teory of flight (fixed wing)

8/12/2019 Teory of Flight (Fixed Wing)

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FOR TRAINING PURPOSE ONLY

Subject Code: AKD20503Issue No : 00 Page No: 1

AKD20503 AUTOFLIGHT SYSTEM





THEORY OF FLIGHT

(Fixed Wing)





Content:

Forces on the aircraft

Stability –dihedral, sweptback, keel effect and weight distribution

Control Axis

Primary control surfaces – operation and effect on the aircraft

Secondary controls surfaces

Functions of tabs- Trim, balance and servo.

Forces during turns. Coordinated turns, slip and skid in a turn.

High speed buffet and stall conditions

Auto-pilot control axis and wing levellersVersine generation and application

Turbulence penetration and the effect an autopilot





Upon completion of this subject, students should be able to:

Explain the forces acting on the aircraft.

Explain and relate the stability and it effect on dihedral,

sweptback, keel effect and weight distribution on aircraft.

Explain aircraft control axis and it primary and secondary control

surfaces operation and identify it effect.

Explain the functions of trim, balance and servo tabs.

Compare the forces acting on aircraft during turn.

Define high speed buffet and stall conditions

Define autoflight control axis and single axis wing levellers

Define versine generation and application.

Define turbulence penetration and the effect an autopilot





Introduction

Automatic Flight Control Systems (AFCS) relieve the human pilot

and other members of the flight crew of the tedious duty of keeping the

aircraft on course for periods of many hours.

The Autoflight system automatically controls:

– Airplane heading, Track, Speed, Altitude, Attitude, Navigation

paths and Go-around.

Early Autoflight System just control the aircraft in a single-axis. It

usually operates the ailerons only and is often referred to as a wing

leveler.

Today in the invent of digital computer and advance system which can

control all aircraft phase of flight is introduced. This system is called

'Flight Management System'





Forces on the aircraft

There are 4 force acting on aircraft that is Lift, Weight (Gravity),

Thrust and Drag.

– Lift

Oppose the downward force of weight, produced by the dynamiceffect of air acting on airfoil. Act perpendicular to the flight path

through the Center of Lift (CL). Most of the lift created by the

airfoil can be attributed to Bernoulli's Principle. The amount of lift

is in a direct relationship with the speed of the airplane. As it

increases speed, the amount of lift acting upon it increases. Lift

can also be manipulated by increasing or decreasing the angle of

attack but, if the angle of attack is increased to much the aircraft

will stall.





Weight

– The combine load of the aircraft. It pulled the aircraft down due to

gravity. Oppose lift and act downward through aircraft Center of

Gravity (CG)

Drag

– Oppose trust and act rearward parallel to the relative wind.

Caused by the wing, fuselage and other protruding objects.

There are two kinds of drag, inducing drag and parasite drag.

Inducing drag is caused by the development of lift while Parasite

drag is the result of all of the un-aerodynamic features of the

airplane.





- Trust

Oppose drag. It is a forward force produced by the powerplant

/propeller or rotor.





STABILITYBasic concepts of stability

The flight paths and attitudes in which an airplane can fly are limited

only by the aerodynamic characteristics of the airplane, its

propulsive system, and its structural strength.

These limitations indicate the maximum performance in term ofcontrollability and maneuverability of the airplane.

It must be safely controllable to the limits without exceeding the

pilot‘s strength or requiring exceptional flying ability.

If an airplane is to fly straight and level along any flight path

condition, the forces acting on it must be in static equilibrium.

The reaction of any body when its equilibrium is disturbed is referred

to as stability.

There are two types of stability. Static and Dynamic.





StaticThe following definitions apply:

Equilibrium— All opposing forces acting on the airplane are balanced;

(i.e., steady, unaccelerated flight conditions).

