flight controls

2012 March 14th

Flight Controls

Group 1Z

Thijs Buurmeijer Daniël Driessen Martijn van de Grift Mats Heij Luuk van der Kolk Mitchel Pappot Joost Scholtens Jordi Smit Benjamin Wever

Aviation Studies Flight Controls

Project group: Z 1

Table of Contents Summary ................................................................................................................................................. 3

Introduction ............................................................................................................................................. 4

Chapter 1 ................................................................................................................................................. 5

Theory .................................................................................................................................................. 5

1.1.1 Laws of aerodynamics ............................................................................................................ 5

1.1.2 Characteristics of an airfoil ..................................................................................................... 6

1.1.3 Airflow around an airfoil......................................................................................................... 7

1.1.4 Forces on the airplane ............................................................................................................ 7

1.2 Primairy flight controls ........................................................... Fout! Bladwijzer niet gedefinieerd.

1.2.1 Ailerons ............................................................................ Fout! Bladwijzer niet gedefinieerd.

1.2.2 Rudder ............................................................................. Fout! Bladwijzer niet gedefinieerd.

1.2.3 Elevator ............................................................................ Fout! Bladwijzer niet gedefinieerd.

1.3 Secondary Flight Controls ....................................................... Fout! Bladwijzer niet gedefinieerd.

1.3.1 Spoilers ............................................................................ Fout! Bladwijzer niet gedefinieerd.

1.3.2 Leading edge devices ....................................................... Fout! Bladwijzer niet gedefinieerd.

1.3.3 Trailing edge devices ....................................................... Fout! Bladwijzer niet gedefinieerd.

1.3.4 Trim devices ..................................................................... Fout! Bladwijzer niet gedefinieerd.

1.4 Requirements and regulations ............................................... Fout! Bladwijzer niet gedefinieerd.

1.4.1 Regulations ...................................................................... Fout! Bladwijzer niet gedefinieerd.

1.4.2 Requirements ....................................................................................................................... 17

1.5 Flight control comparison to size ........................................... Fout! Bladwijzer niet gedefinieerd.

1.5.1 Primary flight controls ..................................................... Fout! Bladwijzer niet gedefinieerd.

1.5.2 Secondary flight controls ................................................. Fout! Bladwijzer niet gedefinieerd.

1.6 Function Research ....................................................................................................................... 18

1.6.1 Input ..................................................................................................................................... 18

1.6.2 Conversion ............................................................................................................................ 18

1.6.3 Correction ............................................................................................................................. 19

1.6.4 Transportation ...................................................................................................................... 19

1.6.5 Amplify.................................................................................................................................. 19

1.6.6 Output .................................................................................................................................. 19

1.6.7 Feedback ............................................................................................................................... 19

1.7Summary ...................................................................................................................................... 19

Chapter 2 ............................................................................................................................................... 20

2.1 Boeing 737 NG ............................................................................................................................. 20

2.1.1 Ailerons Boeing 737 NG ........................................................................................................ 20

2.1.2 Spoilers/speed brakes Boeing 737 NG ................................................................................. 21

2.1.3 Flight laws Boeing 737 NG .................................................................................................... 22

2.1.4 Back-ups Boeing 737 NG ...................................................................................................... 22


Project group: Z 2

2.2 Airbus A320 ................................................................................................................................. 23

2.2.1 Primary flight controls Airbus A320 ..................................................................................... 23

2.2.2 Spoilers in an Airbus ............................................................................................................. 24

2.2.3 Flight control laws ................................................................................................................ 24

2.2.4 Airbus back-up ...................................................................................................................... 25

2.3 Differences between Airbus and Boeing ..................................................................................... 26

2.3.1 Vision of the manufacturer .................................................................................................. 26

2.3.2 Aileron and spoiler controlling ............................................................................................. 27

2.3.3 Flight control laws Boeing .................................................................................................... 27

2.3.4 Back-up ................................................................................................................................. 27

2.4 Pros and cons research ................................................................................................................ 27

2.4.1 Conventional system ............................................................................................................ 27

2.4.2 Fly-by-wire system ................................................................................................................ 27

2.5 conclusion .................................................................................................................................... 28

Chapter 3 ............................................................................................................................................... 29

3.1 Maintenance procedures ............................................................................................................ 29

3.1.1 Maintenance procedures Boeing 737 NG ............................................................................ 29

3.1.2 Maintenance procedures Airbus a320 ................................................................................. 30

3.1.3 Maintenance differences...................................................................................................... 30

3.2 Expenses ...................................................................................................................................... 31

3.2.1 General assumptions ............................................................................................................ 31

3.2.2 Airbus A320 .......................................................................................................................... 31

3.2.3 Boeing 737 NG ...................................................................................................................... 32

3.2.4 Comparison .......................................................................................................................... 32

3.2.5 Conclusion and recommendation ........................................................................................ 32

Bibliography ........................................................................................................................................... 34


Project group: Z 3

Summary The assignments, that was given by the direction of the ALA (Amsterdam Leeuwenburg Airline) to project group Z, is the description of the different systems between Boeing and Airbus. The differ-ences will be made for the Boeing 737NG and the Airbus A320. And a second assignment is a finan-cial overview of the maintenance costs of both Boeing 737NG and the Airbus A320. To accomplish the assignments there is a distribution of three chapters.

The first chapter is a description of the theories to explain getting and keeping an airplane into the skies. Theories that will be discussed are the law of continuity en Bernoulli’s equation. Furthermore, de primary and secondary flight controls are described. The primary flight controls are: the ailerons, rudder and elevator. The secondary flight controls are: the spoilers, leading edge devices, trailing edge devices and trim devices. To make a proper description of the flight controls and maintenance costs the demands are very important. There are two different demands: the demands of the direc-tion of the ALA or the requirements. And the laws or the regulations. The source of the regulations is Certification Specifications for large airplanes CS-25. Furthermore, in the first chapter a comparison is made between a large commercial airplane and a small plane. For this comparison the Cessna 172 is compared to a large commercial airplane so the differences between the two flight control systems can be explained.

In the second chapter there will be a closer look at one primary and one secondary flight control. The primary flight control are the ailerons and the secondary flight control are the spoilers. Also, there is a description of the following subjects: the operation of the primary and secondary flight controls, flight control laws and back-up systems. Airbus has flight control law because Airbus uses a fly-by-wire system which means that the airplane is controlled by computers, in opposite to Boeing be-cause Boeing uses a mechanically transfer between the control column and the flight controls. After describing these subjects it is possible to compare the fly-by-wire system of Airbus and the conven-tional system of Boeing. At last it is possible to make a conclusion about the two systems which one is preferred.

In the third and final chapter three maintenance procedures are described. The maintenance proce-dures are about the ailerons, elevator and the spoilers. For the ailerons and the elevator an opera-tional check is described and for the spoiler the lubrication of it. The description of the maintenance procedures are for both Airbus and Boeing the same, so it is possible to make a good comparison of the costs of these procedures. When these costs are known it is possible to display a financial over-view, also there is a comparison of the financial overview in ten years for both Airbus and Boeing. Now that the financial overview is displayed it is possible to make a conclusion and a recommenda-tion. From the financial overview can be concluded that the maintenance procedures of the Boeing 737 NG are less expensive than the Airbus A320. However, the fly-by-wire system uses control laws to prevent the pilot from making human mistakes and therefore makes it fertilely impossible to crash the airplane. Further is the fly-by-wire system lighter and the maintenance procedures are shorter because of the BITE. These features makes the Airbus A320 in our opinion the best option.


Project group: Z 4

Introduction In the first year of the study Aviation studies at the university of applied science, project group 1Z got an assignment from the low cost airline of the University of applied science, Amsterdam Leeuwen-burg Airlines (ALA) to write an advisory report for expanding their fleet of airplanes. The low-cost airline ALA wants to expand its fleet with a Boeing 737 NG or an Airbus A320. The assignment is to write an advisory report for the choice between a Boeing 737NG and an Airbus A320 to expand its fleet. The advisory report provides a financial overview between the operational costs for both flight control systems.

The advisory report is divided into three chapters. The general theory, flight control principles for a sports airplane and the function research (Chapter 1). The operations of the flight control systems are discussed for an Airbus A320 and Boeing 737NG. Just as the specific operations of the ailerons and spoilers for both systems (Chapter 2). At last, three maintenance tasks, usually carried out for both airplanes, are compared by time and costs for maintenance. Using the differences between the costs and time for maintenance will result in an advisory report for the choice between a Boeing 737 NG or an Airbus A320 (Chapter 3).

The most important literature used in the advisory report are the aircraft maintenance manual’s from the Boeing 737NG and the Airbus A320. Other literature is listed on the literature list on page 38. The advisory report is written on the basis of the plan of approach. For a complete list of all at-tachments, there is an attachment list after the report. Some of the attachments are: the project assignment, group information and the planning


Project group: Z 5

Chapter 1 Amsterdam Leeuwenburg Airlines (ALA) want to expand their fleet and have asked project group Z to evaluate the Boeing 737NG and the Airbus A320 and present which of the two aircrafts is the best option based on operational costs of their flight control system. To do so, a solid orientation phase is necessary, first the theory behind the airfoils, as well as lift and drag will be explained (1.1). In the following chapters, both the primary and the secondary flight controls will be explained (1.2 & 1.3). After doing the demands will be summed up (regulations and laws) (1.4). Paragraph (1.5) will com-pare the flight controls on commercial airplane (>5000KG) and a Cessna. In the last two paragraphs a function research will be conducted (1.6) followed by a summary (1.7).

