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Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 1
This sub-module complies with Part-66 11.1.1 / CAT B1.1/1.2
TABLE OF CONTENT: Subject: Page: 11.1.1 Aeroplane Aerodynamics
& Flight Controls ............................... 4 Aircraft
Control
......................................................................................
6
Primary Flight
Controls...................................................................
6 Secondary Flight
Controls..............................................................
6
Control Handles and Levers
................................................................. 8
Pitch and Roll Controls
..................................................................
8 Yaw Control
...................................................................................
8 Trim Controls
.................................................................................
8 Horizontal (Movable/Trimable) Stabilizer
Control........................... 8 Flaps and Slats
Control..................................................................
8 Spoiler and Speed Brake
Control................................................... 8
The Function of Flight Control Surfaces
............................................. 10 Aerodynamic
Principles................................................................
10 Maneuverability
............................................................................
10 Mechanical
Stops.........................................................................
10 Hinge
Moments............................................................................
12 Direct Mechanical Control
............................................................ 12
Aerodynamic Balancing
............................................................... 12
Tab Balancing
..............................................................................
12
Powered Flight
Controls......................................................................
16 Power Boosted Control
................................................................ 16
Fully Powered
Control..................................................................
16 Artificial Feel & Centering
............................................................ 16
Fly-By-Wire
Principle....................................................................
16
Longitudinal (Pitch)
Control.................................................................
18 Elevators
......................................................................................
18 All Moving Tail Planes
(Stabilizers).............................................. 18
All-Flying
Tails..............................................................................
20
Directional (Yaw) Control
....................................................................
22 Turn Coordination
........................................................................
22 Yaw
Damping...............................................................................
22
Engine Failure
Compensation......................................................
22
Lateral (Roll)
Control...........................................................................
24 Aileron Roll Control
......................................................................
24 Roll
Spoilers.................................................................................
24 Aileron
Reversal...........................................................................
24
Adverse yaw
.......................................................................................
26 Lift Inducing
Devices...........................................................................
28
Augmentation of CLMAX
.................................................................
28 Trailing Edge Flaps
......................................................................
28 Leading Edge Devices
.................................................................
32 Slots and Slats
.............................................................................
32 Leading Edge Flaps (Droop Nose)
.............................................. 34 Krueger Flaps
& Variable Camber LE-Flaps................................ 34
Combining Slats & LE-Flaps
........................................................ 34
Drag Inducing
Devices........................................................................
36 Spoilers
........................................................................................
36
Speed-brakes...............................................................................
36 Drag
Chutes.................................................................................
36
Combined Flight Controls
...................................................................
38 Flight Control
Protections....................................................................
40
Rudder
Limiters............................................................................
40 Flaps Load Relief
.........................................................................
40 Asymmetry of High Lift Devices
................................................... 40 Q-Feel
..........................................................................................
40 Control Divergence &
Reversal.................................................... 42
Flutter & Control Surface Static Balance
..................................... 42
Buffeting.......................................................................................
44 Wing Structural Protection
........................................................... 44
Vortex devices & Vortex
Lift................................................................
46 Wing Fences
................................................................................
46 Vortex
Generators........................................................................
46
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Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 2
Vortilons
.......................................................................................
46 Saw-Tooth Leading
Edges........................................................... 46
Super Critical
Airfoils....................................................................
46 Vortex Lift
.....................................................................................
48 Lift and Control From Strakes
...................................................... 48
Stall
Warning.......................................................................................
50 Deep
Stalling................................................................................
52 Advanced Stall Warning
Systems................................................ 52
The Canard
Concept...........................................................................
54 Effects of Down-Springs & Bob
Weights............................................. 56
Down-springs
...............................................................................
56 Bob
Weights.................................................................................
56
11.1.1 Glossary of Terms & Abbreviations
......................................... 58
Edition: 1/MAR06 Revision: Responsible: NEP Module:
TM11.1.1-2
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Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 3
”THIS PAGE INTENTIONALLY LEFT BLANK”
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Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 4
11.1.1 AEROPLANE AERODYNAMICS & FLIGHT CONTROLS The purpose
with this submodule is to describe common practical ap-plications
and the controlling of the aerodynamic forces introduced in
submodule 8.3 and 8.4 (Basic Aerodynamics & Theory of Flight).
This module does not explain from where the aerodynamic force
origi-nates, but uses the laws of aerodynamics to explain the
functions and purposes of; • Maneuvering flight controls, • Control
principles, • Lift and drag inducing devices, • Boundary layer
control (vortex devices), • Vortex lift, • Stall warning, •
Aerodynamic protections, • Etc…
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Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 5
RUDDER
ELEVATOR
AILERON
FLAPS
AILERONELEVATOR
AILERON
RUDDER
ELEVATOR
TRIMABLE HORIZONTALSTABILIZER (THS)
ROLL SPOILERS
GROUND SPOILERS(LIFT DUMPERS)
SPEED BRAKES
43
22
3
4
5
1
AILERON
SLATS
FLAPS
INTRODUCTION – LIGHT & HEAVY AIRCRAFT FLIGHT CONTROLS
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Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 6
AIRCRAFT CONTROL Aircraft must be controlled in all three axes.
For example, the pilot need to be able not only to set the pitch
angle, but also to control the rate at which the angle changes.
Aircraft motion is not limited only to motion about the main axes;
an aircraft can also move in the plane along the axes (up/down,
forward/rearward and transverse). Therefore, six degrees of freedom
exist. There are several possible control systems which could be
used to achieve this controllability. The Wright Brothers for
instance obtained lateral control by "wing warping". They did this
by twisting the wings to increase the angle of attack on one wing
while reducing the angle of at-tack on the other wing, instead of
conventional surface deflection. In generally the control system
used depends on the whether the air-craft is: • Conventional, •
Tailless (or delta), • Canard. A conventional (or classic) aircraft
is one which has a separate main wing and horizontal tail and with
the horizontal tail behind the main wing. An example of a
conventional aircraft is shown below, with differ-ent tail
configurations. Primary Flight Controls The most common control
arrangement on the conventional aircraft is ailerons on the main
wing and a horizontal tail known as the stabilizer with moveable
elevators and a vertical fin (stabilizer) with a rudder. They are
designed to change and control the moments about the roll, pitch,
and yaw axes. The three different control surfaces are
tradition-ally classified as the primary flight controls; • The
elevator controls pitch or the longitudinal motion and thus is
of-
ten called the longitudinal control,
• The ailerons control the roll or lateral motion and are
therefore of-
ten called the lateral controls, • The rudder controls yaw or
the directional motion and thus is called
the directional control. These control surfaces are flap-like
surfaces that can be angularly de-flected at the command of the
pilot. The figure hereunder introduces and defines the primary
flight control surfaces. The ailerons are located at the trailing
edge of the wing. Simi-larly, the elevator is located at the
trailing edge of the horizontal stabi-lizer, and the rudder is at
the trailing edge of the vertical stabilizer. The main control
surfaces are attached to the airframe on hinges so they may move
and thus deflect the air stream passing over them. This redirection
of the air stream generates an unbalanced force to rotate the plane
about the associated axis. Note: Other flight control surfaces can
be added to the group of pri-mary flight controls if they have
taken over a primary control function. Some aircraft achieves pitch
control by a moveable horizontal stabilizer rather than an
elevator. Other aircraft accommodate lateral control by roll
spoilers (lateral control spoilers) rather than ailerons (or by
combi-nation of the two). Secondary Flight Controls To the group of
secondary flight controls we will traditionally find con-trol
surfaces that are not directly involved with aircraft maneuvering,
like; • Various tab controls (trim tabs, servo tabs, balance tabs,
etc…), • Movable (trimable) stabilizers, • Spoilers/speed brakes, •
Leading/trailing edge flaps, • Slats, etc…
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Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 7
LONGITUDINAL/ROLL AXIS (X-AXIS)
CENTER OFGRAVITY (CG)
PITCH AXIS(Y-AXIS)YAW AXIS
(Z-AXIS)
REFERENCE AXIS
PITCHING
YAWING
ROLLING
AILERON (RH)
AILERON (LH)
ELEVATOR (LH)
ELEVATOR (RH)RUDDER
VERTICALSTABILIZER(FIN)
HORIZONTALSTABILIZER
CONVENTIONAL PRIMARY FLIGHT CONTROL LAYOUT
WING
CANARD(FIXED)
MAIN WING
TAIL PLANE (T-TAIL)
CANARD AIRCRAFT (PIAGGIO AVANTI)
DELTA AIRCRAFT (AEROSPATIALE/BAC CONCORDE)
DELTA AIRCRAFT WITH CANARD (EUROFIGHTER)
SLENDER DELTA(OGIVE WING)
CANARD(MOVABLE)
DELTAWING
CONVENTIONALTAIL DESIGN
T-TAILDESIGN
VERTICALSTABILIZER
HORIZONTALSTABILIZER
VENTRALFIN
DORSALFIN
TWIN TAIL
V-TAIL(BUTTERFLY TAIL)
AIRCRAFT CONTROLS
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Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 8
CONTROL HANDLES AND LEVERS Traditionally aircraft are controlled
by a column with a control wheel (also called a yoke) for elevator
and aileron control. This can also be achieved by a control stick
located in front of the seat or to the side. The rudder is
controlled by the pedals. The mechanical (or electrical) connection
between the controls and the flight control surfaces is not a topic
for this submodule to describe. Pitch and Roll Controls Moving the
column forward or rearward controls the pitch of the air-craft.
