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Aircraft Flight Control

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Jamie-Leigh Tan

on 3 January 2016

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Transcript of Aircraft Flight Control

Main group of flight control:
1) Primary flight control
2) Secondary flight control
3) Auxilliary flight control
What do flight control systems consist of?
Flight control surfaces
Cockpit controls
Connecting linkages
Operating mechanisms to control aircraft's direction in flight
Aircraft engine controls
Aircraft Flight Control
Flight controls
1. Primary
1.1) Elevator
1.2) Aileron
1.3) Rudder

2. Secondary
2.1) Elevator trim tab
2.2) Rudder and Aileron trim tab

3. Auxiliary
3.1) Flaps
3.2) High lift devices
1.1 Elevator
Controls aircraft pitch which affects angle of attack
Mounted on the tail portion of the aircraft
Controlled by a control yoke/control column
1.2 Aileron
Mounted on trailing edge of each wing near the wingtips
Both move in opposite directions
Reduces/increases lift when controlled
Causes plane to bank and turn
Primary flight controls
1.3 Rudder
Mounted on the back edge of the fin of the empennage
Deflecting the rudder causes the nose to yaw in the same direction
Controlled by the rudder pedals
Secondary flight controls
2.1 Elevator Trim Tab
Balances control forces to maintain aerodynamic down force on tail
A lot of trim could be required to maintain desired angle of attack
2.2 Rudder and Aileron Trim Tab
Used to counter the effects of slip stream/centre of gravity not being centralized
Etc. when one side of the aircraft is heavier than the other
Auxiliary flight controls
3.1 Flaps
Hinged surfaces on the trailing edge of the wings
Reduces stalling speed when extended
Increases camber of airfoil; raising lift coefficient
lift coefficient, lift, speed
Extending flaps will reduce stalling speed
Types of flaps
Kruger flap: hinged flap on the leading edge
Plain flap: rotates on a simple hinge
Split flap: upper and lower surfaces are separate
Fowler flap
Slotted flap
Blown flap
3.2 High Lift Devices
High lift devices are movable surfaces or in some cases, stationary components that are designed to increase lift during some phases or conditions of flight.
Used to disrupt airflow over the wing & increase the amount of drag
Allows pilot to lose altitude without gaining excessive airspeed
Also known as lift dumpers
When it can be used asymmetrically it is called spoilerons
Also known as Leading Edge Devices
Extension to the front of a wing for lift augmentation
Reduces stalling speed by altering airflow over the wing
May be fixed or retractable
Fixed slats excellent slow speed & STOL capabilities, but compromises high speed performance
Retractable slats reduces stalling speed for take-off and landing, retracted for cruising
Leading Edge Extension
Also known as leading edge root extensions/ strakes/ chines
Fillets added to the front of the wing to provide usable airflow at high angles of attack
Normally triangular shape, running from leading edge of wing root to a point near the cockpit
Wing Vortex Generators
Installed perpendicular to the surface of the wing
Reduces drag caused by supersonic flow over portion of the wing
Mounted in complementary pairs
Leading Edge Cuffs
Fixed aerodynamic device
Employed on fixed-wing aircraft to modify airfoil use
It will droop the leading edge of the airfoil
Allows lower approach speeds and shorter landing distances
Types of high-lift devices
Leading edge high-lift device (LEHLD or slat)
Trailing edge high-lift device (TEHLD or flap)
Leading Edge High-lift Devices (LEHLD or slat)
Fixed slot
The Kruger Flap
The Leading Edge Slat
Hinged Leading Edge (Droop Nose)
Variable-camber Leading Edge

