Projectreport ‘Flight Controls’ - Weeblyjoeyschuitemaker.weebly.com/uploads/1/9/1/7/19171461/… · Web viewProjectreport ‘Flight Controls ... project group 1N was ordered

Hogeschool van AmsterdamDomein Techniek

Aviation

Flight controls

Groep 1NScarlett Driessen

André GooijersJason OudshoornRodney Rabeling

Joey SchuitemakerMichael Verheul

Mark visserGuus WitzelAmsterdam, 27 maart 2013

Projectreport

Projectreport ‘Flight Controls’March 27th, 2013

Inhoudsopgave

SUMMARY.....................................................................................................................................3

INTRODUCTION...............................................................................................................................4

1 INTRODUCTION TO FLIGHT CONTROLS..................................................................................51.1 PRINCIPLES OF FLIGHT.................................................................................................................5

1.1.1 Forces while flying.................................................................................................................51.1.2 Law of continuity..................................................................................................................61.1.3 Law of Bernouilli...................................................................................................................61.1.4 The third law of Newton.......................................................................................................71.1.5 Airfoils..................................................................................................................................81.1.6 Lift equation.........................................................................................................................91.1.7 Axes of an aircraft................................................................................................................9

1.2 PRIMARY FLIGHT CONTROLS..........................................................................................................101.2.1 Ailerons...............................................................................................................................101.2.2 Elevator..............................................................................................................................111.2.3 Rudder................................................................................................................................12

1.3 SECONDARY FLIGHT CONTROLS......................................................................................................141.3.1 Flaps...................................................................................................................................141.3.2 Trim....................................................................................................................................151.3.3. Secondary flight controls of an airliner............................................................................16

1.4 REQUIREMENTS............................................................................................................................171.4.1 Requirements by law..........................................................................................................181.4.1 Requirements by customer.................................................................................................19

1.5 FUNCTIONAL RESEARCH................................................................................................................19

2 TECHNICAL RESEARCH................................................................................................................212.1 B737NG (CONVENTIONAL SYSTEM)...................................................................................................21

2.1.1 System used by Boeing 737NG............................................................................................212.1.2 Elevator Boeing 737NG.......................................................................................................232.1.3 Secondary flight controls on a Boeing.................................................................................25

2.2 AIRBUS A320 (FLY BY WIRE SYSTEM)..................................................................................................272.2.1 System used by Airbus A320...............................................................................................282.2.2 Elevator Airbus A320...........................................................................................................332.2.3 Secondary flight controls on an Airbus, trim.......................................................................34

3 MAINTENANCE........................................................................................................................373.1 DESIGN ASPECTS...........................................................................................................................37

3.1.1 Boeing 737NG.....................................................................................................................373.1.2 Airbus A320........................................................................................................................38

3.2 ADVICE........................................................................................................................................40

LIST OF TERMS..............................................................................................................................42

LIST OF SOURCES...........................................................................................................................43

LIST OF APPENDIXES......................................................................................................................44

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SummaryFlight controls are the tools for a pilot to control the aircraft he is flying in. The flight controls can be split in primary and secondary flight controls: the primary flight controls control the movement of an airplane about its three axes, while the secondary flight controls reduce the workload of the pilot. The primary flight controls are the ailerons, the elevator and the rudder, while the secondary flight controls consist of the flaps, trim, slats, spoilers and the yaw damper. The primary flight controls are the same on every airplane, but the secondary flight controls on a Cessna-172 differ from those on an airliner. A Cessna-172 only has flaps and trim, while the other secondary flight controls only appear on airliners.

The flight controls of a Boeing 737NG and an Airbus A320 differ from each other too. The biggest difference between these two are the principles the flight controls work on: Boeing aircraft make use of the principles of mechanics and hydraulics, while Airbus aircraft make use of the principles of electronics. Boeing has three (partly) separated hydraulic systems: system A, system B and a standby system. Airbus however, has three (partly) separated systems, which are electrically controlled and hydraulically activated: the yellow, green and blue (standby) system. Both flight control systems are built-up safely, but the maintenance of them differs.

To make a precise comparison between the maintenance costs of a Boeing 737NG and those of an Airbus A320, a specific maintenance task will be highlighted: the removal and installation of the units that power the elevator. Looking at the man hours of this task, the removal and installation of the power control units of a Boeing 737NG take less time than the same task on an Airbus A320. However, Airbus flight control systems have less wear and tear than Boeing systems have. Therefore, Airbus flight control systems will have a longer lifespan (and therefore higher maintenance costs) than the systems in Boeing. Unfortunately, that’s just a general thesis (electronics will last longer than mechanics do) and therefore this thesis isn’t considered in the advice. Therefore, projectgroup 1N advises ALA to buy Boeing 737NG aircraft, looking at the maintenance costs.

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IntroductionOn January 30th, project group 1N was ordered by Amsterdam Leeuwenburg Airlines (ALA) to compare the flight control systems in a Boeing 737NG and those in an Airbus A320. The airliner wants to expand its fleet so new airplanes have to be acquired. ALA wants to get a perception of the difference between the costs of maintenance of these two airplanes, focused on the flight control systems. The report of the project group of this investigation is divided in three phases: the phase of definition, the phase of investigation and the phase of implementation at last.

In the phase of definition, the theoretic principles of the flight control systems in a Cessna-172 are explained. First the basic steering of an airplane can be clarified with the help of aerodynamics and construction methods in a small airplane, then the flight controls in general are enlightened and finally the differences between flight controls in small and large aircraft are expounded (1).

The second phase of the report is the phase of investigation. In this phase, the conventional system of a Boeing 737NG and the fly by wire system of an Airbus A320 are compared: first the conventional system, the fly by wire system next. The features and working of the systems will be explained, to focus on one primary and secondary flight control afterwards (2).

The costs of the maintenance of the two flight control systems are compared in the phase of implementation. The costs of the maintenance differ because one system is based on electric principles, while the other one is based on the principles of mechanics. With a difference in man hours needed in maintenance, an advice can be made to ALA with which the airliner can make a decision between the Boeing 737NG and the Airbus A320 (3).

The most important sources of this report are John David Anderson (2004) and the Federal Aviation Administration (2008) for the research to the theoretic principles of aerodynamics and flight controls. For the research of the maintenance aspects of the Boeing 737NG and the Airbus A320, the maintenance manuals of both airplanes were the most important sources. In this report, (figure 1.1) refers to an image, (formula 1.1) refers to a formula, (Appendix I) refers to an appendix and italic words will be explained in the list of terms.

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1 Introduction to flight controlsTo understand the working of a flight control system, aerodynamic knowledge is required (1.1). The primary flight controls, which can rotate an airplane about its three axes, are working on the principles of this aerodynamic knowledge (1.2). The secondary flight controls don’t control the movement of an airplane about its three axes, like the primary flight controls do (1.3). There are several requirements, which are established by law and the customer. The requirements by law are made to guarantee the quality of the primary and secondary flight controls, while the requirements of the customer are drawn up in his own advantage (1.4). Finally, the introduction of the flight controls is concluded with a functional research (1.5). In this functional research the composure of a flight control system is clarified.

1.1 Principles of flightFor the very basics of flying, there is knowledge acquired about all the forces while flying (1.1.1). To create the most important force, the lift, there are several physics laws needed. Without the law of continuity (1.1.2) there couldn't have been the law of Bernoulli (1.1.3). An second law to create lift is the third law of Newton (1.1.4). To make good use out of these laws, there are good shaped airfoils (1.1.5) needed. With all the lift that's created there is a lift equation (1.1.6). When finally airborn an aircraft can move in three dimensions, over the three axes of an aircraft (1.1.7).