Forward motion makes the nose drop; rearward motion makes the nose
rise. The control wheel (attached to the column) controls the roll
of the air-craft. Moving the wheel counterclockwise (CCW) makes the
aircraft roll to the left, and a clockwise (CW) motion makes the
aircraft roll to the right. The control stick works in the same
manner. The stick is able to be cy-clic moved in a circumferential
path in its pivoting attachment. Control sticks are typically used
on military fighter aircrafts. The civilian Airbus A320 to 380’s
uses a side stick instead of the traditional column. Yaw Control
The two pedals are mechanical interconnected. When one pedal is
pushed forward the other pedal is moved aft. A push on the left
pedal makes the nose of the aircraft yaw to the left, and vise
versa. The pedals also accommodate brake control by tipping the
pedals for-ward with the tiptoes. Trim Controls Most aircraft can
be trimmed around all three axes. The function of the trim control
system in an aircraft is to ease the control force input re-quired
of the pilot during steady flight, and reducing the workload.
Trimming is typically achieved by turning or rotating a handle or
by op-erating an electrical switch.
Smaller aircraft are typically trimmed by a mechanical operated
handle. Larger aircraft are mostly trimmed by electrical actuation,
from switches located on the control wheel or center pedestrial
panel. The control stick sometimes comprises an electrical trim
switch on the top of the grip, for pitch and roll trimming.
Horizontal (Movable/Trimable) Stabilizer Control Pilot control
input to a movable (trimable) horizontal stabilizer can be achieved
either by input to a mechanical control wheel, located on the
pedestrial panel (most large aircraft), or operating an electrical
switch on the control wheel (yoke). Electrical (or digital) Flight
Control Computer (FCC) systems are in many cases also provided with
trim authorities of the stabilizer. Flaps and Slats Control Cockpit
(flight deck) commands of the flaps and slats systems are mostly
operated by handles or levers. Detents (or gated positions) al-low
the pilot/flight crew accurately to set a specific position (in
units or degrees). If slats are installed they will be operated in
conjunction with the flaps handle/lever. Few aircraft facilitates
independent control of flaps of slats (as a backup feature).
Spoiler and Speed Brake Control Spoiler panels, installed on the
upper side of the wings, are used as flight spoilers (roll and
drag/speed-brake control) and ground spoilers (lift dumpers). Speed
brakes are panels located on the wings or fuse-lage) that provides
additional drag when deployed. A control handle/lever on the
pedestrial panel controls the deflection of spoilers/speed brakes.
If the panels also are used as ground spoilers an automatic
deployment may occur at touch-down. If the flight spoilers take
part in the roll control of the aircraft, a me-chanical or
electrical signal is provided in proportion to input of the
con-trol wheel (or stick).
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Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 9
SIDESTICK
PEDALS
CONTROLWHEEL
CONTROLCOLUMN
RUDDERPEDALS
SPEED BRAKE/SPOILER LEVER
FLAP/SLATLEVER
HORIZONTALSTABILIZERTRIM WHEEL
STALL WARNINGSTICK SHAKER
CONTROLWHEEL
FLAPCONTROLLEVER
TYPICAL LIGHT AIRCRAFT CONTROLS (CESSNA)
SPEEDBRAKE/SPOILER LEVER
FLAPS/SLATSLEVER
HORIZONTALSTABILIZERTRIM WHEEL
MODERN FLY-BY-WIRE AIRCRAFTCONTROLS (AIRBUS)
B737NG AIRCRAFT CONTROLS
CONTROL WHEEL COMMANDS
NEUTRAL POSITION
LEFT ROLLRIGHT ROLL
CW
FWDPUSH
CCW
PITCHDOWN
PITCHUP
REARWARDPULL
RIGHTYAW
LEFTYAW
PEDAL COMMANDS
NEUTRALPOSITION
RUDDERPEDALS
YOKE CONTROL (BEAVER)
YOKE
CONTROL STICK (PILATUS)
TRIMWHEEL(S)
HORIZONTALSTABILIZERTRIM SWITCH
FLIGHT DECK/COCPIT CONTROLS & LEVERS
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Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 10
THE FUNCTION OF FLIGHT CONTROL SURFACES Flight control surfaces
that act as a deflectable part of the airfoil trailing edge are
essential based on the same aerodynamic properties. The deflectable
part, called a flap (not to be mistaken as a flaps sys-tem),
regulates the effective shape (camber) of the airfoil and wing
sec-tion. Aerodynamic Principles In the aerodynamic sense a change
in camber will vary the effective angle of attack (AOA) and the
local coefficient of lift, CL. A downward deflection of the control
surface (aileron or elevator) causes an abrupt change in rearward
curvature of the wing section. The low pressure region accelerates
the airflow across the upper side of the wing, increasing the
coefficient of lift (and the lift). A high pressure area is located
on the lower side in the flap region. The overall result is an
increase in the upward acting force. An upward deflection causes
the opposite. The airflow is accelerated on the lower side and
slowed down on the upper side. The result is an overall decrease in
the upward acting force. A rudder which is given a sideward
deflection will cause asymmetry in lift between the two sides of
the vertical stabilizer (fin), creating a side-ward force. The
change in force that is produced as the result of a certain
deflec-tion is governed by the aerodynamic rules. Flying with low
airspeed requires higher deflection angle to obtain a re-quired
force; flying fast requires less. The density of air will also
affect the force from the deflection. High alti-tude flying tends
dampen the effect of a given deflection.
Maneuverability Motion is assumed to take place around the
Center of Gravity (CG) which then involves forces and arms. Varying
the force provided by horizontal stabilizer generates control
moments about the pitch axis. Varying the force provided by the
vertical stabilizer generates control moments around the yaw axis.
Varying the differential left and right wing forces produces
control moments about the longitudinal (roll) axis. The arm
distances between the CG and the control forces highly af-fects the
control moments. The CG will mostly change longitudinal but lateral
changes may occur if because of fuel imbalance. Rearward CG
location will reduce the yawing and pitching moment as-sociated
with a given control surface deflection, because the effective
control arm is reduced. Forward movement results in the opposite.
Mechanical Stops Over-deflecting the control surface may cause
boundary layer separa-tion making the rear portion of the airfoil
stall. Mechanical stops pre-vent the pilot from applying too large
deflections and loss of control. One set of mechanical stops
(secondary stops) normally prevents too large control input, by
limiting the input from control device (stick, yoke, column, wheel,
pedals, etc.). Another set of stops (primary stop), lo-cated
adjacent to the control surface, prevents too large deflections.
Mechanical stops are adjustable allowing for rigging by the
mainte-nance staff.
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Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 11
MEAN CAMBER LINE
CHORD�
�
EFFECT OF CONTROL SURFACE (FLAP)
DOWNWARDDEFLECTION
�
NEUTRALAILERON
UPWARDDEFLECTION
INCREASEDLIFT
DECREASEDLIFT
NET LIFT (L)
NEUTRAL “FLAP”
NET LIFT (L)
�L
DOWNWARD DEFLECTION
NET LIFT (L)
�L
UPWARD DEFLECTION
CMAXL
0AOA
CL
0 10
0
1.0
1.6
EFFECT OF CHANGED CAMBER & AOA
RUDDERFORCE
ELEVATORFORCE
AILERONFORCE
CG
CONTROL FORCES AND ARMS
PITCHAXIS
ROLLAXIS
YAWAXIS
PRIMARY STOP(PRINCIPLE)
SECONDARY STOP(PRINCIPLE)
STICKMOVEMENT
DEFLECTIONRANGE
FUNCTION OF THE STOPS
THE AERODYNAMIC FUNCTION OF A FLIGHT CONTROL SURFACE
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Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 12
Hinge Moments If an aerodynamic force acts on a control surface,
it will try to rotate the control around its hinge in the direction
of the force. Aerodynamic forces will seek to set the control in an
equilibrium position. The hinge moment is a product of the force
times the distance from the hinge line to the control surface
center of pressure (CP). The force is due to the control surface
area (S), its angular deflection and the dy-namic pressure (½ρv2).
Note: The distance must be set perpendicular to the force. To move
the control surface to a desired angular deflection and main-tain
it in that position, the pilot has to overcome (balance) the hinge
moment. This is done by applying a force to the cockpit control
(stick force). The larger the control surface, deflection or
dynamic pressure, the larger the stick force is required. Therefore
the hinge moment gives the pilot a feel for the control. Direct
Mechanical Control The simplest method of controlling the surface
it the direct mechani-cal control. The pilot controls the surface
by push-pull rods, pulleys and wires using only simple mechanical
advantages (gear ratios), from levers, bell cranks, etc. An
advantage of this control form is that the pilot has direct feel of
the loadings on the aircraft, because the aerodynamic loadings is
felt di-rectly in proportion with the hinge moments. This control
form is typi-cally used on smaller aircraft operating with low
airspeed and hinge moments not excessive to the pilot. For larger
and faster aircraft the resulting aerodynamic forces could give
hinge moments (stick forces) which would be too high for easy
operation of the controls. In this cane the pilot will require
assistance to move the controls in these conditions. This can be
done either by using by using some form of aerodynamic balancing
(achieved in a number ways) or powered (hydraulic) flight
controls.
