FLIGHT CONTROLS

AE 2252Aircraft systems and

Instrumentation

G PRABHAKARANDEPARTMENT OF AERONAUTICAL

ENGINEERINGJEPPIAAR ENGINEERING COLLEGE

SYLLABUS

UNIT 1

AIRPLANE CONTROL SYSTEMS 10

Conventional Systems – Fully powered flight controls – Power actuated systems – Modern control systems – Digital fly by wire systems – Auto pilot system active control Technology,

FLIGHT CONTROL SYSTEMSFlying controls are hinged or movable airfoils designed to change the

attitude of the aircraft during flight.

PURPOSE1.TO ENABLE THE PILOT TO EXERCISE CONTROL OVER THE AIRCRAFT DURING ALL PORTIONS OF FLIGHT.

2.IT ALLOWS TO MANOEUVRES IN PITCH,ROLL AND YAW.

These can be divided in to 3 groups such as:

(a) PRIMARY CONTROLS(b) SECONDARY CONTROLS(c) AUXILARY CONTROLS

PRIMARY FLIGHT CONTROL SRUFACESAilerons, Elevators and Rudder are the primary controls. These controls are used to maneuver the aircraft about its 3 axes.

1. ELEVATOR2. AILERON3. RUDDER

FLIGHT CONTROL SYSTEMSSECONDARY FLIGHT CONTROL SYSTEMS:

Flaps, Spoilers, Slats or Leading edge flaps come under this category.Flaps and slats are the lift augmenting device.

Spoiler again grouped as Ground spoiler and Flight spoiler. Ground spoiler extended only after the aircraft lands thereby assisting in braking action. The flight spoiler assists in lateral control by extending whenever aileron on the wing is moved up

FLAPS SLATS SPOILERS SPEED BRAKES

AUXILLARY FLIGHT CONTROL SYSTEMS:

Tabs come under this category. Tabs are the small airfoils attached to the trailing edges of primary control surfaces.

Its purpose is to enable the pilot to trim out any unbalanced condition which may exist during flight.

FLIGHT CONTROL SYSTEMS

COMBINATION FLYING CONTROLS :

STABILATOR:It combines the function of

a horizontal stabilizer and an elevator. Stabilator normally equipped with an anti-servo tab, which doubles as a trim tab. The anti-servo moves in the same direction that the control surface is moved to aid the pilot in returning the stabilator to the trimmed neutral position.



RUDDERVATORS:These flying control surfaces serve the function of the

rudder and elevators. The surfaces are mounted at an angle above horizontal.

When serving as elevators, the surfaces on each side of the tail move in the same direction, either up or down.

When serving as rudder, the surfaces move in opposite direction, one up and one down.

When combined rudder and elevator control movements are made, a control-mixing mechanism moves each surface the appropriate amount to get the desired elevator and rudder effect.



RUDDERVATORS:



FLAPERONS:These are the surfaces combine the operation of flaps and

ailerons. These types of control surfaces are found on some aircraft

designed to operate from short runways. The flaperon allows the area of the wing normally reserved

for aileron to be lowered and creates a full span flap. From the lowered position the flaperon can move up or

down to provide the desired amount of roll control while still contributing to the overall lift of the wing.



FLAPERONS:



ELEVONS:Elevons are aircraft control surfaces that combine the

functions of the elevator (used for pitch control) and the aileron (used for roll control).

It is found on Delta wing aircraft. On this type of aircraft the wings are enlarged and extend to the back of the plane.

There is no separate horizontal stabilizer where you would find the elevators on conventional straight-wing aircraft.



ELEVONS:


TABS:

• TABS are small secondary flight control surfaces set into the trailing edges of the primary surfaces.

• These are used to reduce the work load required of the pilot to hold the aircraft in some constant attitude by “loading” the control surface in a position to maintain the desired attitude.

• It may also used to aid the pilot in returning a control surface to neutral or trimmed-center position.

• It controls the balance of an aircraft to maintain straight and level flight without pressure on CONTROL COLUMN or rudder pedal.

• Movement of the tab in one direction causes a deflection of the c/surface in the opposite direction


TABS:


TYPES OF TABS:

FIXED TRIM TABADJUSTABLE TRIM TABSBALANCE TABANTI-SERVO TABSSERVO TABSPRING TABS

FLIGHT CONTROL SYSTEMSTYPES OF TABS:

FIXED TRIM TAB:

A fixed trim tab is normally a piece of sheet metal attached to the trailing edge of a control surface.

This fixed tab is adjusted on the ground by bending it to appropriated direction.

Adjustment is only trial and error method and the aircraft must be flown and the trim tab adjusted based on the pilot’s report.

Found on light aircraft and are used to adjust rudders and ailerons.


ADJUSTABLE TRIM TABS :

These tabs are controlled from cockpit to alter the camber of the surface and create an aerodynamic force that will hold the control surface deflected.

Movement of the tab in one direction causes deflection of control surface in opposite direction.


BALANCE TABS:

To decrease the very high control forces the balance tabs are used. In this arrangement, when the control surface is moved, the tab moves in the opposite direction. Thus the aerodynamic force acting on the tab assists to move the main control surface. .


