sizing of actuators for flight control ...847029/...3.2 ema sizing an ema is an actuator driven by...

SIZING OF ACTUATORS FOR FLIGHT CONTROL SYSTEMSAND FLAPS INTEGRATION IN RAPID

Alejandro Diaz Puebla and Raghu Chaitanya MunjuluryLinköping University, Linköping, Sweden

Keywords: EHA, EMA, actuator sizing, flight control surfaces, RAPID, CATIA V5, KnowledgePattern, Parametrization.

Abstract

The architecture of the flight control system, es-sential for all flight operations, has significantlychanged throughout the years. The first part ofthe work consists of a preliminary sizing modelof an EHA and an EMA. The second part of thework consists of the development of parametricCAD models of different types of flaps and theirintegration in RAPID. This thesis addresses theactuation system architecture of what it is namedas more electric aircraft with electrically poweredactuators. This consists of the development offlexible parametric models of flight control sur-faces, being able to adapt to any wing geometryand their automatic integration in RAPID. Fur-thermore, it represents a first step in the develop-ment of an automatic tool that allows the user tochoose any possible wing control surface config-uration.

Abbreviations

MEA More Electric AircraftFBW Fly by WirePBW Power by WireHA Hydraulic ActuatorEHA Electro-Hydrostatic ActuatorEBHA Electrical Back-up Hydraulic

ActuatorEMA Electro-Mechanical ActuatorCATIA Computer Aided Three

Dimensional Interactive DesignCAD Computer Aided DesignV BA Visual Basic for Applications

EKL Engineering Knowledge LanguageUDF User Defined FeatureRAPID Robust Aircraft Parametric

Interactive DesignLE Leading EdgeTE Trailing Edge

List of Symbols

lAcc Accumulator LengthdAcc Accumulator DiameterF Actuator ForceArod Rod AreaKr Rod Area Constantpm Maximum Allowable Stressdrod Rod Diameterdpiston Piston DiameterM Hingemomentm Single/Dual Actuator Parameterpmaxsys Maximum System Pressurer Actuator Hinge Armφ Swept AngleApiston Piston AreaQnom Max Flow RateVg Volumetric Displacement of the Pumpnnom Nominal Speed of the Motortau Torque of the MotorPmotor Powerx∗ Parameter Scaling Ratioxref Reference Parameterl∗ Length Scaling Ratiolref Reference LengthV ∗ Volume Scaling RatioVref Reference Volume

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DIAZ PUEBLA, MUNJULURY

V Volumel Lengthρ Densityρ∗ Density Scaling RatioM∗ Mass Scaling RatioF ∗ Force Scaling RatioT ∗ Torque Scaling RatioGSD Generative Shape DesignDcyl Cylinder DiameterLcyl Cylinder LengthDring Ring Diameter

1 Introduction

At the beginning of the aircraft industry, flightcontrol systems were controlled by manpower.As the aerodynamic forces that appeared on thoseaircraft were not excessive, the systems consistedof pushrods, cables, and pulleys. The increase inthe size of the aircraft and therefore in the size ofthe control surfaces caused the implementation ofmore complex systems which could apply to thegreater forces that were needed.

Hydraulic systems have been an essential partof the flight control system for decades, due to itsadvantages; as the capacity to apply large loads orthe accurate control it permits to be applied. Dur-ing the last years, there has been a general trendin the aeronautical industry to increase the use ofelectrically powered equipment. This leads to theconcepts of "More Electric Aircraft" (MEA) and"Power by Wire" (PWB), which have introducednew types of actuators for moving the flight con-trol surfaces of an aircraft: Electro-HydrostaticActuators (EHA) and Electro-Mechanical Actua-tors (EMA), both are powered by an electric mo-tor. In the EHA, a self-contained hydraulic sys-tem moved by the electric motor is used while inthe EMA the hydraulics are replaced by a screwmechanism moved by the motor.

These actuators are being implemented to beused in flight control systems moving flight con-trol surfaces. These can be divided into primary(ailerons, rudder and elevator) and secondaryflight control surfaces (flaps, spoilers, and slats).The construction and integration in RAPID ofCAD models of some of the mentioned control

surfaces are also addressed in this work. To un-derstand this concept, it must be explained thatRAPID [1] is a knowledge-based conceptual de-sign aircraft developed in CATIA at LinköpingUniversity with the objective of creating a robustparametric conceptual designing tool.

