Ppt Aero 6sem CSC

8/10/2019 Ppt Aero 6sem CSC

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Department of Aeronautical engineering

School of Mechanical engineering

Vel Tech Dr RR & SR Technical University

Course Material

U6AEA Aircraft Sta!ility Control

U6AEA A"RCRA#T STA$"%"T A'D C('TR(% % T ) C

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* + + *

($,ECT"VE

To study the performance of airplanes under various operating conditions and the static and dynamic

response of aircraft for both voluntary and involuntary changes in flight conditions

U'"T " "ntro-uction To Sta!ility .

Degree of freedom of a system - Static and dynamic stability - Need for stability in an airplanes -Purpose of controls - Inherently and marginally stable airplanes, Equations of motion of a rigid body,

Inertial forces and moments Equations of motion of flight vehicles, aerodynamic forces and moments,

Decoupling of longitudinal and lateral-directional equations !ineari"ation of equations, #erodynamic

stability and control derivatives, $elation to geometry, flight configuration, Effects of po%er,

compressibility and fle&ibility

U'"T "" Static %ongitu-inal Sta!ility An- Control / #i0e- An- #orce- Control .

Stic' (i&ed) *asic equilibrium equation - Stability criterion + ontribution of %ing and tail and elevator

to pitching moments - Effect of fuselage and nacelles - Effects of center of gravity location - Po%er

effects - Stabili"er setting and center of gravity location + Elevator po%er+ Elevator to trim Trim

gradients ontrol fi&ed static stability + ontrol fi&ed neutral point Stability margins Effects of

releasing the elevator inge moment coefficients + ontrol forces to trim ontrol free neutral point +Trim tabs #erodynamic balancing of control surfaces .eans of augmentation of control

U'"T """ Maneuver Sta!ility .

ontribution of pitch damping to pitching moment of flight vehicle - Effect on trim and stability ontrol

deflections and control forces for trim in symmetric maneuvers and coordinated turns ontrol deflectionand force gradients ontrol fi&ed and control free maneuver stability .aneuver points .aneuver

margins

U'"T "V Static %ateral An- Directional Sta!ility An- Control .

Dihedral effect - oupling bet%een rolling and ya%ing moment - #dverse ya% - #ileron po%er - #ileron

reversal /eather coc'ing effects + $udder po%er !ateral and directional stability- definition ontrol

surface deflections in steady sideslips, rolls and turns one engine inoperative conditions - $udder loc'

U'"T V Dynamic Sta!ility An- Response To Control .

Solutions to the stability quartic of the linearised equations of motion The principal modes Phugoid ,Short Period Dutch $oll and Spiral modes - (urther appro&imations $estricted degrees of motion

Solutions $esponse to controls #uto rotation and spin

T(TA%1 23 perio-s

TE4T $((5S

0 oughton, E!, and arruthers, N*, #erodynamics for Engineering Students, Ed%ard #rnold

Publishers !td, !ondon, 01213 .cormic, */, #erodynamics, #eronautics 4 (light .echanics, 5ohn /iley 0116

RE#ERE'CE $((5S

0 Per'ins D, 4 age, $E, #irplane Performance, Stability and ontrol, /iley Toppan 0178

3 Nelson, $, (light Stability and #utomatic ontrol, .c9ra% ill 0121

U'"T/"

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Degree of freedom of a system

Static and dynamic stability

Need for stability in an airplanes

Purpose of controls

Inherently and marginally stable airplanes,

Equations of motion of a rigid body,

Inertial forces and moments

Equations of motion of flight vehicles,

#erodynamic forces and moments,

Decoupling of longitudinal and lateral-directional equations

!ineari"ation of equations

#erodynamic stability and control derivatives,

$elation to geometry, flight configuration,

Effects of po%er, compressibility and fle&ibility

Degrees of free-om

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Degrees of free-om mechanics78independent displacements and:or rotations

that specify the orientation of the body or system

Degrees of free-om statistics78the number of values in the final calculation of

a statistic that is free to vary

Si0 -egrees of free-om

$efers to motion of a rigid bodyin three-dimensional space, namely the ability to

move for%ard:bac'%ard, up:do%n, left:right combined %ith rotationabout three

perpendicular a&es ;pitch, ya%, roll


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#s any vehicle moves it %ill be sub>ected to minor changes in the forces that act on

it, and in its speed

If such a change causes further changes that tend to restore the vehicle to its

original speed and orientation, %ithout human or machine input, the vehicle issaid to be statically stable The aircraft has positive stability