ANTI-SERVO TABS:

All moving tail plane (horizontal stabilizer) do not have a fixed stabilizer in front of them, and the location of their pivot point makes them extremely sensitive.

To decrease this sensitivity, an anti-servo tab may be installed on the trailing edge.

• This tab works in the same manner as the balance tab except it moves in the same direction(balance tab moves in opp to c/surface)

• The fixed end of the linkage is on the opp side of the surface from the horn on the tab, and when the trailing edge of the stabilator moves down the tab also moves down.


ANTI-SERVO TABS:


SERVO TABS:

In large aircrafts the control surfaces are operated by power operated hydraulic actuators controlled by valves moved by control yoke and rudder pedals.

In the event of hydraulic system failure, the control surfaces are controlled by servo tabs in a process known as manual reversion.

In the manual mode the flight control column moves the tab on the c/surface and the aerodynamic forces caused by the deflected tab moves the main control surface.


SPRING TABS:

A small auxiliary tab fixed at the trailing edge of a primary control surface on high speed airplane.

The control surface is attached to the control horn through a torsion rod. Under normal flight loads, the spring tab remains fixed to the control surface and serves no purpose.

But, when the air loads are high and a large amount of force is needed to move the control surface, the torsion rod twists, and the control rod moves the spring tab in a opposite to that of the surface on which it is mounted.

It acts as a servo tab and aids the pilot in moving the control surface.

FLIGHT CONTROL SYSTEMSMETHODS:

1. PUSH-PULL CONTROL ROD SYSTEM2. CABLE AND PULLY SYSTEM

FLIGHT CONTROL SYSTEM COMPONENTS OR COMPONENTS OF MECHANICAL LIKAGES FLIGHT CONTROL SYSTEM:

1. CABLES2. PULLEYS3. TURNBUCKLES4. PUSH PULL RODS5. BELL CRANKS6. QUANDRANTS.7. TORQUE TUBES8. CABLE GURARDS

FLIGHT CONTROL SYSTEMSCOMPONENTS OF MECHANICAL LINKAGES

1. PUSH PULL ROD:

• Many airplanes and almost all helicopter use push pull rods rather than control cables for control system.

• Made of heat treated aluminum alloy tubing with threaded ends riveted to its ends.

• End fittings which have a drilled hole are screwed on to these threads and to be sure that the rod ends are screwed far enough in to fitting a safety wire when inserted in to the hole it should not pass through the fittings.

• A check nut is screwed on to the rod end and when the length of the push pull rod is adjusted the nut to be screwed up tight against the end fitting.

• Push pull rods are extensively used along with bell cranks to change direction and to gain or decrease the mechanical advantage of control movement.

FLIGHT CONTROL SYSTEMSPUSH PULL ROD:

FLIGHT CONTROL SYSTEMSPUSH PULL ROD:

FLIGHT CONTROL SYSTEMSTORQUE TUBE:

Torque tube is a hollow shaft by which the linear motion of cable or push pull rod is changed to rotary motion.

A torque arm or horn is attached to the tube by welding or bolting and imparts motion to the tube as the arm is moved back and forth.

FLIGHT CONTROL SYSTEMSBELL CRANK:

It is used to transmit force and permit a change in direction of force. Normally a push pull rod is used with bell crank lever.


QUADRANT :

• A quadrant serves the same purpose as a wheel.

• It moves through a small arc (as much as 100 deg).

• Often employed at the base of a control column or control stick to

impart force and motion to a cable system.

FAIRLEADS

• It serves as a guide to prevent wear and vibration of a cable.

• Made of phenolic material, fiber, plastic or soft aluminum.

• It is of either split or slotted to install a cable.


TYPES OF FLAPS:

BLOWN FLAPSKRUEGER FLAPPLAIN FLAPSPLIT FLAPFOWLER FLAPSLOTTED FLAP


TYPES OF FLAPS:

BLOWN FLAPS: Systems that blow engine air over the upper surface of the flap at certain angles to improve lift characteristics.


TYPES OF FLAPS:

KRUEGER FLAP :

It is hinged flap on the leading edge and is often called a "droop."


TYPES OF FLAPS:

PLAIN FLAP: It is attached to the trailing of main plane and rotates on a simple hinge.


TYPES OF FLAPS:

SPLIT FLAP: It is hinged at the bottom part of the wing near the trailing edge. The lower surface operates like a plain flap, but the upper surface stays immobile or moves only slightly.

FLIGHT CONTROL SYSTEMSTYPES OF FLAPS:

FOWLER FLAP: It slides backwards on tracks before hinging downwards, thereby increasing both camber and chord, creating a larger wing surface better tuned for lower speeds. It also provides some slot effect. The Fowler flap was invented by Harlan D. Fowler.


TYPES OF FLAPS:

SLOTTED FLAP: A slot (or gap) between the flap and the wing enables high pressure air from below the wing to re-energize the boundary layer over the flap. This helps the airflow to stay attached to the flap, delaying the stall.

FLY BY WIRE CONTROL SYSTEMS

IT IS ONE IN WHICH WIRE CARRYING ELECTRICAL SIGNALS FROM THE FLIGHT CONTROLS BY REPLACING MECHANICAL LINKAGES.