2 Objectives

The aim is to offer a general view to self-contained electric actuators sizing and supple-ment control surfaces implementation in theexisting applications of RAPID. Therefore, toachieve these purposes, the main objectives are:

• Development of a preliminary sizingmodel for EHAs and EMAs offering a gen-eral view of the actuator sizing.

• Design of parametric CAD models of dif-ferent flight control surfaces.

• Automatic integration of the previouslymentioned CAD models in RAPID.

• Allow parametric modifications of the in-stantiated models by the user to achievemultiple wing control surfaces configura-tions.

• Guarantee the models flexibility throughparameters as well as by automatic adjust-ment to the wing geometry.

3 SIZING OF ACTUATORS

The current aviation tendency is the developmentof MEA concept, this section presents, a generaloverview of the sizing of EHA and EMA actua-tor.

3.1 EHA Sizing

This section is based on a general analysis of thesizing of an EHA. EHA is an actuator based onan electric motor and driven pump connected to ahydraulic cylinder. In order to be able to size anEHA, it’s main components must be identified:

• Hydraulic cylinder

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Sizing of Actuators for Flight Control Systems and Flaps Integration in RAPID

• Fixed-displacement pump

• Electric Motor

• Accumulator

• Power electronics

First of all, it is assumed that the motor andthe pump are positioned on the same axis, parallelto the hydraulic cylinder. This criterion is usuallyused in large aircraft or high power requirements,as shown in Figure. 1.

Fig. 1 EHA (left) and EMA (Right) [2]

The accumulator is considered as a cylinderand its size is determined by volume within somelimits of lAcc/dAcc ratio, lAcc and dAcc are thelength and diameter of the accumulator respec-tively. Power electronics size is usually deter-mined by its cooling surface, thus the same con-siderations apply as with the accumulator, but fora cuboid [3]. As the design is focused on con-trol surface actuators, a sizing method is obtaineddepending on the main inputs that appear on thecontrol surface. In other words, the desired ob-jective is to obtain a connection between the con-trol surface and the actuator. Hence, in this siz-ing procedure the actuator force and the controlsurface hinge moment are used as main inputs.Therefore,

Arod = krF

pm(1)

Where F is the actuator force, pm is the max-imum allowable stress in the material and kr isa constant related to the rod diameter, includinga safety factor in order to achieve the structuralrequirements.

The diameter of the rod is given by the fol-lowing formula:

drod2 =

4

πArod (2)

drod the required rod diameter, With the roddiameter as a known parameter and the hingemoment applied to the control surfaces as an in-put, the diameter of the piston can be calculatedthrough the next equation:

dpistion =

√drod

2 +4M

πmpmaxsysr cosφ2

[4] (3)

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, ris the actuator hinge arm and φ is the swept an-gle. The parameter m is a factor describing thetype of actuator used: if the actuator is a singleactuator m=1 and if it is a tandem actuator m=2[4].

The piston area can be finally obtainedthrough the next equation:

Apistion =π

4drod

2 (4)

Once the piston parameters have been ob-tained, the next step is to calculate the flow pa-rameters: the maximum required flow rate andthe volumetric displacement of the pump. To ob-tain the first parameter:

Qnom = VnApistion (5)

Where Qnom is the maximum required flowrate and Vn is the maximum loaded velocity ofthe actuator (the required velocity for the correctflight control actuation). With the max flow rate itis possible to obtain the volumetric displacementof the pump with the following formula:

Vg =Qnom

nnom(6)

Where Vg is the volumetric displacement ofthe pump and nnom is the nominal speed of themotor. Finally, the motor size can be varied asa function of its nominal torque within some l/d

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limits. Thus, the torque of the motor must be ob-tained:

τ =Pmotornnom

(7)

τ is the nominal torque of the motor and P_motorthe required motor power. Now all the mainvariables of the main components, piston dimen-sions, pump volumetric displacement and torquemotor are used in a design model of the EHA.

With the above calculated values, the Table 1can now be used:

Table 1 Dimensions of an EHA [3]

The obtained parameters and Table 1 makesit 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-isting EHAs. It is possible to use the dimensionsof those EHAs components and extrapolate themto obtain the constant values. A Microsoft Exceltable can be used in order to apply the equationsand see how the parameters affect to the globaldimensions of the actuator. An example is shownin Table 2.

3.2 EMA Sizing

An EMA is an actuator driven by an electric mo-tor connected to the control surface by a me-chanical linkage. The major components are abrushless DC motor (either cylindrical or annu-lar), a mechanical gear reducer, a ball screw anda power off brake [5]. The aim of a preliminarysizing is the development of simple yet quite pre-dictive models, with lower levels of detail thanthe required for specific designs. For this pur-pose, a good approach is a use of scaling laws.The scaling laws, also known as similarity laws,allow to study the effect of varying representativeparameters of a given system [6].