Static Stability—The initial tendency that the airplane displays after its

equilibrium is disturbed.Positive Static Stability—The initial tendency of the airplane to return to

the original state of equilibrium after being disturbed. (move-return)

Negative Static Stability—The initial tendency of the airplane to

continue away from the original state of equilibrium after being

disturbed. (move-continue)

Neutral Static Stability—The initial tendency of the airplane to remain in

a new condition after its equilibrium has been disturbed. (move-stop)





Static stability

It is defined as the initial tendency that the airplane displays after being

disturbed from its equilibrium condition.

Stability of an airplane in flight is slightly more complex because the

airplane is free to move in any direction and must be controllable in

pitch, roll, and yaw.When designing the airplane, engineers must compromise between

stability, maneuverability, and controllability.

The problem is compounded because of the airplane‘s three-axis of

movement.

Too much stability is detrimental to maneuverability, and similarly, not

enough stability is detrimental to controllability.





Type of static stability





Dynamic stabi l ity Dynamic stability refer to aircraft response over time after its

equilibrium is disturbed.

Three type of dynamic stability are:-

Positive Dynamic Stability— Over time, the motion of the displaceobject decreases in amplitude and return to the original state of

equilibrium. (displace-slowly stop)

Negative Dynamic Stability— Over time, the motion of the displace

object increases. (displace-increase)

Neutral Dynamic Stability— Once displaced, the displace object

neither decrease or increase in amplitude. (displace-maintain)





A – Positive Dynamic Stability

B – Neutral Dynamic StabilityC – Negative Dynamic Stability





Amber - Positive Dynamic Stability

Green - Neutral Dynamic Stability

Red - Negative Dynamic Stability





Longitudinal stability (pitching)

Longitudinal stability about the lateral axis is considered to be themost affected by certain variables in various flight conditions of an

airplane.

Longitudinal stability makes an airplane stable about its lateral axis.

It cause the pitching of the airplane‘s nose up and down in flight.

A longitudinally unstable airplane has a tendency to dive or climbprogressively into a very steep dive or climb, or even a stall.

Static longitudinal stability or instability in an airplane is dependent

upon three factors:

– 1. Location of the wing with respect to the center of gravity.

– 2. Location of the horizontal tail surfaces with respect to the

center of gravity.

– 3. The area or size of the tail surfaces.





Most aircraft are designed so that the wing‘s CL is to the rear of theCG.

This makes the aircraft ―nose heavy‖ and requires that there be aslight downward force on the horizontal stabilizer in order to balancethe aircraft and keep the nose from continually pitching downward.

Compensation for this nose heaviness is provided by setting thehorizontal stabilizer at a slight negative AOA. The downward forcethus produced holds the tail down, counterbalancing the ―heavy‖nose.





Lateral stability (rolling)

Stability about the airplane‘s longitudinal axis, which extends from

nose to tail, is called lateral stability.

This stabilize the lateral or rolling effect when one wing gets lower

than the wing on the opposite side of the airplane.Four main design factors that make an airplane stable laterally are:-

– dihedral

– keel effect

– Sweepback

– weight distribution.





Dihedral

The wings is build with an angle of one to three degrees above

perpendicular to the longitudinal axis.

The wings on either side of the aircraft join the fuselage to form a

slight V or angle called ―dihedral.‖

The amount of dihedral is measured by the angle made by eachwing above a line parallel to the lateral axis.





Sweepback

Sweptback wing is one in which the leading edge slopes backward.

If an aircraft with sweepback to slip or drop a wing due to

disturbance, the low wing presents its leading edge at an angle that

is perpendicular to the relative airflow.

As a result, the low wing acquires more lift, rises, and the aircraft is

restored to its original flight attitude.

Sweepback also contributes to directional stability. When turbulence

or rudder application causes the aircraft to yaw to one side, the right

wing presents a longer leading edge perpendicular to the relative

airflow.

The airspeed of the right wing increases and it acquires more drag

than the left wing. The additional drag on the right wing pulls it back,

turning the aircraft back to its original path.





Keel Effect and Weight Distribution

Aircraft always has the tendency to turn the longitudinal axis of theaircraft into the relative wind and exerts a steadying influence on theaircraft laterally about the longitudinal axis.