Theory Before the flight controls will be explained a basic understanding of aerodynamics is needed. In order to understand basic aerodynamics, certain laws will be explained (1.1.1). In the following paragraph the characteristics of an airfoil will be explained (1.1.2). The effects an airfoil has on the airflow will be explained in (1.1.3) The last paragraph will explain the forces an airplane experiences inflight (1.1.4).

1.1.1 Laws of aerodynamics The full Law of Continuity is based on constant mass flow (formula 1).

Formula 1, mass flow

Because the mass flow is constant, the formula for the law of continuity is given in (formula 2).

Formula 2, law of continuity

Because there are no compressibility symptoms, the density will be equal, the reduced law of conti-nuity (formula 3).

Bernoulli’s equation

Formula 3, reduced law of continuity

The Bernoulli’s equation (formula 4) describes the behavior of a airflow along a streamline. Hereby the static and dynamic pressure can be determined at different places. Bernoulli’s equation only applies in the following conditions:

1. Incompressible air 4. Stationary flow

2. Ideal gas 5. Non viscous flow

3. Adiabatic

Formula (2) air density kg/m3 air speed m/s surface area m2

Formula (3) air speed m/s surface area m2

Formula 1

m = Formula (1)

m mass flow kg/s density kg/m3 speed m/s surface m2


Project group: Z 6

Formula 4, Bernoulli’s equation

1.1.2 Characteristics of an airfoil An airfoil is the cross-section of a wing (Figure 1), and has a leading (1) and trailing edge (2). The line that connects these both points is the cord line. The main camber line (3) is the center line between the upper and lower surface of the airfoil. The maximum camber is the maximum distance between the main camber line and the chord line. The maximum thickness is the biggest distance between the upper and lower surface. When the camber line lies above the chord line (Figure 2), the profile is defined as positive (1). When the camber line lies below the chord line the profile is defined as nega-tive (2). When both the camber line and the chord line coincide, the profile is defined as symmetrical (3). When a symmetrical profile is set under an angle of attack of 0˚, no lift will be created. A positive profile creates lift even with an angle of attack of 0˚. A negative profile creates negative lift with an angle of attack of 0˚

1 3 2

1 Leading edge 2 Trailing edge 3 Main camber line

Figure 1, cross-section of a wing

1 2 3

1 positive profile 2 symmetrical profile 3 negative profile

Figure 2, wing profiles

density kg/m3

speed at location one m/s g local acceleration of gravity m/s2 height at position one m

standard pressure at position one Pa

Formula (4)


Project group: Z 7

1.1.3 Airflow around an airfoil The main purpose of an airfoil is to generate lift. An airfoil is able to generate lift by creating a differ-ence in the pressure underneath and above the airfoil. According to Bernoulli’s equation when the air speed increases, the pressure decreases. This creates an over-pressure under the airfoil and an under-pressure above the airfoil. The angle of attack, airspeed and the shape of the airfoil determine the magnitude of the pressure difference. The air around the airfoil is able to flow in different ways (figure 3). At low speeds the air flow is laminair. Airflow layers close to the airfoil are slowed down to slow speeds due to friction between the air flow layers. This occurrence is called the laminar bounda-ry layer (1). With high speeds the air will move in vortices, this causes the flow lines to move in an irregular pattern (2). This is called a turbulent boundary layer. The point where the laminar boundary layer changes in to a turbulent boundary layer is called the turning point (3). In (figure 3) this turning point is shown.

The state of a boundary layer and the transition point dependents on the number gained from Reyn-olds equation. Reynolds equation is show below (formula 5).

Formula 5, Reynolds equation

1.1.4 Forces on the airplane During flight four types of forces (figure 4), lift (1), thrust (2), drag (3) and weight (4), influence the airplane. Lift and weight are each other’s opposite, the relation between these two forces determine whether the airplane is ascending or descending (1.1.4a). Thrust and drag are each other’s opposite, the relation between these two determine whether the airplane is accelerating or decelerating (1.1.4b).

Figure 4, flight forces

Reynolds equation Formula (5)

Re = Reynolds number (-) l = chord length (m) ρ = air density (kg/m3) µ= dynamic viscosity (Pa s) v = airspeed (m/s)

1. 1:Laminair flow

2. 2:Turbulent

3. 3: flow turning point

Figure 3, Airflow

1. Lift

2. Thrust

3. Drag

4. Weight

Lift

Weight

Thrust

Drag


Project group: Z 8

1.1.4a Lift and Weight The magnitude of the Lift depends on the angle of attack, the speed of the airplane relative to undis-turbed airspeed, the size of the wing and the characteristic of the wing. Weight is determined by the mass of the plane times the gravity acceleration. As the name would suggest depends the magnitude of this force on the total mass of the airplane. With these knowledge we are able to get (formula 6) and (formula 7).

Formula 6, lift Formula 7, weight

1.1.4b Thrust and Drag The thrust is the forward pushing force created by the engines of the airplane. During flight the air-plane will experience induced and parasitic resistance, the total amount of these resistance is known as drag. Induced resistance is the resistance an airplane experiences as side effect of the pressure difference above and under the air foil. As air always tends to flow from high to low pressure areas it creates lift around the airfoil. Wings are not endless, vortices emerge at the wingtip because of this effect. These vortices cause induced resistance. This induced resistance is higher when the airplane is flying at low speeds and reduces when flying at high speeds. Parasitic resistance is the resistance the airplane experiences because of the friction between the air and the fuselage. Because the parasitic resistance can be harmful to the airplane it is best to keep this resistance as low as possible. The par-asitic resistance can be kept low by making the airplane streamlined. The drag can be calculated with formula 8.

Formula 8, Drag

1.2 Primary flight controls This section contains information about the primary flight controls. In the first paragraph the ailerons are explained (1.2.1). In the following paragraph the rudder is described (1.2.2). In the last paragraph information about the elevator is given (1.2.3).

1.2.1 Ailerons The following will be explained in this section: the function of the aileron (1.2.1a), the location (1.2.1b), the operation of the aileron (1.2.1c), followed by the side effects (1.2.1d) and in the last paragraph the different types of execution will be explained (1.2.1e). The Cessna 172, has been used throughout this section as an example to describe the aileron.

Lift formula formula (6) Weight formula Formula (7)

m

L = Lift (N) Weight = the weight (N) CL = lift coefficient g = gravity acceleration (m/s2) ρ = the density (kg/m3) m = total mass of the airplane (kg) v = airspeed speed (m/s) s = surface (m2)

Drag formula Formula (8)

D= Drag (N) v = airspeed speed (m/s) CD= drag coefficient s = surface (m2) ρ = the density (kg/m3)


Project group: Z 9

1.2.1a Function In order to change the course of the airplane, the vertical forces have to be altered. Newton's first law cites: If an object is at rest or at constant velocity, all forces are equal to zero. So in order to change the current heading, a second force is re-quired. This can be done using the ailerons. When an airplane is in a straight and level flight (Figure 5), there are two vertical forces: the lift (1) and gravity (2). If the control column is turned to the right, the right aileron deflects up and the left aileron deflects down. This creates different forces: total lift which is separated into two forces the vertical component and the horizontal component. Of which the vertical component is the opposite to gravity. The horizontal component of the lift pulls the airplane towards to turn. The horizontal component can also be defined as the centripetal force, which is opposite to the centrifu-gal force.

1.2.1b Location The ailerons are located at the trailing edge of each wing. On large airplanes (>5000KG) there are four ailerons, two on each wing. Which aileron an airplane will use depends on the airspeed of the airplane. The inner ailerons are used when flying at high airspeeds, when an airplane flies at high speeds the forces on the wings are very high. To make sure that the ailerons will not get damaged, the aileron closest to the root of the wing is deployed, at this point the aspect ratio (AR) is higher than at the tip, and can therefore withstand higher forces. For low airspeeds the outer ailerons are deployed, creating a bigger momentum around the longitudinal axis.

1.2.1c Operation In (Figure 6) the mechanical transmission is shown. When turning the control stick the ailerons will deflect (1). The deflection of the ailerons is completely mechanical in a Cessna (2). First the input goes from the control stick to the “control U” (3). Using pulleys, gears, chains, cables and push/pull tubes movement from the stick is deflected to the ailerons(4). Push/pull tubes work together in op-posite direction, this is to ensure that both ailerons never go up or down at the same time.

Figure 6, mechanical transmission

1.2.1d Side effects A side effect of the ailerons is adverse yaw. when turns, the ailerons work opposite to each other. The wing with the aileron in downward position produces more lift then the aileron in upward posi-tion. This results in a yawing motion towards the wing which experiences an increase in drag.

Figure 6 Ailerons Control System

11.Lift

22.Gravity 1

2

1

3

4

2

1. Stick

2. Ailerons

3. Control “U” 4. Cables

Figure 5, lift and gravity


Project group: Z 10

1.2.1e Types of execution To prevent adverse yaw there are two types of ailerons.

1. Frise-type ailerons

2. Differential ailerons

Ad1 Frise-type ailerons Since the aileron that deflects up creates lift and therefore no induced drag compared to the down going aileron. On figure 7 frise-type ailerons (1) the up going aileron creates induced drag this is achieved by moving some of the aileron down into the airflow (2). This will then balance the drag on both ailerons. Thus there is no adverse yaw anymore.

Figure 7 Frise-Type Ailerons

Ad2 Differential ailerons Differential ailerons (Figure 8) can also be used; the down going aileron (1) creates lift and therefore induced drag. To even everything out, the up going aileron (2) deflects more than the down going aileron. Again this should help keep the two wings generating a similar amount of drag.

