Heinkel designed a low-wing cantilever monoplane that incorporated various measures to minimise drag, including its use of an aerodynamically efficient elliptical wing, a smooth external finish, and a retractable undercarriage.

The He 70 was powered by a single nose-mounted BMW VI 7.3 Z engine and cooled via a relatively compact retractable radiator as a further drag-reducing measure.

The Heinkel He 70 Blitz (Lightning) was designed in the early 1930s 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.

[2] Around this time, Germany was already experimenting with producing high-speed mail planes that could compete with American offerings; furthermore, it was generally recognised that the speed of an aircraft was a major competitive advantage over other modes of transportation.

[2] A low-wing cantilever monoplane configuration was selected in order to achieve low drag along with a permissible fuselage cross-section for the desired cabin space, which needed to accommodate two pilots, five passengers, and their baggage.

[2] The arrangement was distinct from that of those of the rival aircraft manufacturer Junkers, possessing greater aerodynamic performance for the fuselage section in proportion to its usable cabin space.

[6] Various wing configurations were considered, the design team having to balance pure aerodynamic performance against various other factors and characteristics, such as roll damping, weight, and the need to accommodate the retractable undercarriage.

[7] Particular care was paid to obtain a high level of torsional stiffness and a sufficient margin against any oscillations, which was a particular problem for cantilever wings.

[8] The wing was composed of wood and had a twin-spar structure that extended into two box-shaped recesses in the fuselage where they were secured to the main frames using bolts.

[14] It was typically flown by a crew of two, a pilot and radio operator, who were seated in a tandem configuration in a fairly central position within the fuselage that was slightly elevated for better visibility.

This radiator, which was located beneath the fuselage, had one-third of the frontal surface area of a conventional counterpart and could be retracted when the aircraft was flying at high speeds to further reduce drag.

Between 1934 and 1936, the type was also flown internationally from Stuttgart to Seville; this route was part of the South American mail service provided by Luft Hansa which continued via Bathurst, The Gambia to Natal, Brazil, using Junkers Ju 52/3m and Dornier Wal flying boats.

[citation needed] The He 70K (later given the RLM number: He 170) was a fast reconnaissance airplane export variant used by the Hungarian Air Force.

Parts of the airframe were made out of an extremely flammable magnesium alloy called "elektron", though the majority of the monocoque fuselage was duralumin.

[citation needed] Other problems included poor defensive armament, short range and poor view from the cabin, all of which led to the Hungarian He 170A fleet being prematurely retired and replaced with obsolescent Heinkel He 46 parasol-wing monoplanes, until Focke-Wulf Fw 189 "Uhu" medium altitude observation aircraft could be introduced.

[citation needed] While the He 70 saw only limited service in training capacities during the Second World War, it was the Luftwaffe's first Schnellbomber and served as the antecedent for some of the bombers involved in the Battle of Britain.

The He 70 was essentially scaled down to produce the He 112 fighter which lost out on competition against the Messerschmitt Bf 109, but was nonetheless built in small numbers.

[27]The Günther brothers had already used an elliptical wing for the Bäumer Sausewind sports aircraft[citation needed] before they joined Heinkel.