TYPES OR THE WAYS OF USING FBW:

• ANALOG FBW• DIGITAL FBW


ANALOG FBW:

In analog fly by wire system operation, movements of the control column and rudder pedals, and the forces exerted by the pilot, are measured by electrical transducers, and the signals produced are then amplified and relayed to operate the hydraulic actuator units which are directly connected to the flight controls surfaces.

The fly by wire control employed in the Boeing 767 (spoiler) as illustrated in the figure is appended in the next slide:

The main components involved in this system are as follows:

1. POSITION TRANSDUCER (RVDT)2. SIGNAL CONTROL MODULE3. LINEAR VARIABLE DIFFERENTIAL TRANSFORMER (LVDT)4. POWERED FLYING CONTROL UNIT (PFSCU)



DIGITAL FBW:

• A digital FBW system is similar to its analogue counterpart. However the signaling processing is done by digital computers.

• The pilot can literally say “fly-via-computer”. This increases flexibility as the digital computers can receive input from any aircraft sensor.

• It also increases stability, because the system is less dependent on the values of critical electrical components as in analogue controller.

FLY BY WIRE CONTROL SYSTEMSDIFFERENCE BETWEEN ANALOG AND DIGITAL FBW

SL. NO.

ANALOGUE FBW DIGITAL FBW

01 The FBW eliminates the complexity, fragility and weight of the mechanical circuit of the hydromechanical flight control systems and replaces it with an electrical circuit.

This increases flexibility as the digital computers can receive input from any aircraft sensor. It also increases electronic stability, because the system is less dependent on the values of critical electrical components in an analog controller.

02 The hydraulic circuits are similar except that mechanical servo valves are replaced with electrically-controlled servo valves, operated by the electronic controller. This is the simplest and earliest configuration of an analog fly-by-wire flight control system,

The computers "read" position and force inputs from the pilot's controls and aircraft sensors. They solve differential equations to determine the appropriate command signals that move the flight controls in order to carry out the intentions of the pilot.

http://en.wikipedia.org/wiki/Differential_equation

FLY BY WIRE CONTROL SYSTEMSDIFFERENCE BETWEEN ANALOG AND DIGITAL FBWSL. NO.


03 In this configuration, the flight control systems must simulate "feel". The electronic controller controls electrical feel devices that provide the appropriate "feel" forces on the manual controls.

The programming of the digital computers enable flight envelope protection. In this aircraft designers precisely tailor an aircraft's handling characteristics, to stay within the overall limits of what is possible given the aerodynamics and structure of the aircraft. Software can also be used to filter control inputs to avoid pilot-induced oscillation.

04 In more sophisticated versions, analog computers replaced the electronic controller. Analog computers also allowed some customization of flight control characteristics, including relaxed stability.

Side-sticks, center sticks, or conventional control yokes can be used to fly such an aircraft. While the side-stick offers the advantages of being lighter, mechanically simpler, and unobtrusive,

FLY BY WIRE CONTROL SYSTEMSDIFFERENCE BETWEEN ANALOG AND DIGITAL FBW

SL. NO.


05 ----------------------- As the computers continuously "fly" the aircraft, pilot workload can be reduced. It is now possible to fly aircraft that have relaxed stability. The primary benefit for military aircraft is more manoeuvrable flight performance and so-called "carefree handling" Digital flight control systems enable

06 -------------------------- Improves combat survivability because it avoids hydraulic failure. With a fly-by-wire system, wires can be more flexibly routed, are easier to protect and less susceptible to damage than hydraulic lines.

07 Digital fly-by-wire systems is reliability, even more so than for analog systems.


ADVANTAGES:

1. WEIGHT SAVING2. REDUCED MAINTENANCE TIMES3. LESS SPACE4. IMPROVED HANDLING5. Fuel saving:6. Automatic maneuver envelope protection7. Gust load alleviation (lessening)

ADVANTAGES OF FBW:1. WEIGHT SAVING2. REDUCED MAINTENANCE TIMES3. LESS SPACE4. IMPROVED HANDLING

AUTOPILOT SYSTEM ACTIVE CONTROL TECHNOLOGY:

AUTOPILOT IS A SYSTEM OF AUTOMATIC CONTROLS WHICH HOLDS THE ARICRAFT

ON ANY SELECTED MAGNETIC HEADING AND RETURNS THE

ARICRAFT TO THAT HEADING WHEN IT IS DISPLACED FROM IT.

PURPOSE:TO REDUCE THE WROK STRAIN AND FATIQUE OF

CONTROLLING THE AIRCRAFT IN FLIGHT BY THE PILOT.

COMPONENTS:1. GYROS (TO SENSE WHAT AIRPLANE IS DOING)2. SERVOS (TO MOVE CONTROL SURFACES)3. AMPLIFIER (TO INCREASE THE STRENGTH OF GYRO SIGNALS TO OPERATE SERVOS)

THREE CHANNELS.1. RUDDER CHANNELS2. AILERON CHANNES.3. ELEVATOR CHANNELS

Documents

FLIGHT CONTROLS