If one wing of the aircraft dips, the fuselage weight acts like apendulum returning the airplane to its original attitude.

Laterally stable aircraft are constructed so that the greater portion ofthe keel area is above and behind the CG.

So if the aircraft slips to one side, the combination of the aircraft‘sweight and the pressure of the airflow against the upper portion ofthe keel area (both acting about the CG) tends to roll the aircraftback to wings-level flight.





Vertical stability (yawing) Stability about the airplane‘s vertical axis (the sideways moment) is

called yawing or directional stability.

It is easily achieved by designing the airplane area of vertical fin and

the sides of the fuselage aft of the center of gravity.

It can be seen that if exactly the same amount of surface were exposed

to the wind in front of the pivot point as behind it, the forces fore and aft

would be in balance and little or no directional movement would result.

Similarly in an airplane, the designer must ensure positive directional

stability by making the side surface greater aft than ahead of the center

of gravity.





Aircraft acts on three separate axis, namely lateral axis, longitudinal

axis and vertical axis

The three axis would enable the aircraft to be controlled when

airborne and all three axis acts from the C of G and perpendicular to

each other.

The rotating motions and the corresponding axis are:-

– Roll (wing down or up)- Longitudinal axis (wing tip to wingtip)

– Pitch (Nose up or Down)- Lateral axis (Nose to Tail)

– Yaw (Nose left or right)- Vertical axis (C of G up)

Control Axis





If we consider an imaginary center-line or "longitudinal axis" fromthe front to the rear of the aircraft, then a left to right twist or rotation,

with one wing up and the other down is referred to as the ROLL.

If we consider an imaginary line from one wing tip to the other or

"lateral axis" then as the nose of the aircraft moves up or down on

this axis, this rotation is referred to as the PITCH.

As the aircraft rotates to the left or the right around a ―vertical axis",

this rotation is called the YAW.






The Primary control surfaces on the aircraft are:

– The two AILERONS on the two wings

– The two ELEVATORS

– The one RUDDER on the Tail

Primary control surfaces






The two Ailerons on the wings,

– if set in opposite directions, one up and the other down, control

the Roll which then affects the Heading of the aircraft.

The two Elevators control the Pitch of the Aircraft and thus have an

effect on controlling the altitude.

The Ailerons also control the Pitch of the aircraft when they are set in

the same direction and the ailerons thus control the changing of the

altitude as well.

When keeping a constant altitude, adjusting the pitch also has an

effect on the aircraft Speed.






The Rudder on the tail affects the Yaw which also has an effect on theHeading.

On larger aircraft, there are many more control surfaces, typically:

– An Outboard Aileron and an Inboard Aileron

– An Outboard Elevator and an Inboard Elevator

– Upper and Lower sections of the Rudder as well as others.






MD11 Control Surface






Pushing the control column forward lowers the trailing edge of thestabilator and pitches the airplane nose down.

Because stabilators pivot around a central hinge point, they areextremely sensitive to control inputs and aerodynamic loads, so

Antiservo tabs are incorporated on the trailing edge to decrease

sensitivity and increase the force required to move the stabilator

prevent pilot from over controlling.

StabilatorStabilator is essentially a one-

piece horizontal stabilizer that

pivots from a central hinge point.

Pulling back the control column

raises the stabilator‘s trailing edge

and pitches the airplane‘s nose up.






Some aircraft pivot the stabilator about its rear spar. Movement is

accomplished by use of a jackscrew mounted on the leading edgeof the stabilator.





Elevon - It an aircraft control surfaces that combine the functions ofthe elevator (pitch control) and the aileron (roll control).

Frequently used on tailless or aircraft without horizontal stabilizer.

Elevons are installed on each side of the aircraft at the trailing edge

of the wing. – When moved in the same direction (up or down) they will cause

a pitching force (nose up or nose down).

– When moved differentially, (one up, one down) they will cause a

rolling force to be applied.