If such a change causes further changes that tend to drive the vehicle a%ay

from its original speed and orientation, the vehicle is said to be statically

unstable The aircraft has negative stability

If such a change causes no tendency for the vehicle to be restored to its

original speed and orientation, and no tendency for the vehicle to be driven

a%ay from its original speed and orientation, the vehicle is said to be neutrally

stable The aircraft has "ero stability

(or a vehicle to possess positive static stability it is not necessary for its speed and

orientation to return to e&actly the speed and orientation that e&isted before the

minor change that caused the upset It is sufficient that the speed and orientation do

not continue to diverge but undergo at least a small change bac' to%ards the

original speed and orientation

%ongitu-inal static sta!ility

The longitudinal stability of an aircraft refers to the aircraft?s stability in the

pitching plane - the plane %hich describes the position of the aircraft?s nose in

relation to its tail and the hori"on ;=ther stability modes are directional

stabilityand lateral stabilityective flying qualities evaluations such as ooper-arper ratings

;The ooper-arper rating scale is a set of criteria used by test pilotsand flight test

engineers to evaluate the handling qualities of aircraft during flight test The scale

ranges from 0 to 0@, %ith 0 indicating the best handling characteristics and 0@ the

%orst< are used to distinguish bet%een Agood-flyingA and difficult-to-fly aircraft

Ne% aircraft designs can be simulated to determine %hether they are acceptable

Such real-time, pilot-in-the-loop simulations are e&pensive and require a great deal

of information about the aircraft Earlier in the design process, flying qualities

estimate may be made on the basis of various dynamic characteristics =ne can

correlate pilot ratings to the frequencies and damping ratios of certain types of

motion

#light -ynamics

(light dynamics is the study of dynamics of flightthrough the air, or beyond

planetary bodies? atmospheres It is chiefly concerned %ith vehicle attitude, angles

and rates of change of angles of the vehicle as %ell as speed and changes of speed

%ith respect to time

In another %ord it is the science of airvehicle orientation and control in three

dimensions The three critical flight dynamics parameters are the angles of

rotationin three dimensionsabout the vehicle?s center of mass, 'no%n

as pitch, roll and ya%

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http://en.wikipedia.org/wiki/Test_pilothttp://en.wikipedia.org/wiki/Flight_testhttp://en.wikipedia.org/wiki/Flighthttp://en.wikipedia.org/wiki/Aircrafthttp://en.wikipedia.org/wiki/Angles_of_rotationhttp://en.wikipedia.org/wiki/Angles_of_rotationhttp://en.wikipedia.org/wiki/Dimensionshttp://en.wikipedia.org/wiki/Center_of_masshttp://en.wikipedia.org/wiki/Test_pilothttp://en.wikipedia.org/wiki/Flight_testhttp://en.wikipedia.org/wiki/Flighthttp://en.wikipedia.org/wiki/Aircrafthttp://en.wikipedia.org/wiki/Angles_of_rotationhttp://en.wikipedia.org/wiki/Angles_of_rotationhttp://en.wikipedia.org/wiki/Dimensionshttp://en.wikipedia.org/wiki/Center_of_mass


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#ircraft engineers develop control systemsfor a vehicle?s orientation ;attitudeect?s Aamount of resistance

to change in velocityA ;%hich is quantified by its massect not sub>ect to any net e&ternal force moves

at a constant velocity Thus an ob>ect %ill continue moving at itscurrent velocityuntil some force causes its speed or direction to change