1.1.1 Forces while flyingOn an aircraft there are four forces created (figure 1.1). These forces are as follow: thrust (1), drag (2), weight (3) and lift (4). Thrust is the force that makes the airplane move forward. The forward force is created by an engine and is critical to create lift. Drag is the opposite of thrust. Drag is the force that slows the plane down. Drag is the resistance created by the wind pushing against the wings and body of the plane. Weight is the force that's created by gravity pulling the aircraft down. Lift is the most important force of flying. Lift is the opposite force of "weight". The aircraft can fly when the Lift is bigger than the weight. The law of continuity, the law of Bernoulli and the third law of Newton are needed to create lift.

Figure 1.1, forces created on an aircraft

1. Thrust2. Drag3. Weight4. Lift

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1.1.2 Law of continuityThe law of continuity declares that air that flows per second into a tube must be equal as the air that flows per second out of the tube (figure 1.1) (formula 1.1). This law is only valid when the current is stationary. A stationary current means that current lines do not cross each other. In surface A1 (1), air flows with speed v1 (2) and pressure p1 into the tube. In surface A2 (3), air flows with speed v2 (4) and pressure p2 out of the tube. This leads to the form of the continuity equation. If the density is considered equal, than the continuity equation changes (formula 1.2).

Figure 1.2, law of continuity in a tube

Formula 1.1, continuity equation

Formula 1.2, changed continuity equation

1.1.3 Law of BernouilliThe law of Bernouilli is derived from the law of continuity. The differences in pressure can be calculated with this law. Lift arises by differences in pressure in a current around the wing. This equation represents the connection between the speed of the air and the pressure on that point. The law of Bernouilli says that the pressure decreases while speed increases. When the wing has a positively curved profile, the air at the upside of the profile will be flow faster than at the underside of the profile. The speed above the wing is higher. This is because it has to cover a longer distance around the wing. It is concluded that the pressure under the wing has to be higher than above the wing. Therefore the pressure causes an upward force.

The law of Bernouilli (formula 1.3) is only valid when the current is stationary and

ρ ∙ v1 ∙ A1= ρ∙ v2 ∙ A2

In this equation is:ρ = Density [kg/m³] v = Speed [m/s]A = Surface [m²]

v1 ∙ A1=A2 ∙ v2

In this equation is:v = Speed [m/s]A = Surface [m²]

1. Surface A12. Speed V13. Surface A24. Speed V2

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frictionless. Only when a liquid has is incompressible and the current is adiabatic, the law of Bernouilli can be used. Adiabatic means that the flowing molecules do not exchange mutual energy. This law says that the total quantity energy per volume of the air is equal, so the sum of the static pressure and dynamic pressure in the air is equal. This equation can be split in the formulas for the static (formula 1.4) and the dynamic pressure (formula 1.5).

Formula 1.3, law of Bernoulli

Formula 1.4, static pressure

Formula 1.5, dynamic pressure

1.1.4 The third law of NewtonThe third law of Newton(figure 1.1) says that every action has an opposite reaction. The force of the action and reaction is equal. For example: an engine thrusts a lot of air backwards (1). Because of that the aircraft moves forward with the same amount of energy (2). The third law of Newton is also used by wings to create lift. The wing is shaped so that the airflow will bent down a little. The same amount of energy that the wing uses to push the airflow down, is used by the airflow to push the wing up. This is called lift.

p+ρ ∙g ∙h+ 12∙ ρ∙ v2=equal

In this equation is:p = Pressure of the surroundings [Pa]ρ = Density of the air [kg/m³]g = Gravitational acceleration of earth [m/s²]h = Height [m]v = Speed of the current [m/s]

p+ρ ∙g ∙h=static pressure

In this equation is:p = Pressure of the surroundings [Pa]ρ = Density of the air [kg/m³]g = Gravitational acceleration of earth [m/s²]h = Height [m]

12∙ ρ∙ v2=dynamic pressure

In this equation is:ρ = Density of the air [kg/m³]v = Speed of the current [m/s]

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Figure 1.3, third law of Newton

1.1.5 AirfoilsThe surface of a wing vertical on the longitudinal is called the airfoil (figure 1.4). An airfoil has characteristics that influence the lift of a wing. An airfoil is constructed of a number of parts. The shape of the wing depends on these parts. The nose of the profile is called the leading edge (1), the tail is called the trailing edge (2). Between these two edges is an imaginary line, this line is called the chord line (3).

The line that gives the shape of the wing is called the mean camber line (4). When virtual circles are drawn in the airfoil and a line is drawn trough the middles of the circles, the camber line is born. The maximum camber (5) of the profile is the maximum distance between the camber line vertical on the chord line. The maximum thickness (6) is the maximum thickness of the profile from upper to the lower surface. The most used airfoil shapes are positively or negatively curved airfoils. In a positively curved airfoil, the camber is placed above the chord line while it is placed under the chord line in negatively curved airfoils. The profile is called symmetric when the chord line and camber are equal.

Figure 1.4, airfoil

The quantity of lift also depends on the angle(figure 1.5) where the chord line, in relation to the undisturbed airflow, of the profile stands. This angle is called the angle of attack (1). The angle is measured from the direction of the undisturbed airflow (2) to the chord line(3) of the airfoil.

Figure 1.5, angle of attack

1. Air thrust backwards2. Plane moves forward

1. Leading edge 2. Trailing edge3. Chord line4. Camber line5. Maximum camber6. Maximum thickness

1. Angle of attack 2. Undisturbed airflow3. Chord line

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1.1.6 Lift equationThe force of lift from a wing can be calculated by the equation of lift (formula 1.6). The lift equation depends on the lift coefficient, the density, the speed and the surface. The density of the air can be calculated or it is written in the ISA-table with the standard values. The surface in the equation applies the square meters on the upside of the airfoil. Also the airspeed is important for lift because when the speed increases the lift will also increase.

Formula 1.6, equation of lift

1.1.7 Axes of an aircraftThere are three imaginary axes (figure 1.6) that go through an aircraft. These can be considered as axes where an airplane can rotate about. The axis that passes from nose to tail is called the longitudinal axis (1), the axis from wingtip to wingtip is the lateral axis (2) and the axis that passes vertically on the chord line is the vertical axis (3).

Figure 1.6, axes of an aircraft

L=cL ∙12∙ ρ ∙ v2∙ S

In this equation is:L = Lift [N]cL = Liftcoefficient [dimensionless]ρ = Density[kg/m³]v = Speed [m/s]S = Surface of the wing [m²]

1. Longitudinal axis 2. Lateral axis3. Vertical axis

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1.2 Primary flight controls The primary flight controls are required to move the airplane about its three axes of rotation. The primary flight controls consist of the ailerons, the elevator and the rudder. The pilot needs all three of them to make a coordinated turn with the aircraft. The pilot can move the steering stick with his hands and the pedals with his feet to influence the control surfaces, and with that, the movements of the airplane. To get a basic understanding of the flight controls, the primary flight controls of a Cessna-172 will be highlighted. First the ailerons are highlighted (1.2.1), secondly the elevator (1.2.2) and lastly the rudder (1.2.3).

1.2.1 Ailerons The ailerons provide primary flight control of the aircraft about its longitude axis. This movement is known as rolling. With use of the aileron control, the aircraft can change its longitudinal horizontal level. The ailerons are installed at the tip of each wing and move simultaneously and opposite from each other.

1.2.1a Operations The ailerons are connected to the steering stick in the flight deck by a series of mechanical linkages. Left movement of the steering stick deflects the left aileron surface up and the right aileron in opposite direction (figure 1.7). Because the right aileron moves downwards, the right wing will get more camber and therefore, create more lift. At the left wing, the camber will dwindle, thus lessen the lift. The mentioned actions above will result in a changed resulting force rolling movement of the airplane.

Figure 1.7, effects of deflected ailerons

1.2.1b Side EffectsHowever, using the ailerons also creates a side effect, also known as adverse yaw. When the steering stick is moved left, the right wing creates more lift. Apart from increased lift, it also produces more drag. Because of this additional drag the right wing slows down. This leads to a vertical rotation towards the wing that creates more lift. To put it simply: whenever a pilot wants to roll to the left, the plane will yaw to the right. The pilot will need to use the rudder to counteract this adverse yaw. At lower airspeeds, the amount of adverse yaw becomes more prominent. Due to the lower aerodynamic pressure, greater control inputs are needed to maneuver the plane, thus resulting in more adverse yaw.