Elevon





Ruddervator - are an aircraft control surfaces that combine thefunctions of rudder (yaw control) and elevator (pitch control).

Normally used on a V tailed aircraft.

Ruddervator are installed on each side of the aircraft V trailing edge

tail

– When moved in the same direction (up or down) they will cause

a pitching force (nose up or nose down).

– When moved differentially, (one up, one down) they will cause a

yawing force to be applied

Ruddervator





Secondary controls

The secondary flight control device is used in addition to the 3

primary control device.

They are:

– Trimming devices – Trim Tab which is fitted to the trailing edge of

one of primary control. It is controlled separately.

– Control force reducing device - Ballance or Antiservo Tab which is

fitted to the trailing edge of one of primary control. It is move

automatically or indirectly.

– Lift control device – May consist of Flaps, Slats, Spoilers andSpeed Brake.

Flap – Used to increase lift at slow speed during take-off and landing

or increase drag for steep rates of descent.





Slat – Used to increase lift at high angle of attack and has a stabilizing

effect of airflow over the wingSpoiler – Wing mounted device which spoiling lift. They are operated

mechanically before landing to dump lift. Ground Spoiler are operated

after landing only.

Speed Brake – are wing or fuselage mounted device. It act as anaerodynamic brakes. Used to increase rates of descent or enable

steeper dives or improve maneuverability of high speed aircraft.





Speed brake





Trim Tabs

Trim tab are attached to the trailing edgeof the elevator.

Most trim tabs are manually operated by a

small, vertically mounted control wheel or

trim crank may be found in some aircraft.

The flight deck control includes a trim tab

position indicator. Placing the trim control

in the full nose-down position moves the

trim tab to its full up position. With the trim

tab up and into the airstreams, the airflow

over the horizontal tail surface tends toforce the trailing edge of the elevator

down. This causes the tail of the airplane

to move up, and the nose to move down





Balance TabsThe control forces may be excessively high in some aircraft, and, inorder to decrease them, the manufacturer may use balance tabs.

They look like trim tabs and are hinged in approximately the sameplaces as trim tabs.

The difference between the two is that the balancing tab is coupledto the control surface rod so that when the primary control surfaceis moved in any direction, the tab automatically moves in theopposite direction.

The airflow striking the tab counterbalances some of the airpressure against the primary control surface, and enables the pilot

to move more easily and hold the control surface in position.If the linkage between the balance tab and the fixed surface isadjustable from the flight deck, the tab acts as a combination trimand balance tab that can be adjusted to any desired deflection.





Antiservo Tabs

Antiservo tabs work in the same manner as

balance tabs except, instead of moving in the

opposite direction, they move in the same

direction as the trailing edge of the stabilator.

In addition to decreasing the sensitivity of thestabilator, an antiservo tab also functions as a

trim device to relieve control pressure and

maintain the stabilator in the desired position.

The fixed end of the linkage is on the opposite

side of the surface from the horn on the tab;

when the trailing edge of the stabilator moves

up, the linkage forces the trailing edge of the

tab up and vise versa.





Ground Adjustable TabsMany small aircraft have a non movable

metal trim tab on the rudder.

This tab is bent in one direction or the

other while on the ground to apply a

trim force to the rudder.

The correct displacement is determined

by trial and error.

Usually, small adjustments are

necessary until the aircraft no longer

skids left or right during normal cruising

flight.





Forces in turns

If the forces acting on the airplane actually could be seen, two forces(lift and weight) would be apparent, and if the airplane were in a

bank it would be apparent that lift did not act directly opposite to the

weight, it now acts in the direction of the bank.





The fact that when the airplane banks, lift acts inward toward the center of the

turn, as well as upward. Thus an airplane requires a sideward force to make itturn.

In a normal turn, this force is supplied by banking the airplane so that lift isexerted inward as well as upward.

The force of lift during a turn is separated into two components at right anglesto each other.