Aerodynamic Balancing Aerodynamic balancing involves using the
aerodynamic forces on the control surfaces to reduce the hinge
moments. a) An inset (or offset) hinge, meaning that the hinge line
is moved
towards the aerodynamic force, will effectively reduce the hinge
moment. An inset hinge does not reduce the effectiveness of the
control.
b) Horn balance is another effective way to reduce the hinge
moment.
By extending the control area forward of the hinge line, the
force on this part will give hinge moments which are in opposite
directions to the moments on main part of the surface. The overall
hinge moment is therefore reduced without reducing the control
effectiveness.
c) The balance panel (or internal balance) works similar to the
inset
hinge, but the aerodynamic balance area is located inside the
wing. Deflection of the control surface causes pressure changes on
the
control, and these pressure changes are felt by the balance
panel. Suppose that the control is deflected downwards to improve
the
camber. The pressure above the airfoil is reduced and the
pressure below increases. The pressure differential is felt across
the balance panel. Recall that force equals pressure times area (F
= P · A). The force produces a hinge moment which is in opposite
directions to the hinge moment on main part of the surface. The
overall hinge moment is therefore reduced. This type of balancing
is sometimes used in conjunction with powered flight controls.
Tab Balancing Tab balancing is a specialized from of aerodynamic
balancing, used on numerous aircraft of all categories. The control
stick only moves a small part of the main control surface, thus,
the stick forces remains low (even at high speed). The arm from the
tab force to the hinge line produces the hinge moment that
oper-ates the main control surface (it is an aerodynamic ratio
changer).
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Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 13
FORCE
HINGEMOMENT
ARM(HINGE
DISTANCE)
FORCE
REDUCEDHINGE MOMENT
REDUCEDARM
HINGE MOMENT
ANGULARDEFLECTION
INSET (OFFSET) HINGE
HINGELINE
HORNWING/STABILIZER
CONTROLSURFACE
HORN BALANCE
a
bF1
F2
HORNANGULARDEFLECTION
M2
M1
F1
a
F1
F2
M1
M1
M2
SERVO TAB PRINCIPLE
A)
B)
C)b
c
ELEVATOR UP COMMAND(SERVO TAB IS MOVED)
NEUTRAL (OR TRIMMED) CONDITION
F x b = F x c1 2
�M = 0
MAIN CONTROLSURFACE
TAB
CONTROLLINKAGE
BALANCE PANEL
FORCE
HIGH PRESSUREREGION
LOW PRESSUREREGION PRESSURE
DIFFERENTIAL
BALANCEPANEL
BALANCECHAMBER
ELEVATOR IS MOVEDBY SERVO TAB
THE SERVO TAB REDUCES THEREQUIRED STICK FORCE
HINGE MOMENTS & AERODYNAMIC BALANCING
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Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 14
The tab is basically a small auxiliary control surface integral
with the main control surface, and is used as a servo mechanism for
the main surface, or as mean to avoid unwanted side effects from
the deflection of the main control surface. Tabs are regarded as
secondary flight controls (though it actually con-trol or biases a
primary control surface). Tabs are classified into two main groups;
• Control tabs, and • Geared (gear) tabs. Control tabs are found in
three sub-groups; • Servo tabs, • Trim tabs (actually a fixed or
trimable servo tab), and • Spring tabs. Geared tabs are found in
two main groups; • Balance tabs, and • Anti-balance tabs. Note: An
important detail is that control tabs are moved “before” the main
surface is moved (the tab moves the main control), whereas a gear
tab is moved by the main control (the gear tab is moved after).
Servo tabs: Servo tabs are used to ease the required stick force
ap-plied by the pilot. As explained the servo tab is an aerodynamic
ratio changer. The control moments that the pilot applies (M1 = F1
x a) is proportion-ally less than the effective hinge moment
applied to the main surface (M2 = F2 x c). The main surface will
seek an equilibrium where F1 x b = F2 x c) which result in a
certain deflection. Servo tabs are sometimes also seen on hydraulic
powered flight con-trols, used for manual reversion if the normal
hydraulic supply fails, providing sufficient servo assistance.
Trim tabs: The trim tab operates in the manner as the servo tab.
The trim tab can be fixed or adjustable. The deflection of the trim
tab produces a hinge moment that forces the main surface into a new
neutral position, that otherwise was for the pi-lot to keep.
Trimming is sometime accomplished by adjusting the servo tab
control linkage. Spring tab: A disadvantage of the servo tab can be
the lag of re-sponse when operating at low speed. The lowered
dynamic pressure requires large control input to produce the
required change in aerody-namic forces. In fact, direct control
would be preferred at low speed. The spring tab combines the best
from the two control methods. At low speed the spring forces
exceeds the aerodynamic loads on the surface and the complete
control operates, which is ideal for low speed operation. As the
speed increase the aerodynamic loading on the con-trol increases,
causing the spring pack to compress, thus allowing the servo tab to
move. Geared tabs are either used to assist the deflection of the
control sur-face or to counteract deflection, if, for some reasons,
the control force is too excessive. A connecting rod is at one end
attached to the tab and in the other end attached to the
wing/stabilizer structure. A deflec-tion of the main surface will
cause the geared tab to move caused by the geometry of the linkage.
• The balance tab moves in the opposite direction of the main
sur-
face, creating an aerodynamic force that aids the movement of
the control (like a servo tab).
• The anti-balance tab moves in the same direction as the main
sur-
face, creating a force that counteracts the movement of the
control (increase the stick force). This can be used as a mean to
dampen the defection of the main control (for instance used on many
stabila-tor tail-planes). Or as a mean to increase the artificial
feel (stick forces) as the deflection of a control surface
increases.
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Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 15
SPRING FORCE EXCEEDSAERODYNAMIC LOAD
LOW SPEED - LOW DYNAMIC PRESSURE(DIRECT CONTROL OF COMPLETE
SURFACE)
HIGH SPEED - HIGH DYNAMIC PRESSURE(CONTROL OF SPRING TAB
ONLY)
AERODYNAMIC LOADSPRING FORCE
EXCEEDS
- SERVO TAB
- TRIM TAB
- SPRING TAB
GEARED TAB
- BALANCE TAB
- ANTI BALANCE TAB
CONTROL TAB MOVES THE MAIN CONTROL SURFACE
IS BY THE MAIN SURFACEMOVED CONTROL
REDUCES THE STICK FORCE
REDUCES THE STICK FORCE AT HIGH SPEED
ADJUSTS THE NEUTRAL POSITION
REDUCES THE STICK FORCE
INCREASES THE STICK FORCE
SPRING TAB
SPRINGCONTROLINPUT
THE TAB FORCE MOVESTHE MAIN SURFACE
TABMAINSURFACE
CONTROL (OR GEAR) TAB
TRIM TAB
F1
F2
M1
M2
b
c
F x b = F x c1 2
�M = 0
SERVO TABF1
a
M1
TYPICAL TAB APPLICATION
MAIN CONTROLSURFACE
TAB
ADJUSTABLETRIM LINKAGE
TRIM KNOB/WHEEL(COCKPIT)
TRIM LINKAGEMD80 AILERON TABS
CONTROLTAB
TRIMTAB
TRIM TABS
FIXED RUDDER TRIM TAB
ANTI BALANCE TAB
BALANCE TAB
DECREASES THESTICK FORCES
INCREASES THESTICK FORCES
GEARED TABS TAB OVERVIEW TABLE
AERODYNAMIC BALANCING (CONTROL TABS & GEARED TABS)
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Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 16
POWERED FLIGHT CONTROLS Powered flight controls are equivalent
to hydraulic actuation. Hydraulic pressure at 3,000 PSI (and even
in excess of that) is able to generate tremendous forces when
exposed to a control area (piston area). Pow-ered flight control is
classified into two sub categories; • Power assisted (power
boosted), • Fully powered (fully in-reversible). Power Boosted
Control The actuator assembly, - often called a Power Control Unit
(PCU), has a main piston (or ram) hydraulic controlled by the small
pilot oper-ated pilot/servo valve. The pilot valve controls the
distribution of the supplied hydraulic pressure to the main piston.
Power assisted/boosted control principle is similar to that used in
many automobile vehicles. The cockpit control is mechanically
connected to both the control surface (direct control) and the PCU
pilot valve. An in-put command will move both the control surface
and the pilot valve. Movement of the pilot valve makes the PCU
assist moving the control linkage to the control. Note that the
piston rod-end is attached to fixed structure. When hy-draulic
pressure is applied to one side of the piston the complete PCU
housing moves, also operating the control linkage to the surface.
The housing also moves relative to the pilot valve and when the
housing has moved the required distance (stroke) it has closed the
pilot valve again. The relative motion between the housing and the
pilot valve is called “follow-up” and allows for proportional
control of the PCU. How much of the required stick force that comes
from the pilot and how much that comes from the PCU depends on the
boost ratio. A boost ratio of 5:1 means that the PCU delivers 80%
of the required stick force, thereby reducing the required the
cockpit. The mechanical geometry determines the boost ratio. The
feedback from the control surface to the cockpit control is
proportional to the boost ratio.
