On the Mirage III, the “Souris” made it possible to control the shock wave at high Mach speeds. A decisive mechanical solution for supersonic aviation.
In summary
The Mirage III made combat aviation history not only for its supersonic performance, but also for a discreet yet decisive technical solution: the “Mouse”, a mechanical system for manually managing the shock wave at the air intake. At a time when electronics were still limited, Dassault chose a simple, robust, and effective approach to ensure a stable fuel supply to the engine at high speeds. These movable half-cones allowed the shock wave to be precisely positioned in order to slow the air to speeds compatible with the turbojet engine. This choice made sustained flight beyond Mach 2 possible, while maintaining engine reliability. The effectiveness of this solution influenced more complex architectures on subsequent aircraft, both civil and military. Understanding the “Souris” means understanding how a major physical constraint was transformed into a lasting operational advantage.
The Mirage III faces the challenge of supersonic flight
When it entered service in the late 1950s, the Mirage III was designed for a clear mission: to intercept quickly, high, and far. Its delta wing gave it good high-speed qualities, but it also imposed compromises at low speeds. The real challenge, however, was not aerodynamic. It was internal.
A supersonic aircraft cannot simply “swallow” the ambient air. Above Mach 1, shock waves cause sudden changes in pressure and flow velocity. However, a turbojet engine such as the Atar 9 requires a subsonic, stable, and homogeneous airflow at the compressor inlet. If this condition is not met, the engine may stall, lose thrust, or even shut down.
At Mach 2 (approximately 2,470 km/h at high altitude), the slightest instability in the intake becomes critical. In the 1950s, there were no fast computers or digital control laws capable of adjusting the geometry of air intakes in real time. Engineers therefore had to find a physical solution that was reliable and understandable to the pilot.
The birth of the “Souris” (Mouse), a simple answer to a complex problem
The “Mouse” is not a gadget. It is a central feature of the Mirage III. It consists of movable half-cones installed in each side air intake. Their role is to control the position of the main shock wave created when supersonic air is slowed down before entering the engine.
Unlike a fixed air intake, the “Mouse” allows the internal geometry to be adapted to the speed. At low and medium speeds, the half-cones remain in the rear position. As the aircraft accelerates and approaches Mach 1.4, they gradually move forward. This translation changes the angle and location of the shock wave.
The objective is clear: to force the shock wave to form at a point where air deceleration is controlled. At the shock outlet, the flow becomes subsonic, with a pressure compatible with the compressor stages. The engine is thus protected from sudden changes in speed.
The physical operation of shock wave management
To understand the purpose of the “Souris,” it is necessary to recall a fundamental principle. A supersonic flow cannot be slowed down gradually. It undergoes a discontinuity: the shock wave. Through this wave, the speed drops sharply, while the pressure and temperature increase.
On the Mirage III, the “Mouse” acts as a shock wave positioner. As it moves forward, it shifts the point where the wave forms. This allows the optimal compromise between total pressure loss and flow stability to be chosen. Too far forward, the wave causes excessive losses. Too far back, it becomes unstable and can oscillate, which is catastrophic for the engine.
The solution chosen by Dassault is based on robust mechanics. The displacement is controlled by the pilot, according to a defined procedure, depending on the flight regime. This choice may seem archaic, but it has one major advantage: predictability. The pilot knows exactly how the intake will behave at each stage of flight.
Measurable efficiency in operational performance
The Mirage III is not only supersonic on paper. It is capable of maintaining Mach 2.2 at high altitude (approximately 2,350 km/h at 11,000 m), which was remarkable for a single-engine fighter of this generation. This performance would not have been possible without a stable air intake.
Tests showed that the “Souris” significantly reduced the risk of compressor surging at high speed. It also improved thrust consistency, which translated into better acceleration capability in supersonic flight. In interception missions, every second counts.
Operationally, this reliability allowed the Mirage III to be deployed in a wide variety of climates and conditions, from deserts to temperate regions, without compromising its supersonic capabilities. For many air forces, this consistency was a decisive factor.
The “Souris” and the limitations of automation at the time
Let’s be clear: the “Mouse” is a manual solution because automation was not yet mature. But this manual nature is not a flaw. It reflects an intelligent compromise between complexity and safety.
At the time, a poorly tuned automatic system could be more dangerous than a simple control. A sensor failure or computer malfunction could have caused the shock wave to be positioned incorrectly, without the pilot immediately understanding the cause. With the “Mouse,” the link between action and effect is direct.
This choice also made maintenance easier. The mechanisms were accessible, understandable, and repairable without heavy tools. In the context of international deployment, this simplicity enhanced the Mirage III’s appeal for export.
The technical legacy left to supersonic aviation
The idea of physically controlling air intake did not disappear with the Mirage III. On the contrary, it served as the basis for more sophisticated solutions.
On the F-14 Tomcat, movable air intake ramps perform a similar function, but with greater automation. The principle remains the same: placing the shock wave where it is most effective. The Concorde also uses variable geometry air intakes, which are essential for maintaining stable thrust at Mach 2 during cruise.
The “Souris” showed that a well-designed mechanical solution could rival more complex systems. It proved that shock wave management is a central element of supersonic performance, just like the airframe or the engine.
A technology that reveals the Dassault philosophy
Beyond the technical aspects, the “Souris” illustrates a philosophy. Dassault has often favored robust, understandable, and effective solutions over overly complex architectures. This approach is found in other programs, where functional simplicity is seen as a guarantee of operational reliability.
In the case of the Mirage III, this philosophy made it possible to quickly put a credible supersonic fighter into service, without waiting for electronic advances that were still hypothetical. The result is an aircraft that flew, fought, and evolved for decades.
What the “Souris” still tells us today
With hindsight, the “Souris” may seem rudimentary.
It is not. It is the product of a detailed understanding of the physics of flow and a keen sense of operational constraints.
In a world where modern aircraft rely on digital control laws and multiple sensors, this solution reminds us of a simple truth: well-designed mechanics remain cutting-edge technology. They do not need to be invisible or automated to be effective.
The Mirage III was not just a symbol of speed. It was a flying laboratory, where bold technical choices shaped the future of supersonic aviation. The “Souris” is one of the most striking examples of this.
Sources
– Dassault Aviation, Mirage III technical documentation
– Aerodynamic studies on supersonic air intakes, ONERA
– Historical analyses of air intake on supersonic aircraft, Jane’s
– Technical publications on shock wave systems, NASA
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