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1.2.1c PlacementThe flight controls of the Cessna aircraft are fully mechanical (figure 1.8). This means that the ailerons and controls are connected with cables, push-pull rods and/or pulleys. The steering stick is connected with a push pull rod (1), which in turn is connected at the end with cables. The cables go through the body of the aircraft with the support of multiple pulleys (2) to reach the ailerons. The cables tension can be influenced by turnbuckles, which connects multiple cables together where needed. The ailerons (3) are installed to the wing with a horizontal axis, which gives them the freedom to move up and down.

Figure 1.8aileron control system

1.2.2 ElevatorThe elevator provides primary flight control of the aircraft about its lateral axis. This movement is named as pitch. With use of the elevator control, the aircraft can change its angle of attack. The elevator is a part of the horizontal stabilizer that is located at the tail of the aircraft.

1.2.2a OperationsThe elevator is connected to the steering stick in the flight deck by a series of mechanical linkages. Aft movement of the steering stick deflects the trailing edge of the elevator surface up and makes the aircraft elevate to a upper position, because the tail of the aircraft moves down and the nose of the aircraft moves up. This pitching moment takes place at the center of gravity. Forward movement of the control column deflects the trailing edge of the elevator down and makes the aircraft elevate to a down position, because the tail of the aircraft moves up and the nose of the aircraft moves down (figure 1.9).

1. Steering stick2. Cables3. Ailerons

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Figure 1.9 effects of deflected elevators

1.2.2b PlacementThe flight controls of the Cessna aircraft are fully mechanic (figure 1.10). This means that the elevator and controls are connected with cables, push-pull rods and pulleys. The steering stick is connected with a push-pull rod (1), which is connected with a cable at the end. The cable goes through the body of the aircraft with the support of pulleys (2) to reach the elevators. The cable is double connected, one for pulling up and the other for pulling down. The tension on the cables can be influenced by turnbuckles, which connects multiple cables together where needed. The elevator is connected with two cables and one free horizontal axis where the elevator turns on (3).

Figure 1.10, elevator control system

1.2.3 RudderThe rudder provides primary flight control of the aircraft about its vertical axis. This movement is named as yaw. With use of the rudder, the aircraft can change its heading from left to right. The rudder is part of the vertical stabilizer that is located at the tail of the aircraft.

1.2.3a OperationsThe rudder is connected to the steering stick in the flight deck by a series of mechanical linkages. Left movement of the steering stick deflects the trailing edge of the rudder surface to the left and makes the aircraft turn to a yawing position, because the tail of the aircraft moves right and the nose of the aircraft moves left. This yawing moment takes place at the center of gravity. Right movement of the steering stick deflects the trailing edge of the rudder right and makes the aircraft turn to a yawing position,

1. Steering stick2. Cables3. Elevator

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because the tail of the aircraft moves left and the nose of the aircraft moves right (figure 1.11).

Figure 1.11, effects of a deflected rudder

1.2.3b PlacementThe flight controls of the Cessna aircraft are fully mechanic figure 1.12). This means that the rudder and controls are connected with cables push-pull rods and pulleys. The pedals are connected with a push pull rod (1), which is connected with a cable at the end. The cable goes through the body of the aircraft with the support of multiple pulleys (2). The cable is double connected, one for pulling left and the other for pulling right. The tension on the cables can be influenced by turnbuckles, which connects multiple cables together where needed. The rudder is connected with two cables and one free vertical axis where it turns on (3).

Figure 1.12, rudder control system

1. Pedals2. Cables3. Rudder

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1.3 Secondary flight controlsThe secondary flight controls don’t control the movement of an airplane about its three axis, like the primary flight controls do. The secondary flight controls on a basic airplane are the flaps (1.3.1) and the trim (1.3.2). The flaps can create extra lift and trim tabs can reduce the workload of the pilot. Besides the flaps and trim, there are secondary flight controls that can only be found on an airliner (1.3.3).

1.3.1 FlapsFlaps are devices that can extend out of the wing to increase the drag and therefore the lift, without getting in a stall. The devices are mounted to the trailing edge of the wing. There are five types of different flaps: plain flaps, split flaps, slotted flaps, fowler flaps and slotted fowler flaps.

1.3.1a OperationsBecause extended flaps (figure 1.13) create more drag, the coefficient of lift increases (figure 1.14). The increased drag causes a lower flying speed; the increased coefficient of lift causes more lift. With flaps extended, airplanes have a shorter takeoff distance (figure 1.15) and can land with a bigger angle of descend, so the pilot has a better view of the runway while landing the airplane (figure 1.16). A disadvantage of extended flaps under takeoff is that the angle of climb is smaller than with a takeoff with retracted flaps.

Figure 1.13, standard extended flaps

Figure 1.14, effect on the coefficient of lift with flaps extended

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Figure 1.15, effect on the angle of climb under takeoff with flaps extended

Figure 1.16, effect on the angle of descend under landing with flaps extended

1.3.1b PlacementFlaps are always mounted on the trailing edge of the wings. The devices are manually operated from the cockpit, where a handle leads to a hydraulic actuator via steel cables. Because there are huge aerodynamic forces working on the flaps during a flight, an actuator is needed so the pilot doesn’t need to move the handle in the cockpit with too much power.

1.3.2 TrimTrim tabs are secondary flight controls that can be used when an airplane has a deflection in its normal flight direction. The tabs are attached on the trailing edge of one or more primary flight controls.

1.3.2a OperationsWhen an airplane constantly deflects from its direction while none flight controls are used, the pilot constantly has to manually correct the direction of the airplane. To take away the need of the pilot of constantly giving pressure on the flight controls, trim tabs are used. Trim tabs are small surfaces on the trailing edge of one or more primary flight controls, which can be set in a fixed position by the pilot. When the tab is fixed in a position that is not aligned with the chord of the relevant flight control, a strong aerodynamic force pushes against the tab until there is a balance in forces (figure 1.17). In this balance, the whole flight control is a little deflected so the airplane will react like the pilot is giving a little force to its joystick.

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Figure 1.17, effect of trim tabs on the pitch of an airplane

1.3.2b PlacementTo trim the airplane, the pilot usually controls the trim tabs with a vertically mounted control wheel in the cockpit. However, a control crank to control them can be found in some small airplanes too. The wheel or crank is connected to the tab via a screw thread, so the wheel or crank won’t be pushed back when the tabs are set and aerodynamic forces are working on them.

1.3.3. Secondary flight controls of an airlinerA Boeing 737NG normally has more flight controls than a small Cessna-172. It has extra slats and spoilers. But through the higher airspeed the air force is stronger and will it cost more power to use the secondary flight controls. These forces are too heavy to control them by hand with cables and pulleys, so hydraulic pressure or electronic engines will assist the pilot.

1.3.3.a Leading edge devicesLeading edge devices (figure 1.18), also called slats, look like flaps but flaps are placed on the rear side of the wing. Slats are connected on the leading edge of the wing, the front side (1). When they are extended (2), they will create a higher lift coefficient and the maximum angle of attack will be increased. Theoretically, the slats will increase the surface of the wing and the camber line, which creates more lift. With normal cruising speeds there are no slats needed because the slats will otherwise generate a lot off drag. Only by the landing slats are necessary, for flying slower and an increased maximum angle of attack. With a slatshandle in the cockpit the slats can be controlled.

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Figure 1.18, leading edge device

1.3.3.b SpoilersSpoilers are valves on the wing (figure 1.19), from the beginning to halfway of the end and also called lift dumpers. These spoilers create a lot of drag and dump the lift when they are extended, because they are disturbing the perfect airstream around the profile. The two most used reasons for using the spoilers are losing speed or loss of height without increasing any speed. When the plane is landed on the ground, the spoilers will be fully extended and create a lot of downward force on the landing gear, so the wheels have a better traction on the runway for a faster stop.