Fixed Slot
Provides access for high-pressure air from the lower surface to flow to the upper surface
Its shape accelerates the flow and somehow energizes the airflow over the upper surface of the airfoil, yielding a higher stall AOA and max coefficient of lift
Effective and inexpensive
Simple in construction
Ideal for very simple slow flying aircrafts
Delays the flow separation, allows airfoil to reach a high AOA and thus increase Clmax
Prevents laminar flow beyond its trailing edge
Greatly increases the drag of the airfoil
The Kruger Flap
Types of Kruger Flaps:
Simple Kruger flap
Folding, Bull-nose Kruger flap
Variable-camber Kruger flap
Simple Kruger Flap
Increases the curvature of the camber of the airfoil to which it is mounted
Flap rotates into a position of 110 deg to 140 deg
Used in some commercial jet-liners to improve high-lift capability of the under-cambered airfoil near the root of the fuselage and delay flow separation
Used on the inboard part of the wing
The outside mold line of the device inflicts an aeodynamic limitation on its shape
Effectiveness with variations in AOA is generally considered poor
Is not used on any modern aircraft
Folding, Bull-nose Kruger Flap
Increases the curvature of the airfoil camber
Round nose improves the effectiveness of the flap over a larger range of AOA
Ideal surface to control stall progression along the wing
Requires a slaved mechanical linkage
Limited increase in maximum coefficient of lift
Variable- Camber Kruger Flap
Improves the shape of simple and bull-nosed kruger
Develop far superior curvature to improve its aerodynamic properties
Flap deflects through approximately 120 deg angle from the stowed position
Flexible panels acts like bug shields and protect the leading edge from contamination
Sophistication of the actuation mechanism of the flap system is impressive
Tight tolerances between each part ensures the system works reliably
Expensive to manufacture and maintain
Flap must be carefully rigged to prevent undesirable distortion of the panels
Flap must be preloaded to avoid panel bulging
The Leading-Edge Slat
Types of Leading Edge Slap:
The Airload-actuated Slat (or the Automated Handley-Page Slat)
The Maxwell Leading Edge Slot
Three-position Slats
The Airload-actuated Slat (or the Automated Handley-Page Slat)
Designed to be extracted and retracted by the magnitude of the pressure acting at the leading edge of the wing
When airplane is at a low speed it deployed and when at high speed the slat is stowed,automatically.
Pressure drop around the leading edge, stall AOA and max coefficient of lift are increased when deployed position.
Drag of the slat is reduced when airplanes accelerates to higher airspeeds and the slat retracts.
Ideal for aircraft intended for STOL operations
May produce violent roll departure when airplanes rolling rapidly at high speeds(fighter aircraft)
The Maxwell Leading Edge Slot
Operates through rotation about the leading edge.
Additional of hinged door at the airfoil.
Cruise configuration of the airfoil is relatively smooth.
Installation is mechanically simple.
Coefficient of lift increases rapidly as the the airplane accelerates.
Would trip the laminar boundary layer on both upper and lower surfaces if used with an Natural-Laminar-Flow airfoil.
Drag of slat increases with gap size between the slat and hinged door.
Three-position Slats
Features three positions: Retracted,Take-off, Landing.
Slat rests against the leading edge of the main airfoil to prevent air from flowing from the lower to the upper surface.
Increases the camber of the basic airfoil.
Its airfoil geometry offers higher L/D than open slot configuration.
Improves T-O and climb performance.
Most common leading edge high-lift device in use.
Track and mechanism required to move the slat is complicated
Hinged Leading Edge (Droop Nose)
Increases the leading edge camber and to increase max coefficient of lift.
Reduces the stalling speed and roll stability.
Low cost
Relative ease of manufacturing
Low impact on weight and drag
Increase in max coefficient of lift is limited due to the small-radius curvature on the upper surface,which may induce flow separation.
Variable-camber Leading Edge
Increases the airfoil camber at the leading edge while minimizing impact on cruise drag.
Increases the low-pressure peak at higher AOAs and therefore max coefficient of lift.
Offers improved continuity in the upper surface curvature.
Smooth upper surface
Reduced impact of drag at cruise.
High cost
Complex manufacturing of mechanical
moderate impact on weight
Reduced maximum lift due to absense of slot flow
Not suitable for jetliners.
Trailing Edge High-Lift Devices (TEHLD or Flap)
Plain Flap
Split Flap
Junkers Flap or External Flap
The single-slotted Flap
Double-slotted Flaps
Flowler Flaps
Gurney Flap

Plain Flap
Simple high-lift surface that only moves through rotation without translation.
Control surface is effectively a semi-circle joined at the base of a triangle.
Contain a reliable control system to control the deflection of flap.
Low cost
Effective in generating lift
Provided large deflections are not needed.
Relatively low increase in max coefficient of lift.
Plain flap surfaces with the hingeline are difficult to mass balance.
Requires the addition of structural arms to carry block of mass balance.
Split Flap
Types of Split Flap:
Split Flap
Zap Flap