– Component, which acts vertically and opposite to the weight (gravity), iscalled the ―vertical component of lift.‖

– Component, which acts horizontally toward the center of the turn, is calledthe ―horizontal component of lift,‖ or centripetal force. The horizontalcomponent of lift is the force that pulls the airplane from a straight flightpath to make it turn.





Centrifugal force is the ―equal and opposite reaction‖ of the

airplane to the change in direction and acts equal and opposite to

the horizontal component of lift.

This explains why, in a correctly executed turn, the force that turns

the airplane is not supplied by the rudder.

An airplane is not steered like a boat or an automobile; in order for it

to turn, it must be banked. If the airplane is not banked, there is no

force available that will cause it to deviate from a straight flight path.

Good directional control is based on the fact that the airplane will

attempt to turn whenever it is banked.





Merely banking the airplane into a turn produces no change in thetotal amount of lift developed.

Since the vertical component of lift decreases as the bank angleincreases, the angle of attack must be progressively increased toproduce sufficient vertical lift to support the airplane‘s weight.

At a given airspeed, the rate at which an airplane turns dependsupon the magnitude of the horizontal component of lift. To provide avertical component of lift sufficient to hold altitude in a level turn, an

increase in the angle of attack is required.

To compensate for added lift, which would result if the airspeedwere increased during a turn, the angle of attack must bedecreased, or the angle of bank increased, if a constant altitudewere to be maintained.





If the angle of bank were held constant and the angle of attack decreased,

the rate of turn would decrease. Therefore, in order to maintain a constant

rate of turn as the airspeed is increased, the angle of attack must remain

constant and the angle of bank increased.

It must be remembered that an increase in airspeed results in an increase of

the turn radius and that centrifugal force is directly proportional to the radius

of the turn.

In a correctly executed turn, the horizontal component of lift must be exactly

equal and opposite to the centrifugal force. Therefore, as the airspeed isincreased in a constant rate level turn, the radius of the turn increases.

This increase in the radius of turn causes an increase in the centrifugal force,

which must be balanced by an increase in the horizontal component of lift,

which can only be increased by increasing the angle of bank.





In a slipping turn, the airplane is not turning at the rate appropriate to

the bank being used, the airplane is banked too much for the rate of

turn, so the horizontal lift component is greater than the centrifugal

force.

Equilibrium between the horizontal lift component and centrifugal

force is reestablished either by decreasing the bank, increasing the

rate of turn, or a combination of the two changes.





A skidding turn results from an excess of centrifugal force over thehorizontal lift component, pulling the airplane toward the outside of

the turn. The rate of turn is too great for the angle of bank. Correction

of a skidding turn thus involves a reduction in the rate of turn, an

increase in bank, or a combination of the two changes.

To maintain a given rate of turn, the angle of bank must be varied

with the airspeed or a loss of altitude will occur unless the angle of

attack is increased sufficiently to compensate for the loss of vertical

lift.





High Speed Buffet and Stall Condition

In subsonic aerodynamics, the theory of lift is based upon theforces generated on a body and a moving gas (air) in which it is

immersed.

Subsonic aerodynamic theory also assumes the effects of viscosity

are negligible, and classifies air as an ideal fluid, conforming to the

principles of ideal-fluid aerodynamics such as Bernoulli‘s principle.

In reality, air is compressible and viscous. While the effects of

these properties are negligible at low speeds, compressibility

effects in particular become increasingly important as speed

increases.

Compressibility is of paramount importance at speeds approaching

the speed of sound. In these speed ranges, compressibility causes

a change in the density of the air around an aircraft.





During flight, a wing produces lift by accelerating the airflow over the

upper surface. This accelerated air can, and does, reach sonicspeeds even though the aircraft itself may be flying subsonic.

At some extreme AOAs, in some aircraft, the speed of the air over

the top surface of the wing may be double the aircraft‘s speed.

It is therefore entirely possible to have both supersonic and subsonicairflow on an aircraft at the same time.