=n the surface of the Earth inertia is often mas'ed by the effects of frictionand

gravity, both of %hich tend to decrease the speed of moving ob>ects ;commonly to

the point of restects %ould move only as long as force %as applied to them

"'ERT"A #(RCES

Inertia

o Tendency for an ob>ect at rest to remain at rest, or

o Tendency of an ob>ect in motion to remain in motion

(orce

o The energy required to move or accelerate the ob>ect

Inertia forces

o (orces that move or accelerate an ob>ect

o They are proportional to the ob>ect?s %eight

o Seismic forces on buildings are inertia forces and are %eight driven

Sta!ility -erivative vs< Control -erivative

Stability derivatives and ontrol derivatives are related because they both are

measures of forces and moments on a vehicle as other parameters change =ften22
http://en.wikipedia.org/wiki/Classical_physicshttp://en.wikipedia.org/wiki/Motion_(physics)http://en.wikipedia.org/wiki/Matterhttp://en.wikipedia.org/wiki/Forceshttp://en.wikipedia.org/wiki/Isaac_Newtonhttp://en.wikipedia.org/wiki/Philosophi%C3%A6_Naturalis_Principia_Mathematicahttp://en.wikipedia.org/wiki/Newton's_laws_of_motionhttp://en.wikipedia.org/wiki/Velocityhttp://en.wikipedia.org/wiki/Frictionhttp://en.wikipedia.org/wiki/Aristotlehttp://en.wikipedia.org/wiki/Classical_physicshttp://en.wikipedia.org/wiki/Motion_(physics)http://en.wikipedia.org/wiki/Matterhttp://en.wikipedia.org/wiki/Forceshttp://en.wikipedia.org/wiki/Isaac_Newtonhttp://en.wikipedia.org/wiki/Philosophi%C3%A6_Naturalis_Principia_Mathematicahttp://en.wikipedia.org/wiki/Newton's_laws_of_motionhttp://en.wikipedia.org/wiki/Velocityhttp://en.wikipedia.org/wiki/Frictionhttp://en.wikipedia.org/wiki/Aristotle


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the %ords are used together and abbreviated in the term AS4 derivativesA They

differ in that stability derivatives measure the effects of changes in flight

conditions %hile control derivatives measure effects of changes in the control

surface positions)

# stability derivative measures ho% much change occurs in

a forceor momentacting on the vehicle %hen there is a small change in a flight

condition parameter such as angle of attac', airspeed, altitude, etc ;Such

parameters are called AstatesAections of the relative %ind vector

on to the three body a&es, rather than in terms of the translational motion of

the vehicle relative to the fluid #s the body rotates relative to direction of

the relative %ind, these components change, even %hen there is no net

change in speed

Moments an- angular rates aroun- each of the a0es

! is used to indicate the ArollingmomentA, %hich is around the J a&is

/hether it is around the J body a&is or the J stability a&is depends on

conte&t ;such as a subscript


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The body is oriented at angle ;psi< %ith respect to inertial a&es The body is

oriented at an angle Q ;beta< %ith respect to the velocity vector, so that the

components of velocity in body a&es are)

u R Ccos Q

v R Csin Q

%here C is the speed

The aerodynamic forces are generated %ith respect to body a&es, %hich is not

an inertial frame In order to calculate the motion, the forces must be referred to

inertial a&es This requires the body components of velocity to be resolved

through the heading angle ;Q< into inertial a&es

$esolving into fi&ed ;inertial< a&es)

ufR Ccos;Q


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(romNe%ton?s Second !a%, this is equal to the force acting divided by the mass

No% forces arise from thepressuredistribution over the body, and hence are

generated in body a&es, and not in inertial a&es, so the body forces must be

resolved to inertial a&es, as Ne%ton?s Second !a% does not apply in its simplest

form to an accelerating frame of reference

$esolving the body forces)

JfR Jcos;< Bsin;ect or system the

magnitude of the compressibility depends strongly on %hether the process

is adiabaticor isothermal #ccordingly isothermalcompressibility is defined)

/here the subscript T indicates that the partial differential is to be ta'en at

constant temperature

A-ia!aticcompressibility is defined)