Split Flap
Flap is deflected through rotation only.
Enlarges and magnifies the high-pressure region on the lower surface of wing.
Provides great attitude and glide-slope control.
Increases lift, but sharply reduces the L/D ratio,making the device easier to control.
Superior to a spoiler.
Common used for fighter and bomber aircrafts.
Increase in max coefficient of lift is low
Not used on any modern airliner.
Zap Flap
Consists of an actuator that forces the leading edge of the flap backward.
Presence of a special linkage forces the device to simultaneously rotate into position, increasing the chord.
Increases wing area.
Generate higher lift than the split flap.
Leads to relatively small shift in the stall AOA.
May cause severe buffeting if deployed at high speed.
Hinge moment of the flap may reverse if there is an enlargement of gap between the wing and the leading edge of flap.
Junkers Flap or External Flap
Resides entirely outside the wing.
Reduces the airfoil drag when neutrally deflected.
Modest increase in max coefficient of lift.
Adds pratically no drag to the installation.
Effective at low deflection angles than identically sized conventional ailerons.
Flap may suffer from excessive adverse yaw
Must be reacted by external hardpoints that increase the drag of the configuration.
Flap does not generate a large enough max coefficient of lift.
The single-slotted Flap
Consists of an airfoil mounted to a hinge that if offset from the main airfoil.
Increases the airfoil chord length by some 5-10%.
Simple installation mechanically.
Low cost
Low pressure peak over the leading edge of the flap.
May suffer from lower max coefficient of lift.
Double-slotted Flaps
Types of Flaps:
Fixed-vane Double-slotted Flap
Articulating-vane Double-slottle Flap
Triple-slotted Flap
Fixed-vane Double-slotted Flap
A vortex placed at the leading edge of each segment reduces the pressure peak, delaying the flow separation.
Configuration increases the maximum lift of the slotted flap.
Made by very light material.
Less expensive.
Does not suffer from reduced improvement in max coefficient of lift.
Configuration increases drag over that of the single-slotted flap.
Articulating-vane Double-slotted Flap
The vane of the flap are usually spring-uploaded and rest up against a stop.
The actuator of the flap n be such that the vane closes the slot between it and the flap's main element, to reduce drag of the configuration, helping to improve T-O and climb performance.
The articulation allows an increase in the total chord over that of the fixed vane with no increase in stowed space requirements.
Has mechanical complexity and weight
Triple-slotted Flap
Flap increases airfoil chord length and camber.
A very large increase in max coefficient of lift reduces the stalling speed.
A very comples interaction of gap jet airspeeds that combine to reduce flow separation over elements.
Generates higher section lift coefficients.
Complicated and heavy mechanical system.
Flaps generate higher loads that require substantial structure to support.
Suffers from great loss of lift due to flap tip vortices.
Fowler Flap
Increases both wing area and camber
Allows to produce lift at a slower airspeed.
Less runway is required for take-off and landing.
Since the section lift coefficient is based on the shorter stowed chord, this greatly boosts its value.
Gurney Flap
Increases max coefficient of lift..
Decreases the angle of attack to zero.
Increases the nose down pitching moment.
Generates high lift.
Extremely simple to fabrication
Type of Flight Control Configurations
1. Common Types
2. Unconventional Types
Common Types of Flight Control Configurations
1. Conventional Tail
Fuselage mounted tail or conventional tail configuration. Both horizontal and vertical tails are located and mounted to the aft of fuselage.

Simplest configuration and the most convenient to perform all tail functions.
1. H- Tail
2. T-Tail
3. V-Tail
4. Y-Tail
5. Cruciform Tail
6. Pelikan Tail
7. Twin Vertical Tail
8. Canard

Hybrid Control Surfaces

Unconventional Types of Flight Control Configurations
A twin tail is a specific type of vertical stabilizer arrangement found on the empennage of some aircraft. Two vertical stabilizers often smaller on their own than a single conventional tail would be are mounted at the outside of the aircraft's horizontal stabilizer. As it resembles a capital "H" when viewed from rear.
Job, Macarthur and Steve Swift. JAL 123: 520 Lost - It's 20 years since the world's worst single aircraft airliner accident. In: Flight Safety Australia. - Vol. 9, no. 4 (July, August 2005) page 28-33. http://www.casa.gov.au/wcmswr/_assets/main/fsa/2005/aug/28-33.pdf
Flight safety Foundation, Aviation Safety Network http://aviation-safety.net/database/record.php?id=19850812-1
Gudmundsson Snorri (2014). General aviation aircraft design. Kidlington, Oxford, UK; Watharn, MA: Butterworth-Heinemann
Youtube, Japan Airlines Flight 123 Cockpit Voice Recordings [IN-FLIGHT STRUCTURAL DUE TO MAINTENANCE ERROR].
At high angles of attack, the vertical tail is not influenced by the turbulent flow coming from fuselage.