Figure 1.19, spoilers

1.3.3c Yaw damperA yaw damper is a device that reduces the rolling and yawing oscillations during a ‘dutch roll’. A dutch roll occurs when the aircraft makes a turn. When the aircraft turns, it wants to get back to its balanced position. As a result, the airplane starts to roll and yaw, which is called the dutch roll. There are sensors attached to the rudder of the plane. These sensors collect data of the airstream for damping the rudder deflection. This results in a more comfortable flight for the passengers.

1.3.3.d Control of the secondary flight controlsLeading edge devices and spoilers will be both powered by hydraulic pressure or by electronics. It is simply not possible to control the spoilers and the leading edge devices without the help of hydraulic pressure systems or by electronics, because of the heavy air forces. In the cockpit, there are levers to set the leading edge devices in the right stance. These levers are connected to the hydraulic and electronic system and will set the slats or spoilers to the right position.

1.4 RequirementsIn the aviation world there are requirements, some of these requirements are by the law and others by the costumer. The requirements are because there are many automatic devices in the cockpit that helps the pilot, however these devices need to be certified. The safety is in the Aviation one of the largest weight factor, if a plane is not safe according to the law and some certificates it is not allowed to fly. To secure a plane is

1. Placement of slats2. Extended slats

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safe, there are some laws edited by Country’s this is explained in (1.4.1). Also the costumer has some requirements, low maintenance and low costs, this is explained in (1.4.2).

1.4.1 Requirements by law In the Aviation there are authorities that edit the laws for civil aviation. In Europe this is the European Aviation Safety Agency (EASA), in the Netherlands this is the ‘Inspectie Leefomgeving en Transport’ (ILT). These two have general regulations (1). In the cable system are also requirements (2). In the movements of automatic devices are also laws and certificates (3).

ad 1 General regulationsIn every flight the plane has to be safe during the whole flight. Every device that is dealing with the flight controls has to be in range of the pilot during the flight. Every device of the flight controls, the primary and also the secondary flight controls, has to be calibrated on precise measurements. If the possibility occurs that there are wrong measurements, then the pilot must be able to manually calibrate it.

Every system has to have at least two or more independent sources of electrical energy.

Two systems for every flight controls are necessary, each accessible from both pilot stations. The systems have to be designed and installed in such a way that failure of one system will not preclude operation of the other system.

It must be possible to produce and to correct roll and yaw by unreversed use of aileron and rudder controls, up to the time the airplane is stalled.

ad 2 Cable systemIn an airplane, there are many cable systems. These systems contribute to the communication with the hydraulics. If the flap control lever is pulled upwards there will be a signal that is transported from the cockpit trough a cable to the hydraulics. Malfunction of cabling systems will directly lead to dangerous situations, if the cables are not working properly the pilot cannot reach his hydraulics. High level of law requirements and certifications prevent these possible dangerous situations.

Cables smaller than 3.2 mm in diameter may not be used in aileron, elevator or rudder systems.

Each cable system must be designed so that there will be no hazardous change in cable tension throughout the range of travel under operating conditions and temperature variations.

Fairleads must be installed so that they do not cause a change in cable direction of more than three degrees.

Turnbuckles must be attached to parts having angular motion in a manner that will positively prevent binding throughout the range of travel.

There must be provisions for visual inspections, pulleys, terminals, and turnbunckles.

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ad 3 Movements of automatic devicesThis is the movements of the automatic devices explained, also the maximum forces of torque cannot be exceeded.

Ailerons: side stick to the right to move the right wing and the left wing up, this cannot exceed the torque of 445N.

Elevator: side stick to the back to move the nose up, this cannot exceed the torque of 1112N.

Rudder: right pedal to the front to move the nose to the right, this cannot exceed the torque of 1335N.

Flaps: flap control lever to the front to open up the flaps to above, this is a lever and does not have a torque to over exceed.

1.4.1 Requirements by customerThe requirements by the customer can be divided into maintenance requirements (1) and costs requirements (2).

ad 1 MaintenanceThe maintenance has to be on an Airbus A320 or a Boeing 737NG. The costumer wants the airplane that has the lowest costs and maintenance has a direct influence on the costs.

ad 2 CostsThe costs of the flight controls have to be as low as possible, without affecting the safety. We can say the safety has the main priority after the costs for the customer. Also the system has to be very accessible for maintenance so the time the aircraft is on the ground, is as low as possible.

1.5 Functional Research Several functions are required to put the flight controls into action. There are many options to execute these functions, but the functions per option need to be described before those options can be considered. These functions are as follow:

1. Measuring 2. Converting3. Transporting4. Comparing 5. Correcting 6. Amplifying 7. Executing

ad 1 Measuring When the pilot wants to change the direction of the airplane, the quantity of requested movement needs to be measured.

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ad 2 ConvertingThe measured signal needs to be converted to a signal that can be worked with in the further system. If the signal is not right, it can’t be transported.

ad 3 TransportingThe signal needs to be transported from the measuring point up to the executing point.

ad 4 Comparing The signal needs to be compared to external measuring systems. If the signal isn’t equivalent to the external measuring system, than the signal isn’t usable.

ad 5 CorrectingThe signal isn’t a smooth flow. All high and low values are removed by correcting the signal, so the signal will be smooth.

ad 6 AmplifyingThe signal isn’t strong enough to put the flight controls into action. To do so, it needs to get stronger. By amplifying the signal it will be strong enough to deflect the flight controls.

ad 7 ExecutingThe signal will reach its destination and the flight control will move. The desired change in direction will occur.

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2 Technical research As well known, the systems used in Boeing aircraft and those in Airbus aircraft differ from each other. The systems used in Boeing aircraft work on the principles of hydraulics, while the systems used in Airbus aircraft work on the principles of electronic controls. Systems used in Boeing aircraft are called ‘conventional systems’ (2.1), while the systems used in Airbus Aircraft are called ‘fly by wire systems’ (2.2).

2.1 B737NG (conventional system)A flight control system on a Boeing 737NG works with pressure fluid. This pressure fluid is divided in three hydraulic systems. These three hydraulic systems deliver the power to control both the primary as the secondary flight controls (2.1.1). The controls of the primary flight controls are quite the same, so only the composition of an elevator control system in Boeing aircraft will be highlighted (2.1.2). Also the controls of the secondary flight controls are quite the same, so for the secondary flight controls only the trim will be highlighted (2.1.3).

2.1.1 System used by Boeing 737NGThe Boeing 737NG flight control system is based on three hydraulic systems: A, B and standby (figure 2.1). A hydraulic system means that it works on the pressure of liquid. When the pressure in system A, system B or both of them get lost, the standby system is used. The hydraulic systems provides power for the flight controls, the leading edge flaps and slats, landing gear, trailing edge flaps, wheel brakes, thrust reversers, nose wheel steering and the autopilots.

Figure 2.1, schematically distribution of the hydraulic systems

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Each hydraulic system has a fluid reservoir, which is located in the main wheel area. The reservoir of the standby system is connected to the system B reservoir for pressurization and servicing. Pressurization of all reservoirs ensures positive fluid flow to all hydraulic pumps. The quantity of a reservoir of a system will change if a leak occurs. The power transfer unit and the landing gear transfer unit are used to get volume of a hydraulic fluid.

2.1.1a Hydraulic systems A and BThe hydraulic system A powers the ailerons, rudder, elevator, elevator feel, flight spoilers, ground spoilers, alternate brakes, number 1 thrust reverser, autopilot A, normal nose wheel steering, landing gear and power transfer unit.

The hydraulic system B also powers the ailerons, rudder, elevator, elevator feel and flight spoilers but instead of the alternate brakes by system A, system B powers the normal brakes. System B also powers the number 2 thrust reverser, autopilot B, landing gear transfer unit, auto slats, yaw damper and the trailing edge flaps. Instead of the normal nose wheel steering by system A, system B powers alternate nose wheel steering.