/here S is entropy, for a solid, the distinction bet%een the t%o is usually

negligible

The inverse of the compressibility is called thebul' modulus, often

denoted V ;sometimes *


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performance is reali"ed %hen the %ing is e&cited by a non-linear resonance at 0:

of the natural frequency Specifically, at $eynolds numbers of 76, 36@ and 0@@@,

the aerodynamic performance that is characteri"ed by the ratio of lift coefficient to

drag coefficient is respectively increased by 32X, 3X and 30X %hen compared

%ith the corresponding ratios of a rigid %ing driven %ith the same 'inematics (orall $eynolds numbers, the lift generated per unit driving po%er is also enhanced in

a similar manner The %a'e capture mechanism is enhanced, due to a stronger flo%

around the %ing at stro'e reversal, resulting from a stronger end of stro'e vorte& at

the trailing edge The present study provides some clues about ho% fle&ibility

affects the aerodynamic performance in lo% $eynolds number flapping flight In

addition, it points to the importance of considering non-linear resonances for

enhancing aerodynamic performance

U'"T/""

Stic' (i&ed) *asic equilibrium equation

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Stability criterion

ontribution of %ing and tail and elevator to pitching moments

Effect of fuselage and nacelles

Effects of center of gravity location

Po%er effects

Stabili"er setting and center of gravity location

Elevator po%er

Elevator to trim

Trim gradients

ontrol fi&ed static stability

ontrol fi&ed neutral point

Stability margins

Effects of releasing the elevator

inge moment coefficients

ontrol forces to trim

ontrol free neutral point

Trim tabs

#erodynamic balancing of control surfaces .eans of augmentation of control

Static sta!ility

#s any vehicle moves it %ill be sub>ected to minor changes in the forces that act on

it, and in its speed

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If such a change causes further changes that tend to restore the vehicle to its

original speed and orientation, %ithout human or machine input, the vehicle is

said to be statically stable The aircraft has positive stability

If such a change causes further changes that tend to drive the vehicle a%ay

from its original speed and orientation, the vehicle is said to be staticallyunstable The aircraft has negative stability

If such a change causes no tendency for the vehicle to be restored to its

original speed and orientation, and no tendency for the vehicle to be driven

a%ay from its original speed and orientation, the vehicle is said to be neutrally

stable The aircraft has "ero stability

(or a vehicle to possess positive static stability it is not necessary for its speed and

orientation to return to e&actly the speed and orientation that e&isted before the

minor change that caused the upset It is sufficient that the speed and orientation donot continue to diverge but undergo at least a small change bac' to%ards the

original speed and orientation

%ongitu-inal sta!ility

The longitudinal stability of an aircraft refers to the aircraft?s stability in the

pitching plane - the plane %hich describes the position of the aircraft?s nose in

relation to its tail and the hori"on ;=ther stability modes are directional

stabilityand lateral stability

If an aircraft is longitudinally stable, a small increase in angle of attac'%ill cause

thepitching momenton the aircraft to change so that the angle of attac' decreases

Similarly, a small decrease in angle of attac' %ill cause the pitching moment to

change so that the angle of attac' increases

The pilot?s tas'

The pilot of an aircraft %ith positive longitudinal stability, %hether it is a human

pilot or an autopilot, has an easy tas' to fly the aircraft and maintain the desired

pitch attitude %hich, in turn, ma'es it easy to control the speed, angle of attac'

and fuselageangle relative to the hori"on The pilot of an aircraft %ith negative

longitudinal stability has a more difficult tas' to fly the aircraft It %ill benecessary for the pilot devote more effort, ma'e more frequent inputs to the

elevator control, and ma'e larger inputs, in an attempt to maintain the desired pitch

