From Mirage 2000 and 4000 to Rafale, electric flight controls have enabled the transition from stable aircraft to deliberately unstable fighters that are more agile and safer.
In summary
The introduction of electronic flight controls (EFC) has profoundly transformed the design of French fighter aircraft. With the Mirage 2000, Dassault opted for an airframe with aerodynamic instability in pitch, made possible by fully computer-assisted flight control. The fighter became capable of natural instability flight and could reach flight forces of +9 g while remaining controllable and safe. The Mirage 4000 then served as a flying laboratory: a twin-engine aircraft equipped with active canards and three-axis EFC, it validated the architectures that would be used on the Rafale. The latter takes this logic to its conclusion with quadruple digital redundancy supplemented by an analog backup chain, and close integration between flight controls and weapons systems. The flight control laws no longer simply stabilize the aircraft: they automatically protect the protected flight envelope, manage landings, mitigate turbulence, and optimize tactical efficiency. The innovation is therefore not only electronic, but also doctrinal: it changes the way fighter aircraft are designed and the role of the pilot.
The revolution in fly-by-wire systems
Fly-by-wire systems replace the traditional mechanical links between the control stick and the control surfaces with electronic signals processed by computers. The pilot commands a movement intention, not directly a surface deflection. Sensors (speed, altitude, angle of attack, acceleration) feed data to computers, which calculate in real time the best combination of control surfaces to achieve the desired response.
This architecture paves the way for an idea that was once impossible on a fighter aircraft: designing an inherently unstable airframe to achieve performance gains. By shifting the center of gravity slightly toward or beyond the aerodynamic center, the wing’s moment of lift is reduced. The aircraft becomes more “responsive” in pitch, and therefore more agile, but it is also unable to fly without constant assistance. The CDVE provides this active stabilization continuously, several dozen times per second.
The Mirage 2000, France’s first unstable fighter
A delta wing and a deliberately rearward center of gravity
The Mirage 2000 marked the return of the large delta wing to French fighter aircraft, but with a radically new philosophy compared to the Mirage III. It has an increased wing area, a profile optimized for high angles of attack, and, above all, a center of gravity setting that gives it a reduced, even negative, margin of static stability in pitch.
In practical terms, this means that if the CDVEs were “cut off,” the aircraft would tend to spontaneously amplify pitch disturbances. The nose would rise or drop without sufficient feedback, until it left the flight envelope. This aerodynamic instability is accepted in order to make better use of the delta wing: at high angles of attack, the vortex at the leading edge generates high lift, which is useful in close combat, as long as the flight controls keep the aircraft in a safe zone.
Flight control laws centered on the load factor
The CDVE of the Mirage 2000 is based on “g-controlled” flight control laws: at the stick, the pilot primarily controls a load factor rather than a simple angle of attack. The computer translates the request into optimal deflections of the control surfaces and leading edge slats across the entire flight envelope.
The result: the aircraft can fully exploit its structure, which is designed for high loads (up to approximately +9 g), while automatically respecting certain limits in terms of angle of attack and load factor. In practice, the pilot pulls the stick “all the way back” without fear of overloading the airframe or exceeding a critical angle of attack. This protection is particularly valuable at low altitudes, where overloading or loss of control can quickly prove fatal.
Pilot testimonials confirm that the Mirage 2000, despite its “instability” and large delta wing, remains surprisingly docile as long as the CDVE is functioning: the aircraft moves quickly from one state to another, but the machine filters out excessive control inputs and compensates for some of the errors.
The Mirage 4000, a flying laboratory for CDVE
Designed as a heavy twin-engine jet, the Mirage 4000 never found an operational outlet, but it played a decisive role in the maturation of Dassault’s flight controls. The airframe combines a delta wing with movable canard wings, controlled by CDVE on three axes.
The canard wings, positioned in front of the main wing, introduce an additional layer of instability but offer enormous potential for controlling pitch, adjusting instantaneous lift, and optimizing aerodynamic load distribution. On the Mirage 4000, these are “active canards”: they participate in real time in controlling the aircraft, in coordination with the wings and tailplane, under the supervision of the computers.
This demonstrator makes it possible to validate several technical components that were subsequently used on the Rafale:
- multi-axis flight control laws for an unstable delta-wing canard airframe;
- advanced integration between avionics, CDVE and load management;
- redundancies and computing architectures adapted to a new-generation fighter.
The Mirage 4000 also demonstrates that a large, heavily armed twin-engine jet can remain highly maneuverable if instability is properly exploited. This lesson will be central to the future French multi-role fighter.