Both of the hydraulic systems have an engine-driven pump and an alternating current (AC) electric motor-driven pump. The engine-driven pump of system A is powered by engine number one and the engine-driven pump of system B is powered by engine number two. The on/off switch controls the engine-driven pump output pressure, but the pump will continue rotating as long as the engine is operating. Pulling the engine fire warning switch shuts off the fluid flow to the engine-driven pump and deactivates the related low pressure light.

2.1.1b Standby hydraulic systemThe standby hydraulic system is a backup system if system A, B or both pressures are lost. This system uses a single electric motor-driven pump to power the thrust reversers, rudder, leading edge flaps and slats and the standby yaw damper. The system can be activated automatically or manually.

2.1.1c Hydraulic leaksIn all of the three systems, a leak can occur. But in every system occurs something else then in the other systems when a leak is developed (1, 2 and 3).

ad 1 Leak in system AIn the reservoir stands a stand-pipe which prevents a total system fluid loss when a leak occurs. With fluid level at the top of the stand-pipe, the quantity of the reservoir indicates approximately 20% full. The hydraulic pressure in system A is maintained by the electric motor-driven pump. When a leak occurs in the electric motor-driven pump or its related lines, the quantity in the reservoir will decrease to zero and all system pressure gets lost.

ad 2 Leak in system BWhen a leak occurs in the pump, the line or a component of system B, the quantity will decrease until it approximately gets zero and the pressure in system B will get lost. Also in the reservoir of system B, a stand-pipe is present. This standpipe supplies fluid to the

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electric motor-driven pump and the engine-driven pump. With fluid level at the top of the stand-pipe, the fluid stays in the reservoir of system B and is enough for power transfer unit operations. A leak in system B has not any effect on the operation of the standby system.

ad 3 Leak in standby system When a leak occurs in the standby system, the quantity of the reservoir decreases to zero. The low quantity light will be lightened when the reservoir is approximately half empty. If this happens, system B will operate normally but the fluid level indication of the reservoir of system B decreases and stabilizes at 72% full.

2.1.1d Power transfer unitThe power transfer unit is used to get extra volume of hydraulic fluid. This is needed when the volume of the hydraulic pump of system B is lost. It is to operate the auto-slats and leading edge flaps and slats at the normal rate. The power transfer unit uses the pressure of system A to power a hydraulic motor-driven pump. The power transfer unit will operate automatically only when all of the next conditions are applied:

1. The system B engine-driven pump hydraulic pressure falls below limits2. The aircraft is airborne3. Flaps are less than 15 degrees but not up4. Flaps are not up

2.1.2 Elevator Boeing 737NGThe elevator is a primary flight control flap that is located at the horizontal stabilizer at the tail of the aircraft. The elevator can be operated by all three of the systems in a Boeing aircraft, while it also has its own back-up system.

2.1.2a Elevator operated systemsThe control column offers the manual operating way for controlling the elevators (figure 2.2). The control columns of the captain and the first officer are linked to each other by means of cables. The cables are routed to the Elevator Feel and Centering Unit (EFCU), which is located at the tailcone. From there, the cables go to the Power Control Unit (PCU) that operates the elevators. The PCU is powered by the hydraulic systems A and B, which work separated from each other. The autopilot is the second operating way for controlling the elevators. The autopilot sends a signal to the EFCU. This signal is combined with the hydraulic pressure, pitot-static tube inputs and the position of the stabilizer in the Elevator Feel Computer (EFC). The EFC then sends the signal to the elevator PCU, which controls the elevators and adds feel to the control columns with the EFCU.

The Mach trim is the third operating way for controlling the elevators. This is an automated system that eliminates the effect of the airplane pitching down at speeds approaching the speed of sound and provides speed stability at the higher Mach numbers. The system operates at speeds higher than Mach 0.615. The Air Data Inertial Reference Unit (ADIRU) senses the airspeed with the pitot-static tube inputs and sends a signal to the Flight Control Computer (FCC). The FCC sends a command to the Mach trim

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actuator, which in turn sends a signal to the EFCU. The EFCU moves the elevator with the PCU and adds feel to the control column.

2.1.2b Elevator Back-up systemThe elevator control system is powered by the hydraulic systems A and B. If one of the systems fails due to pressure lost, the other system is sufficient enough for operating the elevators. If both hydraulic systems fail, the mechanical control can also be used to operate the elevators. The horizontal stabilizer trim is electrically operated and in case of a failure in the electrical system, it is possible to operate the horizontal stabilizer by rotating the stabilizer trim wheel manually.

Figure 2.2, elevator-operated system

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2.1.3 Secondary flight controls on a BoeingThe Boeing 737NG makes use of the following trims: aileron trim, rudder trim, elevator trim and stabilizer trim.

2.1.3a Aileron trimThe aileron trim switch brings the aileron in its neutral position. The aileron trim switches give an electric signal to the EFCU, which is attached to the PCUs (figure 2.3). The PCUs will put the ailerons in position with their hydraulics.

Figure 2.3, aileron trim system

2.1.3b Rudder trimTo trim the rudder there is a little switch. The little switch sends an electric signal to the rudder FCU (figure 2.4), which will control the hydraulic PCUs.

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Figure 2.4, schematic rudder system

2.1.3c Elevator trimFor the elevator trim, there is an electric switch in the cockpit that sends a signal straight to an electric motor attached to the elevator trim flap.

2.1.3d Stabilizer trimThe horizontal stabilizer (figure 2.5) gives the pilot the opportunity to move the center of gravity during the flight. The stabilizer causes downwards pressure so the airplane is in balance. If there is a very heavy load in the back so the airplane is out of balance, the stabilizer can change its pitch so a lower down force is created, in that way the aircraft is always in balance. There are multiple ways to trim the stabilizer: the autopilot can do it, the control column can do it or the stabilizer trim wheel can fix the job. The trim wheel is mechanically connected to the stab trim mechanism. The autopilot and the control column send an electric signal to the stabilizer trim wheel to turn in the wanted direction.

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Figure 2.5, schematic stabilizer trim system

2.2 Airbus A320 (fly by wire system)A flight control system on an Airbus A320 works with electric signals and computers. Because of that, the pilot his control of the airplane is limited: for instance, computers calculate if a maneuver is possible when the pilot wants to make one. This calculation is done by seven separate computers, which work combined (2.2.1). Like on a Boeing, the controls of the primary flight controls are quite the same, so only the composition of an elevator control system will be highlighted so it can be compared to the system used in Boeing aircraft (2.2.2). Also the controls of the secondary flight controls are quite the same, so for the secondary flight controls only the trim will be highlighted (2.2.3).

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2.2.1 System used by Airbus A320All flight controls of the 737NG are conventional and hydraulically powered by two independent, hydraulic systems with manual reversion for ailerons and elevator. However, Airbus aircraft make more use of electric principles (figure 2.6). As a conventional system of Boeing, Airbus only has two pressure systems that can operate as a mechanic system. Seven flight control computers (two Elevator Aileron Computers (ELACs), three Spoiler Elevator Computers (SECs) and two Flight Augmentation Computers (FACs) process pilot and autopilot inputs according to normal, alternate, or direct flight control laws. The flight control laws are the manufacturer’s built-in computer instructions that are executed by the flight control computers following a predetermined set of rules. The instructions define flight control movement, flight characteristics and aircraft limitations. For safety there are four flight control laws and a mechanical backup: normal law (1), alternate law (2), abnormal alternate law (3), direct law (4) and mechanical backup (5).

ad 1 Normal lawNormal law is the normal operating configuration of the system. It covers three-axes control, flight envelope protection and load alleviation. It has three modes according to the specific phase of flight. Failure of any single computer does not affect normal law.

ad 2 Alternate lawWhen a minimum of two or more failures of redundant systems occur, the flight controls will revert to alternate law.

ad 3 Abnormal alternate law If extreme conditions cause the airplane to enter an unusual attitude, for instance severe turbulence, abnormal alternate law is activated. Abnormal alternate law is alternate law without protections and stabilities except for load factor protection. This allows the pilots to recover from the unusual attitude.

ad 4 Direct lawDirect law is the lowest level of computer flight control and occurs only with certain multiple system failures. It is possible for the flight control system to degrade from normal law straight to direct law. Direct law result in a direct stick to flight control surface relationship: the computers have no authority to modify or override the stick inputs, thus no protections or stabilities are provided.

ad 5 Mechanical backup Occurs in case of a complete loss of electrical flight controls. The aircraft can be controlled by trim wheels, rudder pedals and engine thrust. Mechanical backup provides a means of aircraft control until a higher law can be restored.