When flow velocities reach sonic speeds at some location on an

aircraft (area of maximum camber on the wing), further acceleration

results in the onset of compressibility effects such as shock waveformation, drag increase, buffeting, stability, and control difficulties.

Subsonic flow principles are invalid at all speeds above this point.





The speed of an aircraft in which airflow over any part of the aircraft

first reaches Mach 1.0 is termed ―critical Mach number‖ or ―Mach

Crit.‖

Critical Mach number is the boundary between subsonic and

transonic flight and is largely dependent on the wing and airfoil

design.

Subsonic—Mach numbers below

0.75

Transonic—Mach numbers from

0.75 to 1.20

Supersonic—Mach numbers from

1.20 to 5.00

Hypersonic—Mach numbers above5.00





Critical Mach number is an important point in transonic flight.

When shock waves form on the aircraft, airflow separation followed

by buffet and aircraft control difficulties can occur.

Shock waves, buffet, and airflow separation take place above critical

Mach number.

A jet aircraft typically is most efficient when cruising at or near its

critical Mach number.

At speeds 5 –10 percent above the critical Mach number,

compressibility effects begin.

Drag begins to rise sharply then buffet, trim and stability changes,

and a decrease in control surface effectiveness. This is the point of

―drag divergence.‖





VMO /MMO is defined as the maximum operating limit speed.

VMO is in knots calibrated airspeed (KCAS), while MMO is in Mach

number.

VMO operations at lower altitudes and deals with structural loads andflutter

MMO operations at higher altitudes and is usually more concerned with

compressibility effects and flutter.





VMO /MMO must not be exceeded to prevents:-

– Structural problems due to dynamic

pressure or flutter.

– Degradation in aircraft control response

due to compressibility effects (e.g., Mach

Tuck or aileron reversal).

– Separated airflow due to shock waves

resulting in loss of lift or vibration and

buffet.

Any of these phenomena could prevent the

pilot from being able to adequately control

the aircraft





Stalls

An aircraft will stall when a rapid decrease in lift caused by theseparation of airflow from the wing‘s surface brought on by

exceeding the critical AOA.

People often believe an airfoil stops producing lift when it stalls,

actually it cannot generate adequate lift to sustain level flight. If it

did, the aircraft would fall to the Earth

Since the CL increases with an increase in AOA, at some point the

CL peaks and then begins to drop off.

This peak is called the CL-MAX. The amount of lift the wing

produces drops dramatically after exceeding the CL-MAX orCritical AOA, but it does not completely stop producing lift.

One symptom of an approaching stall is slow and sloppy controls.





In most straight-wing aircraft, the wing is designed to stall the wing

root first.The wing root reaches its critical AOA first making the stall progress

outward toward the wingtip thus maintain aileron effectiveness at the

wingtips enable controllability of the aircraft.

Methods used are:-

Twisted the wing to a higher AOA at the wing root (wing washout)

Installing stall strips on the first 20 –25 percent of the wing‘s

leading edge.

Most aircraft are designed for the nose of the aircraft to drop during a

stall, reducing the AOA and ―unstalling‖ the wing.

The ―nose-down‖ tendency is due to the CL being aft of the CG. The

CG range is very important when it comes to stall recovery

characteristics.




Stalling speed of a particular aircraft is not a fixed value for all flight

situations. Aircraft always stalls at the same AOA regardless of airspeed,

weight, load factor, or density altitude.

Each aircraft has a particular AOA where the airflow separates from

the upper surface of the wing and the stall occurs.

This critical AOA varies from 16° to 20° depending on the aircraft‘s

design.

Each aircraft has only one specific AOA where the stall occurs.

Three flight situations in which the critical AOA can be exceeded:-

Low speed - Stall Speed (Bellow)

High speed - Mach Critical (Exceed)

Turning - Horizontal Component and Centrifugal Force





What is the purpose of the modification above?





Autoflight control axis

Autopilots types can be described as:

– Single-axis - usually operates the ailerons only and is often

referred to as a wing leveler

– Two-axis - ailerons and elevator only

– Three-axis - all the three control surfaces that is aileron, elevator

and rudder

Rudder controls aircraft rotation about or around the vertical or yaw

axis.