Scaling laws make it possible to have a com-plete estimation of a product range with just onereference component. Their main principle is toestablish a valid relation between a componentand its parameters, such as dimensions or phys-ical properties, so it is possible to calculate thenew values when varying one of the parameters.One of the advantages of the scaling laws, incomparison with other models, is the relativelylow complexity of the problem of obtaining thedimensions and physical properties of a compo-nent from its primary characteristics, mainly dueto two assumptions[7]:

• All the material properties are assumed tobe identical to those of the component usedfor reference. All corresponding ratios arethus equal to 1. This means that physicalproperties such as the density of the ma-terial or the Young’s modulus will remainconstant.

• The ratio of all the lengths of the consid-ered component to all the lengths of the

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reference component is constant. There-fore, all the dimension variation ratios willbe equal to a global dimension variation.

Consequently, using scaling laws reduces sig-nificantly the number of inputs and simplifies themodel to obtain all the main parameters as a func-tion of one specific parameter, called as the Def-inition Parameter [7]. The first step is to definethe scaling ratio of a given parameter, being usedthe notation proposed [8] for scaling laws calcu-lation:

x∗ =x

xref(8)

x is the studied parameter, xref is the param-eter of the component taken as reference and x∗

is the scaling ratio of x. Geometric proportionsare kept when using scaling laws, being able tolink geometric dimensions through a geometricsimilarity. All the dimensions variations will beequal to a generic length variation l∗. The vari-ation of a cylinder radius r or volume V can bethus expressed as:

r∗ = l∗ (9)

V ∗ =V

Vref=

πr2l

πr2ref lref(10)

This last result remains valid for any othergeometry. Using the same procedure it is pos-sible to obtain the variation of other parameters,as mass M as function of l∗:

M =

∫ρ∂V ⇒M∗ = V ∗ = l∗3(ρ∗ = 1) (11)

For mechanical components, basing the de-sign on a fixed constraint σmax allows to link thevariation of efforts to the variation of length l∗

[6]:F ∗ = l∗3 (12)

Where F ∗ is the transmitted force scaling ra-tio. Therefore, the nominal torque ratio T ∗ of amechanical component can be estimated as:

T ∗ = l2 (13)

Estimations models can now be applied indi-vidually to each of the components of an EMA.The aim of the models is to minimize the entryparameters required to have a complete definitionof the component. For mechanical components,particularly bearings and ball and roller screws(See Figure. 2.), a model as the one showed inTable 3 is applied:

Fig. 2 General Program Diagram


For the others mechanical and electro-mechanical components, speed reducers andbrush-less motors, similar models are used, asshown in the Table 4 and Table 5


The typical operational area of the motor willdepend on its type. With all the relations it is pos-sible to use the estimation models to create a pre-liminary sizing of an EMA using existing actua-tor components as references. The validity of theequations is applied to a single component per-formance. Nevertheless, before applying those

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formulas the scaling laws used must be validatedby comparison with manufacturer data.

4 CAD Implimentation

The CAD modelling has been carried out in CA-TIA R© [9]. CATIA is a one of the widely usedCAD commercial software in the engineering in-dustry as a design tool. Three are the work-benches used in the utilization of CATIA in thisthesis: Generative Shape Design (GSD) work-bench, Knowledge Advisor workbench and forthe use of Knowledge Pattern the Product Knowl-edge Template workbench is used. Each of themis used in different levels and applications of themodelling work and has different characteristicsthat are going to be briefly explained in this chap-ter.

4.1 Parametric Actuator Models

A parametric CAD model of both types of actu-ators (EHA and EMA) were developed. The aimwas to have a basic 3D model through parametricdesign so it was possible to change its dimensionsand position it in a quick and simple way.

4.1.1 EHA Model

The model had to be flexible and cover a widerange of different measures of the components.The result is shown in Figure. 3, with all the com-ponents specified. It has been tried to achieve asimilar model to the ones shown in Figure. 1, thatwere EHAs for flight control surfaces for largeaircraft and the one developed by TRW respec-tively.Through the parametric design it is possi-ble to vary its dimensions by changing the valuesof the corresponding parameters.