The Rafale, the culmination of the CDVE philosophy
An unstable airframe and quadruple redundancy architecture
The Rafale uses the canard-delta configuration, but in an optimized version: more compact wings, large canards, and an even further rearward center of gravity. The aircraft was designed from the outset to be unstable and incapable of flying without electronic assistance.
To control this configuration, the Rafale relies on a quadruple digital redundancy architecture: three independent digital channels, connected by redundant links (including fiber optic technologies for certain generations), and a completely different analog backup channel.
Each digital channel has its own computers, powered by separate sensors. If one channel fails, the others immediately take over. If the entire digital system were to be compromised, a simple analog backup system would allow for degraded but controllable flight control. Dassault claims more than one million accident-free flight hours attributable to the Rafale’s flight controls, which gives an idea of the level of mastery achieved.
An intimate fusion between CDVE and weapons system
The big difference with the Mirage 2000 is not only in the geometry or redundancy, but in the fusion between CDVE and weapons system. On the Rafale, the flight controls do more than just stabilize the aircraft. They are in constant communication with the mission avionics, sensors, and fire control computers.
A few functions illustrate this degree of integration:
- Automatic speed vector control for Rafale M carrier landings: the computer maintains the optimal trajectory and approach angle, compensating for wind gusts and deck movements.
- Dynamic protection of the protected flight envelope: automatic limitation of load factor, angle of attack, and speed, even during sudden maneuvers or in stressful situations.
- Anti-turbulence and load reduction laws: at very low altitude and high speed, the CDVE filters out some of the gusts, reducing structural fatigue and improving pilot comfort at the critical moment of penetration and weapon delivery.
The pilot no longer just manages a machine, but operates an integrated system that optimizes stability, trajectory accuracy, and safety in the background. This translates directly into tactical effectiveness: reduced preparation time, increased accuracy on the attack trajectory, and better repeatability of flight profiles.
How controlled instability changes things for the pilot and tactics
Aerodynamic instability only makes sense if it provides a tangible advantage in combat. On the Mirage and Rafale, the gain can be measured in several ways:
- better pitch and roll response, and therefore the ability to generate high turn rates in the vertical plane;
- reduced compensation drag during cruise, thanks to a rearward center of gravity, which improves range and fuel consumption;
- ability to fly at high angles of attack, useful in close combat to point the nose independently of the speed vector.
The downside is total dependence on the integrity of the CDVEs. Dassault has responded with a “no manual mode” philosophy: the pilot never reconfigures the aircraft to return to purely mechanical control. Everything is designed so that redundancy, dissimilarity of chains, and software quality are sufficient to maintain a level of safety at least equivalent to, and often superior to, conventional aircraft.
Tactically, this confidence in the system allows crews to operate the fighter close to its structural limits without censoring themselves. Whereas a previous-generation pilot had to constantly “manage the margin,” a Mirage 2000 or Rafale pilot knows that the protections and flight laws will prevent the most brutal out-of-domain situations. The mental load can then be shifted to the mission: managing the tactical situation, using weapons, cooperating with other platforms.
A structural innovation for future generations
From the first analog CDVEs to the natural instability flight of the Mirage 2000, from the demonstrator role of the Mirage 4000 to the maturity of the Rafale, France has built a coherent line of aircraft designed around their flight controls. The future SCAF/NGF, like most 6th generation fighter programs, will take this logic even further with more automation, artificial intelligence, and human-machine cooperation.
But the essentials are already there: the modern combat aircraft is no longer a “flying object” that is stabilized after the fact. It is a dynamic system whose aerodynamic instability is chosen, controlled, and exploited to gain maneuverability, payload, and performance. Electric flight controls are at the heart of this system. Without them, the elegant silhouette of the Mirage and Rafale would remain a mere exercise in style. With them, it becomes a coherent weapon, capable of operating as close as possible to physical limits without exceeding them.
Sources
– COMAERO / Académie de l’Air et de l’Espace, “Un demi-siècle d’aéronautique en France” (Half a century of aeronautics in France), chapters on CDVE and instability, 2000.
– F. Alcalay, “Estimation of aircraft flight parameters and fault detection,” ISAE-SUPAERO thesis, 2018 (flight domain protections).
– Dassault Aviation fact sheet, “Rafale – Design and optimize” and “Rafale – Introduction,” data on the unstable airframe and flight control system.
– Technical data sheet and documentation on the Mirage 2000 (Wikipedia FR, Mirage-jet.com, flight guides), information on the unstable delta wing, CDVE and g-controlled laws.
– Airvectors.net, “Dassault Mirage 2000 & 4000,” historical and technical description of the programs, role of the Mirage 4000 as a demonstrator.
– Various pilot testimonials and analyses (Portail-Aviation, Mirage 2000 interviews, technical popularization documents) on flight qualities and tactical use.
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