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Development of numerical models fo aircraft systems to be used within the JTI/GRA Shared Simulation Environment

Final Report Summary - E-BIRD (Development of numerical models fo aircraft systems to be used within the JTI/GRA Shared Simulation Environment)

Executive Summary:

E-Bird developed a Modelica Library to simulate electromechanical actuators (EMA) with a high level of physical realism. These EMAs can be used in many application models. In order to evaluate the EMA models directly and also for use in the Green Regional Aircraft Integrated Simulation Environment, three application models, one for a typical aircraft main landing gear (MLG) one for a typical nose landing gear (NLG) and one for an all-electric flight controls system (FCS) consisting of ailerons, flaps, spoilers, elevators and a rudder have been designed. For each of these models a simulation test bed is included in the library so each component and each setup can be tested. The library is subdivided into three packages, which contain the EMA, LG, and FCS models. Although the EMAs form a component of the MLG, NLG and FCS systems, they have been placed in a separate package to facilitate the development process of Bausch-Gall (responsible for EMA) and TWT (responsible for LG, FCS). The Electromechanical Actuators package contains individual models of EMAs. The basic EMA model is the same for all of the variants, however parameters relating to delivered torque, gear box and controller are different and tailored to their designated application. The naming of the models reflects their application (i.e. ElectroMechanicalActuatorSpoiler). There is also a simple EMA model with a much reduced complexity of modelling. The details of each of the model classes are explained in the Modelling Manual.

The Models themselves are developed from the components in the corresponding EMA Components package and standard Modelica library classes. For each of the Components dedicated test models exist.

The final output from EBird is a library of modelica models for EMAs and LG/FCS assemblies. These models are already used in the CSJU project iSSE in the full electrical system simulation of the GRA ITD. The project has been presented in a paper at the 2013 Airtec fair with good response from the audience and TWT GmbH and Bausch-Gall GmbH both expect that the models find widespread use in the optimisation of power consumption and design of green regional aircraft.

Project Context and Objectives:

Today, the vast majority of aircrafts use mechanical and hydro-mechanical actuators to reposition the control surfaces (e.g. ailerons, elevator, rudder, flaps) of the flight control system (FCS) and to retract/lower the landing gear (LG) to/from the undercarriage. The prospects of replacing these mechanical/hydro-mechanical actuators by potentially more ecological electro-mechanical actuators (EMAs) are investigated within the All Electric Aircraft Domain (AEA, GRA3).

This project makes a key contribution to the AEA through the development of novel and modular simulation models for the quantitative evaluation of the mechanical, electrical, and thermal behaviour implied by the use of EMAs. This goal will be achieved via innovative developments on different levels (not to be confused with the three “tasks” in WP3.2 of AEA, GRA3). Firstly, the physicalmathematical models of both the EMAs and the FCS/LG will be set-up in such a way that they can be interlinked through the exchange of common parameters, typically EMA-positions and aerodynamic forces/torques. Secondly, the individual components will be integrated into a single simulation model (see Fig. 1), which is targeted to interface with the Shared Simulation Environment (SSE) of AEA, GRA3. Thirdly, component based test scenarios will be defined, which are adequate for the verification of the electro-mechanical and electro-thermal outputs. The electro-thermal data involved in these test scenarios differs from that normally considered for mechanical/hydro-mechanical systems. Adequate emphasis will be put on this issue. To ensure that the simulation models can readily be integrated into existing aircraft concepts and simulation tools, standards will be used wherever possible (see description of WP2). Based on this approach, the modularity of the subsystem models can be established, including clear concepts for updating and modifying not only the models, but also the related input parameters. Moreover, support manuals in terms of a modelling, a user, and a check manual are subsequently build and maintained throughout the entire activity.Concerning the EMA model, the LG model and the FCS model, the following modelling and abstraction consideration will be taken.