Fig. 3 EHA and its components

Figure. 4 show possible configurations of theEHA through the variation of the parameters

Fig. 4 Different configurations of the EHA para-metric 3D model

4.1.2 EMA Model

As in the case of the EHA, the EMA model mustbe simple and contain the main components of anelectro-mechanical actuator:

• Electric motor

• Gearbox reducer

• Ball screw

The most sought in the model is the flexibil-ity to cover a wide range of measures. The re-sult of the EMA model is shown in Figure. 5,where it can be appreciated that for the electricmotor it has been chosen a cylindrical one. Fig-ure. 6 shows possible combinations using differ-ent components.

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Fig. 5 EMA Model and its components

Fig. 6 Different configurations of the EMA para-metric 3D model

5 Flaps Integration in RAPID

One of the objectives as mentioned before is thedevelopment of different types of CAD modelsfor control surfaces through automatic paramet-ric design in CATIA V5 and its integration inRAPID. The majority of those control surfacesare different types of flaps.

RAPID [1] (Robust Aircraft Parametric Inter-active Design) is a knowledge based aircraft con-ceptual design tool developed in CATIA. For thecontrol surfaces integration references have beentaken from it, as it will be further explained inthis section.The following control surfaces havebeen developed:

• Aileron

• Plain Flap

• Double Slotted Flap

• Triple Slotted Flap

• Fowler Flap

• Split Flap

• Zap Flap

• Slat

Each of the models allows the user to choosethe corresponding angle deflection and extendedlength of the control surface, as well as position-ing and sizing it along the wing, among other pa-rameters. It is also possible to combine each ofthe control surfaces along with slats.

5.1 Positioning and Sizing

As all the models can be positioned and their spancan be chosen, in the same way, this section alsoprovides information of the positioning and spansizing implementation. The control surface spanstarts on what it is going to be named Left Airfoiland finishes in the Right Airfoil. These airfoilsare going to be considered the first and the lastcontrol surfaces airfoils, respectively. Figure. 7shows all the elements involved to help the fol-lowing procedure description.

Fig. 7 Positioning and Span Sizing of the ControlSurface

The Leading Edge Points are the most for-ward points of the airfoils, and all of them set upthe Leading Edge (LE). The Leading Edge startson the Left Airfoil and ends in the Right Airfoil.A Reference Line is then created with the wingspan (transverse axis) direction. Reference linegoes from Left Airfoil to the plane that containsRight Airfoil. In that line, two planes are created:Start Plane and End Plane. These planes definewhere between the Left Airfoil and the Right Air-foil the control surface starts and ends. Two pa-rameters control the position of both planes.

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5.2 Control Surfaces CAD Models

This section presents the control surfaced createdin CAD and the instantiation of the same.

5.2.1 Aileron and Plain Flap

The similarities between these control surfacesmake possible to integrate both surfaces in thesame model. Actually, even the single slotted flapcan be included, just adding a slot to the controlsurface as it is going to be later explained. TheCAD model is as shown in Figure. 8:

Fig. 8 Aileron or Plain Flap and different config-urations

5.2.2 Double Slotted Flap

This model is similar to the plain flap, a secondslot has been added to represent double slottedflap as shown in Figure. 9.

Fig. 9 Double Slotted Flap and different Config-urations

5.2.3 Triple Slotted Flap

The triple slotted flap has an added slot to thedouble slotted flap is as shown in Figure. 10

Fig. 10 Triple Slotted Flap and different Config-urations

5.2.4 Fowler Flap

The Fowler Flap model is shown in the figure be-low Figure. 11

Fig. 11 Fowler Flap and different configurations

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5.2.5 Split and Zap Flap

The similarities between these control surfacesmake possible to integrate both surfaces in thesame model. The Zap Flap is like the split flapwith the added feature of the translation of thecontrol surface. Figure. 12 shows a screenshot ofthis CAD model.

Fig. 12 Split & Zap Flap and different configu-rations

5.2.6 Slat

A slat model has also been developed to makepossible a closer configuration of a real wing.This CAD model is shown in Figure. 13.

Fig. 13 Slat and its deflected configurations

5.3 Results and Flexibility of the Model

One of the main objectives of the work based onthis chapter was not only to achieve the flap inte-gration in RAPID but also to guarantee the flex-ibility of the instantiated models. Through theparametric design the user is able to modify eachof the control surface parameters as well as thewing parameters- and observe how each of themaffects the whole model and the different config-urations that can be achieved. The possibility ofchoosing the position and the span length of thecontrol surfaces through the two positioning pa-rameters makes the model quite flexible and al-lows the user to define precisely the placementof the control surface, adapting the model to theneeded requirements. Moreover, the possibilityof changing the root and the tip chord lengthof the control surfaces provides the models withmultiple configurations.