attitude

.ost successful aircraft have positive longitudinal stability, providing the

aircraft?s center of gravitylies %ithin the approved range Some acrobatic and

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http://en.wikipedia.org/wiki/Directional_stabilityhttp://en.wikipedia.org/wiki/Directional_stabilityhttp://en.wikipedia.org/wiki/Angle_of_attackhttp://en.wikipedia.org/wiki/Pitching_momenthttp://en.wikipedia.org/wiki/Autopilothttp://en.wikipedia.org/wiki/Fuselagehttp://en.wikipedia.org/wiki/Center_of_gravityhttp://en.wikipedia.org/wiki/Directional_stabilityhttp://en.wikipedia.org/wiki/Directional_stabilityhttp://en.wikipedia.org/wiki/Angle_of_attackhttp://en.wikipedia.org/wiki/Pitching_momenthttp://en.wikipedia.org/wiki/Autopilothttp://en.wikipedia.org/wiki/Fuselagehttp://en.wikipedia.org/wiki/Center_of_gravity


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combat aircraft have lo%-positive or neutral stability to provide high

maneuverability Some advanced aircraft have a form of lo%-negative stability

called rela&ed stabilityto provide e&tra-high maneuverability

Center of gravity

The longitudinal static stability of an aircraft is significantly influenced by the

position of the center of gravity of the aircraft #s the center of gravity moves

for%ard the moment arm bet%een the hori"ontal stabili"er increases and the

longitudinal static stability of the aircraft also increases #s the center of gravity

moves aft, the longitudinal static stability of the aircraft decreases

The limitations specified for an aircraft type and model include limitations on the

most for%ard position, and the most aft position, permitted for the center of

gravity No attempt should be made to fly an aircraft if its center of gravity is

outside the approved range, or %ill move outside the approved range during the

flight

#nalysis

Near the cruise condition most of the lift force is generated by the %ings, %ith

ideally only a small amount generated by the fuselage and tail /e may analy"e the

longitudinal static stability by considering the aircraft in equilibriumunder %ing

lift, tail force, and %eight The moment equilibrium condition is called trim, and

%e are generally interested in the longitudinal stability of the aircraft about this

trim condition

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http://en.wikipedia.org/wiki/Relaxed_stabilityhttp://en.wikipedia.org/wiki/Stabilizer_(aircraft)http://en.wikipedia.org/wiki/Mechanical_equilibriumhttp://en.wikipedia.org/wiki/Trim_(aircraft)http://en.wikipedia.org/wiki/File:AirStability.svghttp://en.wikipedia.org/wiki/Relaxed_stabilityhttp://en.wikipedia.org/wiki/Stabilizer_(aircraft)http://en.wikipedia.org/wiki/Mechanical_equilibriumhttp://en.wikipedia.org/wiki/Trim_(aircraft)


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Equating forcesin the vertical direction)

/ R !% !t

%here / is the %eight, !%is the %ing lift and !tis the tail force

(or a symmetrical airfoil at lo% angle of attac', the %ing lift is proportional tothe angle of attac')

%here S%is the %ing area !is the ;%ing< lift coefficient, G is the angle of

attac' The term G@is included to account for camber, %hich results in lift at

"ero angle of attac' (inally q is the dynamic pressure)

/here Y is the air densityand v is the speed

Trim

The tail planeis usually a symmetrical airfoil, so its force is proportional

to angle of attac', but in general, there %ill also be an elevatordeflection

to maintain moment equilibrium ;trim


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so the main %ing should stallbefore the tail, ensuring that the stall is

follo%ed immediately by a reduction in angle of attac'on the main

%ing, promoting recovery from the stall ;In contrast, in

a canardconfiguration, the loading of the hori"ontal stabili"er is

greater than that of the main %ing, so that the hori"ontal stabili"er

stalls before the main %ing, again promoting recovery from the stallet aircraft In the event of a very

high angle of attac', the hori"ontal stabili"er became immersed in the

do%n%ash from the fuselage, causing e&cessive do%nload on the

stabili"er, increasing the angle of attac' still further The only %ay an

aircraft could recover from this situation %as by >ettisoning tail

ballast or deploying a special tail parachute The phenomenon

became 'no%n as ?deep stall?