The flight control systems are also displayed in the cockpit on a screen; this is the Electronic Centralized Aircraft Monitoring and the Flight control (ECAM).

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Figure 2.6, schematically distribution of the electric systems

2.2.1a Hydraulic system of AirbusAirbus aircraft have three continuously operating hydraulic systems: blue (1), green (2) and yellow (3) (figure 2.7). Each system has its own hydraulic reservoir. Normal system operating pressure is 3000 psi. Hydraulic fluid cannot be transferred from one system to another, like on Boeing aircraft.

ad 1 Blue systemAn electric pump pressurizes the blue system. A pump driven by a Ram Air Turbine (RAT) pressurizes this system in an emergency situation.

ad 2 Green systemA pump driven by engine 1 pressurizes the green system.

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ad 3 Yellow systemA pump driven by engine 2 pressurizes the yellow system. An electric pump can also pressurize the yellow system, which allows yellow hydraulics to be used on the ground when the engines are shut down. Crewmembers can also use a hand pump to pressurize the yellow system in order to operate the cargo doors when no electrical power is available.

Figure 2.7, systems of airbus

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2.2.1b ELACsThe ELAC is a flight control computer, but also a backup flight control computer. The ELAC controls the ailerons and the elevators and the trimmable horizontal stabilizer as a secondary flight control. If an error occurs, there has to be a backup, Airbus made this so that the computers that control the main flight controls, also control the backup controls in combination with another computer. The backup of the ELACs is of the ailerons and the elevator. The ELAC 1 normally controls the ailerons, but if ELAC 1 fails, the system automatically transfers aileron control to ELAC 2. If both ELACs fail, the ailerons revert to the damping mode.

2.2.1c SECsThe SEC is a flight controller, but more of a backup computer as it will almost be used as a backup system. It has the backup instruments of the ailerons, elevators and the stabilizer. The spoiler has a conventional backup system of a speed brake lever on the pedestal. SEC 3 controls the N 2 spoilers, SEC 1 the N 3 and 4 spoilers and SEC 2 the N 5 spoilers. If a SEC fails, the spoilers are automatically retracted.

2.2.1d FACsThe FAC is a flight control computer, it controls the rudder trim. FAC 1 controls motor number 1 that drives the trim, while motor number 2, controlled by FAC 2, remains as a backup. The pilot can apply rudder trim manually by rotating the rudder trim selector on the pedestal. There are several specifications of the rudder trim on an Airbus A320, which are important to mention:

The maximum deflection of the rudder trim is 20 degrees Rudder trim speed is one degree per second The pilot can use a button on the rudder trim panel to reset the trim to zero

Also the yaw rate order is being transferred from the ELAC to the FACs.

2.2.1e ECAMOn the ECAM view, it is possible to see the situations of the primary flight controls and the secondary flight controls: spoilers/speed brakes indication (1)(1), hydraulic system pressure indication (2)(2), ELAC/SEC indication (3)(3), aileron position indication (4)(4), aileron and elevator actuator indication (5)(5), elevator position indication (6)(6), pitch trim position indication (7)(7) and yaw control indications (8)(8).

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Figure 2.8, ECAM

ad 1 Spoilers/speed brakes indication : Spoiler deflected by more than 2.5 degrees (green) - : Spoiler retracted (green) : Spoiler fault deflected (amber) 1 : Spoiler fault retracted (amber)

ad 2 Hydraulic system pressureNormally green changes to amber if pressure in the hydraulic system gets low.

ad 3 ELAC/SEC indicationNormally green changes to amber if there is a failure in the ELAC or the SEC, or if the ELAC or SEC pushbutton is off, or if both flight control data concentrators fail. The surrounding box is normally grey. It changes to amber if the ELAC or SEC indication does.

ad 4 Aileron position indicationThe aileron position indication has a white scale and a green index. It changes to amber, when neither (green nor blue) servojack is available.

ad 5 Aileron and elevator actuator indication“G” and “B” are normally displayed in green. The colour changes to amber in case of a low pressure in the green or blue hydraulic system. The partial box also changes to amber if the associated computer or actuator fails.

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ad 6 Elevator position indicationThe elevator position indication has a white scale and a green index, like the aileron position indication. The index changes to amber, when both associated actuators are not available.

ad 7 Pitch trim position indicationThe pitch trim numbers are in green. They change to amber, if the hydraulic pressure gets low in the systems. The “pitch trim” legend is in white. It changes to amber, if there is a pitch trim jam. This occurs when maintenance that is done, is done incorrectly.

ad 8 Yaw control indicationsThe rudder position indicator is the nail in the middle of the screen. The rudder symbol becomes amber, if the hydraulic pressure is low. The rudder travel limiter is below the nail, which indicates the high-speed position. Rudder trim position is the line at the bottom, which is normally displayed in blue. It changes to amber, if the rudder trim reset fails.

2.2.2 Elevator Airbus A320All the flight control surfaces of the Airbus A320, including the elevator, are electrically controlled and hydraulically activated. Two elevators and the Trimmable Horizontal Stabilizer (THS) control the aircraft in its pitch. The maximum deflection of the elevator is 30° nose up and 17° nose down. The maximum THS deflection is 13,5° up and 4° down. Both the pilot as the copilot is able to use a sidestick to manually control the pitch of the airplane. The sticks are placed on the pilot’s lateral consoles. Both sticks are not mechanically connected and send separate signals to the flight control computers. Also on the Airbus A320, there is sidestick priority. This prevents that, when both pilots use the sidestick, dibble or conflicting deflections occur. According to the pilots input, computers will interpret the data and move the elevators desirably. In normal law situations however, the computers will prevent any excessive input made by the pilots to guarantee a safe maneuver.

2.2.2a Electrical controlOne Elevator Aileron Computer (ELAC) is used for the normal elevator and stabilizer controls. In addition, two Spoilers Elevator computers (SECs) are used for the standby elevator and stabilizer controls. The data from the ELAC and SEC is acquired by a Flight Control Data Concentrator (FCDC) and sent to the electronic instrument system (EIS) and the centralized fault display system (CFDS). ELAC2 (figure 2.9) controls the elevators and the horizontal stabilizer in normal situations. The green and yellow hydraulic jacks are responsible for the left and right elevator surfaces. If, by some circumstances, ELAC2, the associated hydraulic systems or the hydraulic jacks themselves fail, the system automatically shifts operating pitch control to ELAC1. ELAC1 then controls the surfaces via the blue hydraulic jacks. In a situation when both ELAC1 and ELAC2 fail, there is a second and third backup system in place, consisting of SEC1 and SEC2. Depending on their own status either one of them will take control of the pitch.

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Figure 2.9, Pitch control

2.2.2b ActuatorsAs mentioned before, two electrically controlled hydraulic servojacks drive each elevator surface. Each servojack has three modes:

Active: Position of the jack is electrically controlledDamping: The jack follows the elevators surface movementCentering: The jack is hydraulically retained in the neutral position

In normal operation, one jack is always in active mode and the other in damping mode. Some maneuvers however require the second jack to become active as well. If the active jack fails, control is taken over by the second jack, where the previously active servojack automatically becomes damping. When none of the jacks is being controlled electrically, both of them switch to centering mode. When neither jack is being controlled hydraulically, both enter damping mode. If one of the elevators fails completely, the deflection of the other elevator gets limited to avoid excessive stress on the tailplane or rear fuselage.

