SIZING OF ACTUATORS FOR FLIGHT CONTROL SYSTEMS AND FLAPS INTEGRATION IN RAPID Alejandro Diaz Puebla and Raghu Chaitanya Munjulury Linköping University, Linköping, Sweden Keywords: EHA, EMA, actuator sizing, flight control surfaces, RAPID, CATIA V5, Knowledge Pattern, Parametrization. Abstract EKL Engineering Knowledge Language UDF User Defined Feature The architecture of the flight control system, es- RAP ID Robust Aircraft Parametric sential for all flight operations, has significantly Interactive Design changed throughout the years. The first part of LE Leading Edge the work consists of a preliminary sizing model TE Trailing Edge of an EHA and an EMA. The second part of the work consists of the development of parametric CAD models of different types of flaps and their List of Symbols integration in RAPID. This thesis addresses the actuation system architecture of what it is named lAcc Accumulator Length as more electric aircraft with electrically powered dAcc Accumulator Diameter actuators. This consists of the development of F Actuator Force flexible parametric models of flight control sur- Arod Rod Area faces, being able to adapt to any wing geometry Kr Rod Area Constant and their automatic integration in RAPID. Fur- pm Maximum Allowable Stress thermore, it represents a first step in the develop- drod Rod Diameter ment of an automatic tool that allows the user to dpiston Piston Diameter choose any possible wing control surface config- M Hingemoment uration. m Single/Dual Actuator Parameter pmaxsys Maximum System Pressure Abbreviations r Actuator Hinge Arm φ Swept Angle MEA More Electric Aircraft Apiston Piston Area F BW Fly by Wire Qnom Max Flow Rate P BW Power by Wire Vg Volumetric Displacement of the Pump HA Hydraulic Actuator nnom Nominal Speed of the Motor EHA Electro-Hydrostatic Actuator tau Torque of the Motor EBHA Electrical Back-up Hydraulic P motor Power Actuator x∗ Parameter Scaling Ratio EMA Electro-Mechanical Actuator xref Reference Parameter CAT IA Computer Aided Three l∗ Length Scaling Ratio Dimensional Interactive Design lref Reference Length CAD Computer Aided Design V ∗ Volume Scaling Ratio V BA Visual Basic for Applications Vref Reference Volume 1 DIAZ PUEBLA, MUNJULURY V Volume surfaces are also addressed in this work. To un- l Length derstand this concept, it must be explained that ρ Density RAPID [1] is a knowledge-based conceptual de- ρ∗ Density Scaling Ratio sign aircraft developed in CATIA at Linköping M ∗ Mass Scaling Ratio University with the objective of creating a robust F ∗ Force Scaling Ratio parametric conceptual designing tool. T ∗ Torque Scaling Ratio GSD Generative Shape Design 2 Objectives Dcyl Cylinder Diameter Lcyl Cylinder Length The aim is to offer a general view to self- Dring Ring Diameter contained electric actuators sizing and supple- ment control surfaces implementation in the existing applications of RAPID. Therefore, to 1 Introduction achieve these purposes, the main objectives are: • Development of a preliminary sizing At the beginning of the aircraft industry, flight model for EHAs and EMAs offering a gen- control systems were controlled by manpower. eral view of the actuator sizing. As the aerodynamic forces that appeared on those aircraft were not excessive, the systems consisted • Design of parametric CAD models of dif- of pushrods, cables, and pulleys. The increase in ferent flight control surfaces. the size of the aircraft and therefore in the size of the control surfaces caused the implementation of • Automatic integration of the previously more complex systems which could apply to the mentioned CAD models in RAPID. greater forces that were needed. Hydraulic systems have been an essential part • Allow parametric modifications of the in- of the flight control system for decades, due to its stantiated models by the user to achieve advantages; as the capacity to apply large loads or multiple wing control surfaces configura- the accurate control it permits to be applied. Dur- tions. ing the last years, there has been a general trend • Guarantee the models flexibility through in the aeronautical industry to increase the use of parameters as well as by automatic adjust- electrically powered equipment. This leads to the ment to the wing geometry. concepts of "More Electric Aircraft" (MEA) and "Power by Wire" (PWB), which have introduced 3 SIZING OF ACTUATORS new types of actuators for moving the flight con- trol surfaces of an aircraft: Electro-Hydrostatic The current aviation tendency is the development Actuators (EHA) and Electro-Mechanical Actua- of MEA concept, this section presents, a general tors (EMA), both are powered by an electric mo- overview of the sizing of EHA and EMA actua- tor. In the EHA, a self-contained hydraulic sys- tor. tem moved by the electric motor is used while in the EMA