Power assisted/boosted systems often accommodate manual
rever-sion which means that the pilot can attain full control of
the control sur-face if the hydraulic supply fails (for instance by
tab control). This re-quires that the two sides of the piston are
interconnected and a mechanism that provide override of the input
to the pilot valve. Fully Powered Control In a fully powered
(in-reversible) system the cockpit control only oper-ates the servo
valve in the PCU. In-reversible means that the pilot can deflect
the control surface, but forces generated on the control surface
can not be felt on the stick (or column/wheel/pedals). This is due
to the hydraulic lock in the PCU. The PCU uses follow-up for
proportional control. Artificial Feel & Centering Because the
pilot only feels the load necessary to move the pilot valve in the
PCU, an artificial feel system must be added to a powered con-trol
the system. Artificial feel can simply be added by springs tension
(or compression). The spring increases the stick forces when the
de-flection increases giving the pilot a surrogate feeling of the
aerody-namic load on the aircraft. The spring also provides
centering of the servo mechanism so that the neutral position can
be identified. Some controls have variable feel, achieved by a
mechanical computer (Q-feel) that takes airspeed (and perhaps other
data as well) into ac-count, to produce a more accurate “feel” for
the pilot. Fly-By-Wire Principle Fly-By-Wire (FBW) control means
that the mechanical control linkage to the PCU/actuator and the
pilot valve has been replaced by an Elec-tro-Hydraulic Servo Valve
(EHSV). The result is substantial weight savings. The EHSV controls
the hydraulic fluid to the main piston when current excited from a
driver in a digital (or analog) computer. The computer receives a
feedback from an electric position sensor which provides
proportional control of the PCU, by electrical follow-up.
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Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 17
HYDRAULICSOURCE
P R
CONTROL INPUT FROM PILOT
CONTROL INPUT FROM PCU
PILOT VALVE
STRUCTURE
MAIN PISTON/RAM(STATIONARY)
COLUMN
PIVOT
LINKAGE
CONTROLSURFACE
POWER CONTROLUNIT (PCU)
HINGELINE
POWER BOOSTED (ASSISTED) CONTROL SYSTEM
FULLY POWERED (IRREVERSIBLE) CONTROL SYSTEM
HYDRAULICSOURCE
PR
TO PILOTVALVE
ARTIFICIAL FEEL & CENTERING MECHANISM
CAMROLLER SPRING
CAM SPRING ISCOMPRESSED
PROGESSIVEINCREASE INFEEL FORCE
OVALHOLE
NOTE: FEEDBACK FROM CONTROL
SURFACE TO COLUMN IN PROPOR-
TION TO THE BOOST RATIO
NOTE: NO FEEDBACK FROM CONTROL
SURFACE TO COLUMN BECAUSE OF A
HYDRAULIC “LOCK” IN THE PCU
HYDRAULICSOURCE
PR
FULLY POWERED FLY-BY-WIRE (FBW) CONTROL SYSTEM
SIDESTICK
STM
PCU FEED-BACK (LVDT)
EHSV (TM)
STEERING COMMANDS
STRUCTURE
PCU
ACTUATOR FEEDBACK (FOLLOW-UP)
SU
RFA
CE
PO
SIT
ION
FE
ED
BA
CKEXCITATION
Q-FEEL COMPUTER(FEEL INCREASESWITH AIRSPEED)
PITOT
STATIC
CAM
CONTROL LAW DATA(AIRDATA, AOA, WEIGHT,CG, A/C CONFIG,
LOAD-FACTOR (n), ETC...)
AIRCRAFT MOTION
AUTOPILOT(AUTOFLIGHT)
POWERED FLIGHT CONTROLS (PRINCIPLES)
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Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 18
LONGITUDINAL (PITCH) CONTROL Pitch control is a by far the most
important control axis on the aircraft, because aircraft pitch, is
closely related to control the angle of attack (AOA). The AOA is
used to adjust for weight and CG changes, speed changes, different
aircraft configurations (flaps, slat, etc.). Elevators Aircraft
pitch control is traditionally achieved by the elevators. An
ele-vator is mounted on the back edge of the horizontal stabilizer
on each side of the fin. They move up and down together. Pulling
back on the column, control wheel or stick will deflect the
eleva-tors upward, making the aircraft pitch nose-up (ANU). This
makes the wings fly at a higher angle of attack which generates
more lift. Pushing the control forward will make the aircraft pitch
nose down (AND). Cen-tering the control the elevators to neutral
and stops the change of pitch. All Moving Tail Planes (Stabilizers)
A stabilator is a combination of a stabilizer and an elevator.
Instead of pure elevator motion the complete tailplane angle of
incident can be changed. This increases or decreases the tailplane
angle of attack; hence also the tail lift and aircraft pitch. The
neutral point (angle of in-cidence) of the stabilator can be
changed for trimming purposes. An anti-balance tab (a geared tab)
is fitted to the Piper example be-low. The anti-balance tab
produces an aerodynamic force that coun-teracts the direct pilot
input to the stabilator. The tab makes sure that the “stick forces”
gets proportionally higher and higher as the stabilator angle of
incidence increases. It also pre-vents “aerodynamic run-away”.
Recall that the location of the center of pressure changes with
angle of attack (AOA). If the lift force of the sta-bilator attacks
ahead of the pivot line; a moment assisting the input de-livered by
the pilot could make the stabilator uncontrollable.
Supersonic military fighter aircraft are almost exclusively
equipped with a pure all-moving tailplane which operates like the
stabilator (without the tab), often referred as a slab tail. An
important advantage of the all-moving tail is the large control
mo-ments that can be created, even with small angle changes. An
all-moving tail will in general produce less drag than a
conventional stabi-lizer equipped with an elevator system. This has
a particular interest when is comes to longitudinal trim forces. An
all-moving tail performs far better in transonic and supersonic
air-flows. Conventional elevator control will typically suffer
control losses when operating in the transonic speed region,
because of induced shock separation (see submodule 11.1.2 – High
Speed). Shock separation near the trailing edge of a wing section
will reduce the authority of any control surface located here
(aileron, elevator, etc…). As the all-moving tail controls the lift
over the entire tail area, it will not suffer as badly as an
elevator operating in the wake.
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Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 19
ELEVATOR
CG
AIRCRAFT PITCH CONTROL
PITCHAXIS NEUTRAL
PITCHINGMOTION ANU
AND
FIXED TAIL WITH ELEVATOR (CESSNA)
STABILATOR WITH BALANCE TAB (PIPER PA28)
HORNBALANCE
ELEVATOR
ANTI-BALANCETAB
STABILATOR
ALL-MOVING TAIL (F4 PHANTOM)
SLAB TAIL
ALL-MOVING TAIL
DEFLECTIONRANGE
TRANSONIC MACH NUMBER EFFECTS
SHOCK INDUCED SEPARA-TION CAUSES AERODYNAMICINEFFECTIVINESS
SHOCKWAVE
CONVENTIONAL CONTROL
SLAB TAIL CONTROL
SHOCK INDUCED SEPARATION
PITCH CONTROL
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Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 20
High speed “tuck-under” (or mach tuck) is a phenomenon that
occurs at high mach numbers because a shift in the location of the
wing aero-dynamic center (AC) occurs. A supersonic lift
distribution is somewhat more flattened out than the one of a
subsonic. This results in a rear-ward motion of the center of
pressure that, with respect to the CG, causes the aircraft to pitch
down. The higher control authority of an all-moving tail makes it
easier to counteract this by mach trimming the air-craft nose-up.
If chock stalling of the tail occur an all-moving tailplane can
easier be recovered, because the tailplane AOA effectively can be
changed. All-Flying Tails Most jet transportation category aircraft
have all-moving horizontal sta-bilizers, equipped also with a
conventional elevator. This arrangement is often referred to as an
all-flying tail. The elevator is used as a maneuvering control
device coupled to the column/control wheel/stick (or autopilot) for
pitch control. Trimming the aircraft for CG movement and
aerodynamic phenomena’s (for instance mach trimming) is achieved by
adjusting the stabilizer angle of inci-dence. The stabilizer is
controlled by a screw-jack driven through a transmis-sion system.
Manual control is possible by a cable-wire drive system. Automatic
control is made possible either by electrical motors or by
hy-draulic motors. The Flight Control Computer (FCC) system is
often designed so that when a long term elevator deflection is
sensed (by position sensors), the elevator deflection is cancelled
out by auto-trimming of the horizon-tal stabilizer. A trimable
horizontal stabilizer is a powerful control surface. A stabilizer
run-away (uncommanded motion) caused by failure in the auto-flight
systems, flight control computers (FCC’s) or stabilizer control
circuit
could be fatal. In most aircraft it is therefore possible for
the crew to manual override the electrical control circuit.
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Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 21
ELEVATOR
TRIMABLESTABILIZER
BALANCE TAB
ALL-FLYING TAIL (B737)
ELEVATOR
PIVOT
STABILIZER
ALL-FLYING TAIL
TRIMRANGE
BEFORE TRIMMING
AFTER TRIMMING
TRIMABLE HORIZONTAL STABILIZER SYSTEM (TYPICAL)
M
COLUMNELECTRICAL TRIM SIGNALS
S
S
FCC’s
ELEVATORDEFLECTION
POS SIGNALS
STAB TRIMWHEEL
MANUAL TRIM SIGNALS
PITCH (ELEVATOR) COMMANDS
SCREWJACK
BALLNUT
STABDRIVE
FCC’s
MACHTRIM
HIGH SPEED TUCK-UNDER (MACH TRIMMING)
CGAC
- ML
LT
LOW MACH NUMBER TRIM
LOW SPEEDPRESSUREDISTRIBUTION
LT
CG AC
- ML
TRANSONIC MACH NUMBER TRIMHIGH SPEEDPRESSUREDISTRIBUTION
PITCH CONTROL
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Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 22
DIRECTIONAL (YAW) CONTROL Yawing or directional control,
accomplished by the rudder, is important in several aspects, such
as; • Turn coordination, • Yaw damping (Dutch Roll), • Engine
failure compensation (multi engine aircraft), • Runway alignment
(de-crapping) during landing, etc… The rudder is mounted on the
back edge of the fin in the tail. The rud-der works just like an
elevator, except in a vertical plane. Deflection of the rudder to
either side increases the camber of the fin and creates a force in
opposite direction. This force, having an arm with respect to the
CG, causes a yawing moment to act in the horizontal plane about the
CG. When the pilot pushes the left pedal, the rudder deflects left.