Ta'ing moments about the center of gravity, the net nose-up moment

is)

%here is the location of the center of gravity behind

the aerodynamic centerof the main %ing, is the tail moment

arm (or trim, this moment must be "ero (or a given ma&imum

elevator deflection, there is a corresponding limit on center of

gravity position at %hich the aircraft can be 'ept in equilibrium

/hen limited by control deflection this is 'no%n as a ?trim limit?In principle trim limits could determine the permissible for%ards

and rear%ards shift of the centre of gravity, but usually it is only

the for%ard cg limit %hich is determined by the available control,

the aft limit is usually dictated by stability

In a missile conte&t ?trim limit? more usually refers to the

ma&imum angle of attac', and hence lateral acceleration %hich

can be generated

Static sta!ility

The nature of stability may be e&amined by considering the

increment in pitching moment %ith change in angle of attac' at

the trim condition If this is nose up, the aircraft is longitudinally

unstable if nose do%n it is stable Differentiating the moment

equation %ith respect to G)

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http://en.wikipedia.org/wiki/Stall_(flight)http://en.wikipedia.org/wiki/Angle_of_attackhttp://en.wikipedia.org/wiki/Canard_(aeronautics)http://en.wikipedia.org/wiki/Stall_(flight)#Deep_stallhttp://en.wikipedia.org/wiki/Stall_(flight)#Deep_stallhttp://en.wikipedia.org/wiki/Center_of_gravityhttp://en.wikipedia.org/wiki/Aerodynamic_centerhttp://en.wikipedia.org/wiki/Stall_(flight)http://en.wikipedia.org/wiki/Angle_of_attackhttp://en.wikipedia.org/wiki/Canard_(aeronautics)http://en.wikipedia.org/wiki/Stall_(flight)#Deep_stallhttp://en.wikipedia.org/wiki/Center_of_gravityhttp://en.wikipedia.org/wiki/Aerodynamic_center


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Note) is a stability derivative

It is convenient to treat total lift as acting at a distance h ahead

of the centre of gravity, so that the moment equation may be

%ritten)

#pplying the increment in angle of attac')

Equating the t%o e&pressions for moment increment)

The total lift ! is the sum of !%and !tso the sum in the denominator can be

simplified and %ritten as the derivative of the total lift due to angle of attac',

yielding)

/here c is the mean aerodynamic chordof the main %ing The term)

is 'no%n as the tail volume ratio Its rather complicated coefficient, the ratio of

the t%o lift derivatives, has values in the range of @6@ to @W6 for typical

configurations, according to Piercy ence the e&pression for h may be %ritten

more compactly, though some%hat appro&imately, as)

h is 'no%n as the static margin (or stability it must be negative ;o%ever, for

consistency of language, the static margin is sometimes ta'en as h, so that

positive stability is associated %ith positive static margintimes the location cgof the center of gravity is

equal to the sum of the %eight 9of each component times the distance -of that

component from the reference location)

Center of gravity of an aircraft

The center-of-gravity ;9< is the point at %hich an aircraft %ould balance if it

%ere possible to suspend it at that point It is the mass center of the aircraft, or the

theoretical point at %hich the entire %eight of the aircraft is assumed to be

concentratedZ0[Its distance from the reference datum is determined by dividing the

total moment by the total %eight of the aircraftZ3[The center-of-gravity point

affects the stability of the aircraft To ensure the aircraft is safe to fly, the center-of-

gravity must fall %ithin specified limits established by the manufacturer

Terminology

$allast

*allast is removable or permanently installed %eight in an aircraft used to bring the