the hydraulics are replaced by a screw 3.1 EHA Sizing mechanism moved by the motor. These actuators are being implemented to be This section is based on a general analysis of the used in flight control systems moving flight con- sizing of an EHA. EHA is an actuator based on trol surfaces. These can be divided into primary an electric motor and driven pump connected to a (ailerons, rudder and elevator) and secondary hydraulic cylinder. In order to be able to size an flight control surfaces (flaps, spoilers, and slats). EHA, it’s main components must be identified: The construction and integration in RAPID of CAD models of some of the mentioned control • Hydraulic cylinder 2 Sizing of Actuators for Flight Control Systems and Flaps Integration in RAPID • Fixed-displacement pump The diameter of the rod is given by the fol- lowing formula: • Electric Motor 2 4 drod = Arod (2) • Accumulator π drod the required rod diameter, With the rod • Power electronics diameter as a known parameter and the hinge moment applied to the control surfaces as an in- First of all, it is assumed that the motor and put, the diameter of the piston can be calculated the pump are positioned on the same axis, parallel through the next equation: to the hydraulic cylinder. This criterion is usually used in large aircraft or high power requirements, s as shown in Figure. 1. 2 4M dpistion = drod + φ [4] (3) πmpmaxsysr cos 2 dpistion is the diameter of the actuator piston, M is the hinge moment for a flight control sur- face, pmaxsys is the maximum system pressure, r is the actuator hinge arm and φ is the swept an- gle. The parameter m is a factor describing the type of actuator used: if the actuator is a single actuator m=1 and if it is a tandem actuator m=2 Fig. 1 EHA (left) and EMA (Right) [2] [4]. The piston area can be finally obtained The accumulator is considered as a cylinder through the next equation: and its size is determined by volume within some π limits of l =d ratio, l and d are the A = d 2 (4) Acc Acc Acc Acc pistion 4 rod length and diameter of the accumulator respec- tively. Power electronics size is usually deter- Once the piston parameters have been ob- mined by its cooling surface, thus the same con- tained, the next step is to calculate the flow pa- siderations apply as with the accumulator, but for rameters: the maximum required flow rate and a cuboid [3]. As the design is focused on con- the volumetric displacement of the pump. To ob- trol surface actuators, a sizing method is obtained tain the first parameter: depending on the main inputs that appear on the control surface. In other words, the desired ob- Qnom = VnApistion (5) jective is to obtain a connection between the con- Where Qnom is the maximum required flow trol surface and the actuator. Hence, in this siz- rate and Vn is the maximum loaded velocity of ing procedure the actuator force and the control the actuator (the required velocity for the correct surface hinge moment are used as main inputs. flight control actuation). With the max flow rate it Therefore, is possible to obtain the volumetric displacement F of the pump with the following formula: Arod = kr (1) pm Qnom Vg = (6) Where F is the actuator force, pm is the max- nnom imum allowable stress in the material and kr is Where Vg is the volumetric displacement of a constant related to the rod diameter, including the pump and nnom is the nominal speed of the a safety factor in order to achieve the structural motor. Finally, the motor size can be varied as requirements. a function of its nominal torque within some l=d 3 DIAZ PUEBLA, MUNJULURY limits. Thus, the torque of the motor must be ob- Table 2 Dimensions of an EHA [3] tained: P τ = motor (7) nnom τ is the nominal torque of the motor and P_motor the required motor power. Now all the main variables of the main components, piston dimen- sions, pump volumetric displacement and torque motor are used in a design model of the EHA. With the above calculated values, the Table 1 can now be used: Table 1 Dimensions of an EHA [3] The obtained parameters and Table 1 makes it possible to have sizing of an EHA, de- pending on the value of several constants (k0; k1; k2; k3; k4andk5). The values of these con- stants can be obtained with the dimensions of ex- Scaling laws make it possible to have a com- isting EHAs. It is possible to use the dimensions plete estimation of a product range with just one of those EHAs components and extrapolate them reference component. Their main principle is to to obtain the constant values. A Microsoft Excel establish a valid relation between a component table can be used in order to apply the equations and its parameters, such as dimensions or phys- and see how the parameters affect to the global ical properties, so it is possible to calculate the dimensions of the actuator.