In a multiengine turboprop aircraft, vertical tails are located behind the prop-wash region. This causes the vertical tail to have higher performance in the inoperative engine situation.

The vertical tail end-plate effect improves the aerodynamic performance of the horizontal tail.

The H-tail allows the twin vertical tail span to be shorter.
The H-tail is slightly heavier than conventional and T-tail configuration. The reason is that the horizontal tail must be strong enough to support both vertical tails.
A T-tail is an empennage configuration in which the horizontal surfaces are mounted to the top of the vertical stabilizer.
1. It kept well out of the disturbed airflow behind the wing and fuselage, giving smoother and faster flow and better pitch control.

2. T-tail configuration allows high performance aerodynamics and excellent glide ratio as the horizontal tail empennage is less affected by wing and fuselage slipstream.

3. It has a better lift slope, less interaction drag than a cruciform tail and a more efficient vertical tail.

1. Aircraft might be suffering a dangerous deep stall condition, where blanking of the airflow over the tailplane and elevators by a stalled wing at high angles of attack can lead to total loss of pitch control.

2. The vertical stabilizer must be made considerably stronger and stiffer to support the forces generated by the tailplane.

3. The control runs to the elevators are more complex, and elevator surfaces are much more difficult to casually inspect from the ground.
V-tail also known as ruddervators combination of the elevators and rudder.
1. V-tail is lighter, has less wetted surface area, and thus produces less drag.

2. V-tails are used to avoid placing the vertical stabilizer in the exhaust of the engine, which would disrupt the flow of the exhaust, reducing thrust and increasing wear on the stabilizer, possibly leading to damage over time.

1. Combining the pitch and yaw controls is difficult and requires a more complex control system.

2. When the aircraft is pitching and yawing a greater stress on the rear fuselage.
The Y-tail is an extension to the V-tail, since it has an extra surface located under the aft fuselage. This extra surface reduces the tail contribution in the aircraft dihedral effect. The lower section plays the role of vertical tail, while the two upper sections play the role of the horizontal tail. Therefore, the lower surface has rudder, and the control surface of the upper section plays the role of the elevator.
1. The complexity of the Y-tail is much lower than the V-tail.

2. This tail configuration is used is to keep the tail out of effect of the wing wake at high angles of attack.
The lower section may limit the performance of the aircraft during take-off and landing, since the tail hitting the ground must be avoided.
Cruciform Tail
When viewed from the aircraft's front or rear, looks much like a cross. The usual arrangement is to have the horizontal stabilizer intersect the vertical tail somewhere near the middle, and above the top of the fuselage.
The cruciform tail gives the benefit of clearing the aerodynamics of the tail away from the wake of the engine, while not requiring the same amount of strengthening of the vertical tail section in comparison with a T-tail design.
It have more torsion load as compared to conventional tail
Pelikan Tail
The Pelikan tail is an experimental tail design for fighter jets. It has been considered or included in design specifications in the original Boeing X-32 fighter design.
Greater pitch control at high angles of attack and that two tails would have a lower radar signature.
1. Two larger control surfaces instead of four might make the aircraft heavier.

2. Bigger hydraulic pumps and cylinders needed to operate the larger surfaces would add 800 to 900 pounds of weight to the design.

Twin Vertical Tail
A twin vertical tail configuration has a regular horizontal tail, but two separate and often parallel vertical tails.
1. The twin vertical tail largely improves the directional controllability of an aircraft.

2. A twin tail has the same directional control power, while it has a less negative effect of the roll control.
They have slightly heavier weight as compared to the conventional tail.
Canards just to generate lift near the front during landing. It also provide more lift at high angle of Attack and for better balance.
1. A canard has a higher efficiency when compared with aft tail. The reason is that it is located in front of wing, so the wing wake does not influence the canard aerodynamic characteristics.