center of gravity into the allo%able range

Center/of/gravity limits

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http://www.grc.nasa.gov/WWW/k-12/airplane/geom.htmlhttp://www.grc.nasa.gov/WWW/k-12/airplane/turbine.htmlhttp://www.grc.nasa.gov/WWW/k-12/airplane/fuselage.htmlhttp://www.grc.nasa.gov/WWW/k-12/airplane/elv.htmlhttp://www.grc.nasa.gov/WWW/k-12/airplane/wteq.htmlhttp://www.grc.nasa.gov/WWW/k-12/airplane/cg.htmlhttp://www.grc.nasa.gov/WWW/k-12/airplane/weight2.htmlhttp://en.wikipedia.org/wiki/Center_of_gravity_of_an_aircraft#cite_note-FAA-1-0http://en.wikipedia.org/wiki/Center_of_gravity_of_an_aircraft#cite_note-faa-3-1http://www.grc.nasa.gov/WWW/k-12/airplane/geom.htmlhttp://www.grc.nasa.gov/WWW/k-12/airplane/turbine.htmlhttp://www.grc.nasa.gov/WWW/k-12/airplane/fuselage.htmlhttp://www.grc.nasa.gov/WWW/k-12/airplane/elv.htmlhttp://www.grc.nasa.gov/WWW/k-12/airplane/wteq.htmlhttp://www.grc.nasa.gov/WWW/k-12/airplane/cg.htmlhttp://www.grc.nasa.gov/WWW/k-12/airplane/weight2.htmlhttp://en.wikipedia.org/wiki/Center_of_gravity_of_an_aircraft#cite_note-FAA-1-0http://en.wikipedia.org/wiki/Center_of_gravity_of_an_aircraft#cite_note-faa-3-1


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9 limits are specified longitudinal ;for%ard and aft< and:or lateral ;left and righteight an- !alance/hen the %eight of the aircraft is at or belo% the allo%able limit;s< for its

configuration ;par'ed, ground movement, ta'e-off, landing, etc< and its center of

gravity is %ithin the allo%able range, and both %ill remain so for the duration of

the flight, the aircraft is said to be %ithin %eight and balance Different ma&imum

%eights may be defined for different situations for e&ample, large aircraft may

have ma&imum landing %eights that are lo%er than ma&imum ta'e-off %eights

;because some %eight is e&pected to be lost as fuel is burned during the flight


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point ;the "ero point of the datum, in this caseect is from this

point, the greater the force it e&erts .oment is calculated by multiplying the

%eight of an ob>ect by its arm

Mean Aero-ynamic Chor-MAC7

# specific chord line of a tapered %ing, #t the mean aerodynamic chord, the centerof pressure has the same aerodynamic force, position, and area as it does on the

rest of the %ing The .# represents the %idth of an equivalent rectangular %ing

in given conditions =n some aircraft, the center of gravity is e&pressed as a

percentage of the length of the .# In order to ma'e such a calculation, the

position of the leading edge of the .# must be 'no%n ahead of time This

position is defined as a distance from the reference datum and is found in the

aircraft?s flight manual and also on the aircraft?s type certificate data sheet If a

general .# is not given but a !e.# ;leading edge mean aerodynamic chord


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calculate fore-aft balanceeight

l!7

Arm

in7

Moment

l!/in7

Empty

%eight0,816@

0@0

8

060,61

@

Pilot and

passenger

s

2@@ W8@ 38,3@@

52


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(uel ;@

gallons

`

W lb:galet aircraft, have electric trim controls

.any airplanes also have rudderand:or ailerontrim systems =n some of these, the

rudder trim tab is rigid but ad>ustable on the ground by bending) it is angledslightly to the left ;%hen vie%ed from behind< to lessen the need for the pilot to

push the rudder pedal constantly to overcome the left-turning tendencies of some

prop-driven aircraft =ther aircraft have hinged rudder trim tabs that the pilot can

ad>ust in flight

/hen a trim tab is employed, it is moved into the slipstream opposite to the control

surface?s desired deflection (or e&ample, in order to trim an elevator to hold the

nose do%n, the elevator?s trim tab %ill actually rise up into the slipstream The

increased pressure on top of the trim tab surface caused by raising it %ill then

deflect the entire elevator slab do%n slightly, causing the tail to rise and theaircraft?s nose to move do%nZ0[In the case of an aircraft %here deployment of

high-lift devices ;flaps< %ould significantly alter the longitudinal trim, a

supplementary trim tab is arranged to simultaneously deploy %ith the flaps so that

pitch attitude is not mar'edly changed

The use of trim tabs significantly reduces pilots? %or'load during continuous

maneuvers ;eg) sustained climb to altitude after ta'eoff or descent prior to

landingoystic', and is thereby easy to maneuver< is used all the time after the flying pilot

has disabled the autopilot, especially after each time the flaps are lo%ered or at