Pushing the right pedal causes the rudder to deflect right.
Deflecting the rudder right pulls the tail left and causes the nose
to yaw right and vise versa. Centering the rudder pedals returns
the rudder to neutral and stops the yaw. Note: Asymmetrically
engine thrust on multi-engine aircraft will also in-troduce yawing
moments that must be outbalanced by a rudder input. Additionally, a
necessary rudder deflection can be cancelled by asym-metrically
engine thrust, in order to reduce the rudder trim drag. Turn
Coordination Turning can be performed in a number of ways (however,
most of them unpleasant for the crew and passengers). Turning must
be made coor-dinated meaning that the force couple (gravity and the
centrifugal force) acts along the vertical center line of the
aircraft. Aircraft turn because of the banking created by the
ailerons, not be-cause of a rudder input. Yawing is used to assist
the banking to pre-vent side skidding (side slipping) during
turning.
Turning will normally combine all three primary control systems;
aileron to bank the aircraft, elevator to increase the AOA and keep
up the nose during the turn and yaw pedals to make avoid
coordinated turn. A coordinated turn is also called a balanced
turn. Correct turning can most easy be understood by illustrating
the turn and slip indicator. Correct turning is achieved when the
“ball” in the slip indicator is lo-cated in the in the
middle/bottom of the indicator. If the centrifugal force is
dominant (to little pedal input) the ball moves outwards. If the
too much pedal input is applied (the nose moves far too deep into
the turn) the ball moves inwards. On larger aircraft turn
coordination is mostly provided by the Flight Control Computers
(FCC) and not the pilot. Yaw Damping Yaw damping is provided to
dampen “Dutch Roll” (a dynamic instability mode) as explained in
submodule 8.4 - Aircraft Stability & Dynamics. Dutch roll
damping is carried out by a part of the FCC system or other flight
augmentation system. Yaw damping is provided as a parallel input to
the rudder actuation system as an electro/hydraulic command without
any feedback to the pedals (which makes the pilot unaware of these
rudder motions). Engine Failure Compensation Multi-engine aircraft,
with lateral located engines (on the wings or at the tail) may use
the rudder to outbalance the thrust asymmetry in case of engine
failure. The size of the vertical stabilizer is typically related
to the magnitude of the thrust loss and the additional drag
associated with an engine failure. The distance between the AFT CG
limit and the sta-bilizer is also an important design parameter.
Multi engine propeller (turboprop) aircraft generates high drag if
the propeller fails to feather in case of engine failure, which
requires a large stabilizer and rudder area to outbalance.
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Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 23
RUDDERFORCE
CG
AIRCRAFT YAW CONTROL
YAWAXIS
YAWING
RUDDERDEFLECTION
WINDCOMPONENT
RUNWAYHEADING
HEADING
WINDCOMPONENT
APPROACH WITHCROSS WIND
(RUDDER INPUT)
RUDDER
VERTICAL FIN/STABILIZER
RUDDERSIDE FORCE
ROLL(BANKS THEAIRCRAFT)
PITCH(KEEPS THEALTITUDE)
YAW(PREVENTSSKIDDING)
CONTROLING THE TURN (TURN COORDINATION)
CENTRIFUGALFORCE (SKID)
4 MIN TURN
TURN AND SLIPINDICATOR
NO SLIP/SKID
INSUFFICIENTYAWING (SKID)
TO MUCHYAWING
LH TURN(4 MIN)
W
FC
LW
WT
CENTRIFUGALFORCE
CENTRIPETALTURNINGFORCE
L =T FCL +W
CENTERLINE
TURNINDICATOR
SLIPINDICATOR
22
DE-CRAPPING(WITH RUDDER)
DIRECTIONAL (YAW) CONTROL
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Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 24
LATERAL (ROLL) CONTROL Roll control can be achieved by several
design methods. Traditionally ailerons are used to generate a
rolling motion around the longitudinal axis. Another often used
method is roll spoilers (lateral control spoil-ers) which are
panels located on the upper wing surface, which can be deployed
into the airflow lowering the wing lift. Aileron Roll Control
Ailerons are mounted on the back edge of each wing near the
wingtips, and move in opposite directions. The word aileron is
French for "little wing". The ailerons change the effective airfoil
camber of the part of the wing covered by the ailerons, and thereby
the wing lift. With greater downward deflection, the lift will
increase in the upward direction. An upward deflection causes the
upward lift to decrease. A left or counterclockwise control input
causes the lift on the right wing to increase and the lift on the
left wing to decrease. When the pilot moves the stick left (or
turns the control wheel counter-clockwise) the left aileron goes up
and the right aileron goes down, and vise versa. This cause the
aircraft to bank left and an unbalanced side force component of the
wing lift force causes the aircraft's flight path to curve to the
left. As previously explained aircraft turn because of the banking
created by the ailerons, not because of a rudder input. Centering
the stick returns the ailerons to neutral maintaining the bank
angle. The plane will continue to turn until opposite aileron
motion re-turns the bank angle to zero to fly straight. The actual
character of the lateral stability will greatly influence on the
behavior after the stick (or wheel) is centered. For both wings,
the lift force of the wing section through the aileron is applied
at the aerodynamic center of the section which is some dis-tance
(an arm) from the aircraft center of gravity. This creates a
mo-ment (torque) about the center of gravity. If the forces (and
distances) are equal there is no net rolling moment on the
aircraft. But if the forces are unequal, there is a net torque and
the aircraft rotates about its cen-ter of gravity.
Roll Spoilers Some aircraft has roll control only accomplished
by roll spoilers (no ai-lerons). The spoiler panel(s) will only
deflect on the down-going wing causing the aircraft to roll by
“lift dumping” (reducing the coefficient of lift – CL). A side
effect is that the drag is increased only on the down-going wing,
making it slow down compared to the up-going wing. At first glance
this seems to be a disadvantage. But it is not, because it
compensates for adverse yawing (see next text page). This
arrangement makes movement of the spoiler dependent upon movement
of the aileron. The linkage to the aileron is devised so that the
spoiler is extended only when the aileron is raised. In other
words, when the aileron moves downward, no deflection of the
spoiler takes place. Aileron Reversal Large aileron deflections at
high speed (high dynamic pressure) can be a serious treat for high
speed aircraft. Wing sweep and taper causes the airfoil thickness
to decrease towards the wing tips, reducing the tor-sional
stiffness of the outboard wing section. A downward aileron mo-tion
may actually reduce the angle of incidence (and the local AOA) so
violently that the aircraft rolls to the opposite side than the
com-manded. This phenomenon is called aileron reversal. An upward
de-flection can cause the opposite effect. Flight testing must make
sure that the aileron reversal speed is outside the normal speed
envelope. One method to limit outboard wing torsion is by
progressively lower the maximum aileron deflection angle as the
speed increases, or by pre-venting aileron motion above a given
speed. Lateral control may in-stead be achieved by another set of
ailerons (called high speed ailer-ons or all-speed ailerons)
located closer to the fuselage, where the wing structure is much
more rigid. Frequently spoiler control is used as a mean to achieve
high-speed lateral control. Both methods have the purpose to move
the aerodynamic force inboard, to a position where the wing
structure is more rigid.
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Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 25
LATERAL CONTROL(ROLL)
AILERON (RH)
AILERON (LH)
WING
RH ROLL
RH ROLL
NEUTRAL POSITION
LEFT ROLL
RIGHT ROLL
“AFT LOOKING FORWARD (ALF)”
ROLL (LATERAL) SPOILERS(INITATES A RH ROLL)
PANAVIA TORNADO (PHOTO BY MICHAEL HIND)
HIGHSPEEDAILERON
LOWSPEEDAILERON
FLIGHT (ROLL)SPOILERS
ROLL/LATERAL CONTROL (BOEING B727)
TAILERONS
HIGH (ALL)SPEEDAILERON
LOWSPEEDAILERON
LARGEARMSMALL
ARM
FLIGHT (ROLL)SPOILERS
TORSION
AILERONLIFT
AOA ISLOWERED
AILERON REVERSAL
LATERAL (ROLL) CONTROL
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Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 26
ADVERSE YAW An unwanted secondary effect of aileron operation is
adverse yawing - a yawing moment in the opposite direction to the
turn. In other words, using the ailerons to roll an aircraft to the
right would produce a yawing motion to the left. Deflection of the
ailerons introduces adverse yawing mainly because of two effects.
The first effect arises from drag differences between the two wing
halves caused by the changed wing geometry. This can be visualized
this way; • The wing with the down moving aileron achieves
increasing camber
increasing both lift and drag, and the opposite takes place on
the wing with the up-moving aileron. The difference in lift makes
the air-craft roll and the difference in drag make the aircraft
yaw. Because the down-going wing has less drag it moves relatively
faster than the up going wing making the yawing opposed to the
roll. When moving the stick (or control wheel) to the left to bank
the wings, ad-verse yaw moves the nose of the airplane to the
right. This is called the secondary effect of the ailerons.
