At a time when Concorde is preparing for retirement, we can again measure from a technological point of view how far in advance of its time this aircraft was. For example, the “beautiful bird” was already fitted with an electrically controlled braking system, the first of its type, which had been especially developed by Messier- Bugatti. 40 years later, Messier-Bugatti is still ahead of the world with the FFBW braking systems on the very latest Airbuses! At a time when we are able to envisage the all electric aircraft in more detail, the complete electrification of the braking system, including the power source for each actuator, is back on the agenda.
A logical evolution
For Messier-Bugatti as a world specialist in aeronautical braking, the innovation made at the time on Concorde shows that the concept of an electric brake is the logical outcome of a long process. Thus the company has been working on this concept for several years and today is carrying out several test bed trials both on the brake itself and its control unit. Thanks to the major resources provided, these tests are being simultaneously carried out on all the static (with real time simulation), dynamic and endurance aspects.
Messier-Bugatti is one of the players in the European research programme POA (Power Optimized Aircraft) which is logically evaluating the overall electrification of all the on-board systems – and in particular, all the systems related to the landing gear – the only way of optimising the profitability of the concept.
Some attractive qualities
The attractions of an all electric aircraft, completely free of any other form of on-board energy source, notably hydraulic, relate to volume, bulk and price. More specifically, the many other qualities can be illustrated in the example of the electric brake. Firstly, there is superior braking efficiency and comfort resulting from the fact that the force applied to each actuator is separately driven. There is also increased reliability and maintainability, in particular very easy diagnosis of problems, as well as a significantly increased life span for the actuators, which may be replaced twice in the course of the life of an aircraft. In addition, accurate measurement of brake wear has become a very easy to realise reality as it is now merely a question of measuring the displacement of a simple micrometer screw…
These qualities are so attractive in the eyes of the aircraft manufacturers that the concept of the all electric brake is already being envisaged for tomorrow’s aircraft. In fact, at the request of Boeing, Messier-Bugatti has responded to a request for preliminary information for the 7E7 project. Similarly, this concept is being suggested for a cargo version of the A380 as well as for "reengineering" some aircraft already in service.
The third generation
Until now the main electro-hydraulic type braking system circuit has been electrically controlled (from the order given to the pedal by the pilot going to a solenoid valve, activating the hydraulic energy) via a computer, the BSCU (Braking and Steering Control Unit). However, the power continues to be hydraulic, through servo-valves activating the pistons on each brake. This system, usual on modern aircraft, is in fact that of "Brake by Wire" (referring to the braking order, given in electric form).
Subsequently, the emergency circuit also became electrically controlled (hence the name "Full Brake By Wire", applied notably on the Airbus A340-500/600). Local automatic hydraulic generation then followed with the EHA (Electro Hydrostatic Actuator): a micro-pump driven by an electric motor that allows the brake pistons to be activated using a decentralised hydraulic circuit (applied on the A380).
The electric brake thus represents the third generation in the process of electrifying the braking system, electrifying the energy source itself and thus freeing it from any hydraulic system. Control continues to be electric – using a dedicated BSCU type computer, or special software housed in an IMA – but the power itself has become completely electric. This time the braking order arrives at a control unit common to several brakes, the EBC (Electrical Braking Controller), which transmits the order directly and individually to each actuator. The actuator consists of a motor that activates a screw through a reducer, allowing the rotors to be pressed against their respective stators, based on the nut and bolt principle. With a motor for each actuator the force applied to each can be individually driven. Braking on each wheel is fed by two electric circuits, based on the dual distribution at the level of the actuators, to ensure a satisfactory level of safety: if one of the circuits fails, the other circuit continues to provide sufficient power to the actuators for maintaining efficient braking.
40 years of experience of use
Messier-Bugatti’s expertise, relating both to brakes and braking systems, gives it an overview of the problems and allows it to understand all aspects of electrification, in particular from the point of view of integration. This quality means the company is well qualified to develop optimal solutions.
