Heinkel He 70
In autumn 1931, the American aircraft manufacturer Lockheed introduced with "Orion" a revolutionary concept for fast commercial aircraft. Designed as a low-wing monoplane the aircraft possessed a retractable undercarriage as well as a aerodynamically-cowled power plant. The cruise speed was 256 km/h, top speed 358 km/h. This was amazing back then since the best fighters achieved a maximum speed of 300 km/h.
The Deutsche Luft Hansa (DLH) faced the fact they could only stay in business with a comparable aircraft. Therefore, DLH decided upon a specification handed over to the Junkers works. The Ju 60-named aircraft did not achieved the desired performance, whereupon a development contract was closed with Ernst Heinkel in mid-January 1932.
He immediately sent one of his best engineers, Siegfried Günther, to the USA to survey the state-of-the-art US aircraft construction. Following his return, work started on the aircraft, named He 65. Designed as a low-wing monoplane with retractable undercarriage, final assembly of the aircraft was set for summer 1932. According to the development schedule, a cruise speed of 238 km/h was to be achieved in the beginning which was to be improved upon during the following developments. Work intensified when Swissair instaled an improved "Orion" on the route Zurich-Munich-Vienna, with a cruise speed of roughly 290 km/h.
Immediately, Heinkel stopped work on the He 65 in agreement with DLH, because in his opinion, only a completely new designed aircraft was able to compete with the "Orion". After only four days, work started on the new He 70. Now, a monoplane with retractable undercarriage and place for a crew of two and four passengers or 500 kg payload or mail was planned. For this purpose, the aircraft was designed with elliptically shaped wings and a streamlined, drop-form fuselage. Planned as well were the coating with sheet metal including recessed rivets, both completely new techniques. In order to lower the frontal air resistance, cooling by evaporation of the 630 HP BMW VI aero engines by means of glycol was utilised. All equipment parts were either inside of the fuselage or the wings or could be lowered. Due to the high speed, the fuselage diameter had to be narrow but the passenger cabin was spacious. Right from the drawing board, the He 70 was designed with a radio unit for instrumentation flights - a unique advantage over "Orion".
The first prototype desinate He 70 A took off in commemoration of the 10th anniversary of the Heinkel works on December 1, 1921. Its performance exceeded all expectations: Maximum speed was 377 km/h, cruise speed 323 km/h.
The second prototype was improved upon following proposals of DLH, such as flaps, and was designated He 70 B. With it, the first world record-breaking flights were flown.
The German Air Force, which was in the process of starting up its organisation, was interested in the airplane as they perceived it as a possible light bomber. Heinkel re-equipped the forth prototype for a military role. The German Air Force received some of these He 70 C designated versions.
The He 70 D was equipped with a BMW VI 7,3 Z power plant with 759 HP. Three of these aircraft were sold to the Lufthansa and were used from June 15, 1934 onward on the route Frankfurt-Cologne-Hamburg-Berlin. During the year of 1934 the aircraft was used on routes abroad, too. He 70 D-1, a for military purposes equipped version, saw service with the German Air Force as a fast courier and headquarters airplane.
From the beginning, He 70 E-1 was designed as a light, fast bomber. It was followed by the He 70F series. They served primarily as multi-purpose aircraft. Delivery started in 1934. Crew members were not very fond of the He 70 because of the hard to handle retractable undercarriage and the poor visibility. From 1939 on, they were replaced by more modern aircraft types and were delivered to air schools or courier squadrons where they were in service until VE-day. Those He 70 which were sent to Spain in 1936 remained in service until the early 1950s.
In early 1937, the He 170 was developed for Hungary. It was He 70 F-3 with a 910 HP radial engine. A total of 20 aircraft went to Hungary and saw combat until the end of 1941.
In spring 1938, the prototype He 270 designed for the German Air Force was started. Thanks to its Daimler-Benz aero engine, with 1175 HP, it achieved a speed of 460 km/h at maximum weight. It never entered series production since the German Aircraft did not see no future need for this type of aircraft.
At this stage, series production of the former revolutionary He 70 ended, after 296 assembled aircraft of all versions.
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