2. Canard aircraft produces less lift-dependent drag to longitudinally trim the aircraft. However, this feature may leads in a larger wetted area.

3. Provide more lift at high angle of attacks and for better balance.
1. It is not appropriate to employ canard when the engine is pusher and located at the fuselage nose. The reason is that the aircraft nose will be heavy and the cg adjustment is difficult.

2. The distance between aircraft neutral point and aircraft center of gravity is shorter. This makes the canard aircraft longitudinally statically less stable.

3. The design of a canard is more time intensive and more complicated than the conventional tail design.

4. A canard obscures the view of the pilot.
Hybrid Control Surfaces
A combination of rudder and elevators, usually located at trailing edge of V-tail empennage. Movement of the control stick fore and aft cause ruddervators to move together in the same directions, providing pitch control, when the pedals are actuated, the ruddervators move in opposite direction, providing yaw control.
Spoilers that can be used asymmetrically to achieve the effect of ailerons, to roll an aircraft by reducing the lift of one wing but unlike ailerons not increasing the lift of the other wing.
As a side effect a raised spoileron also increases the drag on one wing which causes the aircraft to yaw which can be compensated with the rudder.
But since roll and yaw motion are both to the wing with the raised spoileron, it's usually desirable.
Spoilerons can be used to assist the ailerons or replace them entirely, thus reducing the number of control surfaces.
A combines aspects of both flaps and ailerons. In addition to controlling the roll or bank of an aircraft, as do conventional ailerons, both flaperons can be lowered together to function similarly to a dedicated set of flaps.
A combination of elevator and ailerons. When the control stick move fore and aft, the elevons move together in the same directions and acts as the elevators providing pitch control. However when the control stick is moved left or right, each side of the elevens will move in opposite directions, and acts as ailerons providing roll control.
Accidents due to flight controls failure
Japan Air 123

Aircraft specifically configured for domestic flights with a
high density seating arrangement.
June 2, 1978
(flight to Osaka)
-Floated after touchdown

-Tail struck the runway on
second touchdown
Replaced the lower part of the rear fuselage and a portion of the lower half of the bulkhead.
Repaired by Boeing
In the incorrect repair, technicians tried to connect two doubler plates, which forced the middle row of the rivets to carry too much load
Date: Monday, 12 August 1985
Time: 18:56

Has been in operation for
11 years and 7 months
Vibrations felt 12mins after takeoff
Impact force raised the
of the aircraft
Control problems
were experienced.
Crew got indications of problems with the R5 door.
The rear pressure bulkhead had
resulting in pressure rushing to the fuselage tail.
Hydraulic pressure dropped
, causing the
loss of fuselage tail
vertical fin
hydraulic flight control systems
Pilot tried to control aircraft using
engine thrust
approx. 45mins
after takeoff, JA8119 struck the Osutaka Ridge and
burst into flames
Vertical fin and APU of the plane were ripped off
520 out of 524 people died
(crew and passengers)
Airplane is completely destroyed

Tail cone was blown off
Outline shows the part that was destroyed when rear pressure bulkhead failed
Destruction of Rear Pressure Bukhead
Destruction of Rear Pressure Bukhead
Destruction of Rear Pressure Bukhead
Rear pressure bulkhead (darker blue) contain tremendous force from the pressure difference at altitude between the cabin and outside air.

Line of cracks were formed midway between the upper and lower parts of the dome
Line of cracks: Bulkhead was destroyed after the cracks ran past the tear stop straps
Improper maintenance
of rear pressure bulkhead
Cycles of
pressurization and depressurization
resulted in
fatigue failure
Pressurization lead to the
loss of hydraulics
Flight Control Failure
Maintenance inspection
was not taken
as fatigue cracks propagating at the spliced portion of the bulkhead's webs was
not found during inspection.
Flight Control Failure
Group Reflection
In this project, we have learnt more about flight controls and how important each of them are. We have also learnt more about the common and uncommon types of control configurations such as the twin vertical tail, canards and more. A minor problem will become a major problem in the long run and some problems are harder to detect until present for a significant period of time. When detected it may be too late, hence, maintenance and repair must be taken seriously without any mistakes so that accidents can be prevented.
Cockpit Voice Recordings
Seow Jia Min, Clarice
Tan Jamie-Leigh
Ang Zhi Peng
Tan Kong Tat Clement
Full transcript