State of the Art - Background

Reducing the power consumption and thus the fuel burn is a major target for the next generation of aircraft. Two technological areas that can contribute to the power saving are wing load alleviation and electrical actuation. Load alleviation is a technique for redistributing aircraft loads encountered during flight with the purpose of reducing the wing root bending moment, hence allowing a lighter wing design with a resulting weight saving, reduction of the needed propulsive power. Electrical actuation can contribute to the reduction of the non-propulsive power because electromechanical actuators, when compared to the hydraulic actuators, rely on a power less subject to losses and lighter to distribute, besides presenting higher reliability and maintainability with a lower life-cycle cost.

Load alleviation (LA) and electrical actuation are two technological areas that have been widely addressed in the past years. A number of wing alleviation load systems have been proposed based on continuous non-conventional control of primary and secondary flight control surfaces, while technological progresses in electromechanical actuators (EMA) for flight control surfaces have been pursued in several research programmes.

Over the last years, several industrial programmes initiated the concept of a More Electric Aircraft. The aero-equipment industry has in particular launched several studies and developments on more electrical actuation with Electro Hydrostatic Actuators (EHA) and started to introduce EMA for auxiliary equipment. This has provided incremental approaches to address hydraulic circuits issues with Power-by-Wire technologies (A320, B777 and Falcon 7X), introduction of the 2-hydraulic/2-electric (2H/2E) power distribution architecture where flight controls are powered in backup mode by EHA using a local hydraulic reservoir (A380, A350XWB) and use of EMAs for some systems (spoilers, brakes and engine starters).

Several collaborative research and development projects also started to develop the All-Electric Aircraft. The POA FP5 and the MOET FP6 projects have demonstrated on specific systems the effectiveness of electrical actuation. More recently, Actuation2015 FP7 was focused on developing standardised modular EMA technologies with the development of standard components and supporting design and validation tools. EMA systems are consequently viewed as the best candidate for the aircraft of the future (i.e. the All- Electric Aircraft) when considering they are:

  • Less complex because of the absence of hydraulic system
  • Better suited to long term storage since there is no leak potential
  • Energy saving with respect to hydraulic systems
  • Installation and maintenance is easier (no filtration, no bleeding)
  • Power distribution and management easier (power transmitted without mass transfer)

But, compared to hydraulic actuators or EHAs, technological barriers still persist for a wide adoption of EMA especially when considering these issues:

  • Envelope constraints created by the adoption of thin wings and associated flight control surfaces
  • Sensitivity to certain single point of failures that can lead to mechanical jams, resulting in a reluctance to adopt EMAs for flight safety critical applications as solutions are heavy and costly (redundancy, fail safe behavior, etc.), thus creating difficulties for adoption and certification and impacts on costs
  • Need to optimise the electrical distribution and heat rejection within the aircraft

Moreover, application of EMAs for continuous control of flight control surfaces requires a thorough optimisation effort in terms of architecture, design, materials and sensors in order to come up with a product which can be certified for the next generation of aircraft.

EMA technologies were not considered mature enough in 2007 (TRL too low) to be part of the CLEAN SKY Systems for Green Operations (SGO) programme. Recent advances in several features of EMAs and the results achieved in Actuation 2015 FP7 programme encourage a re-evaluation of EMA technology for aircraft flight critical applications, ranging from actuation of primary flight control and load alleviation surfaces to actuation of the landing gear.

The promising perspectives of load alleviation / load control technologies as well as electrical actuation for flight control surfaces and landing gear need to be thoroughly investigated and verified in order to gain the necessary confidence and maturity level for moving to their implementation in a flying demonstrator. This requires:

  • Development of suitable prototype components integrating the innovative features capable of making electrical actuation an accepted proposition for future flight controls and landing gears
  • Design and construction of an integration test rig (Iron Bird) allowing verification and validation of:
    • Enhanced electrical power distribution and load management technology
    • Electrical landing gear technology
    • Flight control system technology
  • Development of a health monitoring platform able to collect and process data provided by the sensors of the aircraft structure and systems such to assess the aircraft health status

The iron bird will enable integration and testing of the new technologies in a relevant environment and support the permit-to-fly achievement for the demo flight configuration of the R-IADP Flight Test Bed#1 (FTB#1).The iron bird will need to incorporate advanced features such as: real-time generation and control of the actuators loads, injection of degradations in the equipment components, assessment of the merits of a health management system in a representative environment.