The Heinkel He 70 was designed as a high-speed four seat passenger aircraft, and with its streamlined fuselage and elliptical wings was a forerunner of many later Heinkel military aircraft, not least the He 111, early versions of which used a very similar wing.
The development of the Heinkel He 70 was triggered by the appearance of the Lockheed Orion, which with its top speed of 190mph (305kph) was as fast as most contemporary fighter aircraft. In the summer of 1931 Swissair placed an order for a number of Orions, forcing her European competitors to respond. Deutsche Lufthansa decided to issue specifications for an even faster aircraft, capable of cruising at at least 198mph, and of carrying six passengers on non-stop flights of 620 miles (1000km). Junkers and Heinkel were both approached to produce aircraft.
The first Heinkel design, the He 65, was submitted to Lufthansa and the Transport Ministry in January 1932. It would have been a single-engined low-wing monoplane, with streamlined fairings for the non-retractable undercarriage, and with a cruising speed of only 148mph. Work continued on the He 65 until May 1932. In that month one of Swissair's Orions made its first scheduled flight between Zurich, Munich and Vienna, at a cruising speed of 180mph. Ernst Heinkel decided to halt all work on the He 65 and move onto a new, much more advanced design.
In June Heinkel submitted the first plans for the new aircraft. At the cost of reducing the number of passengers from six to four Heinkel guaranteed a cruising speed of 179mph. The new design was approved on 14 June 1932, and at the start of July Heinkel's design team began detailed work on the He 70.
The new aircraft was given elliptical wings (similar in plan to those of the Supermarine Spitfire), but with an inverted gull-wing shape with the retractable landing gear built into the lowest point on the wing. This lifted the engine further from the ground that would otherwise have been possible, and was an approach later used on the Chance Vought Corsair. The wings smoothly merged into the fuselage, which was constructed of panels riveted edge-to-edge instead of overlapping, giving the aircraft a very smooth surface, while the engine was given a streamlined cowling. One unusual feature was the asymmetrical position of the cockpit, on the left side of the fuselage.
The prototype He 70 was designed and built impressively quickly, making its maiden flight on 1 December 1932. Its performance was even more impressive than had been promised. When it was publicly unveiled at Tempelhof airport on 28 February 1933 it achieved a cruising speed of 200mph, and a few months later reached a speed of 234mph on a timed flight.
The He 70 had a relatively short civil career. Lufthansa received twenty eight aircraft, using them for airmail from March 1933 and for fast passenger flights (the Blitz-Dienst or Lightning Service routes) from June 1934. The He 70A was followed into civil service by the He 70G. On this version the cockpit was moved to the centre line, and the crew reduced from two to one.
The He 70 was slowly phased out in favour of larger twin engined aircraft, in particular the civil versions of the Heinkel He 111 and Junkers Ju 86, and the last Lufthansa aircraft were withdrawn in 1938.
The high speed of the He 70 made it very attractive to the young Luftwaffe, and a military conversion soon followed. This made the He 70 one of the few Luftwaffe aircraft genuinely converted from a civil aircraft. Although it was widely believed that this was true of a number of later aircraft, most were designed from the start in both military and civil forms.
The He 70C was the first military version. A single prototype was produced early in 1934, with a wider cockpit, an open machine-gun position at the back of the cabin and a bomb bay. By the end of 1934 the prototype had been joined by eleven He 70Cs.
The He 70D was given a more powerful 750hp BMW VI 7.3 engine. This would become the standard engine for the military aircraft. It was otherwise similar to the He 70C. Nine were in service by the end of 1934, and around a dozen were built in all.
The He 70E was the first proper military version. It was a light bomber with three vertical bomb magazines, each capable of carrying two 50kg bombs, giving the aircraft a payload of 300kg (660lb). Deliveries of the He 70E began early in 1935.
The He 70F followed later in 1935. It was a reconnaissance aircraft, capable of carrying a jettisonable fuel tank in the forward bomb bay and a camera in the rear bomb bay.
When the He 70F entered service it was faster than the He 51 fighter, then the Luftwaffe's main frontline fighter, but it wasn't a successful military aircraft. It has slightly erratic flying characteristics that didn't endear it to its crews, but it would be the elliptical wings that were its main weakness. Their position, and large chord (distance between the front and back of the wing) meant that they blocked the view from the cabin. The low roof to the cabin was also a problem, and together these features made it a poor reconnaissance aircraft. There was also a concern that the wooden wings were a fire risk.
Eighteen He 70F-2s were sent to Spain in the autumn of 1936, where they served with A/88, the reconnaissance element of the Condor Legion. The type's limitations as a military aircraft soon became clear, and they were replaced by the Dornier Do 17F. The surviving twelve He 70s were transferred to the Spanish Nationalist Air Force, and remained in service into the 1950s.
The He 70's biggest impact on the Luftwaffe probably came on 3 June 1936, when General Wever, the first chief-of-staff of the Luftwaffe, was killed when his He 70 crashed during take-of. Wever was one of a small number of Luftwaffe officers who supported the development of a strategic air force with heavy bombers. Without his support the development of heavy bombers soon came to an end, to be revived only after the American entry into the war, way too late for any of the new designs to enter service.
Heinkel were always aware that the He 70 needed a more powerful engine. At first it was hoped that the Rolls Royce Kestrel would be the answer, and Heinkel hoped to swap a number of He 70 airframes for Kestrel engines. Only one such swap took place before the Nazis blocked the idea, but the single He 70 to reach Britain did prove Heinkel's theory. When powered by a Kestrel V the aircraft reached 257 mph/ 415 kph, and in October 1938, when powered by a Peregrine I, it reached 298 mph/ 481 kph (the fastest German version, the single He 270, reached 286mph). The aircraft remained in use as an engine test bed until 1944.
Heinkel made two further attempts to re-engine the He 70. The He 170 used a licence built Gnome-Rhône radial engine, and was sold in small numbers to Hungary, while the sole He 270 used a Daimler Benz DB 601 engine.
Engine: BMW VI 6.0 Z (He 70A) or 7.3 Z (He 70E)
Power: 637hp (A) or 750hp (E)
Wing span: 48ft 6 ½ in
Length: 38ft 4 5/8in
Fully loaded weight: 7,541lb
Max Speed: 224mph
Armament: One 7.92mm MG 15 in rear cabin
Bomb-load: 660lb (300kg) for He 70E