Increasing the camber of a wing makes it increase profile drag and
induced drag.
The second effect comes from the aerodynamic damping described
in submodule 8.4 - Flight Stability and Dynamics; • A down-moving
wing will experience an increase in AOA and vise
versa for an up-going. The down-moving wing increases its lift
and the up going wing will have its lift decreased. As lift attack
perpen-dicular to the resultant airflow the lift will act forward
with respect to a vertical reference plane for the down going wing,
which generates adverse yawing. For the up going wing the lift
reduces acting behind a vertical reference plane with the same
consequence. This is called the secondary effect of the roll.
Adverse yaw is more pronounced for light aircraft with long
wings, such as gliders. It is counteracted by the pilot or the
Flight Control Computer (FCC) system with the rudder.
Several design methods can be used by the manufacture to counter
act adverse yaw, like; aileron differential control, rigging the
ailerons with upfloat, frise ailerons, aileron-to-rudder
interconnection or roll spoilers (lateral control spoilers). •
Aileron differential control causes the upward moving aileron to
a
higher deflection angle than the downward moving aileron. The
higher deflection of the up-going aileron will make this wing
produce additional drag whereas the lowered deflection of the
down-going ai-leron lowers the drag, thus reducing the difference
in drag between the two wings.
• Rigging the ailerons with up-float makes the aileron
deflection be-
have as differential controlled ailerons, reducing the downward
de-flection of the ailerons. This is used on many light
aircraft.
• Frise ailerons have an asymmetric leading edge as shown in
the
figure. The leading edge of the up-going aileron protrudes below
the wing surface, causing higher drag. The leading edge of the
down-going aileron remains shrouded and causes les drag.
• Flight spoilers (roll spoilers), only raised on the down-going
wing,
will increase drag (and reduce lift) on this wing, thus reducing
the difference in drag between the two wings. This arrangement
makes movement of the spoiler dependent upon movement of the
aileron. The linkage to the aileron is devised so that the spoiler
is extended only when the aileron is raised. In other words, when
the aileron moves downward, no deflection of the spoiler takes
place.
• Aileron-to-rudder interconnection is a mechanical (or
electrical)
input automatically provided to the rudder system, in proportion
with the aileron command (which also provides turn coordination).
This typically on many smaller aircraft.
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Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 27
ROLL
ADVERSEYAW
RESTORINGROLL
LIFTDECREASES
LIFTINCREASES
ADVERSE YAW FROM ROLL (LATERAL DAMPING)
vF
vV
vRES
vRES
vF vVADVERSEYAW
ROLL
INCREASEDLIFT
INCREASEDDRAG
DECREASEDDRAG
DECREASEDLIFT
HIGHER INDUCED DRAG& PROFILER DRAG
ADVERSE YAW FROM AILERONS
AILERON DIFFERENTIAL
SMALL DOWN-WARD DEFLECTION
LARGE UPWARDDEFLECTION
FRISE AILERONS
HIGHER DRAG
RIGGING WITH “UP-FLOATING”
ROLL
DRAG
DRAG
DRAG
ROLL SPOILER
ROLL SPOILER COMPENSATION
EQUAL DRAG
ROLL/FLIGHT SPOILER
COUNTERACTING ADVERSE YAW
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Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 28
LIFT INDUCING DEVICES The purpose with lift inducing devices
(high lift device or lift augmen-tation) is to reduce the take-off
and landing distance. This permits op-eration at greater weights
from given runway (RWY) lengths and en-ables greater payloads to be
carried. The term high lift device is somewhat misleading. Remember
that lift must equal weight. The aircraft does not change weight
just because a takeoff or a landing is to be performed. Instead the
stall speed has to be reduced which requires that the maximum
coefficient of lift (CLMAX) is increased. Slow speed device would
therefore be a more relevant term. For a given weight the take-off
and landing distances depends on the speed at the RWY “screen
heights” specified by regulation (see sub-module 8.3 Aerodynamics).
Regulation specifies safe margin to stall for at the screen heights
(min 1.2VS and min 1.3VS) at takeoff and at land-ing). The stalling
speed is determined by the CLMAX of the wing, and to obtain the
lowest distances, the CLMAX must be as high as possible.
Augmentation of CLMAX The lift coefficient is determined by the
airfoil shape. Thickness (or fineness) ratio, leading edge radii
and camber is important. Increasing the camber by leading and
trailing edge devices increases the coeffi-cient of lift for a
given angle of attack (AOA). It also increases CLMAX. For takeoff
and landing a more cambered wing is desirable, but high drag will
be the result at the cruising speed. The camber must there be
variable so that the wing can be optimized for the flight
condition. This is achieved by Trailing Edge (TE) flaps often
combined with Leading Edge (LE) devices. Trailing Edge Flaps A flap
is (as explained on page 10-11) is usually a hinged portion of the
trailing edge on the airfoil section.
Flaps can however also be located at the leading edge
(LE-flaps). The flap is usually used to positive increase the
camber. However, jet fight-ers often use LE-flaps and TE-flaps for
positive and negative variation of the camber. Lowering flaps
increases both lift and drag, but not in the same propor-tion.
Although the lift is the larger force, the proportional increase in
drag is higher, and so the lift to drag ratio (L/D-ratio)
decreases. The L/D-ratio is a measure of the aerodynamic efficiency
and therefore flaps lowers the performance in areas such as range,
endurance, climb angle and glide/decent angle. With flaps down the
range is reduced (more fuel is used), the climb angle is reduced
and the glide angle in-creased. In steady flight lift must equal
the weight (L = W). Lowering the flaps in-creases the AOA for the
same attitude. If the speed is kept constant the AOA must be
reduced by lowered nose. Aircraft will therefore fly more nose-down
with flaps extended, which is an advantage as it gives better
visibility of the approach and landing. Trailing edge flaps changes
the pressure distribution of the wing and therefore also the wing
pitching moment, leading to trim changes when flaps are extended or
retracted. Flaps also increase wing the down-wash, at the tail
force produced by the tail plane. Increased camber tends to produce
nose down pitching moments, increased downwash tends to do the
opposite. The overall effect will be the sum of the two influenced
by the type of flap, tail configuration, etc.
-
Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 29
L = ½ v C S�. . 2. .L
-2kgms
LIFT EQUATION
DENSITY:- ATMOSPHERIC PRESSURE,- TEMPERATURE (OAT)
WING AREA:- MAY BE VARIABLE BYFOWLER FLAPS
COEFFICIENT OF LIFT:- ANGLE OF ATTACK (AOA),- CAMBER (PROFILE
SHAPE),- SURFACE CONDITION,- MACH NUMBER
AIR SPEED:- TRUE AIR SPEED (TAS)
V1
SCREENHEIGHTMIN 35’
VR
V2
50’
APPROACHPATTERN
LOW SPEED/HIGH DRAGCONFIG
MIN 1.3VS
TOUCH DOWN
HIGHTHRUSTSETTING
FINALAPPROACH
3 G/S0
MIN 1.2VS
“ONEENG
INE OUT (O
EO)”
TO PROF
ILE
“NORM
AL”
TOPRO
FILE
E = ½mvKIN2
LOW SPEED/LOW DRAGCONFIG
CLIMBSEGMENT
CLEAN (CRUISE) CONFIGURATION
TAKE-OFF CONFIGURATION
CHORD�
�
CAMBER VARIATION
APPROACH/LANDING CONFIGURATION
�
LOW SPEED/LOW DRAGCONFIG
LOW SPEED/HIGH DRAGCONFIG
LOW PRESSURE REGION
HIGH PRESSURE REGION
LOW SPEED CONFIG PRESSURE DISTRIBUTION
LIFT INDUCING DEVICES
-
Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 30
The basic principle of the trailing edge flap has been adapted
in many ways. The more commonly used types are described hereunder.
• The plain flap (b) is a simple construction and gives good
increase
in CLMAX, although fairly high drag (low L/D-ratio). It is used
mainly on low speed aircraft and where very short take-off and
landing is not required.
• The split flap (c) forms a part of lower surface of the lower
surface
of the trailing edge, the upper surface contour being unaffected
when the flap is lowered. The split flap gives about the same
in-crease in lift as the plain flap at low AOA, and slightly more
at higher AOA as the upper surface camber in is not increased and
so sepa-ration is delayed. The drag is however higher than for
plain flaps because the wake is much stronger.
• Slotted flaps (d) have gaps (slots) allowing high pressure air
from
the lower wing side to add energy to upper surface of the flap
seg-ment. This adds energy to the tired boundary layer, postponing
boundary layer separation to a higher AOA, increasing the CLMAX
even further, as the deflection angle can be increased.
• Fowler flap (e) moves rearwards and then down when
extended.
This gives an increase in camber and wing area. Typically fowler
flaps are also slotted (single or multiple). Multiple slotted
fowler flaps (f) has one or more vanes installed between the wing
trailing edge and the flap section (providing the slot(s).
Multiple slotted fowler flaps have the best performance of all
flap types, but are complex, heavy and volume requiring. Besides it
takes time to extend/retract.
• The zap flap (g) is very similar to the fowler flap but
without the slot. • Powered flaps generally use airflow from the
engine to shape the
flow of air over the wing.
Blown flaps (h) use bleed air from the jet engine's compressor
which is blown over the rear of the wing and flap, adding both
air-flow and energy so that the flow remain attached at high AOA.