Figure 8, differential aileron

1.2.2 Rudder In this chapter the function of the rudder on a small aircraft (Cessna 172) will be explained. The func-tion of the rudder on a small aircraft is similar to commercial aircraft. The function of the rudder will be explained in section (1.2.2a). The operation of the rudder will be explained in section (1.2.2b). In section (1.2.2c) will be explained how to the rudder is controlled by the pilot. The side-effects (1.2.2d) of using the rudder en the different ways of execution of the rudder (1.2.2e) will be ex-plained.

1.2.2a Function of the rudder In small aircraft the rudder is used to steer on the ground and to yaw while flying (Figure 9). Yawing means turning the airplane around the Z-axis (1). The bigger the surface of the rudder the more in-fluence it has on yawing. When the airplane banks there will be more lift produced at one wing then the other (as explained in the previous paragraph (1.2.1)). The airplane becomes unstable because of this effect. The rudder insures that the aircraft is properly flying a turn during the maneuver. The rudder is also used to compensate for crosswind when landing. In commercial airplanes the rudder is equipped with a yaw damper. This system uses the rudder to counter-act the dutch roll and side to side movement of the airplane (Figure 10). The airplane (1) moves with its nose in the shape of a eclipse (2) while flying because of the airflow effects. This moving motion of the airplane is called the Dutch roll.

1

1. Frise-type aileron 2. Aileron in airflow 2

2 1. Down going aileron 2. Up going aileron

1


Project group: Z 11

1.2.2.b. Location Rudder The rudder (Figure 11) is part of the tale of the airplane and is molted to the vertical stabilizer (1). The vertical stabilizer is attached to the fuselage (2) of the aircraft. The rudder also provides stability to the airplane. The rudder has a symmetrical shape and will not create any drag or lift when it is aligned with the vertical stabilizer. The rudder in commercial airplane is made out of two pieces. The lower rudder (3) is used when the airplane flies with high speed. The upper rudder (4) and lower rudder together are used to ma-neuver the airplane when it travels with lower speed. Both rudders are capable of maneuvering separately from each other. Therefore the upper or lower rudder can be used while the computer system is cor-recting with the other rudder.

.2.2b Operation of the rudder In small sports aircraft like a Cessna, the controls are mechanical (Figure 12). The rudder is attached on the vertical stabilizer with joints so the rudder (1) can be moved. The rudder can be moved from side to side. The rudder controls (2) are located in the cockpit. There are two panels one for the right and one for the left feet, the left panel makes the airplane yaw left and the right panel makes the aircraft yaw to the right. The panels are connected by a bar. Two metal wires are attached on the bar. Each metal wire is connected to one side of the rudder. In between the panels and rudder the metal wires run over pulleys.

1.2.2d Side-effects of the rudder When the rudder is used it will create a momen-tum around the Z-axis of the airplane, the airplane will also roll. The outer wing catches wind, going up, increasing relative airflow thereby producing more lift.

1.2.2e Types of execution Rudder The rudder can be controlled in various ways. The way the rudder is controlled depends on the size and type of aircraft. Smaller aircraft are more likely to use a mechanical system to control the rudder. In commercial aircraft the rudder can be controlled mechanically with hydraulic. Or the rudder can be controlled by a computer system that makes a hydraulic piston move to control the rudder. This system is called fly-by-wire and is commonly used in modern airplane.

1.2.3 Elevator In this paragraph, the elevator is discussed. The function of the elevator is explained in paragraph 1.2.3a. In paragraph 1.2.3b, the location of the elevator is defined. How the elevator works is de-

1

2

3

1: Z-axis

2:X-axis

3:Y-axis

Figure 9, axes

1 2

1: airplane 2:roll movement

Figure 10, dutch roll

4 3 1 2

1: Vertical stabilizer 2: Fuselage 3: Lower rudder 4: Upper rudder

Figure 11, the rudder

Figure 12, rudder controls

2 1

1: rudder 2: rudder controls


Project group: Z 12

scribed in paragraph 1.2.3c. The side-effects of the elevator are reported in paragraph 1.2.3d. In the last paragraph (1.2.3d) the types of execution are described.

1.2.3a Function The elevator is designed to produce a pitching movement by the airplane. A pitching movement is a rotation around the lateral axis, pitch changes the angle of attack. Changing the angle of attack in-creases or decreases the altitude. When descending, the elevator points downwards, when the ele-vator is in this position the lift on the elevator increases, lifting the tail up and pointing the nose downwards. When pitching up, the elevator points upwards, this will create a negative lift, pushing the tail of the aircraft down, making the nose point up. When flying level, the wings have a positive lift. In order to create balance, the elevator will have to oppose this force. Therefore torque of these forces has to be equal to each other.

1.2.3b Location The elevator is located at the tail (Figure 13) of the airplane (1). The elevators (2) are hinged to the trailing edge of the horizontal stabilizer (3). The elevator consists of two parts. These two parts are not independent.

1. 2. 3.

1. Tail 2. Elevators 3. Horizontal stabilizer

1.2.3c Operation When pulling the steering column backwards, the cable which is connected to the steering column will be pulled. This cable is located at the top of the right strut. Because the cable is moving towards the steering column, the top of the rod will move to the left. This will cause the bottom of the rod, to move to the right. The push-pull rod is attached to the bottom of the rod, which moves in the oppo-site direction. This will cause the elevator to move upwards. In order to prevent the elevator to be affected by the aero dynamical forces, there is a down spring installed in order to provide a counter force. During the flight there will be an aero dynamical pressure on the elevators. Because of these forces, the spring will stretch in and out.

1.2.3d Types of execution Like the aileron and the rudder, there are different kinds of elevators. On small sports aircraft like the Cessna 172, the elevator is controlled mechanically, as described in paragraph 1.2.3b. In commercial airplanes the elevator is powered by an advanced hydraulic system.

1.3 Secondary Flight Controls This section contains information about the secondary flight controls. In the first paragraph the spoilers will be explained (1.3.1). In the second paragraph the leading edge devices will be described (1.3.2). In the following paragraph the trailing edge devices will be described (1.3.3). In the last para-graph the trim devices will be explained (1.3.4).

1.3.1 Spoilers In this chapter the functions of spoilers on a small aircraft will be explained. The function of the spoilers on small aircraft is the same as on big (>5000kg) aircraft. In paragraph (1.3.1a) the function

Figure 13, elevator location


Project group: Z 13

of the spoilers will be explained, the following paragraph (1.3.1b) will explain and describe the placement of the spoilers. Paragraph (1.3.1c) will illustrate the spoilers operation.

1.3.1a Function Spoilers (Figure 14) are panels mounted on top of the wing, spoilers can be used together with ailer-ons when turning. For example, when turning right, the right spoiler will deploy and increase drag on the right wing. Because of this the right wing will drop and the aircraft will start turning. Small aircraft can also deploy spoilers to increase drag and reduce lift, by doing this the glide path will be greatly increased. Commercial aircraft will mainly use spoilers for landing. Commercial aircraft use spoilers to reduce speed when on ground, deploying the spoilers will increase air resistance and shift the weight of the airplane from the wings to the landing gear. It is procedure to slow the aircraft down as much as possible with the spoilers, before using the brakes, this is done to preserve the brakes from wearing.

1.3.1b Location The spoilers are mounted panels on the top surface of the wing, when the spoilers are deployed the spoilers come up, right into the airflow, and spoil the airflow increasing the drag on the airplane. When the airflow is spoiled, the boundary layer will let loose and. When the boundary layer isn’t attached to the airfoil anymore, the lift will reduce, this is very useful while landing a big airplane. This prin-ciple also applies to turning using the Figure 14, spoilers

spoilers. 1.3.1c Operation Spoilers can be deployed by pulling a lever in the cockpit (Figure 15), this lever will allow the pilot to select if he wants to fully ex-tent the spoilers, or just halfway. When the spoilers are fully ex-tended, for example when landing, the spoilers won’t automati-cally retract. A red ‘’SPEED BRAKE STILL OUT” indicator will start flashing to indicate the spoilers are still deployed. In order to de-ploy the spoilers, hydraulic valves need to be activated, this is all done automatically. When turning, the spoilers are automatically deployed.

1.3.2 Leading edge devices In this section the leading edge devices are discussed. The functions of these devices are explained in paragraph (1.3.2a). In the next paragraph the leading edge devices will be explained (1.3.2b). The third paragraph the operation of the leading edge devices will be explained (1.3.2c). And in the last paragraph the different types of leading edge devices are discussed (1.3.2d).

1.3.2a Function The leading edge devices can be found on a few different types. Leading edge devices extend the front of the wing. A leading edge device is also a way to increase the curvature of a wing. The trailing edge devices can increase the camber, nose radius and the surface of the wing. Flaps are on the trail-ing edge. As a result of the leading edge devices, critical angle of attack increases.

1.3.2b Placement The leading edge devices (Figure 16) (1) can be found at the front of a wing.

1. Spoilers

Figure 15, speed brake lever


Project group: Z 14

1.3.2c Operation The leading edge devices are operated hydraulically, and are controlled automatically by the auto slat computer, or manual. This system is controlled with several switches or levers in the cockpit. Three different settings are available: 1. Up, 2. 1/2 Extended or 3. Fully extended. Leading edge de-vice are automatically deployed if an emergency occurs (stall for example). Leading edge devices are only used during the landing and takeoff. Leading edge devices are only present on commercial air-planes.

