Model Small Gas Turbine Jet Engines

109 Pages·2018·23.43 MB·English

by  Thomas Kamps

Model
THIRD EDITION
BY THOMAS KAMPS
THE MODELLER'S WORLD
s e::- e::- s
R.. ,
THIRD EDITION
BY THOMAS KAMPS
© Auflage 1995 by Verlag fiir Technik und I landwt:rk
Postfach 22-·•. 76492 Baden-Baden
English Language © 1995 Traplel Publications Limitnl
Translated from the original German by Keith Thomas
Technical suppon by Tom Wilkinson
© 2005 Traplet Publications Ltd
All rights reserved. All trademarks an<l registered names acknowkdgell. No tY.•rt of this book mar he copied.
repro<lun:d or transmitted in any form without the written consent of the Publishers.
The information in this book is tme to the best of our knowledgt.> at the time of compilation. Recommendations an::
made without anr guar.intee, implic::<l or otherwise, on the:: part of the author or publisher, who also disclaim any
liability incurre::<l in connection with the:: use of data or specific information containe::d within this publication.
First published by Traplet Publications Limited 1995
Second Edition .2002
Third Edition 2005
Trnplet House.
Pendragon Close,
Malvern,
Worcestershire. WR 14 l(;A
United Kingdom.
ISBN l 9003"."I 91 X
Technical drawings by Lee:: Wisc:tlale
Front Co11er: The Wren M\f/44 is current~)' t/Je smallest
production model afrcraft gas twiJine - a nzan•el of ml11iaturisatiou.
Rack Col'er: Two PST GOOR gas turbines puwcr Dtll'id l..aw's F-1-i Tomcat.
f' ~ I} ~ I I A 1
Printed by Wa Fai Graphic Arts Printing Co. . I lung Kung
About the Author
T homas Kamps. l)ipl.-Kaufmann (approx. GB c::quiv
aknt: U.Sc. business studit's), born 19-0. The
author's liking for technology stretches back as far
as he can rt:mt:mber. No sweets or chocolate in his
Chri:.tma:. stoc.:king: it wa~ full of electrical and mechani
cal components. Following his practical inclinations, he
converted tht: family cellar workshop first into a prc::ci
sion enginc::ering manufacturing workshop. and subse
quently into an engine tc::sting station. He is luck1· - his
ndghbours art: very sympathetic towards his hobby.
llis prJ(.'tic:ll capabilities are matched hr his theoreti
cal understanding - as witnt:~ the efficiem, smooth-nm
ninJ? engines he has made. a number of publisht'.d articles,
and not lt'.ast this h<x>k.
Currentl)' he is li\·ing in Zurich/SwitZt:rland and works
in a major Swiss hank. In addition to mo<ldling he enjoys
in his leisure time. reading, skiing and running.
Foreword
T he idt:a of the gas turhint' cm be 1raccd back to a also reflected in the ac1ivities of the GTBA, the (;as
patent filed by the Frenchman Guillaume in the Turbine Builders Associ:ltion. which has approximately
year I 921, and is therefore quite old. However. it 1,700 members enrolled to date: and which facilitates the
was many years before ii proved possible to put the prin· exchange of ide::as and prnctic;1litics.
ciplt' into practice in tht' form of the jet engine. In the The thrust figures have increased significantly. High
late 1lil1t'teen-thirties Hans-Joachim Pabst von Ohain and tech materials are used in the area of the turbine whe::cls
Sir Frank Whittle sun:eedcd virtually simultaneously in and bearings. By far. no other engine can give:- so much
applying the principle to constnict a working engine. tlight power to a model plane as a small gas turbine.
It has taken us modellers a !!feat deal more time to \.ommercial engine::s offer thrusts of lOON or more.
bring the idea to fruition. T0<.1 complex and too much Electronic starters and control units become more and
trouble - that was always the verdict. Now and then more standard. lberefore I haw paid special attemion to
rumours of succt:s.'iful m1x.lel-s<:ale ga~ turbines filtered lO the constantly increasing number of production rurbines
the outside:: world. but in m:my cases the engines were now on the market and have revised and updated the
only capable of running when their constructor was description of these:: power plants.
dreaming. In my eyes, the rapid devclopmenl has only been pos
As a result we in the model world were truly aston· sible because of an open information exchange by ama
ishcd to learn that amate::urs had actually managed tu pro tt'.urs and home builders. Many commercial engines
duce:: working jet engine::s using relatively straightforward include the knowledge of many amateurs and their con
methods. The:: ke::y to success lay not so much in high-level struction is in many ways very alike tu the:: Microturhine.
precision manufacture. bur in simplicity and careful KJ-66 or its predecessors. In thi~ second edition I have
matching of individual components. As Kurt Schreckling also improved the building instructions to achi('ve an
has shown with his engine~. if the design i:o. right. then it ea'>ier construction with a solid performance.