Nevertheless, although the individual param-eters of the models already make them quite flex-ible, that is not all the flexibility the model canachieve. A great part of the flexibility resides inthe automatic adaptation to the wing geometrymodifications. The main possible modificationsthat the wing can present are:

• Wing Span

• Airfoils Chord

• Dihedral Angle

• Twist Angle

If any of the above parameters is modi-fied, the model will automatically adapt to thechanges. Furthermore, special mention should bemade of the two last elements of the above list:the dihedral and twist angle, due to the difficul-ties had to make possible the model adaptation tothese two parameters.

Figure. 14 shows different wing control sur-faces configurations through the variation of bothindividual and wing parameters. It is obviouslyimpossible to observe some of the configurationsin real airplanes, with different values of twistand dihedral angles in each of the four input air-foils, but it has just been shown to prove the flex-ibility of the model.

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Fig. 14 Different Wing Control Surfaces Config-urations

6 Discussion and Conclusion

The main aim of the work carried out in the ac-tuator sizing was to provide a general overviewof the new actuators that are currently being im-plemented. These actuators are powered by anelectric motor, due to the present tendency of thedevelopment of MEA concept.

It can be considered a first step into a prelimi-nary sizing model of EHAs and EMAs, althoughat this point more research is needed. It is nec-essary for the utilization of the model or of anyother model based on scaling laws- to have anupdated and detailed actuator data table with di-mensions and parameter values of existing flightcontrol surface actuators. It would be also neces-sary a more detailed model of the sizing of bothtypes of actuators in order to achieve a closestsolution to real values beyond preliminary design

models.Furthermore, throughout the development of

this thesis it has been noticed the endless possi-bilities and applications that parametric CAD de-sign can have in the field of engineering. Theparametric design has been the key point of theflaps integration in RAPID to allow the user tochoose any control surface configuration with al-most no effort or previous CAD design knowl-edge.

Moreover, the implementation of automaticinstantiations and procedures has also been an es-sential condition to achieve the objectives sought.Thanks to the automation the users are not onlycapable to instantiate one model, but to createa whole wing configuration and implement in-stantly any possible change.

The use of Knowledge Pattern and UDFs inthe instantiation process involves a considerabledecrease in the complexity of the user interface,as by this instantiation procedure the user inter-face is only composed by the parameters neededto define the model.

To conclude, flexible flight control surface in-tegration in RAPID has been developed, provingthe potential of CATIA GSD and Knowledge Pat-tern workbenches as engineering design tools.

References

[1] Munjulury, R. C., Knowledge Based IntegratedMultidisciplinary Aircraft Conceptual Design,Licentiate Thesis, No. 1661, Linköping Univer-sity, Linköping,Sweden, 2014.

[2] Botten, S. L., Whitley, C. R., and King, A. D.,“Flight control actuation technology for nextgeneration all-electric aircraft,” Technol. Rev. J,Vol. 23, No. 6, 2000, pp. 55–68.

[3] Frischemeier, S., “Electrohydrostatic actuatorsfor aircraft primary flight control-types, mod-elling and evaluation,” 1997.

[4] Berry, P., Aircraft conceptual design methods.,Linköping studies in science and technology. Li-centiate thesis: 1197, Linköping : Department ofMechanical Engineering, Linköpings University,2005.

[5] Budinger, M., Reysset, A., El Halabi, T., Vasiliu,C., and Maré, J.-C., “Optimal preliminary design

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of electromechanical actuators,” Proceedings ofthe Institution of Mechanical Engineers, PartG: Journal of Aerospace Engineering, Vol. 228,No. 9, 2014, pp. 1598–1616.

[6] Budinger, M., Liscouët, J., Orieux, S., and Maré,J.-C., “Automated preliminary sizing of elec-tromechanical actuator architectures,” variations,Vol. 3, 2008, pp. 2.

[7] Budinger, M., Liscouët, J., Maré, J.-C., et al.,“Estimation models for the preliminary designof electromechanical actuators,” Proceedings ofthe Institution of Mechanical Engineers, PartG: Journal of Aerospace Engineering, Vol. 226,No. 3, 2012, pp. 243–259.

[8] Jufer, M., “Design and losses-scaling law ap-proach,” Nordic Research Symposium Energy Ef-ficient Electric Motors and Drives, Skagen, Den-mark, 1996, pp. 21–25.

[9] “CATIA V5 Release21,” "[Online; Accessed 8-Aug-2015]", http://www.3ds.com/.

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