In ef-fect the airflow acts as a sort of a slat for the flaps
allowing higher flap deflection angle. Blown flaps are only used on
few and mostly jet fighters. Thin winged fighters are not able to
contain a complex and volume requiring slotted fowler flap
system.
Another system uses the airflow from the engines directly, by
plac-ing part of the flaps directly in the path of the exhaust, - a
jet flap (i). Most aircraft have split the flap so the portion
behind the engines does not move into the exhaust. But, if the
flaps are made strong enough, the effects can be enormous. The C-17
Globemaster has a flap system using this principle (also called the
Coanda effect).
Note: The action of the flaps is to increase the maximum
coefficient of lift, CLMAX for a given AOA, but stalling AOA is
reduced. Increasing the flap deflection angle increases both lift
and drag. The comparison of the drag polar curves of the different
types of flaps show a considerably difference in the lift and drag
produced. Small de-flection angle will generally increase lift more
than drag. At a given de-flection the increment in lift will be
overtaken by larger and larger in-crement in drag. During takeoff,
drag reduces the acceleration and climb performance and a small
flap deflection is preferred to give as little drag as possible.
For landing however, drag adds to the braking force and so flap
drag is beneficial. Besides, the large flaps settings makes the
aircraft fly more nose-down improving the vision during approach.
High drag on approach requires high engine thrust. This is an
advan-tage in case of a go-around of missed approach, because the
crew does not have to wait long for the engine to accelerate to
go-around thrust. As a part of the procedure drag is reduced by
stepwise retrac-tion of the flaps as speed is gained, to improve
the climb performance.
-
Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 31
PLAIN (SIMPLE) FLAP
SPLIT FLAP
BLOWN (BLC) FLAP
DOUBLE SLOTTED FOWLER FLAP
CLEAN/BASIC WING
A)
B)
C)
E)
D)
“DOUBLE SLOTTED”FOWLER FLAPSYSTEM
VANE
FLAP
H)
PLAIN
FOWLER
SLOTTED
SPLIT
BASIC
FOWLER
SLOTTED
SPLIT
PLAINBASIC
FOWLER
SLOTTED
SPLIT
PLAIN
CL
CD
AOA
CL
FLAPANGLE
�CL
ZAP FLAP
G)
F)
FOWLER FLAP
VERSUS ANGLE OF ATTACK
CMAXL
CMAXL
C ANDL
CD
C VERSUS (L/D-RATIO)L
C VERSUS DEFLECTIONL
SLOTTED FLAP
CESSNA (PLAIN) FLAP
FOWLER FLAP SYSTEM (BOEING B777)
SLOTTED FOWLER FLAP SYSTEM (BOEING B727)
JET FLAP (BY COANDA EFFECT)
SPLIT FLAP
SLOTS
SCREWJACKS
VANE
FLAPS
LEADING EDGELAP(LE) F
TRAILING EDGE(TE) FLAP
FLAP SYSTEM (A340)
TRAILING EDGE FLAPS
-
Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 32
Leading Edge Devices Lift inducing leading edge devices are
groups into either; • Boundary Layer Controlling (BLC) devices, and
• Camber varying devices. The group of Boundary Layer Controlling
(BLC) devices primarily in-cludes fixed slots, automatic and
variable slats. The group of camber varying (or controlling)
devices includes Leading Edge flaps (LE-flaps), krueger flaps and
variable camber LE-Flaps. Besides, the leading edge can be equipped
with other features improv-ing the wing airflow when operating at
low speed (like vortilons). All LE-device prevents the pressure
distribution on the upper side from peaking at the leading edge.
This delays separation to a higher AOA. LE-devices have only with
very little effect on the wing pitching mo-ments. Slots and Slats
The maximum coefficient of lift, CLMAX, can be increased through
the use of leading edge slots. The low speed leading edge problem
is due to the Reynolds number effects, explained in submodule 8.2
(Aerodynam-ics). The slot allows high pressure air from the lower
surface to merge with upper airflow at the leading edge. The slot
airflow causes a laminar boundary layer into a turbulent boundary
layer, much more capable of overcoming wing curvature without flow
separation. The airfoil can then be flown at a higher angle of
attack before stall occurs and thus get a higher CLMAX value. For
angles of attack less than the stall angle, however, the airfoil
lift curve is relatively unaffected whether the slot is opened or
closed. The slot can be a permanent (or fixed) channel in the wing
leading-edge or formed by a leading-edge auxiliary airfoil called a
slat. The slat is either fixed or variable. The opening of the slot
can also be con-trolled by panels (rarely used method).
There are three types of slats – fixed, automatic or variable.
With the fixed slat, the leading-edge slat is mounted a fixed
distance from the airfoil. Its main disadvantage is that it creates
excessive drag at high speeds. The automatic slat depends on the
pressure distribution lifting the slat away from the wing at high
angles of attack to open the slot. At low angles of attack (or high
dynamic pressure), the slat is flush against the wing leading edge
and reduces drag at high speeds com-pared with the fixed slot. Its
main disadvantages are its added weight, complexity, and cost.
Sometimes springs assist the aerodynamic forces in deploying the
slat. Increasing the wing stall angle also has a disadvantage. To
make use of the full CLMAX potential the aircraft must approach for
a landing in an extreme nose-up attitude that reduces visibility.
For that reason slat are seldom used alone, but is used in
combination with trailing edge flaps. Note: The action of the
slot/slat is very different than the flap, as it does not directly
produce extra lift unless the AOA is increased. Its main pur-pose
is to increase the maximum coefficient of lift, CLMAX. The variable
slat is mechanically operated, typically sequenced in steps along
with flaps extension or retraction. The variable slat is typi-cally
a two-position slat (retracted - extended) or a three-position slat
(retracted – extended – fully extended). Slats are mostly used on
swept wings aircraft. Swept wings are used on aircraft flying with
high mach numbers. Sweep increases the opera-tional mach number of
the aircraft, because the local mach number of the wing is lowered.
Slats are typically used on outer part (2/3) of the span, where the
local coefficients of lift are highest (nature of a tapered swept
wing).
-
Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 33
CMAXL
0AOA
CL
CLEA
NCO
NFIG
WIT
HFLA
PS
+SLA
TS
EFFECT OF SLAT AND FLAPS (TYPICAL)0
0
CMAXL
0AOA
CL
CLEA
NCO
NFIG
+ SLATS
0
0
EFFECT OF SLAT (TYPICAL)
PULLINGFORCE
PRESSUREDISTRIBUTION
NO OR TOO LATETRANSITION
EARLY FLOWSEPERATION(STALL)
LOW SPEED FLIGHT
LAMINARBOUNDARYLAYER
DISTRUBINGAIRFLOW
SLATSLOT TRANSITION TURBULENT
BOUNDARYLAYER
SLOT (SLAT) PRINCIPLE
SLOT
SLATSEGMENTS
VARIABLE SLAT
FIXED SLAT (OR SLOT)
MOVABLEPANEL
FIXED SLOT
McD DC8
VARIABLE SLAT (AIRBUS A340)
FIXEDSLOT
CRUISE
LOW SPEED
LOW AOA
HIGH AOA
FIXEDSLAT
KZ VII (FIXED SLOTS) FIESLER STORCH (FIXED SLATS)
RALLYE CLUB
AUTOMATIC SLAT
FLATPEAKY
SLATSCLEANCP CP
SLAT FULLYEXTENDED
SLAT FULLYRETRACTED
LEADING EDGE DEVICES - SLATS & SLOTS
-
Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 34
Leading Edge Flaps (Droop Nose) On high speed airfoils the
leading edge may have very little camber and have a small nose
radius. This can result in flow separation just aft of the leading
edge even a fairly low AOA. The nature of a leading edge stall is
much more violent than a stall that gradually spreads from the
trailing edge, and must be avoided. Leading Edge (LE) flaps (or
droop leading edges) increases the cam-ber of the airfoil nose
section, causing the value of the maximum coef-ficient of lift,
CLMAX, and the stall AOA to increase. LE-flaps are hinged section
of the leading edge which can be deflected downwards. When the nose
is drooped the airfoil meets the incoming airflow more direct,
therefore preventing separation at the leading edge. The stall will
be postponed to a higher AOA. Droop leading edges are often
preferred on thin-winged aircraft (like fighter aircraft) not
having sufficient space for the much more efficient slat system.
There is no known use of hinged leading edges on com-mercial jet
liners. Shaping the nose section with permanent (fixed) droop
causes an ef-fect similar to LE-flaps. Permanent droop may however
have a nega-tive impact on drag at higher speeds. Fixed droop is
used on many smaller and medium sized aircraft. An airfoil with a
droop nose is popu-larly referred to as a “droop snoot”. Krueger
Flaps & Variable Camber LE-Flaps The krueger flap is a part of
the lower surface of the leading edge, which can be rotated about
its forward edge, as shown in the figure. When retracted the
“extension” is stowed away in a cavity at the un-derside nose
structure. To improve efficiency by adding a better leading edge
profile, the cam-ber of the leading edge may be increases as it
deploys, achieved by the variable camber leading edge flaps (also
called a folding nose). To promote root stall (rather that tip
stall) on a swept wing, krueger flaps are used on the inboard
section because they are less efficient than variable camber
leading edge flaps.
The variable camber leading edge flaps are therefore typically
used in the outboard section (instead of slats). The krueger flap
and variable camber leading edge flaps increases lift by increasing
the airfoil camber (the coefficient of lift) and the wing a-rea.
