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Meeting	ACGS Committee Meeting 103 - Seattle - February 2009
Agenda Location	7 SUBCOMMITTEE C – AVIONICS AND SYSTEM INTEGRATION 7.1 Challenges and Solutions for More-Electric Aircraft
Title	Challenges and Solutions for More-Electric Aircraft
Presenter	Frank Thielecke
Affiliation	TUUH - Hamburg Technical University, Inst. of Aircraft Systems Engineering
Available Downloads*	presentation
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Abstract	1. Trend towards More-Electric Aircraft At the Institute of Aircraft System Engineering of the Hamburg University of Technology several projects in collaboration with industrial partners comprise topical challenges and research trends in More-Electric Aircraft. In this contribution several aspects like complexity for energy flow on aircraft level, electromechanical actuators for primary flight control and nose landing gear, on-board cooling as well as tools for systems architecting are analyses and discussed. The tendency to replace pneumatic and hydraulic systems by electrical solutions in the aerospace industry leads to a decreased power system diversity and therefore to an increase in the complexity of the remaining electrical generation and distribution system. Additionally the system design process of such resulting aircraft systems does not solely include the analysis of serial and parallel structures but also complex system topologies with several bridge structures and a state discrete dynamic behavior to ensure safety critical and operational reliability targets. These new system architectures offer an optimization potential in redundancy allocation, component decisions and consumer supply which is difficult to manage without the usage of dedicated analysis and optimization tools. 2. Primary Flight Controls with EHSA and EMA Moving towards the More-Electric-Aircraft, the introduction of electrically powered actuators into primary flight controls is an essential element. Among numerous feasible actuator designs, electromechanical actuators (EMA) are the most straightforward way to convert energy from the electrical power supply systems to mechanical energy required for control surface movement. However, despite the persistent interest in EMA technology, these actuators are not yet employed in any modern large transport aircraft, due to several challenges such as possible jamming, damping characteristics, and actuator passivation. Besides these issues, reliability, mechanical wear, and electrical integration are uncertainties, which today render a purely EMA driven primary flight control surface unlikely. A hybrid configuration with a conventional electrohydraulic servo-actuator (EHSA) is thus a consequent first step to introduce EMA in primary flight controls. For the integration of such a hybrid actuator configuration several tasks were investigated at TUHH. Firstly, different EMA designs – “direct drive”, gear transmission/ballscrew and hingline (rotary) – were compared and evaluated on several criteria: for instance estimated jamming probability, damping characteristics, and passive mode dynamics. Secondly, different control strategies were developed to face the demands of the hybrid configuration as well the different well-known active/active and active/passive operating modes. For validation of the control concepts a test rig is under construction. Further investigations are going to be done regarding the electronic limitation of gust loads and the health monitoring of EMA. 3. Primary Flight Controls and IBC for helicopters with EMA In another research project it has been shown that a helicopter rotor in forward flight can greatly benefit from more complex pitch control schemes than used today. By Individual Blade Control (IBC) in higher harmonic modes and with additional actuators in the rotating system, fuselage vibrations and radiated noise can be reduced and as well other IBC effects. Instead of implementing such additional separate actuators it is worthwhile to consider an integrated actuation system designed to fulfill both the primary control as well as the IBC requirements. With regards to an efficient actuator integration it was derived that the installation of one single electromechanical actuator (EMA) per rotor blade is a preferable solution. This concept implied that all redundancy provisions had to be integrated within one EMA. Therefore a highly redundant electromotor was developed, whose topology is given by a so-called modular permanent-magnet synchronous machine. Key properties of this topology are a physical separation of the phase windings, a complete electrical isolation between phases, an effective thermal isolation between phases and a good magnetic isolation between all phases. A first prototype of the electric machine has been manufactured and tested. 4. On-board Cooling Systems On-board cooling systems supplying cooling capacity for commercial and electrical power consumers, are dealing with rising heat loads as progressive electrification of future aircraft takes place. For the resulting More- or All-Electric-Aircraft, minimisation of system mass and power consumption is a design driver regarding the cooling system to retain an overall benefit. In addition, tendencies to rising power and thus waste heat flux densities account for new cooling solutions. Optimisation of cooling performance and power consumption can be achieved by improving the heat exchange at both heat rejection and absorption through employing phase changing (2-phase), contrary to currently used liquid (single phase) working fluids. 5. Tools for Systems Architecting The presentation includes a new methodology to analyze and optimize complex fault tolerant aircraft systems in the pre-design phase to support the system engineer. The optimization process is based on the analysis functionalities of the SYRELAN (System Reliability Analysis) tool. This includes a hybrid model, imaging the failure-free system architecture by using Reliability Block Diagrams (RBD) on a first level and the state discrete dynamic system behavior with the use of Concurrent Finite State Machines (CFSM) on a second level. This hybrid model is equivalent to the usage of MARKOV chains but allows a local definition of the state discrete dynamic behavior on event level using five different states: active, active-hot, passive-warm, passive-cold and isolated. Based on the hybrid model a multiple redundant system (MRS) is modeled, which includes all possible architecture solutions. This allows the optimization of the system architecture considering the failure-free nominal state but due to the set of system functions also for degraded system states and a defined number of failed components.