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http://en.wikipedia.org/wiki/Elevator_(aircraft)http://en.wikipedia.org/wiki/Rudderhttp://en.wikipedia.org/wiki/Aileronhttp://en.wikipedia.org/wiki/Trim_tab#cite_note-0http://en.wikipedia.org/wiki/Flap_(aircraft)http://en.wikipedia.org/wiki/Air_traffic_controlhttp://en.wikipedia.org/wiki/Elevator_(aircraft)http://en.wikipedia.org/wiki/Rudderhttp://en.wikipedia.org/wiki/Aileronhttp://en.wikipedia.org/wiki/Trim_tab#cite_note-0http://en.wikipedia.org/wiki/Flap_(aircraft)http://en.wikipedia.org/wiki/Air_traffic_control


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every change in the airspeed, at the descent, approach and final Elevator trim is

most used for controlling the attitude at cruising by the autopilot

*eyond reducing pilot %or'load, proper trim also increases fuel efficiency by

reducing drag (or e&ample, propeller aircraft have a tendency to ya%%hen

operating at high po%er, for instance %hen climbing) this increasesparasitedragbecause the craft is not flying straight into the apparent %ind In such

circumstances, the use of an ad>ustable rudder trim tab can reduce ya%

%ongitu-inal Sta!ility an- Trim

The drag of the system is dependent on the distribution of loads bet%een the

surfaces In order to determine this, and to properly si"e the tail surface, %e mustconsider the aircraft?s stability and trim Stability is the tendency of a system to

return to its equilibrium condition after being disturbed from that point T%o types

of stability or instability are important

# static instability)# dynamic instability)

#n airplane must be a stable system ;%ell, %ith some e&ceptions < %ith acceptable

time constants To assure this, a careful analysis of the dynamic response and

controllability is required, but here %e loo' only at the simplest case) static

longitudinal stability and trim This %ill tell us something about the aerodynamic

design of the surfaces -- the load they must carry, the effect of airfoil properties,

and the drag associated %ith the surfaces

If %e displace the %ing or airplane from its equilibrium flight condition to a higher

angle of attac' and higher lift coefficient)

%e %ould li'e it to return to the lo%er lift coefficient

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http://en.wikipedia.org/wiki/Drag_(physics)http://en.wikipedia.org/wiki/Yaw_anglehttp://en.wikipedia.org/wiki/Parasite_draghttp://en.wikipedia.org/wiki/Parasite_draghttp://www.desktop.aero/appliedaero/configuration/unstableac.htmlhttp://en.wikipedia.org/wiki/Drag_(physics)http://en.wikipedia.org/wiki/Yaw_anglehttp://en.wikipedia.org/wiki/Parasite_draghttp://en.wikipedia.org/wiki/Parasite_draghttp://www.desktop.aero/appliedaero/configuration/unstableac.html


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This requires that the pitching moment about the rotation point^, m, become

negative as %e increase !)

%here & is the distance from the system?s center of additional lift to the cg

If & %ere @, the system %ould be neutrally stable &:c represents the margin ofstatic stability and is thus called the static margin Typical values for stable

airplanes range from 6X to 8@X The airplane may therefore be made as stable as

desired by moving the cg for%ard ;by putting lead in the nose< or moving the

%ing bac' =ne needs no tail for stability then, only the right position of the cg

#lthough this configuration is stable, it %ill tend to nose do%n %henever any lift is

produced In addition to stability %e require that the airplane be trimmed ;inmoment equilibrium< at the desired !

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/ith a single %ing, generating a sufficient mat "ero lift to trim %ith a reasonable

static margin and !is not so easy ;.ost airfoils have negative values of m@

Documents

Ppt Aero 6sem CSC