1.3.2d Types of execution There are different types of leading edge devices:

1. Slats

2. Krueger flaps/slats

3. Fixed slots

Ad 1 Slats are curvature valves at the leading edge of an airplane’s wing. Extended slats enhance the lift coefficient; this allows a higher angle of attack even with a lower airspeed. The slats increase critical angle of attack. Ad 2 The difference between Krueger flaps and slats is that the main wing upper surface and its nose are not changed when using them. Instead, part of the lower wing is rotated out in front of the main wing leading edge. The Krueger flaps hinge forwards from the under surface of the wing. Ad 3 A leading edge slot is an aerodynamic feature of the wing of some aircraft to reduce the stall speed and ensure low-speed handling qualities. A leading edge slot is a span-wide gap in each wing, allow-ing air to flow from below the wing to its upper surface.

1.3.3 Trailing edge devices In this section the trailing edge devices are discussed. The functions of these devices are explained in paragraph (1.3.3a). In the subsequent paragraph the placement of the trailing edge devices will be discussed (1.3.3b). In paragraph (1.3.3c) the side effects of the trailing edge devices are discussed. In the final paragraph the different types of flaps are discussed (1.3.3d).

Figure 16, leading edge devices

1. Leading edge devices


Project group: Z 15

1.3.3a Function Trailing edge devices are usually found in the form of flaps. Flaps are used to increase lift at low air-speeds. An extended flap increases the camber which provides an increasing lift coefficient, and re-ducing the stall speed. When landing, the flaps are fully deployed. Besides increasing lift, the flaps will also increases drag. This ensures that the flaps help the airplane slowing down gradually. This offers advantages in the approach.

1.3.3b Placement As the name suggests, the trailing edge devices (flaps) (figure 17) (1) are molted to the trailing edge of a wing. The flaps can be found on both wings next to the ailerons.

1. 1. Trailing edge device

1.3.3c Operation The flaps are controlled by pulling a lever in the cockpit. This lever is divided into several degrees.

1.3.3d Side-effects A side effect when using the flaps is a decrease in aircraft pitch angle which improves the view from the cockpit of the runway over the nose of the aircraft during landing. However the flaps may also cause the nose to pitch up, depending on the type of flap and the location of the wing. Another side effect is that the flaps may decrease the effectiveness of the brakes since the wing is still generating lift, because there will be less weight on the landing gear. That is why, in most circumstances, the pilot will retract the flaps as soon as possible.

1.3.3e Types of execution There are different types of flaps (figure 18). Flaps that are used in an airplanes depends on several aspects as size, maximum airspeed and the complexity of the aircraft.

1. Plain flap 2. Split flap 3. Slotted flap 4. Fowler flap

Ad 1 When using plain flaps(1) the rear portion of the airfoil rotates downwards on a simple hinge mount-ed at the front of the flap. This type of flap is usually found on smaller airplanes. Ad 2 With split flaps (2)the rear portion of the lower surface of the airfoil hinges downwards from the leading edge of the flap, while the upper surface stays immobile. Ad 3 A gap between the flap and the wing forces high pressure air from below the wing over the flap forc-ing the airflow to remain attached to the flap, increasing lift compared to a split flap. Any flap that allows air to pass between the wing and the flap is considered a slotted flap (3).

Figure 17, trailing edge device


Project group: Z 16

Ad 4 A split flap (4) that slides backwards flat, before pointing downwards, thereby increasing chord line and camber. It must slide backward before lowering. This type of flap is still used in a widespread of modern aircraft, often with multiple slots.

1. Plain flap 2. Split flap 3. Slotted flap 4. Fowler flap

1.3.4 Trim devices In this section the trim tabs of an small airplane will be described. In the first paragraph the function of the trim devices will be explained (1.3.4a). In the second paragraph the location of the trim tabs will be discussed (1.3.4b). In the following paragraph the operation of the trim tabs will be explained (1.3.4c). In the last paragraph the three different types of trim devices will be discussed (1.3.4d). 1.3.4a Function Trim devices are used for trimming and balancing the airplane in flight and to reduce the force re-quired to maneuver the primary flight control surfaces. This is accomplished by branching the tab in the opposite direction of the primary control surfaces. The force of the airflow striking the tab causes the main control surface to branch to a position that will correct the unbalanced condition of the airplane. Elsewhere reducing the force required to maneuver the primary flight controls. When using the trim, fuel efficiency increases by reducing drag.

1.3.4b Location A trim tab is a small, adjustable hinged surface attached to the trailing edge of the aileron, rudder, or elevator control surface.

1.3.4.c Operation In many airplanes the trim tabs can be adjusted by controls in the cockpit although in some of the older airplanes the trim tabs can only be adjusted when on the ground. Those which can be adjusted from the cockpit provide a trim control wheel. To trim the airplane, the trim wheel must be moved into the desired direction. The position in which the trim tab is set can usually be determined by ref-erence to a trim indicator that is located in the cockpit.

1.3.4d Types of execution There are different types of trim devices: the adjustable trim, the solid trim and the stabilo trim. The most common trim is the adjustable trims. Another trim device is the solid trims. This device can be found on small propeller airplanes. The solid trims prevent the airplanes to turn around its X-axis. The last type of trim device, the stabilizer trims, can be found in modern aviation. These devices are adjustable on the back-side of the airplanes Sometimes there is trimmed by means of moving the fuel in the tanks. Which the airplane center of gravity will shift back.

1.4 Requirements and regulations This paragraph describes the requirements and regulations used in the CS25. The regulations are described in paragraph (1.4.1). The requirements given by the client are described in paragraph (1.4.2).

Figure 18, flaps


Project group: Z 17

1.4.1 Regulations The regulations for flight control systems set by EASA in the CS25 are shortly described in this para-graph. The first part of this paragraph explains general regulations for all airplanes falling under the CS25 regulations (1.4.1a). The second part of this paragraph explains some regulations for airplanes using cable systems (1.4.1b). 1.4.1a General regulations Adjustable stabilizers must have stops at the limit for the maximum deflection the airplane is de-signed for. There should not be any interference between the tail surfaces in their extreme positions. Each control system must operate smoothly for the function it is designed for. Each element of a flight control system must be designed to minimize the probability of incorrect assembly. The air-plane must be able to fly safe after sustaining one of these errors: a likely single failure, a likely com-bination of failures and a jam in a control position. The airplane must still function properly when all engines fail. Every control system must have stops to limit the range, a stop must be located so that wear does not affect the controls. A trim control must be designed so an abrupt operation can be prevented. The direction of the trim control must be shown according to the airplanes position. The trim control system should stay in a constant fixed position during flight. There must be a device to prevent damage of the control systems and control surfaces from gusts of wind. The device must disengage when the primary flight controls are operated and limit the operation to warn the pilot when starting the take-off. The device should not be able to engage during flight. If parts of the con-trol system are loaded to the maximum, it must be free of jamming, excessive friction and excessive deflection. Every part of the control system must be designed to prevent, jamming, friction, interfer-ence from cargo and passengers, loose objects and freezing or moisture. Lift device controls must be placed so that they can be operated at any time, en-route, approach or landing position. These posi-tions should be indicated. Lift and drag device controls must be designed so inadvertent operation is unlikely. The lift device control must be able to be retracted from fully extended position during steady flight at maximum continuous engine power. The position of each lift and drag device with separate controls must be indicated. When malfunctions or unsymmetrical operations occur, it must be indicated. If extension of the lift and drag controls beyond landing position is possible, the control must be clearly marked to identify the range of extension. It is not allowed to fully extend the flaps and slats on one side and fully retract them on the other side, they must be synchronized by a me-chanical interconnection or by approved equivalent means. An aural warning must sound in the cockpit in the first part of the take-off, when flaps or slats are not in the approved range for take-off or when the spoilers, speed brakes or trim devices are in an unsafe take-off position. This should sound continuous until: the configuration is safe to take-off, the take-off is terminated, the airplane is rotated for take-off or the warning is manually silenced by the pilot. A dual control system must be designed so that force on the control stick of each pilot is between 334N and 445N maximum for the aileron and between 834N and 1112N maximum for elevator. The minimum force for the aileron is 178N and 445N for the elevator. Secondary controls must be designed for the maximum forces a pilot is likely to apply.

1.4.1b Regulations for cable systems Every part of a cable system must be approved. Cables smaller than 3.2 mm cannot be used in the aileron, elevator and rudder systems. Cable tension must not be able to change hazardous while operating. The cable must not be able to rub against the sides of the pulley. Guards must be placed close on the pulley to prevent misplacement of cables. Fairleads must not be able to change the ca-ble direction more than three degrees. It should be able to inspect the cable system visually. Joints that are subjected to angular motion should have a safety factor of 3.33 taken from the softest mate-rial used as a bearing. Exception to this are ball and roller bearing systems. The safety factor for joints in cable control systems is 2.0.

1.4.2 Requirements Amsterdam Leeuwenburg Airlines (ALA) want to expand their fleet and has asked project group Z to evaluate the Boeing 737NG and the Airbus A320 and present which airplane is the best option based


Project group: Z 18

on the operational costs of their flight control system. A set of requirements is made by the client to make sure this is done properly. The requirements are: the system must be checked and apply to the standards set by the law (1.4). The report presented to ALA must contain a clear picture of the opera-tional costs involved by using three important maintenance tasks (3.1). Both the methods and differ-ences of the flight controls used in the aircrafts should be explained (1.5).

1.5 Flight control comparison to size In this paragraph an overview of the difference between the flight controls of a big commercial and a small airplane will be presented. For this overview the Airbus A320 and the Cessna 172 are used. In the first sub paragraph the primary flight controls will be explained (1.5.1). in the last sub paragraph the secondary flight controls are described (1.5.2).