EMA model

1. Electric motor (3-phase synchronous brushless electric motor), whose model shall include

o Magnetic fluxes simulation via equivalent magnetic circuits (to account for secondary flux paths and higher harmonics torque components)
o Temperature sensitivity of motor parameters (e.g. coil resistance, torque constant) to evaluate this possibility in terms of “costs/benefits”

2. Mechanical transmission (Gearbox and low-pitch screw jack), whose model shall include

o Stiffness nonlinearities due to Hertzian contacts Backlash
o Sliding friction (via Stribeck or more accurate models) in one degree-of-freedom (1 DOF)

3. Power electronics (power supply 270 Vdc), whose model shall include:

o PWM drive of the motor coils via MOSFET power switches (H-bridge arrangement), which will be considered at system level, not at electronic component level

4. Control electronics for constant power absorption of electronics, whose model shall include:

o Sensors: in reduced fashion by considered ideal dynamic response
o Closed-loop controls; actuator position, motor shaft speed and vector control of the motor currents in terms of simple controls
o Signal limiting; saturation and rate limiter on the actuator command, peak current saturation, thermal protections

5. Thermal exchange, whose model shall include

o Heat transfer via natural convection for the electric motor and power electronics based an overall heat transfer coefficient

6. Safety devices are not requested (failure events, such as electric motor failure, rod jamming, etc., are not to be considered. This is because SEE will consider only engines failure, as they produce unexpected reduction of electrical power production).

LG model

1. Tricycle architecture, i.e. based on the ATR72 architecture:

o One Nose Landing Gear (NLG)
o Two Main Landing Gears, left (MLGL) and right (MLGR)

2. Mechanical/structural parts, whose model shall include

o Multi-body kinematics and dynamics
o Stiffness of actuator links with A/C structure in terms of a simple spring with ON/OFF
o Backlash effects
o Friction effects again in terms of a simple model having 1 DOF

3. Mdel of the actual load transfer to the EMA. For each LG, the following models shall be considered

o LG weight (including the effects of A/C Euler’s angles)
o Aerodynamic forces on the LG (including the effects of A/C angles of attack and sideslip and the effects of extension / retraction stroke)
o Acceleration effects due to A/C manoeuvres and LG extension / retraction
o Gyroscopic loads (resulting from the wheels rotation at the end of take-off)

4. Lock and un-lock systems, whose model shall permit

o To reset to zero the power absorption at the end of extraction / retraction phases (including simulation of energy absorption when activated, without constant power for a given time)

FCS model

1. FCS reference architecture

Based on the finalized FCS architecture (together with inertial data, etc, …) provided by the CfP proponent (UniPi):

o Two ailerons and two steering spoilers for roll control
o Two elevators for pitch control (actuator for rotating of whole horizontal tail: further details to be provided by CfP proponent in due time)
o One rudder for yaw control
o Two inboard flaps and two outboard flaps for high-lift functions

2. Control devices, whose model (based on an overall heat transfer coefficient) shall include

o Flight Control Computer power absorption and thermal exchange models
o FCS sensors power absorption and thermal exchange models

3. Mechanical/structural parts, whose model shall include

o Multi-body kinematics and dynamics
o Stiffness of actuator links with A/C structure, in terms of a simple spring with ON/OFF

4. Model of the actual load transfer to the EMA, which shall include

o Aerodynamic forces on control surfaces
o Acceleration effects due to A/C manoeuvres

Moreover, the development of models are elaborated to take into account the future necessity of GRA partners to integrate other models.

Project Results:

Summary Desciption.

The current need to reduce emissions from air traffic leads to a rapid transition from ponderous and squandering to lightweight and energy efficient aircraft. Within this development many aircraft systems are electrified in order to eliminate pneumatic and hydraulic power sources. Furthermore, not having to bleed air from the engine compressor increases engine efficiency and the removal of hydraulic fluid contributes to reduce the environmental impact.

Such an aircraft design requires all on-board systems be electric and share a common power source. This necessitates evaluating the electrical performance of the complete aircraft system in order to correctly specify generators, distribution networks and algorithms to reliably manage the distribution of electrical power in various load cases.

To test and validate said energy management, static and dynamic performances of on-board systems need to be assessed with particular focus on electrical loads. These measures must be done early in the design process, ideally through simulations. However, different subsystems are often implemented in various simulation environments, each specifically suited to the task at hand. Consequently, the evaluation of the entire aircraft system requires a shared simulation environment (SSE) integrating individual sub-systems. For the purpose of integrating into such a SSE,, we have developed detailed models of different on-board systems withing the CSJU Project E-Bird. This work was performed within the framework of the CleanSky Green Regional Aircraft (GRA) research programme.