The Krueger flap is somewhat less effective than the slat but is
probably simpler in mechanical design. Some aircraft employ slats
on the outboard portion of the leading edge, where more powerful
flow control is required, and krueger flaps on the inboard portion
of the lead-ing edge. Krueger flaps are a typical Boeing feature.
Unlike trailing edge flaps (and slats) which can be selected to
interme-diate positions, the krueger flap is either stowed or
deployed. Combining Slats & LE-Flaps Modern high speed
transportation aircraft mostly uses a combination of TE-flaps and
slats (eventually supported with krueger flaps in the root
section). Configuring the wing for low speed must be made stepwise
in order not to stall the wing when reducing the speed. On the
other hand structural overspeed of the flaps can happen if extended
at too high airspeed. Extending flaps will lower the wing stall AOA
(which is progressively reduced as the flaps deflection increases).
If a clean wing is operating with high AOA a flap deployment can in
fact stall the wing! Leading edge devices will on the other hand
increase the stall AOA. The lead-ing edge device must therefore be
deployed before the trailing edge flaps are lowered. When
retracting the flaps the leading edge devices must be the last part
retracted. This is accomplished by automatic se-quencing. Some
aircraft are however sequenced differently because of other
aerodynamic characteristics and habits. Slats are often extended in
two steps depending on the selected ex-tension. When extending a
fowler flaps system the first part only con-cerns area reduction
requiring partly slat extension. The downward de-flection comes
later, requiring full slat extension.
-
Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 35
LEADING EDGE WITH FIXED DROOP(DROOP SNOOT)
LE-FLAPS
LEADING EDGE (LE) FLAPS (F16 FIGHTING FALCON)
LOW SPEED CONFIG
BI-CONVEX HIGH SPEED AIRFOIL (CLEAN)
DROOP LEADING EDGE
KRUEGER FLAP
RETRACTED
EXTENDED
VARIABLE CAMBERLEADING EDGE FLAP(FOLDING NODE)
BOEING B747
LEADING EDGE DEVICES ON BOEING B737
INBOARD KRUEGER FLAP (BOEING B737)
SLAT KRUEGER FLAP
SHOWN INTRANSIT....
RETRACTEDLE SLATSLE FLAPS(KRUEGER)
KRUEGERFLAP
VARIABLE CAMBERLE-FLAP
TE-FLAPS
FULL-EXTENDED
EXTENDED
BOEING 737 FLAPS/SLATS SEQUENCING
DOWN
FLAP
UPFLAP
40
30
25
15
10
5
2
1
0
FLAP
0AOA
CL
CLEA
NCO
NFIG
+LE
-FLA
PS
EFFECT OF LE-FLAPS (TYPICAL)0
0
CMAXL
FL 1 - 40
FL 10 - 40
FL 1 - 5
LEADING EDGE FLAPS (DROOP)
-
Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 36
DRAG INDUCING DEVICES Drag inducing devices, besides flaps,
includes; • Spoilers, • Speed-brakes, • Drag chutes. The main
difference between spoilers and speed-brakes is that spoil-ers are
panels located on lift producing surfaces (the wings). Speed brakes
are typically located on non-lifting parts (like the fuselage).
Speed-brakes only provide drag. However, fighter aircraft that
pro-duces fuselage lift will be affected both in terms of drag and
lift when a large speed-brake panel is raised on the upper
fuselage. Spoilers and speed brakes are typical “full aircraft
envelope drag de-vices” which means that they are not structural
speed limited, as for in-stance slats and flaps are. Spoilers
Spoilers are used for decreasing wing lift; however, their specific
de-sign, function, and use vary with different aircraft. The
spoilers on some aircraft are long, narrow surfaces hinged at their
leading edge to the upper wing skin. In the retracted position, the
spoiler is flush with the wing skin. In the extended position, the
spoiler is pivoted up and forward. The maximum deflection differs a
lot but is seldom more than 50-60° above the hinge point. The
spoilers disturb the smooth flow of air over the wing by causing
boundary layer separation. The lift is consequently reduced, and
considerable drag is added to the wing in proportion with the wake.
Another type of spoiler (used by some older aircraft) is a long,
slender, curved and perforated baffle that is raised edgewise
through the upper surface of the wing forward of the aileron. It
also disrupts the flow of air over the airfoil and destroys
lift.
Spoilers are used as; • Roll spoilers (reducing lift and adding
drag), to assist the ailerons
and preventing adverse yawing, • Speed brakes, primarily to
adding drag, to lower the speed of the
aircraft or prevent the aircraft from building up excessive
speed dur-ing decent (dive),
• Ground spoilers (reducing lift and adding drag) during the
landing
run. Reducing lift increases the weight on the landing gear
optimiz-ing braking; increasing drag assists the braking by
unloading of the brakes and reducing the necessary landing run.
Note: The roll spoiler and speed brake spoiler function is
typically achieved by the same part of the spoiler system.
Dedicated spoiler panels, which are only used for the ground
spoiler operation, are typi-cally prevented for deploying in flight
by an interlock system. Speed-brakes Speed-brakes are hinged,
movable control surfaces used for reducing the speed of aircraft,
purely by adding drag. Some manufacturers refer to them as
dive-brakes or dive-flaps. They are hinged to the sides, the top,
bottom or rear of the fuselage. Regardless of their location, speed
brakes serve the same purpose on all aircraft. Their primary
purpose is to keep aircraft from building up excessive speed during
decent/dive. They are also used in slowing down the speed of the
aircraft prior to landing and during the landing run. Speed brakes
are operated hydraulically or electrically. Drag Chutes Drag-chutes
are almost exclusively used on high speed military aircraft to
unload the landing gear and reduce the landing run. Its civil
applica-tion is very, very limited.
-
Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 37
THE EFFECT OF GROUND SPOILERS
GROUNDSPOILERS
SPEEDBRAKES
SPEEDBRAKES
AVRO (BAC) 146
DRAG CHUTE (F117)
SPEED BRAKE (F16)
ROLL
DRAG
ROLL SPOILER(FLIGHT SPOILER)
DRAG
FLIGHT SPOILER(SPEED BRAKE)
DRAG
SPEED BRAKE (CESSNA A37 DRAGONFLY)
SPOILERPANELS
GROUND SPOILERS DEPLOYED (BOEING 737)
GROUNDSPOILERS
GROUNDSPOILER
FLIGHT/ROLL& GROUNDSPOILERS
SPOILER SYSTEM (BOEING 737NG)
FLIGHT SPOILERS DEPLOYED (AIRBUS A319)
INCREASED DRAGAND LIFT DUMP
SPOILER RETRACTED
THE EFFECT OF FLIGHT SPOILERS
SPOILER DEPLOYED
SPEED BRAKE (SUKHOI SU-27)
DEFLECTIONANGLE
SEPARATEDAIRFLOW
DRAG INDUCING DEVICES
-
Aviation
Module 11 Aerodynamics, Structures & Systems
Module 11.1.1 Aeroplane Aerodynamics & Flight Controls/MAR06
Edition 1/Rev 0 TEC Training Manual TM11.1.1-2 page 38
COMBINED FLIGHT CONTROLS Many aircraft are controlled by
combined flight controls rather than the traditional controls
previously introduced. Combined flight control sur-face is one that
has more than just one control purpose (for instance to control
pitch and roll or pitch and yaw). • V-tails (or butterfly tails)
are used by aircraft to control pitch (eleva-
tor function) and yaw (rudder function). Examples are the older
Beech Bonanza V35 and the modern F-117 Nighthawk. When a pure pitch
command is given, both surfaces are deflected equally. A pure yaw
command, say to the left, is achieved by de-flecting the left
surface downward and the right upward (see figure). Combined yaw
and pitch commands are carried out by differentially
deflection.
• Flaperons combines flaps and ailerons. A single surface on
each
wing serves both purposes: used as an aileron, the flaperons
left and right are actuated differentially; when used as a flap,
both flaperons are actuated downwards. Many fighter aircraft uses
flaperons for roll control (F-16, F-18, etc…). Note that when a
flaperon is actuated downwards (i.e. used as a flap) there is
enough freedom of movement left to be able to still use the aileron
function.
• Elevons combine elevators and ailerons and is used by
delta
winged aircraft (like the Concorde or the JAS39 Grippen). When a
pure pitch command is given, both elevons are deflected equally. A
pure roll (lateral) command make the elevons deflect like aileron.
Combined commands are carried out by differentially
deflec-tion.
• Tailerons are used by many military fighter jets (like the
F-14, F-16,
F-18, Tornado, etc.). Each of the two independent (variable
inci-dence) horizontal stabilizers (slab tails), can be moved
differentially (one up, one down, etc.).
Beside normal pitch control this also provides roll control.
Tailerons are often used in combination with flaperons. The Tornado
fighter for instance achieves roll control only by roll spoilers
and tailerons. No traditional ailerons are installed. Modern canard
equipped highly maneuverable fighters uses differ-entially
controlled canards for multiple purposes, like pitch and roll
control but also for aerodynamic braking during the landing
roll-out.
• Spoiler panels may have several purposes. One is to serve
as
speed brakes in flight, two to accommodate roll/lateral control
(or secondary roll assisting the ailerons) and third to serve as
ground spoilers (lift dumpers) during landing and rejected takeoff.
The roll and speed brake function is often referred to as the
flight spoiler function. Spoilers are often sectional div