1.5.1 Primary flight controls The primary flight controls are: the ailerons, elevator and the rudder. The ailerons of the Cessna 172 are large in relation to the size of the plane. On the Airbus A320, the ailerons consist of two parts, the ailerons of the Cessna 172 consist of just one part. The elevators on both planes are trimmed differ-ent. The Airbus A320 has two elevators at each side of the horizontal stabilizer while the Cessna 172 has only one elevator on both sides. The rudder consists of two parts on the Airbus A320, the rudder of the Cessna 172 consists of just one part. The rudder on the Airbus A320 is not used normal flight conditions, but controlled by the yaw-damper.

1.5.2 Secondary flight controls The secondary flight controls are: the spoilers, trim devices, leading- and trailing edge devices. The spoilers consist of: speed brakes, roll spoilers and lift dumpers, but are only build on commercial airplanes. The trim devices used on the Airbus A320 control the angle of the horizontal stabilizer. The trim devices used on the Cessna 172 control the elevator trim tab, which is located on the elevator. The Airbus A320 contains multiple trailing edge devices. The Cessna 172 uses just one flap at each wing. The control of the flaps, controls the flaps and slats simultaneously. The Cessna 172 does not have leading edge devices (slats).

1.6 Function Research The flight control system consists of procedures, when these procedures are completed a result will follow. These procedures are described in figure 19, the procedures are: input (1.6.1), conversion (1.6.2), correction (1.6.3), transportation (1.6.4), amplify (1.6.5), output (1.6.6) and feedback (1.6.7).

1.6.1 Input The input is movement of the controls. Three flight controls can be operated: the rudder, the eleva-tor and the ailerons.

1.6.2 Conversion The input needs to be converted to the proper signal in order to guide it to the transport system.

Input Conversion Correction Transportation Amplify Output Feedback

Figure 19, function research


Project group: Z 19

1.6.3 Correction If the input is converted it is possible that there are a few small errors in the data. To tackle these small errors, the signal has to be corrected before it can be transported.

1.6.4 Transportation The signal that just has been corrected is transported.

1.6.5 Amplify After transportation, the signal has to be amplified because the signal has to travel a certain distance. If the signal is not amplified, a weak signal will reach the output which results in a lower result.

1.6.6 Output The converted, corrected, transported and amplified signal reached the flight controls this will result in a output: movement of the flight controls.

1.6.7 Feedback After the output, the flight controls will give a feedback, and respond, so that a new signal can make a output.

1.7 Summary The principle of flight controls are based on the theory of aerodynamics and physics. In particular the continuity law and the Bernoulli equation. With these laws the airspeed and air pressure can be measured on different places of an airfoil, this information is very important to the flight characteristics of the airfoil. There are primary and secondary flight controls on an airplane, with these controls it is possible to control the airplane. Ailerons, elevator and rudder are the primary flight controls. Leading- and trailing edge devices, spoil-ers and trim- devices are the secondary flight controls. The aileron creates lift on one side of the wing and drag on the other side, this makes it possible to make a turn. The elevator is designed to produce a pitching move-ment. The rudder is used to steer on the ground and to yaw while flying. The leading and trailing edge devices are able to change the airfoil shape, which changes the characteristics of the airfoil. The spoilers in particular are used to reduce speed, this helps to make a turn and to decrease the altitude. The trim is used to reduce the force a that has to be put on the steering column. The flight controls has to comply with the legal regula-tions and the requirements of ALA. Hereafter a comparison is made between a small and a commercial air-plane. In the end a function research has been made, to give an impression on how the input results in an out-put.


Project group: Z 20

Chapter 2 In chapter two the flight control systems of the Boeing 737 NG (2.1) and the Airbus A320 (2.2) are described then the flight control systems of both airplanes will be compared (2.3). After that are the pros and cons (2.4) of both airplanes given. In the last paragraph a conclusion is made (2.5) of both flight control systems.

2.1 Boeing 737 NG Boeing uses a hydraulic system to power the flight controls. The primary and secondary flight con-trols are powered in a different way than with the fly-by-wire system. To explain the differences in primary flight controls and the secondary flight controls, the ailerons (2.1.1) and the spoilers (2.1.2) are described. Boeing also uses a different philosophy on how an airplane is controlled this will be explained in the flight controls laws (2.1.3). In the last subparagraph the back-up systems of Boeing are explained (2.1.4).

2.1.1 Ailerons Boeing 737 NG In appendix IV the roll control of the Boeing 737NG is displayed. To explain the movement of the ailerons the following steps occur: input (2.1.1a), conversion (2.1.1b), transportation (1) (2.1.1c), transportation (2) (2.1.1d), amplify (2.1.1e), output (2.1.1f). An overview of the aileron control sys-tem is shown in figure 20.

2.1.1a Input The input is the movement of the control column. The first officer and the co-pilot are both able to operate three flight controls with the control column, these are: the rudder, the elevator and the ailerons. To operate a roll, the control column is moved to the left or right. The input is send to the Aileron Transfer Mechanism (ATM).

2.1.1b Conversion Figure 2.2.1 shows the control column transfer mechanism. From the control column (1) the signal is send to the ATM (2), it converts a vertical movement into a horizontal movement is done by cables (3). Both control columns are linked, that is why the two columns make the same movement. If the aileron system jams, it is possible to operate both ailerons and spoilers separately. The left control column operates the ailerons and the right the spoilers.

Figure 20, Control column transfer mechanism

1.1.

1

1

1

1.Control Column 2. ATM 3. Cables

1

1

2

1

3

1


Project group: Z 21

2.1.1c Transportation (1) From the ATM a signal is transferred to a feeling and centering mechanism which causes the control column to rotate and redefines the aileron neutral position.

2.1.1d Transportation (2) From the ATM there is transportation to the PCU’s. The transportation from the ATM to the Power Control Units (PCU’s) is achieved hydraulically.

2.1.1e Amplify After transportation, the signal has to be amplified because the signal has to travel a certain distance. If the signal is not amplified, a weak signal will reach the output which results in a lower outcome. The amplifying is done by the PCU’s, there are two PCU’s they are powered by two different hydrau-lic systems: A and B. If these two systems fail there is a back-up system that provides hydraulic pres-sure.

2.1.1f Output The last stage of the roll is the output. From the PCU’s there are cables to the ACQ or Aileron Control Quadrant, the ACQ only can move horizontally, to move the ailerons vertically a transfer is achieved by cables. The result is a movement of the ailerons in cooperation with the air spoilers.

2.1.2 Spoilers/speed brakes Boeing 737 NG In the following segment the placement and the use of hydraulic systems of the spoilers on the Boe-ing 737NG is explained (2.1.2a). The way the speed brakes are operated is explained in (2.1.2b).

2.1.2a Placement and hydraulic systems Spoilers on a Boeing 737 NG are split up into the flight spoilers (for use during flight) and ground spoilers, these are used to slow the airplane down during land-ing. On a Boeing 737 NG there are four ground spoil-ers, two on each wing, and four flight spoilers. Both ground and flight spoilers are deployed using hydrau-lic systems: systems A and B. Each hydraulic system is dedicated to a different set of spoilers, this is done to provide isolation. This way, in case of emergency, ground or flight spoilers can still be operated sym-metrically. Hydraulic system A for example, is dedi-cated to the ground spoilers. When hydraulic system A seizes to work, and hydraulic system B is still opera-tional, instead of four spoilers on both wings, only two will come out (figure 21). This will decrease the effectiveness, but the pilot will still be able to land the plane safely. Figure 21, spoilers hydraulics

2.1.2a Input/operation When the ‘’Speed brakes’’ lever in the cockpit is pulled, all the spoilers will be deployed (both ground and flight spoilers) when the airplane is still in the air, only the flight spoilers will deploy. When the speed brake lever is pulled in midflight, the ground spoilers will not deploy. This is because the con-trol hydraulic valve to the ground spoilers (hydraulic system A) is blocked as long as the right main landing gear is not touching the ground. However, pulling the speed brake lever in midflight will de-ploy the flight spoilers, this will greatly increase the roll rate. Pulling the lever past the ‘’flight detent’’ point is restricted during flight.


Project group: Z 22

2.1.3 Flight laws Boeing 737 NG The Boeing 737-NG does not have flight control laws such as the Airbus A320. This is because move-ments of the control column reach the flight control actuators mechanically. This means that the movements of the control columns are not restricted by flight control computers.

2.1.4 Back-ups Boeing 737 NG To guarantee safety on board a Boeing 737NG there are many back-up systems. For the flight con-trols there are different kinds of back-up. There are back-ups in the hydraulic system (2.1.4a) and there are back-ups for the flight controls (2.1.4b).

2.1.4a hydraulic back-ups Boeing uses a hydraulic system to power the flight controls. This system consists for safety reasons out of three independent systems: system A, system B and the stand-by system. System A and B are very similar they both power the flight control but the systems work independently from each other in case of a malfunction in one of the system. The systems are protected from leaking by hydraulic fuses. These hydraulic fuses close the pipes if there is a sudden increase in the flow, most likely caused by a leak. The hydraulic fuses are placed before the brake system, L/E flap/slat extend/retract lines, nose gear extend/retract lines and the thrust reverser pressure and return lines.

If system B is loses hydraulic pressure through failure of the hydraulic pump is it possible to increase the hydraulic pressure by using the PTU (Power Transfer unit). The PTU is able to increase the hy-draulic pressure of system B by using the hydraulic pressure of system A without mixing the fluids.

The stand-by system is the back-up system that is used in case that both systems A and B are defect. This system is much smaller than systems A and B. The stand-by system only powers the rudder, thrust reversers and the leading edges flaps/slats.