Elevators control aircraft rotation about the lateral or pitch axis.

Ailerons control aircraft rotation about the longitudinal or roll axis.





Basic Autoflight System

Early Autoflight System only relief the pilot of controlling the aircraft

by holding the aircraft straight and level.

It all depend on how many aircraft control axis it control and how

large the aircraft is.

Now day majority of commercial aircraft is fitted with 3 axis autopilot

system or for a more advance system it is fitted with Flight

Management System.

The Flight Management System can controlled the aircraft from

takeoff until it land with some provision of fuel saving.





Terminology Used in Autoflight System

Authority - Is the limit placed on the demanded control signal to

prevent excessive attitude changes.

Couple - Raw data input to the autoflight system for a particular flight

path.

Engaged - Is a switch which turn on the autoflight system or itssystem.

Capture - Is the interception of radio navigation beam by the

autoflight system

Gain - is the pre adjustment of level of feedback and output

processes by autoflight computer.

Washout - Is the process of removing error signal from a servo loop.





Basic autoflight system consist of 4 major element:-

– Sensing element - senses aircraft attitude.

– Command element - input by the pilot to the system.

– Computing element - processes input from pilot and sensor and

provide a controlled output to servomotor (ac/dc) or Hydraulic

servo valve.

– Output element - can be servomotor (ac/dc) or Hydraulic servo

valve which moved the aircraft control surfaces.

Basic Autoflight System





Single Axis Wing Leveler

It a simple autopilot system which maintain the aircraft wing level.System component may consist of:-

– Turn Coordinator - Provide roll information to the autoflight

controller/computer

– Autoflight Controller/Computer - Act as a controller to engage the

autoflight and computer which process the input from the turn

coordinator to provide an output to the servomotor.

– Roll Servomotor - Received input from the computer to move the aileron.

Some wing leveler will used Rate Gyro as the sensor.

When Autopilot Engage/Disengage(AP) Button is pushed, it will engages

the autopilot basic roll (ROL) mode which functions as a wing leveler if all

logic conditions are met.

When pressed again, will disengage the autopilot.





Versine Generation

Versine is a trigonometric function equal to one (for unity) minus the

cosine (1 - cosine) of the angle under consideration.

If an aircraft bank at a same air speed it will loss some of it vertical

lift. Engineers name this loss by its trigonometric function Versine.

So whenever the aircraft banks, there will be an additional nose up

signal to the pitch channel (versine) to make up for lost lift resulting

from that particular bank angle.

This lost of lift is referred to as Nose up Compensation or Versine.

When an aircraft is straight and level the resolver cosine winding will

have a maximum output.





When an aircraft bank to left with the same forward speed the lift will be lostbecause it is not capable of balancing the weight of the aircraft. If not

compensated, it will begin to sink.The vector triangle above the right wing of the aircraft illustrates, with thedashed line, the amount of vertical lift that has been lost.

The hypotenuse of the triangle represents the lift applied 90 to the wings.The vertical side of the triangle represents the vertical component of lift.The angle on the bottom is the bank angle of 30º.

So engineer called this loss of vertical lift as versine.

This loss lift is a function of bank angle. It is unity minus the cosine, orversine.

It a value represents the amount of lift which needs to be added in somemanner so that the aircraft will not lose altitude.

The compensation is made by pitching the aircraft nose up to increase theangle of attack, and therefore the lift on the wings.

So autoflight system provide an additional nose up signal to the pitchchannel (versine) to make up for lost lift resulting from that particular bankangle




Figure above show an aircraft autoflight control panel which cater for a

turbulence penetration.

This TURB mode can only be selected when being in either the HDG or the

go-around mode.

The selection of TURB reduces the AP/FD reaction speed and the bank

angle limit to 12 % and will disengaged if VOR/LOC and/or BACK COURSE

modes selected.




END

teory of flight (fixed wing)

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