First steps taken towards the all-electric aircraft

Citation

(2003), "First steps taken towards the all-electric aircraft", Aircraft Engineering and Aerospace Technology, Vol. 75 No. 3. https://doi.org/10.1108/aeat.2003.12775caf.004

First steps taken towards the all-electric aircraft

The aerospace sector is increasingly making use of on-board actuators and servo-controllers. Traditionally mechanical or hydraulic, these are gradually becoming electric, electronic or computer controlled. Integrated into systems where operational safety and reliability are essential, they have needed long development times because of the constraints in the aerospace sector in terms of weight, mass and resistance to temperature and vibration.

Since the 1970s, power electronics have gradually become established as the favoured means for controlling electrical power. 1980-95 was the golden age for technological innovation in the design of static converters. To meet the requirements of the designer – choice of structure, calculation and evaluation of losses, meeting standards, size, weight and mechanical constraints – research was directed towards more compact devices with high efficiency to move towards the design of partially integrated power electronics. Over the last decade, progress in power electronics has been closely linked to that in static converters. This is because providing control of electrical power supplied from traditional sources (mains network, batteries) leads to improvements in the quality of the power, in better use of actuators and in miniaturisation of these devices.

In the aerospace field, the strategy is to adopt a step by step approach before the technological leap. "There are no aircraft today where the electrical system is the main vehicle for the power and the flight controls. The core system remains hydraulic. The electrical power mainly supplies the commercial loads. It is expected, due to volume and weight considerations, that all the hydraulic systems will be eliminated and replaced with electrical systems. It is obvious that power electronics offer considerable advantages for increasing the amount and quality of the power provided," explained Philippe Ladoux, Head of the Power Electronics and Static Converters Group at LEEI, the Industrial Electronics and Electrotechnics Laboratory, one of the leading laboratories in the electrical engineering field. (A laboratory based in ENSEEIHT in Toulouse, the Ecole Nationale Supérieure d'Electronique, d'Electrotechnique, d'Informatique et d'Hydraulique, one of the four colleges of the Institut National Polytechnique (INPT)).

With 16 electro-hydraulic flight controls, the A380 is taking a step towards all-electric operation, with enormous impact, particularly for the on-board supply systems: reductions in cost and weight, better system integration, easier maintenance, more flexible management of loads as electrical power is transmitted individually to each system. Controls are therefore no longer dependent on a single central hydraulic system.

With regard to future on-board aircraft systems, TFE, based in Toulouse, and specialising in power converters, control of electric motors and actuators (for air conditioning, fuel, flight control, doors etc.) and suppliers to Airbus, Dassault and Embraer, has developed two specific technologies that are unique in the marketplace, explained Thierry Ouplomb, the company's sales manager. The first relates to control of permanent magnet electric motors without rotor position sensors. "Powering brushless electric motors by sinusoidal current usually requires the use of a rotor position sensor for synchronisation of the magnetic fields. For motors intended for harsh environments (temperature, vibration, pressure etc.), integrating this sensor is difficult and expensive. Our method enables us to eliminate it, thanks to a Kalman filter algorithm in a digital signal processor (DSP), which estimates the rotor position from the electrical quantities measured. It is, therefore, possible to combine the ease of integration of an asynchronous motor with the superior performance of a permanent magnet synchronous motor."

The company has also built a reputation in the field of active filtering of current. The integration of variable frequency technology into on-board systems leads to a multiplication of non-linear loads generating current harmonics, which are detrimental to operation of the system. Ouplomb continued, "Our system makes it possible to clean the waveforms of the current consumed by providing exact compensation for the current. This makes it possible to satisfy the requirements of ABD 100 and EN 2282 standards, offers a lower weight compared with existing solutions, greater efficiency and does not cause deterioration in reliability, safety and availability of balanced loads.''

To promote their developments and optimise their expertise, TFE has formed an economic interest group (ENAIR'GIE) together with ELTA, a specialist in severe environment electronics. With customers including TRW, Messier-Bugattia and Airbus, ELTA brings expertise in the control of motors in torque, position and speed and in higher power ranges (from 1 to 100 kW), which enables the two companies to cover the whole spectrum of power electronics technology. ELTA has an additional advantage. For 2 years, a test A320 aircraft has been evaluating an electric flight control system (for the aileron), the only such equipment at this time with more than 500 h of flying time on a civil aircraft.

A year ago, specialist engineering consultancy Prismeca set up an electrical engineering department to design and build electrical and electronic equipment. Already expert in cars and in particular competition vehicles, the company has developed complex and sophisticated technologies which it is intending to apply in other sectors, particularly aeronautics. "We have built up our expertise in linear magnet systems. This type of system replaces a spring, which is often mechanically constrained, complex and requires constant adjustment, with a magnet. Its linearity makes it possible to reverse the force and to modulate it," explained Frédéric Bardet, Manager for Actuator Products.

Together with Aquitaine Électronique, CAUM.ELEC has developed a self-controlled asynchronous motor to control air flow rate. Using technology that is simpler, more compact, more reliable and requires fewer components than an asynchronous motor, it "enables more flexible control of flow rate by means of variation of speed which regulates the voltages and rotates the variable-speed fans". The unit is about to find an industrial application with a regional airline.

By the year 2020, reducing fuel consumption will be a priority and this will include the aerodynamics. Research is being carried out into the use of micro-electromechanical systems. These are available as micro-sensors, a few hundred microns in size and used to detect upstream perturbations, and as micro-actuators for exciting the boundary layer by high frequency micropulsation in order to act in a local region. In this way, they could reduce drag, improve lift and, therefore lighten the wing. A programme called Aeromems is under the aegis of BAE Systems and Dassault Aviation.

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