2.1.4b back-up flight controls Almost all flight controls are powered by both hydraulic system A and B in case one of the systems malfunctions. The primary flight controls are: 1. Ailerons 2. Elevator 3. Rudder Ad 1 The ailerons are normally controlled by the control wheel. If the control wheel malfunctions, there is another control wheel that controls the ailerons. The ailerons can also be moved with the aileron trim switches. The aileron trim switches can be moved right or left but must be moved simultaneous-ly in order to work. The aileron trim sends an electrical signal to the aileron Feel and Centring Unit this changes the ailerons and moves the control wheel to the same position as the aileron trim switches. If the control wheel separates more than ten degrees the spoilers will deploy.

Ad 2 The elevators are interconnected and powered by both hydraulic systems A and B. If these systems malfunction it is still possible to control the elevator manually. If the elevator jams the stabiliser trim should still be available. The elevator contains a computer named the feel computer. If one of the computer systems malfunctions there will be a warning light activated in the cockpit. The feel com-puter is able to switch to another system that still works.

Ad 3 The rudder is powered by both hydraulic system A and B. These hydraulic systems powers the PCU (Power Control Unit) which controls the rudder. The PCU is able to move the rudder when there is at least one hydraulic system working. When both system A and B do not work properly there is a stand-by system. The stand-by system is an individual hydraulic system that powers a stand-by PCU.


Project group: Z 23

With this stand-by system it is the still possible to use the rudder when the pilot needs to fly manual-ly.

2.2 Airbus A320 Airbus uses a fly-by-wire system to control the flight controls. This affects the way the primary and secondary flight controls are powered. To explain the differences in primary flight controls and the secondary flight controls, the ailerons (2.2.1) and the spoilers (2.2.2) are described. Airbus uses a different philosophy on who is in control of the airplane, this will be explained in the flight controls laws (2.2.3). In the last paragraph the back-up systems of the Airbus will be explained (2.2.4)

2.2.1 Primary flight controls Airbus A320 For the flight controls of an Airbus A320, the ailerons and the spoilers are discussed. After this para-graph (2.2.1a) the differences between the conventional system of Boeing and the fly-by-wire system of Airbus are described. In paragraph (2.2.1b) the differences are followed by a pros and cons re-search.

2.2.1a Fly-by-wire The roll control on an Airbus A320 is provided by one aileron on each wing. The ailerons deflection is about 25 degrees. The Airbus A320 is fitted with a fly-by-wire flight control system. This means that the mechanical linkage between the control column and the control surface is replaced by electrical wires. To do this the Airbus A320 has a very sophisticated computer system. The airbus uses seven primary flight control computers. Any deflection of the sidestick is detected by computer sensors. The sensors determines the amount of deflection, or movement, needed in the control surfaces and is send to hydraulic actuators which moves the flight controls.

2.2.1b Ailerons Airbus A320 In appendix 3 the roll control of the Airbus A320 is displayed. To explain the movement of the ailer-ons the following steps occur: 1. Input 2. Conversion 3. Correction 4. Transportation 5. Amplify 6. Output Ad 1 The ailerons (1) are controlled in two different ways. Manual, using the sidestick (2) or automatically by using the autopilot. The sidestick has a priority push-button to overrule the autopilot when neces-sary. When both sidesticks are active, the average deflection of both sticks is used for the input. The autopilot sends commands trough the Flight Management and Guidance Computer (FMGC).

Ad 2 The mechanical input of the sidestick must be transported electrical to the computer. This is why the mechanical input needs to be converted to an electrical signal. This is where the sidestick transducer unit comes in. This device converts the mechanical signal to an electrical one.

Ad 3 These electrical signals are then transported to the active Elevator Aileron Computer (ELAC)(2). In an Airbus A320 there are two ELAC’s on board to ensure command of the aileron control. The ELAC pro-cesses the signals coming from the sidestick or autopilot. The computer uses flight envelope protec-tion. This is a system that influences movement around the three rotating axes.

Ad 4 Inside the Airbus A320 an ARINC 429 data bus is used for the transport of data. The data bus provides a serial connection between computers and various other instruments. Up to twenty instruments can


Project group: Z 24

be attached on this data bus. The transfer rate of this data bus is 100 kb/s. The data is encrypted in 32 bits. Ad 5 The input signals from the cockpit are collected by the ELAC and will transport its signal to the hy-draulic system. The servo valve ensures that the required amount of hydraulic fluid is used. This fluid levels under a pressure of 3000 PSI. In an Airbus A320 there are 3 different hydraulic systems.

Ad 6 After being transported from the ELAC, the signal is processed by the ELAC into an output that acti-vates the hydraulic system actuators, which is connected to the control surfaces. The actuators take care of the mechanical transmission of the ailerons. The ailerons have two electrically controlled hydraulic actuators connected to each aileron. The hydraulic actuators ensures that the ailerons will deflect according to the sidestick’s input.

2.2.2 Spoilers in an Airbus A320 In order to control the spoilers, there are several steps are followed, these steps are the input (2.2.2a), conversion (2.2.2b), correction (2.2.2c), transportation (2.2.2d), amplify (2.2.2e) and the output (2.2.2f). This system is comparable to the one of the ailerons.

2.2.2a Input The spoilers are controlled by using the sidestick or by using the autopilot. After using the sidestick it is necessary to convert the data that will be send to a SEC (Spoiler Elevator Computer). There is no direct relationship between sidestick and control surface.

2.2.2b Conversion The mechanical signal of the sidestick is converted to an electrical signal for the computers to use it. This takes place by the sidestick transducer. 2.2.2c Correction The converted signal is transported to a Spoiler Elevator Computer (SEC), where the signal will be corrected. There are three of those computers in the Airbus A320. Two of them are devoted to standby elevator and stabilizer control. The information of the ELAC will be send to the SEC. 2.2.2d Transportation The corrected signal from the SEC’s is transported to the hydraulic systems of the spoilers. 2.2.2e Amplify Now the signal is converted, corrected and transported needs to be amplified before it is possible for the spoilers to work as needed. 2.2.2f Output The signal is processed in the SEC into an output which activates the hydraulic system actuator. The-se are connected to the spoiler surfaces. The actuator system ensures that the spoilers will deflect.

2.2.3 Flight control laws The flight control system in an Airbus A320 consists of five different modes, these are as following: normal law (2.2.3a), alternate law (2.2.3b), abnormal alternate law (2.2.3c), direct law (2.2.3d) and mechanical back-up (2.2.3e).

2.2.3a Normal law Normal law has three modes this depending on the phase of the flight. These 3 modes are: Ground mode, Flight mode and Flare mode.


Project group: Z 25

- Ground mode is used in take-off, shortly before landing and when the airplane is on the ground. In ground mode the stabilizer trim is automatically set to zero and there is a direct relationship be-tween stick and elevator available before lift-off and after touchdown.

- Flight mode is active shortly after take-off and stops just before landing. In this mode the pilot is protected in five different ways such as: pitch attitude, high speed, high Angle of Attack, load factor limitations and bank angle.

- Flare mode is activated when the altimeter reaches 100 ft. At 50 feet the fly-by-wire system trims the nose down, during the flare the pilot is protected from a high angle of attack or bank angle.

2.2.3b Alternate law Alternate law is entered when there are faults in one of the flight controls. When this law is activated the pilot loses pitch attitude and bank angle protection. Stall during high angle of attack is possible due to the loss of pitch attitude and bang angle protection.

2.2.3c Abnormal alternate law Abnormal alternate law is entered when the airplane is in an unusual attitude or because of failure of two air data reference units. In this law all the protections are lost except for the load factor limita-tion this is to protect the flight controls from overstraining them by high G-forces.

2.2.3d Direct law Direct law is activated when there are faults in both elevators, flame out in all engines and failure in all three of the inertial reference units. In the direct law there is a direct relationship by the sidestick between the elevator and roll control. Yaw control is done by use of the rudder pedals and can only be controlled manually. There are no more protections.

2.2.3e Mechanical Mechanical back-up is entered when there is a complete loss of power. Pitch control is achieved by manual use of the trim wheel and lateral control by use of the rudder pedals. On the PFD the warning “MAN PITCH TRIM ONLY” appears.

2.2.4 Airbus back-up An Airbus A320 has a fly-by-wire system. This means that there are many electrical systems control-ling the flight controls. When an error occurs there must be back-up controls to control the aircraft. The airbus has three kinds of systems as back-up when there is an error with the flight controls. In section (2.2.4a), the Elevator Aileron Computers functions as back-up system will be explained. In section (2.2.4b), the Spoiler Elevator Computers function as back-up system will be described. In section (2.2.4c) the Flight Augmentation Computers function as back-up system will be explained .Since fly-by-wire system is electrical powered there must also be a mechanical back-up when the power is lost. The mechanical back-up systems will be described in paragraph (2.2.4d).

2.2.4a ELAC (Elevator Aileron Computer) There are two elevator aileron computers onboard the Airbus A320 (Appendix I). The elevator aileron computer (ELAC) (1) has two primary functions. It ensures the commands of the elevators (2), the trim able horizontal stabilizer (3) and the ailerons. The second primary function is to monitor the steps of the other ELAC computer. One of the ELAC computers is the active computer. The active ELAC controls the ailerons, elevators and the trim able horizontal stabilizer. The other ELAC is in stand-by mode and monitoring the steps of the active ELAC. When an error occurs or other control systems shut down, the stand-by ELAC will take over the aileron controls and the active ELAC takes control of the elevators and trim able horizontal stabilizer. When one of the ELAC’s is malfunctions or shuts down, the other ELAC will take over. 2.2.4b SEC (Spoiler Elevator Computer)


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There are three spoiler elevator computers (SEC) onboard of the Airbus A320 (Appendix II). The three computers (1) together control the movement of the spoilers. Two out of three SEC’s (2) are devoted to standby elevator and trim able horizontal stabilizer control. When both ELAC computers malfunc-tion the two SEC’s will take control of the elevator and trim able horizontal stabilizer. When both SEC’s controlling the elevator and trim able horizontal stabilizer fail the elevator cannot be used an-ymore, the trim able horizontal stabilizer can be controlled mechanical. There is no back-up system for the spoilers (3) present. When all SEC’s computers fail the spoiler cannot be used. 2.2.4c FAC (Flight Augmentation Computer) There are two Flight Augmentation Computers in the Airbus A320 (Appendix III). The two Flight Aug-mentation Computers (FAC) (1) control the rudder systems . Both FAC’s control the yaw damper systems (2), turn coordination (3) and Rudder Travel Limitation (4). Both FAS’s have a flight envelope function which means that characteristic speeds computation will be shown at the display on the PFD. When both FAC’s fail the airplane can be controlled mechanically. The FAC’s cannot control other primary or secondary flight controls.

