1406441.ppt

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Aircraft Control Devices

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Aim

To introduce the design featuresused to aid in aircraft control

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Objectives

1. State the design features used for aircraft

control2. State the design features used to aid in

control response

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1. Aircraft Control Devices

Control devicesControl devices are used to enhance the controleectivenessControl devices include:

odi!ed aileron design

Spoilers Slots "eading edge strips Speed bra#es $orte% generators Stra#es

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Control devices & odi!ed aileron

designAircraft manufacturers can alter aircraft design tominimise the eects of adverse aileron 'a(Some techni)ues emplo'ed are:

Dierential ailerons

*rise ailerons Spoilers Aileron+rudder interconnect


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Control devices & Dierential

Ailerons,ith dierential ailerons- one aileron is raised agreater distance than the other aileron is lo(eredfor a given movement of the control column

his produces an increase in drag on the

descending (inghe greater drag results from de/ecting the upaileron on the descending (ing to a greater anglethan the do(n going aileron on the rising (ing


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Control devices & *rise Ailerons,ith a frise0t'pe aileron- (hen pressure is appliedto the control (heel or stic#- the aileron that isbeing raised pivots on an oset hinge

his projects the leading edge of the aileron into

the air/o( and creates dragt helps e)ualise the dragcreated b' the lo(eredaileron on the opposite

(ing and reduces adverseaileron 'a(


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Control devices & Spoilers*ound on man' gliders and some aircraft- high dragdevices called spoilers are deplo'ed from the (ingsto spoil the smooth air/o(- reducing lift andincreasing drag

Spoilers are often used for roll control- anadvantage being the reduction of adverse aileron'a(

g- to turn left- the spoiler

on the left (ing is raised-destro'ing some of the liftand creating more drag-the left (ing drops and the

aircraft ban#s and 'a(s to


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Control devices & Spoilers

Spoilers used at the same time 3speedbra#es4 allo(sthe aircraft to descend (ithout gaining speedSpoilers are also used to reduce the ground roll afterlanding- b' destro'ing lift and transferring (eight to

the (heels- therefore improving bra#ingeectiveness


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Control devices & Coupled aileron and

rudderCoupled ailerons and rudder are lin#ed controlshis is accomplished (ith rudder0aileroninterconnect springs- (hich help correct for ailerondrag b' automaticall' de/ecting the rudder at the

same time the ailerons are de/ectedg0 (hen the control (heel is moved to produce aleft roll- the interconnect cable and spring pullsfor(ard on the left rudder just enough to preventthe nose from 'a(ing to the right


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Control devices & Slots

Slots are high lift devices applied to the leadingedge of an aerofoil*i%ed slots direct air/o( to the upper (ing surfaceand dela' air/o( separation at higher AoA5s

he slot does not increase the,ing camber- but allo(s a higherma%imum coe6cient of liftbecause the stall is dela'ed untilthe (ing reaches a greater AoA

he' are usuall' incorporated(ithin the (ing leading edge ahead of theaileron to retain aileron eectiveness


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Control devices & leading edge

strips"eading edge strips A7A stall strips encourageearl' separation of air/o( at high AoAhe' are !tted to the inboard section of the (ing toensure it reaches the critical AoA before the (ing tip

his reduces thetendenc' to (ing drop


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Control devices & vorte%

generators$orte% generators are used to dela' orprevent shoc# (ave induced boundar'la'er separation

he' are small- lo( aspect ratio aerofoilsplaced at 12 to 18 degrees AoA to the

airstreamhe' are usuall' spaced a fe( inches apart alongthe (ing ahead of the ailerons$orte% generators create a vorte% (hich mi%es the

boundar' air/o( (ith the high energ' air/o(just above the surface-his produces higher surface velocitiesand increases the energ' of theboundar' la'er- thus a stronger shoc#(ave is necessar' to produce air/o( separation.


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Control devices & stra#es

Stra#es are devices (hich are !tted to the fuselageto improve stabilit'

hese devices called strakesare )uite common intraining aircraft under the fuselage (hich increase

directional stabilit' at high angles of attac# andreduce the tendenc' to diverge or spinOn some aircraft- stra#es also have the eect ofreducing drag in the cruise b' guiding air/o( overthe lo(er rear area of the fuselage


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2. Aircraft control responses

Control responses

,hen controls are de/ected an aerod'namic forceis created opposite to the direction of de/ectiont is this force (hich (e feel through the controlcolumn

his force is dependant on the hinge position forthe control surface and ho( it is lin#ed to thecontrol columnf the hinge is at the leading edge of the controlsurface it (ill be more di6cult to move than if it is

hinged in the centre

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Control responses

Designers incorporate certain features into aircraftdesign to ma#e them easier to /'- and to give usfeel of (hat the aircraft is doingCertain features such as (ill be described:

Aerod'namic balancing ass balancing 9alance tabs Anti balance tabs Servo tabs


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Control responses & Aerod'namic

balanceAerod'namic balancing can be achieved b' thefollo(ing features: nset hinge orn balance


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Control responses & ass

balancingass balancing is designed to prevent /utteron control surfaces*lutter is a vibration of the control surface(hich is often e%perienced at high speeds

t is caused b' pressure disturbances overthe control surface and can be particularl'bad if the control surfaces Co; is not in line(ith the hinge point

o avoid /utter (e can emplo'

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Control responses & balance tab

he control forces in some aircraft can be e%cessivel'high- and in order to decrease them- themanufacturer ma' use balance tabs

he' loo# li#e trim tabs and are hinged in

appro%imatel' the same placehe essential dierence bet(een the t(o isthat the balancing tab is coupled to thecontrol surface rod so that (hen the primar'control surface is moved in an' direction-

the tab automaticall' moves in the oppositedirection

he air/o( stri#ing the tab counterbalancessome of the air pressure against the primar'

control surface- and enables the pilot to


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Control responses & anti balance

tabAn anti balance tab (or#s on the same principal asthe balance tab- ho(ever- it moves in the samedirection as the control surface

his acts to increase the stic#

force re)uiredt is often used on aircraft (itha stabilator or an all /'ingtailplane


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Control responses & antiservo tab

A servo tab is a variation in the balance tab (herethe pilot control is connected to the tab and not themain control surfaceAs the control input moves the servo tab into the

air/o(- the aerod'namic forces generated drive themain control surface in the opposite direction


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