2.2.3 Secondary flight controls on an Airbus, trimLike many systems on an Airbus, also the secondary flight controls differ from those used in Boeing aircraft. To prove the differences between the secondary flight controls, the trim systems are highlighted. The types of trim used on an Airbus aircraft are the rudder trim and the stabilizer trim.

2.2.3a Rudder trimUnlike rudder control, the system behind the rudder trim on an Airbus A320 is totally electric (figure 2.10). The pilots apply rudder trim with a rotary switch on the pedestal (1). This switch gives an electric signal to the two Flight Augmentation Computers (FACs), which are built-in for electrical rudder control (2). There are two FACs built-in so if one of the two computers breaks down, the other one takes over the functions of the broken one. The FACs send the signal through to motors which convert the electrical

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signal in a motion to deflect the rudder trim (3). Also here, one of the two motors is functioning as a standby one. In normal position, FAC number one is controlling motor number one and FAC number two is controlling motor number two. These motors also power the artificial feel unit for the rudder. Because the rudder trim switch in the cockpit directly gives an electrical signal, the pilots can only control the rudder trim electrically.

Figure 2.10, Rudder trim control

2.2.3b Trimmable horizontal stabilizerTwo elevators and the trimmable horizontal stabilizer provide the pitch control of an Airbus. The pilots can use the horizontal stabilizer to set the center of gravity when the airplane is flying. The horizontal stabilizer can be controlled electrically as well as mechanically (figure 2.11). The electric control is provided by simply moving the side stick (1) while a separate trim wheel (2) is used for mechanical control. When looking at pitch control, the side stick sends an electric signal to both of the Elevator Aileron Computers (ELACs) (3) as the Spoilers Elevator Computers (SECs) (4). The ELACs are for normal control of the elevators, stabilizer and ailerons while the SECs control the spoilers and function as a standby control for the elevators and stabilizer. There are two copies of the ELAC computers as well as the SEC computers, so that makes four in total to control the stabilizer trim. When all the systems are functioning, the horizontal stabilizer trim is controlled by ELAC number two, which sends the electric signal to the first three electric motors (5). When ELAC number two is defect, the electric signal runs through ELAC number one to motor number two. When also ELAC number one is defect, the signal runs either via SEC number one or SEC number two to either motor number two or motor number three, depending on which systems are working normally. The electric motors control two hydraulic motors (6), which drive a screw jack (7) to finally move the horizontal stabilizer. A trim wheel can control the two hydraulic motors too. This trim wheel is found in the cockpit and can be used when all electricity on the airplane has fallen out.

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Figure 2.11, Control of the trimmable horizontal stabilizer

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3 MaintenanceThe Boeing 737NG and the Airbus A320 have different flight control systems; as a consequence they have differences in maintenance. For the size of the project, only the elevator and the trimmable horizantal stabilizer will be compared. To be more precise about the costs of the maintenance of the two different airplanes, the design aspects (3.1) are enlightened. When this comparison is made, airliner ALA will be advised about the costs in maintenance of the flight controls of both the Boeing 737NG as the Airbus A320 (3.2).

3.1 Design aspects The Boeing 737NG has different design aspects than the Airbus A320 has. To compare the differences between the two, there will be a component removal and installation of the hydraulic actuators of the elevators. The man hours will make a comparison which system has a better maintenance design.

3.1.1 Boeing 737NGThe B737NG has an elevator Power Control Unit (PCU) that operates the elevators. The system operates the elevators with the left power control unit and the right power control unit. The current power control unit has to be removed first, before the new one can be installed.

3.1.1a RemovalBefore the PCU (Appendix I and II) can be removed, preparations need to be done. The pressure from the elevator hydraulic systems A and B needs to be removed. To get access of the PCU, three panels the stabilizer trim access door and two tailcone access doors have to be opened.

1. When there is access to the PCU, the nuts (22), washers (21), washers (20) and bolts (19) can be removed to disconnect the four input rods (23) from the four input cranks (18) (two on each elevator PCU).

2. Install the rig pin [E-5] in the elevator aft control quadrant (this holds the elevator in the neutral position).

3. Remove the elevator PCU (6) by removing the nut (17), washer (16) nut (15), washer (14), bolt (12) and bushing (13) that attach the elevator PCU to the mounting brackets.

4. Disconnect the hydraulic lines (3) from the elevator PCU (6). 5. Remove the nut (11), washer (10), washer (9) and bolt (8) that attach the

elevator. Remove the elevator PCU (6) from the airplane.

3.1.1b Installation Before the PCU can be installed, preparations need to be done. There has to be made sure that the pressure to the elevator hydraulic system A and B, is removed.

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1. Lubricate the packing (1) and the new packing (5) with D00153 fluid. Install the packing (1), union (2), the new packing (5) and union (4) in the elevator PCU (6).

2. a. Apply D00633 grease to the bolt (8) and (12).b. Put the elevator PCU (6) in its position. c. Install the bolt (8) with the bolt head inboard, washer (9), washer (10) and nut (11) to attach the elevator PCU (6) to the output torque tube (7). d. Install the bushing (13), bolt (12), washer (14) and nut (15) to attach the elevator PCU (6) to the mounting bracket (tighten the nut (15) to 550-600 pound-inches).e. Install the washer (16) and nut (17) (tighten the nut (17) to 225-250 pound-inches).

3. Remove the rig pin E-5 from the elevator aft control quadrant4. Move the elevator PCU (6) to the fully retracted position.5. Connect the four input rods (23) to the four input cranks (18)(two on each PCU).

Apply D00633 grease to the bolts (19). Install the bolts (19), washers (20), washers (21) and nuts (22).

6. Remove the caps and the plugs from the hydraulic lines (3) and ports. Connect the hydraulic lines (3) to the elevator PCU (6).

7. Put the elevator systems A and B back to the condition before the pressure removal.

8. Do this subtask 27-31-14-820-001: Input rods of the elevator PCU adjustment. 9. Do this subtask 27-31-14-820-002: Elevator surface friction and balance test. 10. Do this subtask 27-31-14-820-003: Elevator limit travel test. 11. Do this subtask 27-31-14-820-004: Manual mode test.12. Do this subtask 27-31-14-820-005: Control column travel and centering test. 13. Do this subtask 27-31-14-820-006: Control column power force test.

Put the airplane back to its usual condition by installing the three access panels, the stabilizer trim access door and two tailcone access doors.

3.1.2 Airbus A320The elevator of the Airbus A320 is actuated by four servo control units (Appendix III, IV and V). Like the process on a Boeing 737NG, the current servo control units have to be removed first before the replacements can be installed.

3.1.2a RemovalBefore the servo control unit can be removed, preparations need to be done. To get access to the servo control unit, the trailing edge access panels need to be opened. The pin-side stick locking in the captain and the first officer side sticks need to be installed. To facilitate the access to the work area, the collar-elevator servo control safety on the servo control that will not be removed, can be installed. The pressure of the hydraulic systems (green, yellow and blue) needs to be removed.

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1. When there is access to the servo control unit, the electrical connectors (1, 2, 3) have to be disconnected. Blanking caps need to put on the disconnected electrical connectors.

2. The hydraulic connections also need to be disconnected. Disconnect the flexible hoses (5, 6) from the servo control unit (4). Remove and discard the unwanted hydraulic fluid and put blanking caps on the flexible hoses and the unions of the servo control unit. Also remove the bonding lead (7), the nut (8), the washer (9) and the bolt (11).

3. For disconnecting the servo control unit from the elevator, first remove the cotter pins (20, 25) and discard them. Then remove the locking cup (21), the nut (22) and the cup washer (24). Now remove the bolt (27) and bush (26).