2.2.4d mechanical back-up Since the fly-by-wire system is electrical powered there should also be a mechanical back-up for when the power is lost. When the power is lost for short time the airplane can be controlled mechan-ical throughout the rudder and trim able horizontal stabilizer (figure 21). The rudder and trim able horizontal stabilizer will ensure adequate control of the airplane in case of temporary loss of all elec-trical power sources including batteries. When the electrical power is lost for long period the pilots should try to level the airplane and use the trim able horizontal stabilizer to keep altitude.

Figure 21, system overview

2.3 Differences between Airbus and Boeing The Airbus A320 and the Boeing 737 NG differ from each other. These differences are due to the vision of the manufacturer (2.3.1) and the different operating systems (2.3.2). Because of the differ-ent operating systems there are also different kinds of back-up systems (2.3.3).

2.3.1 Vision of the manufacturer Airbus and Boeing have different views of who is superior, the pilot or the computer. Airbus believes that computers are always superior to pilots. This is why the computers in an Airbus determine if an actions of the pilot is valet or not. Boeing believes the opposite. In a Boeing the pilot only receives warnings from a computer. The computer in a Boeing is not able to correct the movements of the control column.


Project group: Z 27

2.3.2 Aileron and spoiler controlling The control columns of the Boeing 737 NG are linked mechanically by cables. The movements made by the control column are send out by cables. The Airbus A320 does not have control columns, but uses sidesticks to control the aileron, spoilers and some other flight controls. These sidesticks send out electrical signals to a computer. This computer makes corrections to the movement of the sidestick and decides what to do with the signal. The corrections from the movements of the control columns on the Boeing 737 NG are done mechanically. This mechanical movement is changed to a hydraulic pressure to transfer the movement to the place necessary. Airbus A320 uses the electrical signals to transfer the movement. This movement is changed to the hydraulic pressure near the ai-lerons and spoilers to move them. The movement of the ailerons and spoilers on the Boeing are also done by the hydraulic pressure.

2.3.3 Flight control laws Boeing The Boeing 737 NG’s flight control laws differ from the Airbus A320. This is because movements of the control column reach the flight control actuators mechanically. This means that the movements of the control columns cannot be overruled by flight control computers. The computer does not cor-rect automatically, but it uses warning signals.

2.3.4 Back-up The main differences in the back-up systems come from the fact that airbus uses fly-by-wire system and Boeing uses a hydraulic system. Airbus has a lot of digital back-up/stand-by systems while Boeing uses back-up/stand-by measures inside the hydraulic system. Both airplanes have stand-by measures for the flight controls. Boeing uses two parallel hydraulic systems to power the flight controls in cases one of the systems malfunctions. Boeing also has a back-up hydraulic system for the rudder, thrust reversers and leading edges devices in case both systems malfunction. Airbus uses stand-by comput-ers. These primary task of these computers is to check for errors made by the primary computer. If the primary computer malfunctions the stand-by computer takes over the task of the primary com-puter. Both airplanes have the ability to control the most important flight controls manually.

2.4 Pros and cons research After the differences it is possible to make a pros and cons research. There are two different systems. The first is the conventional system (2.4.1) and the second is the fly-by-wire system (2.4.2).

2.4.1 Conventional system The conventional system is split up into two different sections: the pros (2.4.1a) and cons (2.4.1b)

2.4.1a Pros There is a direct connection. So the input from the control column is in direct connection

with the control surfaces. There is feedback in a conventional system, so it is possible to feel the result of the control

surfaces of the airplane. Through the control column is it possible to view two of the three control surfaces in a quick

look. The system is not sensitive for electrical failures, because it does not utilize any electronics.

2.4.1b Cons

The mechanical components often have to be checked for wastage.

2.4.2 Fly-by-wire system The second system is the fly-by-wire system. This system is also split up into two different sections: the pros (2.4.2a) and cons (2.4.2b)


Project group: Z 28

2.4.2a Pros

The fly-by-wire system is less sensitive for wastage , because there are fewer mechanical components in use.

The computer of the fly-by-wire system calculates different parameters, so it is almost im-possible to stall the airplane or even damage it.

The weight is reduced due to the fact that digital components weigh less than mechanical components.

The maintenance of the fly-by-wire system is quicker than the maintenance of the conven-tional system, because components are easy to check and replace when needed.

The fly-by-wire system reduces the workload. 2.4.2b Cons

The fly-by-wire system is more sensitive for failures, because there are digital components. It is more difficult to control the airplane by sense, because there is not any feedback from

the sidestick.

2.5 conclusion After analyzing both systems a conclusion can be made based on safety (the costs will be discussed in chapter 3.2). The conventional system is extremely vulnerable for wastage and expensive compo-nents have to be replaced on a regular base. In return it is easier to fly an airplane manually with the conventional system because there is a direct feedback from the control column. But failures are unlikely to occur with the fly-by-wire system so there is a very slim change of manual control, be-cause with the fly-by-wire system the computers stay in control. The system uses control laws to prevent the pilot from making human mistakes and therefore makes it fertilely impossible to crash the airplane. The fly-by-wire system reduces weight, maintenance, workload of pilots and it almost eliminates the change of stalling the airplane, which makes it very safe and reliable. Fly-by-wire is the future and makes safe flying very easy.


Project group: Z 29

Chapter 3 In this chapter three similar maintenance procedures (3.1) between the Boeing 737NG and the Air-bus A320 flight controls are compared. After comparing the maintenance planning data (MPD) and the maintenance program manual (MPM) of both airplanes, three similar maintenance tasks will be compared in this chapter. In the first paragraph three maintenance procedures of Boeing are de-scribed. In the following paragraph the financial overview (3.2) is presented.

3.1 Maintenance procedures There are three different maintenance procedures found, three maintenance procedures for the Boeing 737NG (3.1.1) and three for the Airbus A320 (3.1.2). These maintenance procedures are equivalent to the airbus maintenance schedule. In the last section (3.1.3) are the differences be-tween both maintenance procedures.

3.1.1 Maintenance procedures Boeing 737 NG The three maintenance procedures for the Boeing 737NG are: Lubricate the spoiler mechanical con-trol path (3.1.1a), Operational check of the aileron control surfaces (3.1.1b) and an operational check of the elevator control (3.1.1c). These tasks were chosen because they should be performed on both Boeing and Airbus airplanes. However, the way the task is executed is different. 3.1.1a Lubrication of the spoilers mechanical control path On this maintenance task the mechanical control path will be lubricated to guarantee a smooth op-eration of the spoilers. Before executing this maintenance procedure the spoilers must be fully ex-tended. The threshold and repeat frequency of this procedure is about 4000 flight hours. This is a maintenance task which is accomplished at an established frequency other that the routine A or C/D/S –check intervals. This maintenance task is performed by executing the next steps (according to AMM reference 27-61-21). Connect pushrod to ground spoiler control valve. Using ground spoiler control valve rigging tool, position control valve level so that dimension A is 0,70 +- 0,01 inch. Loosen check nut and adjust rod end until rod end bolt fits freely. Lubricate rod end threads with grease. Install rod end bolt and secure with washer, nut and cotter pin. Tighten check nut and check for proper rod end thread engagement. Rod end threads shall be visible in inspection hole. Remove rig-ging tool. 3.1.1b Operational check of the aileron control surfaces For this operational check, the power of hydraulic system must be turned off. With this system turned off the aileron control surfaces can be checked for full range of travel and freedom of move-ment. This is a failure finding task to determine if an item is fulfilling its intended purpose. This is an component of the C-check which is preformed every 6000 flight hours, 24 calendar months or 3500 flight cycles. This maintenance task is performed by executing the next steps (according to AMM reference 27-11-111). Measure relationship of aileron control wheel movement as compared with aileron surface deflection. Rotate captain’s aileron control wheel 87 degrees minimum counter-clockwise from neutral. Check that left aileron moves up and right aileron moves down within limits specified (+- 0,20 inches). Rotate captain’s aileron control wheel 87 degrees minimum clockwise from neutral. Check that left aileron moves down and right aileron moves up within limits (+- 0,20 inches).

3.1.1c Operational check of the elevator control surfaces For this operational check, the elevator control surfaces will be checked for full range of travel and freedom of movement. Before operation this check, the hydraulic pressure must be turned com-pletely off. This is like every other C-check a failure finding task to determine if an item is fulfilling its intended purpose. This C-check is preformed every 6000 flight hours, 24 calendar months or 3500 flight cycles. This maintenance task is performed by executing the next steps (according to AMM reference 27-31-11). Measure breakaway forces required to move elevator. Use spring scale and loading block and apply force to elevator rear spar, adjacent to inboard rib. Slowly rotate elevator by


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hand through full travel up and down and check for roughness or binding. If the elevator moves after releasing it at the neutral position, record the maximum force required to slowly move it back to the neutral position. Record the force at the time the elevator reaches the neutral position. The differ-ence between these forces shall not exceed 1.0 pound.