is possible to use a wooden compressor wheel and still At this point I wish to thank very sincerely all those
achit'vt: a thrust:weight m1io comparable to that of a fuJl who have helped me with tips and idea. ... and espc::ciaHr
size aircra.ft je::t engine. jes(1s Artes de Arcos, Otto Bnihn, Alfred Kittelberger, Ridi
I lowever how do we go ahout designing a working jct Reichstetter, Tom Wilkinson ancl John G. Wright.
e::ngine? Whal special charaete::ristics have to be consid
ered? How do these engines work, anyway? This book Thomas Kamps, April 2002
attempts to answer 1hcse questions and many
01hers. with the overall aim of helping you to understand
this new type of engine::. As such ii is really aimed at the
beginner IO jets. bul c.lon 't give:: up if you are already famil
iar with that speci:ll kerosene fragrance; you will still find
a few useful idea'i here even if you already have some
experience of jet engines.
At this point I would like to offer my j!f'.tteful thanks to
my like-minded friends and colleagues for tht:ir help and
encouragement. My spc::<:ial thanks must go to Kurt
Schreckling, Bennie: van de Goor and Han Jenniskens for
their helpful and useful comments. I wuukl also like to
thank Karl-Heinz Collin and Arno Foerster, who were
vc::ry hdpfol in i.mparting their specialist knowledge :md
information.
Foreword to the second edition
In recem years model jets have hc::comc more and
more common at our firing fields. Many engines are avail
able today. Tht> new power source has been proven
strong and reliable. World Championships have been
held and the winning models were powered by jet
engines. le seems that th<: ducted fan will he replaced
soon. The growing interest in this small turbo engine is
Contents
Page
Introduction ................... .. . .. ......... 11
How do jet engines work? . . . . . . . . .JI
Tbe ope11gas111rl1i11e process . . .11
77.1e qul!sliu11 c!l ej)icienq· . ...... . . .. lj
The development history of the jct engine . .14
It all s1a11ed ill tbe 1930s ....... . . 75
77>e mhustjel e11p,i11es oft he 1950s . . .. /6
Prototypes for model jet engines ............. . .IH
Dm11l! e11p,i11es and APl z~ <Auxiliary Power UuifsJ .IH
I (1'/X'r-<."httf"Ri 118 . 79
B1rly model jet engines ... .. .22
,Ha.\· Vreher:~ Bahr Mamba .............. . ..22
7be Su•edisb PAL .~)~5/em a11d 1/s succes.. ;or Turbo111i11 .. . 22
Kurt Scbrec:klin/!, 's FD series . . . . .23
Turhorec: T210Jivm.fP .\' . .26
Model jet engines 10 date .......... . .28
I.I. 77.u!J-450 l~r Sopbia Prec:isiu11 ..2 9
7.2. lll1T-Ad1•a11ced .ilic:rv T11rf1i11<'!i . .w
I .3. 1l1e 1\.166 . . . . . .. 31
1.4. 111e .-111es-7il1'bi11es .. .J2
1. 5. The Jet Cllf model 111rhi11e J:J
7. 6. The Smallest E11gi11l'S ........... . )4
1. 7. Turtx,p1vp and Sbt!/i Power f;'11giiws .. 36
Chapter 1 The Component Parts of a Model jet Engine .P
Special feature:-s of small gas turhines J7
Comhustio11 ~-
Rotor design .. ..... . .38
Cup losses . . . . . . . . . .J8
C<111d11sio11s relating to the mode/jet e11gi11e .:)9
The compressor ......... . .41
The mdial compressor ............ . .42
Typical culc11llllio11 for a radial comprt-ssor . .M
T11 rlxx:hr1 rp,er co111prr!SS01-s . . . . . . . . . 15
"fl.1e co111pressor c:baracteristic p,mpb . 1'""'
Dijfuser u'heels . . . . . . . . . . . . . . .4H
£w1111ple u/ calculating tbe d!fli1ser -~1·s1e111 .57
'/l1e surge limit ..... . .52
'/be axial compressor . . . . . . . .54
Exnmple calc11/atiu11: axial co111pm-.sor stage . .55
The <.:omhustion <.:hamhc::r . . . . . . ............ . .57
/X>siµu a11d fimctiou uft he cu111lmslio11 chamber .. <;-
The q 11 estw 11 offuel .5H
.I fixture formation .......... . ..6 0
"/be sig11ijica11<:e of re-circ:ulatio11 zones .. . .62
Turhine stage;· and exhaust cone ... . .63
I Jou• the 111rlm1e sWJ<l' u·orks ... . .63
Axial turhlne or radial turbine? . . . . . . . . . . . .65
f)esi~u and 1•ector diap.rams q(an c1.Yial turhi11e . .65
Typical calc11/atio11: turbine desig11for a mode/jet engine . . . . . . . . . . . . . . • . . . . . . . . . . . .66
Ce11tr((ugal loc1cf.<; 011 the rotor uheel . . . . . . . . . . .68
The exhaust cone ........... .. ..................................... ........ .6 9