4. For disconnecting the servo control unit from the horizontal stabilizer structure, first remove and discard the cotter pin (38). Then remove the locking cup (31), the nut (30) and the washer (41). Now remove the nuts (33), the washers (32,36), the bolts (35) and the profile (37).

5. Support the servo control unit and remove the bolt (28) and the washer (29). Then remove the elevator bolt (25).

Remove the servo control unit from the aircraft.

3.1.2b InstallationAlso with the Airbus, before installation can commence, certain preparations have to be made to ensure the safety of the workers and guarantee a proper installment following the regulations. These preparations mainly consist of putting different safety and locking devices and warning notices in place, before handling the aircraft components. After the installation preparations have been made, the actual installation can take place.

A. Installation of the servo control unit to the THS attachment1. Apply common grease to the outer surface of the bush (26 & 27) and install

them.2. Apply special materials to the head and shank of the bolt (28).3. Put the servo control unit (4) in place and support it.4. Install the bolt (28) with the washer (29).5. Apply common grease to the thread of the bolt (28).6. Install the washer (41).7. Install and torque the nut (30) to between 45 and 50 Nm.8. Install the locking cup (31) and the cotter pin (38).9. Install the plate (37) with the washers (32 & 36), the nuts (33) and the bolts

(35).10. Apply special materials to all the remaining unprotected steel attachment

parts of the elevator servo control.

B. Installation of the servo control unit to the elevator attachment1. Apply common grease to the outer surface of the bush (26) and install it.2. Apply special materials to the head and shank of the bolts (27).

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3. Put the servo control unit (4) in position and support it.4. Install the bolt (27).5. Apply common grease to the thread of the bolt (27).6. Install the cup washer (24) and the nut (22).7. Torque the nut (22) to between 45 and 50 Nm.8. Install the locking cup (21) and the cotter pins (20 & 24).9. Apply special materials to all the remaining unprotected steel attachment

parts of the elevator servo control.

C. Hydraulic and electrical connection of the servo control unit to the horizontal stabilizer1. Connect the hydraulic connections.2. Remove the blanking caps from the flexible hoses (5 & 6) and the unions of

the servo control unit (4).3. Connect the flexible hoses (5 & 6) to the servo control unit (4).4. Install the bonding lead (7) with the bolt (11), the washer (9) and the nut (8).5. Connect the electrical connections.6. Remove the blanking caps.7. Connect the electrical connectors.

After the installation and visual inspections have been completed, all the accesses have to be closed. All the equipment, locking and safety devices and the warning notices need to be removed. Lastly, adjustment tests have to be done.

3.1.3 Man hours management In the category maintenance hours the planes are extremely different. Boeing has many less maintenance hours than Airbus. Several reasons for Airbus why it costs more hours to repair and inspect the plane, are the steps that have to be done to repair the target safely and correctly. In addition, Boeing has shutters around the whole aircraft to get fast and easy access to the components. Airbus has fewer shutters. Also inside the Airbus aircraft, there is a small long corridor where the engineers have to crawl in to get to the specified target. The total maintenance hours will be for Airbus 107 hours and for Boeing 77 hours. These maintenance hours are based on the whole flight control system and are officially given by the flight companies.

However, Airbus flight control systems have less wear and tear than Boeing systems have. Therefore, Airbus flight control systems will have a longer lifespan than the systems in Boeing. Unfortunately, that’s just a general thesis (electronics will last longer than mechanics do) and therefore this thesis won’t be considered in the conclusion.

3.2 AdviceFor the basic maintenance, the B737NG requires less man hours then the A320. The man hours required for the Boeing are just 77, compared to the 107 hours that are needed on the Airbus. A Boeing is full of hatches so maintenance staff can easily reach what they are looking for. By the Airbus there are little crawling spaces where it's hard to get everywhere. Another disadvantage of an Airbus is that when a computer breaks down,

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it's very expensive to replace in comparison with Boeing. Therefore, projectgroup 1N advises ALA to buy Boeing 737NG aircraft, looking at the maintenance costs.

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List of termsActuator Hydraulic cylinder

Dutch roll A natural effect on the aircraft caused by the shape of the aircraft

ILT Inspectie Leefomgeving en Transport

Electric hydraulic servo unit Hydraulic valve that makes moving from a flight control possible

Flaps Flaps are extendable part which increase the lift

Flight Control Computer (FCC) A computer, which processes and correct the movements of te side-stich and send them to the hydraulic system.

Leading edge The front of the wing profile

Power Control Unit (PCU) Is a unit that determents parameters.

Servo control Unit A servo controlled piston, which is electrically controlled.

Trim tabs A trailing edge tab that is used to trim that control surface.

Yaw damper Device to prevent a aircraft from making a Dutch Roll

Side stick Unit that controlles the elevator and the ailerons, used by airbus.

Stall Point of fully losing its boundary layer, which results into losing lift.

Slat flap control computer It's a computer that controls and moves the flaps and slats

Rotary Variable Displacement Transducer

It's a transducer that converts an angular displacement into an electrical current.

ELAC Elevator Aileron Computer

SEC Spoiler Elevator Computer

FAC Flight Augmentation Computer

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List of sources

Anderson jr., J.D. (2005). Introduction to Flight. 5e dr. New York: McGraw-Hill Science

Grit, R. (2011) Projectmanagement. 6e dr. Groningen

A320 Aircraft Maintenance manual, subtask 27-24-51

FAA Aviation Handbook - Flight Controls

FAA Aviation Handbook - Aerodynamics of Flight

Projectboek_FC_12-13 F1

B737CL-Flight_Controls

A320-flight_controls

CS-25 book subpart C

CS 25.689

http://www.smartcockpit.com/aircraft-ressources/A319-320-321-Flight_Controls.html Geraadpleegd op 16 februari 2013

http://www.smartcockpit.com/aircraft-ressources/A320-Flight_Controls.htmlGeraadpleegd op 18 februari 2013

http://exploration.grc.nasa.gov/education/rocket/newton3r.htmlGeraadpleegd op 28 februari 2013

http://www.easa.europa.eu/agency-measures/certification-specifications.php#CS-25Geraadpleegd op 14 februari 2013

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http://www.easa.europa.eu/agency-measures/certification-specifications.php#CS-25

http://exploration.grc.nasa.gov/education/rocket/newton3r.html

http://www.smartcockpit.com/aircraft-ressources/A320-Flight_Controls.html

http://www.smartcockpit.com/aircraft-ressources/A319-320-321-Flight_Controls.html

https://dlwo.techniek.hva.nl/studiedelen/AVI-V-1300FLTC11/1213/Documents/a320-flight_controls.pdf

https://dlwo.techniek.hva.nl/studiedelen/AVI-V-1300FLTC11/1213/Documents/B737CL-Flight_Controls.pdf

https://dlwo.techniek.hva.nl/studiedelen/AVI-V-1300FLTC11/1213/Documents/Projectboek_FC_12-13%20F1.pdf

https://dlwo.techniek.hva.nl/studiedelen/AVI-V-1300FLTC11/1213/Documents/FAA%20%20Aviation%20Handbook%20-%20Aerodynamics%20of%20Flight.pdf

https://dlwo.techniek.hva.nl/studiedelen/AVI-V-1300FLTC11/1213/Documents/FAA%20%20Aviation%20Handbook%20-%20Flight%20Controls.pdf


List of appendixesAppendix I, view through the tailcone access door Blz. 44Appendix II, right power control unit (left power control unit is opposite) Blz. 45Appendix III, servo control unit Blz. 46Appendix IV, mounting of the servo control unit to the elevator Blz. 47Appendix V, mounting of the servo control unit to the THS Blz. 48

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Appendix I, view through the tailcone access door

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Appendix II, right power control unit (left power control unit is opposite)

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Appendix III, servo control unit

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Appendix IV, mounting of the servo control unit to the elevator

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Appendix V, mounting of the servo control unit to the THS

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