3.1.2 Maintenance procedures Airbus a320 The maintenance procedures described in this paragraph are: lubrication of the spoilers (3.1.2a), aileron operational check of damping measurement by BITE (built-in test equipment) (3.1.2b) and elevator operational check of damping measurement by BITE (3.1.2c). Maintenance of the elevator is described in this section, because it is a very important component of the airplane.

3.1.2a Lubrication of the spoilers At this maintenance task the actuator attachments of spoilers one to five are lubricated. As prepara-tion for this maintenance task, the flaps and slats must be fully extended. The threshold interval is 2000 flight hours or fifteen months. This task takes fifteen minutes and can be executed by one maintenance engineer. This maintenance task is performed by executing the next steps (according to AMM reference 276400-01). Fully extend the flaps and slats. Clean the greasers. Lubricate the spoiler servo-control bearings with common grease until new grease comes out. Remove the unwanted grease. 3.1.2b Aileron operational check of damping measurement by BITE This operational check is performed by built-in test equipment. If an airplane is flying under FAA re-strictions this check must be performed every 500 flight hours or thirty-six months. When not flying under FAA restrictions this check must be performed every 4000 flight hours of thirty-six months. For both FAA and not FAA restricted, this check takes six minutes and can be executed by one mainte-nance engineer. This maintenance task is performed by executing the next steps (according to AMM reference 271400-01). Turn on the electrical power supplies. Perform the EIS (Electrical instrument system) start procedure. Put the flaps and slats control lever in position 0. Retract the speed brake. Place the sidesticks in neutral position. Pressurize the green hydraulic system. Push the F/CTL key on the ECAM (Electronic Centralized Aircraft Monitor) module. Move one of the sidesticks to the left until it touches the stop. Perform the same procedure by moving the sidestick to the right. Then place the sidestick back in neutral position. Depressurize the green hydraulic system and pressurize the blue hydraulic system. Perform the same procedures with the sidesticks. Depressurize the blue hydraulic system. Perform the EIS stop procedure. At last cut off the electrical power supplies. 3.1.2c Elevator operational check of damping measurement by BITE This operational check is performed by built-in test equipment. If an airplane is flying under FAA re-strictions this check must be performed every 500 flight hours or thirty-six months. When not flying under FAA restrictions this check must be performed every 4000 flight hours of thirty-six months. For both FAA and not FAA restricted, this check takes six minutes and can be executed by one mainte-nance engineer. This maintenance task is performed by executing the next steps (according to AMM reference 273400-01). Energize the electrical systems. Pressurize the hydraulic systems. Perform the EIS start procedure. Push the F/CTL key on the ECAM control panel. Move the sidestick forward and back-ward. Repeat this with putting several circuit breaker on and off. Depressurize the airplane hydraulic systems. Perform the EIS stop procedure. Cut off the electrical systems.

3.1.3 Maintenance differences As can be seen in the maintenance procedures, the main difference is the way how several checks are being executed. At the Boeing 737 NG, the major part has to be done by hand. Mechanics, who maintain an Airbus A320, can use the BITE system for testing. The advantage is that technicians do


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not need to perform more actions, compared to the Boeing 737 NG, for operational testing. On the other hand, the checks are performed more frequently than at a Boeing 737 NG.

3.2 Expenses In order to get a clear overview of the differences between the expenses on the maintenance of the conventional system of Boeing and the fly-by-wire system of Airbus, an expenses overview has been made. In this overview assumptions will been made regarding the expenses (3.2.1). In the following section the expenses and man hours need to perform each check on the Airbus A320 (3.2.2) and the 737NG (3.2.3) have been explained. In the last section the costs of the checks over a course of ten years have been compared (3.2.4).

3.2.1 General assumptions The general assumptions have been divided into paragraphs: hourly cost (3.2.1a), hydraulic fluids and lubricants (3.2.1b) en de threshold interval (3.2.1c). 3.2.1a Hourly cost A maintenance engineer uses tools, hydraulic fluids, lubricants and so forth. These expenses are called the maintenance labor expenses, this represents the expenses made by maintenance crew per hour, both scheduled and non-scheduled maintenance. The nationwide average maintenance labor expenses are: €58,63 per hour per engineer. The average salary for a Maintenance Tech Engineer is €29600,38 per year, or €2466,69 per month. With an average work week of 36 hours, that concludes a total of €17,13 per hour. Hiring a hangar, office, rent, insurance (other than aircraft insurance), utilities, security and janitorial expenses are an average of €17909,41 per airplane per year. Per hour this makes €2,04. Combining the labor expenses, maintenance tech engineer salary, and the hang-ar/office lease expenses makes a total of: €78.40 per hour. 3.2.1b Hydraulic fluids and lubricants The use of hydraulic fluids and lubricants for maintenance of the flight controls, are assumed to be equal on both quantities and costs on both the airplanes. Therefore these are not included in the calculations. 3.2.1c Threshold interval The average flying hours of an airplane are 16 hours per day, flying under FAA regulations. Manuals have been used to acquire the Threshold interval, the threshold interval has been divided by the 16 average flying hours per day. This concludes the frequency of maintenance, when dividing 365 days by this number, the frequency of maintenance per year is concluded.

3.2.2 Airbus A320 Information regarding time and engineers needed for the maintenance procedures was found in the maintenance manuals. This has also been discussed in chapter 3.1.

Maintenance procedures

Threshold interval (FH)

Time needed (minutes)

Engineers needed

Costs hourly

Frequency per year

Costs each time

costs per year

Lubrication of the spoilers 2000 30 1 € 78,40 2,92 € 39,20 € 114,46

Aileron operational check 500 6 1 € 78,40 11,68 € 7,84 € 91,57

Elevator operational check 500 6 1 € 78,40 11,68 € 7,84 € 91,57

Total costs

€ 297,61

Table 1, Airbus A320


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3.2.3 Boeing 737 NG The maintenance manuals of Boeing do not include information regarding the time needed to per-form maintenance procedures, nor the amount of engineers needed. Because of this assumption had been made. In order to do this, the amount of work has been analyzed, after which an estimated time needed to complete the procedure was established. Lubricating the spoilers on the Boeing 737NG, is a similar procedure to the one on the Airbus A320. The only difference being that the A320 has five spoilers on each side opposed to four on the 737NG. Therefore the same time and manpow-er is needed to perform this procedure. The operational check of the ailerons on a 737NG takes a bit longer than on the A320 because of the absence of a BITE. Assuming one engineer performs the check and one dictates the result, 30 minutes per check seems reasonable.

Maintenance pro-cedures

Threshold interval (FH)

Time needed (minutes)

Engineers needed

Cost hourly

Frequency per year

Costs each time

costs per year

Lubrication of the spoilers 4000 30 1 € 78,40 1,46 € 39,20 € 57,23

Aileron operational check 6000 30 2 € 78,40 0,973 € 39,20 € 76,31

Elevator operational check 6000 30 2 € 78,40 0,973 € 39,20 € 76,31

Total costs

€ 209,85

Table 2, Boeing 737 NG

3.2.4 Comparison In order to get a good overview of the costs of the checks made by the Airbus A320 compared to those on the Boeing 737NG, a graph has been made (see figure 22). Figures shown are the total costs for the checks over the course of ten years, assuming no large parts had to be replaced. It is clear that the conventional Boeing system is a lot cheaper in checks (€2.009,85) than the fly-by-wire sys-tem Airbus uses (€2.976,10).

Figure 22, comparison graph

3.2.5 Conclusion and recommendation After examining the three different maintenance procedures it is clear that the Boeing 737NG has proven to be the less expensive option between the two airplanes (€2.009,85 for Boeing against €2.976,10 for Airbus). Therefore the Boeing is the best choice based on the operational maintenance cost. However, the fly-by-wire system uses advanced technology such as ELACS and SECS. The total cost of purchasing the fly-by-wire system will be a lot more in comparison to a conventional system As already explained in section 3.2.5, the fly-by-wire system brings many advantages over the con-

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Costs after 10 years

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Boeing


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ventional system. The Boeing might be cheaper based on a few maintenance checks, but eventually the Airbus will prove to be less expensive because wastage is not as much of an issue. Fewer parts have to be replaced on a regular basis and the system will save weight that can be used for more passengers or luggage. In our opinion the Airbus A320 has proven to be the best option.


Project group: Z 34

Bibliography Siers, F.J. (2004). Methodisch ontwerpen volgens H.H. van den Kroonenberg. Third edition

A318/A319/A320/A321 Flight deck and systems briefing for pilots February 2007

Project book Flight controls (2012)

Aircraft maintenance manual Boeing

Aircraft maintenance manual Airbus

B737-800 maintenance program manual, January 27 2007 revision 16

A318/A319/A320/A321 , October 01 2011 Maintenance planning documents

A318/A319/A320/A321 , February 2007 Flight deck and systems briefing for pilots

European Aviation Safety Agency Rulemaking Directorate CS25 document

Aerodynamic dictate version three, Victor Laban, august 2009

Technische natuurkunde 1, B.H. van Dijk and R.J. van Aalst, 2011

Aviation research costs: http://www.aviationresearch.com/Portals/0/Files/AOC.pdf

http://www.aviationresearch.com/Portals/0/Files/AOC.pdf

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leading edge slot

laminar boundary layer

making human mistakes

trailing edge devices

leading edge devices

turbulent boundary layer

trailing edge device