Green Regional Aircraft model library

We here present the GRA model library containing models of the landing gear system (LGS) and the flight control system (FCS), both coupled to multiple variants of a sophisticated electro-mechanical actuator (EMA). These models are implemented as a hierarchically structured library based on re-usable components with visible source code. In the following, we describe the behavioural (Level 3) models of the EMA, LGS, and FCS developed in E-Bird. The design of the behavioural models has been done in an easy to use and adapt library structure in Dymola/Modelica.

EMA model

The Level 3 EMA mode has been developed by Buasch-Gall GmbH andl consists of an electrical drive, a gear box, and a screw jack. A drive includes a permanent magnet synchronous induction motor and an inverter from 270 V DC to 3-phase AC. The motor model is based on the Electrical.Machines module of the Modelica Standard Library (MSL). It was extended by a thermal model of the motor in order to calculate winding losses in different ambient and load conditions. Parameters for specific losses (friction, stator core or stray load losses, permanent magnet losses) can be chosen by the user. For inverters, two easily replaceable implementations are available: either a power-balance converter for fast simulation of flight manoeuvers or a switching inverter for detailed electrical analysis.

The gear box and screw jack include friction models. A nonlinear spring-damper model for nut-screw contact is available. EMAs for the landing gear and flight control systems have the same structure, with the notable difference that the EMA of the landing gear system can be mechanically locked in end positions.

The EMA uses a cascade control for screw jack position, drive speed, and motor torque/current.

Most control parameters are calculated from physical parameters of the motor and drive train. User defined configurations of the EMAs can easily be created by replacing record-based parameter sets. Component test cases for all EMA configurations and various loads have been created in order to validate the models.

LGS and FCS models

The LGS model refers to the landing gear of a typical turboprop regional aircraft with a single nose and two main LGs. Each LG is extended and retracted by an EMA. The FCS model is composed of primary (ailerons, spoilers, elevators, and rudder) and secondary flight controls (inboard and outboard flaps). The system parameters are those of a typical turboprop regional aircraft. Each control surface is moved by an EMA.

Level 3 LGS model

The Level 3 LGS model has been developed by TWT using the MSL. The model is composed of joints connecting the elementary parts of the landing gear. The geometry of the landing gears is defined by the joint positions of the extended LG. The model includes multi-body kinematics, stiff actuator links with A/C structure, LG weight, aerodynamic forces on the LG including the effects of angle of attack and sideslip, acceleration effects due to A/C manoeuvers and LG extension/retraction, gyroscopic loads from the wheels, Coulomb friction, a free fall assister modeled as a spring, a shock absorber modeled as a parallel spring and damper system, (un)locking mechanisms for the actuator and the drag brace, backlash effects at the end of extension/retraction phases, and a simple thermal model. The landing gear model further includes interfaces to detailed EMA models so that these experience the load profiles during extension/retraction phases.

Level 3 FCS model

The Level 3 FCS model has been developed by TWT using the MSL. Each control surface interfaces with a detailed EMA model; the EMA rotates the control surface through a lever arm. The model includes multi-body kinematics, stiff actuator links with A/C structure, aerodynamic forces on control surfaces, control surface weight, acceleration effects due to A/C maneuvers, and a simple thermal model.

Potential Impact:

The final output from EBird is a library of modelica models for EMAs and LG/FCS assemblies. These models are already used in the CSJU project iSSE in the full electrical system simulation of the GRA ITD. A paper entitled "Co-Simulation for Design, Optimization and Analysis of All-Electric Aircraft Systems” has been presented at the AIRTEC 7th International Conference “Supply on the Wings”, to be held Nov. 5 – 7, 2013 in Frankfurt /Main, Germany. This paper includes a section were the Green Regional Aircraft Modelica Library is presented, together with the LGS model, the FCS model and the various EMA models developed within E-Bird TWT GmbH and Bausch-Gall GmbH both expect that the models find widespread use in the optimisation of power consumption and design of green regional aircraft.

List of Websites:

Main Contact for the project is:

Dr. Markus Pfeil
Innovation Management - Head of Engineering
Science & Innovation
Niederlassung Friedrichshafen
Leutholdstraße 30
D-88045 Friedrichshafen
Tel.: +49 7541 3754-14
Fax: +49 7541 3754-32