 and 1938, though these were fitted with the Gnome-Rhone 14K Mistral Major engine. Armament for these Hungarian exports included a pair of 7.8mm Gebauer machine guns. As the combustible issue became well-known, the Hungarians also retired their He 70s lesser types until Germany could deliver a more modern product.
The British firm of Rolls-Royce purchased at least one He 70G to be used as a flying laboratory of sorts in the testing of various powerplants. The cabin aboard the He 70 served this purpose well for engineers and equipment could be held onboard and monitor performance in real time while in flight. The purchase through the RLM was made in exchange for four Kestrel engines.
Heinkel's other wartime design, the better-known He 111 medium bomber, was born from the lessons learned in the He 70. Looking at the two designs side-by-side, the similarities are apparent, particularly the elliptical planform, quite a difference from the bombers developed by Junkers and Dornier in that same span.