Following the success of the He-111 came the He-115, a seaplane comparable to the Sunderland Flying Boat that was produced in large numbers by the British. The He-116 was designed for long-distance cargo transportation and was used for flights to Japan; the He-117 and He-118 were tactical developments that never got off the ground and the He-119 — which could travel up to 375mph (600km/h) and was to be powered by two DB-603 engines — was never put into production.
A revolutionary high-altitude bomber was proposed as the He-274, intended to be a four-engined bomber with a number of advanced features. Development began in October 1941 and the prototypes of the new bomber were contracted for construction in France by the Société Anonyme des Usines Farman (SAUF) firm in Suresnes, near Paris. The He-274 dispensed with twin coupled engines and instead featured four independent DB-603 A-2 engines with a greater wingspan and a lengthened fuselage. The cockpit would be double-glazed and pressurized to maintain an air pressure for the crew equivalent to an altitude of 8,200ft (2,500m). The aircraft was designed to fly up to 47,000ft (14,300m), far higher than any Allied fighter. In 1937 a Bristol Type 138 high altitude monoplane had reached a world record altitude of 49,967ft (15,230m) but this was an experimental aircraft; the highest a Spitfire XIX ever flew was 44,000ft (13,400m).
As a consequence, the He-274 would require little defensive armament and the plane was designed to carry a forward-firing 13mm (0.51in) MG 131 machine gun with a further two pairs of these guns in turrets. Work on manufacture of the prototypes did not start until 1943 and the advance of Allied forces on Paris in July 1944 forced the evacuation of the German employees before the first flight had taken place. Here too, the German technology pointed to the future. After the war, the French Air Force (Armée de l’Air) finished building the first He-274 and renamed it the AAS-01A. The second prototype was flown in December 1947 AAS-01B. Both were employed as test-bed mother ships for the launch of rockets and advanced jet planes at high altitude, and were in use until they were broken up at the end of 1953.
These amazing aircraft clearly show that Ernst Heinkel was a leading innovator on many fronts, and the best example of this is the introduction of the jet fighter. Jet-propelled planes could have radically altered the course of the war, but they arrived on the scene too late to make a crucial difference. The origin of the aircraft jet engine dates back to July 1926, when a young British engineer named A. A. Griffith published a paper on jet turbines. The idea was followed up by Frank Whittle, then an enthusiastic Royal Air Force (RAF) recruit, but Griffith dismissed the idea of a jet plane since he was convinced that a turbine could never generate the efficiencies needed for flight. Undeterred, in January 1930 Whittle took out a patent for the first jet engine. It attracted little interest with the RAF and they placed no restrictions upon the concept. Whittle made great progress as a pilot, and yet although companies showed some interest in his proposals for a jet plane none were willing to put up the money necessary to build a prototype.
During the following year, an Italian experimenter named Secondo Campini sent a paper on jet propulsion to the Italian Royal Air Force (Regia Aeronautica Italiana) and in 1932 he demonstrated a jet-propelled boat on the Venice lagoon. In 1934 he received the agreement of the Italian Royal Air Force for the development of a jet aircraft. Campini commissioned the Caproni factory to build his prototype. On 27 August 1940 test pilot Mario De Bernardi took the plane into the air and the World Air Sports Federation (Fédération Aéronautique Internationale) recognized this at the time as the first successful flight by a jet aeroplane, until news came of the Heinkel He-178 V1. This had flown for the first time in August 1939, powered by the HeS-3B engine invented by a German designer named Hans Joachim Pabst von Ohain. As we shall see, this highly innovative aircraft would give rise to a revolution in aircraft design — one we are still experiencing today.
However, the reality is that Campini’s aircraft did not have a jet turbine at all. His design featured a 670hp (500kW) Isotta Fraschini piston engine which drove an air compressor, forcing air into the combustion chamber where it mixed with a spray of fuel. Although the exhaust gases propelled the device forward, the use of a piston engine as the compressor means that it was not a jet turbine. Another Italian named Luigi Stipa also designed the Stipa-Caproni experimental aircraft in 1932, which had a ducted fan, and he also tried to claim it as the first jet aircraft. Both his plane and the Caproni-Campini used a jet of gas to propel the plane along, but neither was a pure jet turbine.
Meanwhile, in Britain, Whittle was still trying to develop his jet turbine idea, and in 1934 he was authorized to take the two-year engineering course at Peterhouse College, University of Cambridge, where he graduated with a first-class degree in Mechanical Sciences. Whittle received a note in the mail to remind him that his patent for a jet engine was due for renewal in January 1935. He could not afford the £5 fee. The Air Ministry told him that it was not interested in funding the renewal either, and so the patent lapsed. However, in September 1935 Whittle was introduced to two investment bankers at O. T. Falk & Partners, Sir Maurice Bonham-Carter and Lancelot Law Whyte. Whittle explained that a reciprocating engine, with its metallic components jerking up and down, seemed to him condemned to extinction. He insisted that the smooth-running jet turbine was obviously the way ahead. Whyte felt that this was a proposal of sheer genius, and in January 1936 Power Jets Ltd was formally established.
On 12 April 1937 the Whittle jet engine ran for the first time. It was a stunning success. There was a growing sense that the jet engine had immense promise, but not until March 1938 did the Air Ministry offer any funding. This funding proved to be a mixed blessing, for the project was now subject to Ministerial bureaucracy and the Official Secrets Act made it impossible to discuss the developments as widely as before. From being a topic of growing interest, it suddenly became a matter of the utmost secrecy. Nonetheless, work proceeded on constructing a prototype jet plane, the Gloster-Whittle E 28/39, and on 7 April 1941 near Gloucester the first few hops into the air were made. Whittle himself was at the controls, but had in fact been specifically ordered not to fly the plane as the Ministry did not wish to risk both the aircraft and its designer if anything went wrong. Whittle told the senior officers that he would just take out the plane for some taxi runs, which would warm up the engine; but he accelerated along the runway and (as he later said) ‘it just took off’. The next month, on 15 May, the first formal test flight took off from Cranwell at 7.40pm. The plane flew for 17 minutes at speeds of up to 340mph (545km/h). Days later, it was flying at 370mph (600km/h) up to 25,000ft (7,600m) which was better than anything a conventional fighter could achieve.
Meanwhile, under conditions of top secrecy, jet planes were already taking shape in Germany. In 1936, the gifted young engineer Hans Joachim Pabst von Ohain had taken out a patent for the use of the exhaust thrust from a gas turbine as a means of propulsion. This was six years behind Whittle’s original patent. Ohain presented his ideas to Heinkel, who agreed to help develop the concept. The prototype was speedily developed and built, and Ohain successfully demonstrated his first engine in 1937. It was powered by hydrogen gas which quickly burned through the components, and was extremely simple in design, but it proved that a jet turbine could run just five months after Whittle’s prototype engine. It is remarkable to think of these two gifted young men, each constructing and testing the first jet engines in the world, separately in England and Germany, and at the same time. Although Whittle had been unable to find finance for a year, plans were quickly made in Germany to construct one of these engines to power an aircraft.