Chapter 4 Thrust

8/19/2019 Chapter 4 Thrust

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THRUST


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Counter Drag in level flight

More Thrust for Climb

More for acceleration

PERFORMACE DEPEDS O THRUST

e!ton"s #r$ la!

Push air % Reaction &ushes air&lane

bac'!ar$ for!ar$

Use$ on groun$ as !ell


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Thrust an$ Momentum

Thrust is &rovi$e$ b( giving momentum

Thrust ) Rate of &rovi$ing momentum

Thrust ) mv &er secon$

Same thrust for large mass of air !ith

small change of velocit( an$

vice versa


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Rate of &rovi$ing *E ) +mv, !atts

Po!er being the rate of $oing !or' itta'es lesser amount of &o!er to $o the

same !or' at a slo!er rate

-ess !or' means lesser loss of energ(

Moving a large mass of air !ith small

increase in velocit( is more efficient than

moving a small mass of air !ith large

increase in velocit(


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Conversion of energ(

Chemical energ( of fuel

to

Thermal Energ(

to

Mechanical .or'


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Pure /et

Design Aero$(namic in 0 out

Problem Effective at high s&ee$s

Can not start on its o!n

o thrust at 1ERO velocit(


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Mo$ification of &ure 2et

Thrust Available at 1ERO 3elocit(!ith com&ressor an$ turbine

Flo! Aero$(namic through4 over4effect on bla$es of com&ressor

an$ turbine4 $esign of 5nlet an$

e6haust

7(&ass engines

Turbofan


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5n Piston % Pro&eller combination

Clear cut $ivision at Pro&eller Shaft

Pro&eller is Aero$(namic Consi$eration

An$ Design

Pro&eller is to convert tor8ue at shaft

into Thrust in the $irection of airflo!

5nta'e 9 Ram2et E6haust 9 /et


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Thrust an$ Po!er

Thrust of a 2et is almost same at all s&ee$sPo!er being a &ro$uct of Thrust an$ s&ee$

varies !ith s&ee$: o satisfactor( !a( of

measuring Po!er: Po!er is 1ERO atconsi$erable Thrust !hen a;c stationar(:

5n Pro&eller Po!er


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A bo$( !hich is rotating as !ell as

moving for!ar$ travels in a

Helical Path

Heli6 Angle

Elements at $ifferent ra$ii travel a $ifferent

Helical &ath at a corres&on$ing Heli6 angle

Heli6 angle is the angle bet!een &lane of

rotation an$ relative airflo!: Heli6 angle is

more at root an$ less at ti&:


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For o&timum &erformance of an

aerofoil it must meet the relative airflo! at

a corres&on$ing angle of attac':

5n a &ro&eller4 it varies along the

length of the &ro&eller as the Heli6 angle:

5n a &ro&eller4 the bla$e is given an

angle ) Heli6 angle ? angle of attac'

Hence4 7la$e T!ist or Helical T!ist

7la$e angle ) Heli6 angle ? angle of attac'


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Total Reaction


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A$vance &er Distance move$ for!ar$

Revolution in one revolution

5n fi6e$ &itch &ro&eller4it is not a fi6e$ 8uantit(

@eometric A$vance &er revolution

Pitch at B angle of attac'

Onl( geometr(

to mtrs in fi6e$ &itch

E6&erimental A$vance &er revolution

Mean &itch !hen O thrust


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Sli& Difference bet!een

e6&erimental mean &itch an$

actual a$vance;revolution


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3ariable Pitch

Fi6e$ &itch &ro&eller is goo$ for one set offor!ar$ s&ee$ an$ RPM: Thrust ma( be

ma6 !hen stationar( i:e: goo$ for ta'e off

but not so $uring cruise4 on the other han$

it ma( be goo$ for cruise but not at ta'e off

So efficienc( falls on both si$es

3ariable &itch changes angle as re8uire$

Engine an$ &ro& !or' at high efficienc(

3ariable &itch bla$es re$uce noise > /et


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7la$e angles 9Coarse an$ Fine

Feathere$ 7la$e 9 7e(on$ full( coarse

et force sto&s &ro&eller

Flight Fine Pitch Sto&

Air 7ra'e 9 7e(on$ full( fine

>>ve Thrust 9 7e(on$ B bla$e angle

Engine &o!er re8uire$

High %ve thrust


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Absor&tion of Po!er

Pro&eller shoul$ be able to absorb&o!er generate$ b( engine

Absor&tion can be increase$ b(5ncrease angle of attac'

5ncrease camber

5ncrease s&ee$

5ncrease RPM

5ncrease length of bla$e

5ncrease !i$th of bla$e

5ncrease number of bla$es


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5ncreasing Chor$ is easier but changes

As&ect Ratio an$ re$uces efficienc(

5ncreasing o: of bla$es is more efficient

7est Ans!er Contra rotating &ro&s

Soli$it(

Ratio bet!een &art of &ro& $isc

covere$ b( &ro& to the &art covere$ b( air

@reater the soli$it(4 greater the &o!er

that can be absorbe$


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Sli& Stream

The stream of air being &ushe$ bac'

-i'e a c(lin$er

Contraction in $ia a little $istance behin$

3elocit( behin$ coul$ be $ouble

Drag in sli& stream coul$ be four times


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High velocit( of sli& stream is goo$ for

Ru$$er an$ Elevator control4 &articularl( at

lo! s&ee$

Rotar( motion !ill stri'e one si$e of

aircraft4 more so Fin an$ Ru$$er4 affectsDirectional an$ -ateral balance

Aero$(namic Turning Moment

Centrifugal Turning Moment


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@(rosco&ic Effect

Precession:Direction of rotation of Pro&eller4

if cloc'!ise

Chapter 4 Thrust

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