There have been many strange aircraft in the history of aircraft construction, but perhaps the most unusual were the experimental jet aircraft developed by French engineer Rene Leduc, namely the Leduc 0.10, Leduc 0.21 and Leduc 0.22.
All three aircraft, designed by Rene Leduc, were made to test a new propulsion system - the ramjet (ramjet).
These engines represent the evolution of turbojets: they do not have an initial compressor and therefore no turbine at the end. They use a gap to compress the incoming air, which splits the flow of the incoming air at high speed, acting as a conventional compressor. Therefore, ramjet engines operate at high speeds and have very low structural complexity, since they have no moving parts.
The first ramjet engine dates back to 1915, when the Austrian inventor Albert Fono proposed an artillery projectile in combination with such a system to radically increase the flight range.
However, we can say that the idea of introducing such systems for controlled flight of aircraft came from Leduc himself, who, in 1938, began to develop a new family of aircraft adapted for such a propulsion system. Work also continued during the 2nd World War and culminated in 1947 with the development of the Leduc 0.10.
What is most striking about this aircraft is the fact that the cockpit is located directly inside the stator air intake: the pilot sat practically inside the engine in a gabled cockpit, which in the event of an accident would separate from the rest of the aircraft, saving the pilot. The cockpit design inevitably made the pilot's view very poor. As a result, it was decided to make windows on the outer stator wall so that the pilot could improve lateral visibility.
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The main problem faced by the designers was the need to start a ramjet engine, since it required a stream of air moving at a high speed to start it, although the engine itself did not have an air intake device. The solution was to mount the plane over the fuselage of the transport plane, which would be a kind of mother ship. The aircraft was launched already at a sufficient speed to ensure proper engine operation.
After the first joint flights and various glide path tests, on April 21, 1949, the engine was finally launched in flight for twelve minutes at half power, accelerating the aircraft at a speed of 680 km / h. Subsequently, the aircraft demonstrated the efficiency of ramjet thrust, and the aircraft reached a speed of 0.84 Mach and climb speed (39.6 m / s) - higher than that of the best fighters of that time.
The Leduc 0.10 project proved to be successful and demonstrated that a ramjet engine could be used in flight, although perhaps not as versatile as a turbojet.
It is for these reasons that another model was developed: the Leduc 0.21.
The new model was a slightly (30%) larger version of the Leduc 0.10, which also included some technical and functional improvements (for example, the cockpit located outside the engine).
The aircraft reached an altitude of 20,000 meters and a speed of 900 km / h, which brought closer the possibility of using a ramjet for supersonic flight.
Based on these experiments, it was decided to develop the Leduc 0.22 and in 1956, just three years after the previous model, the plane was ready.
The new aircraft was to become an interceptor capable of speeds up to Mach 2 (2469.6 km / h). To achieve such results, it was necessary to abandon the launch of the aircraft from the "mother ship", and therefore it was decided to integrate a turbojet engine into the stator aeration flap to allow the aircraft to take off on its own and accelerate to the speed required to launch the stator.
However, things did not go further: even during the tests of the Leduc 0.22, the project was closed due to a lack of money. Since then, he has remained an example of his designer's genius and quirkiness.
However, this project was not a waste of time. In fact, all of the developments were used in the famous American Lockheed SR-71, Blackbird.