17.w shc!/i <!la mode/jet enf!.ine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • . . . . . . . .69
Calc:11lati11g rhe critical rotatio11al speed . • . . . . . . . . . . . . . . . . . . . . . . . . . . . . • . 70
Chapter 2 A Home-made Model Jet Engine . . .' ]
Introduction .... ..... . . .. 71
--,
\f'hat too/.<; u·ill ! 11eed.> .....•..• .. /-
Selec:ting material~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
n.1e c:ompres:;or u•heel . , . . . . . . . . . . . . . . . . . . . .... 74
Constructing the engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
Makillf!. the sht!ft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... .. 75
The sbc1ft t11111iel and heari11~ . . . . . . . . . . . . . . . . .. , . . . . . . . . . . ...6
17.1e turbine nozzle p,11ide l'Clll<' SJ:5tem .... ............ ...... .. .. .. .. .. .. .... ..... 78
17.1e turbine tl'beel . . . . . . . . . . . . . . . . . . . . . . . 7H
Balancing . . ........................... .............. .............. . 79
The compressor s_1-:;tem . . . . . . . . . . ..... ...............9
17.1e c:o111h11stio11 chamber . . • • • • . . . . . . . . . . . . . . . . . . . . . • • . . . . . . . . . . . . . . . . . . .80
7be bousing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .82
AsSc'mbling the components . . . . . . . . . . . . . . . . . . . . . . . .HS
Running the engine for the first time . . . . . . . . . . . . . . . . . . . . . . . . . . • . . • . . • . . . . . . . . . . . .85
Bench running stand for kerosene operation . . . . . . . . . , . . . . .87
Pumps, tcmks and other equipme11t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .88
Ru1111i11f!. tbe engine 011 kerosene . . . . . . • . . • . . . . . . . . . . . . . . .H9
General instructions for different compressor!i . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
Optimising the performance of mo<ld jct engines . . . . . . . . . . . . . . . . . . . . . . . . . . ...... .... . 92
Chapter 3 The Engine in Practice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
Safety: the first Commandment . . . . .. , . , . . . . • . . . . . . . .94
Measuring the engine·s perfonnance data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
Rotational speed. pressure cmd thrust . • . . • . . . . . . . • . . . • . . . • . . . . 9'>
Measurements for tbe ad1wzced operator . . . . . . • . . . . • • . . . . . . . . . . . . . . . . • . . . .95
Using jet engines in model aircraft . . . . . . . . . . . . . . . . . . .97
F11ndame11tal spec:ialjea111res . . . . . . . .. .9 7
Nou·jet engines hebave in flight . . ... .•. •...•••.... ......... .............••.. .. 97
Air i11ta/..~e desi}!.n . . . . . . . . . • . • . . . . . . . . . • . . , . .98
Cooling tbefuselage . . • . . . ....... .. ........ .. ..... ....•..... ......... ... . .. . 99
Auxiliary Equipmc::nt ..... .............................••........ .... ... ..•.......... IO I
Particular problems encountered in jet-powered flight . .....••... ... ... ............. .... .1 02
Tbmst delay . . . ........................ . 102
Gyroscopic ~[fec:ts . . . . . . . . . . . . . . . . . . . . . . . . 103
l'ault-finding . . . . . . . . . . .. .....•...... ....... ...... .•....... .... ..... J 04
\f'bat tbe sound qf tbe engine tells you . . . . . , . . . . . . . .. . 104
Exceeding tbe pressure limit (s11~i11f!,) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . 105
A standard prubkm . . . . . . . . . . . . . . • . . . . . . . . . . • • . . . . . . . . • . . ...... 705
l:.xcessim~1· bi~b exhaust !{llS temperature . . . . . . . . . . . . . . . . . . • . . . . . . . . . • . . .. . 105
Maintc::nance and repair . . . . ....................... ...... . 106
Cbec:ki11f!. the bearinp,s . . . . . . . . • . . . • . . . . . . . . .106
Clecmi11,~ tbe engine . . • • • . . . . . . . . . . . . . . • . . . . . . . . ..... .... . ............ . 106
Bibliography . . . . • . . . . . . . . . . . 107
Notes ......................... .......................... .......... . JOH
Introduction
How do jet e11gines work? basic principles. tJ1e jet engine will soon give up its m}'S
terious secrets.
Ga:-. turbint':o. have long since claimed a secure place
for themst'lves in our world. Amon~-;t the most ohvious The open gas turbine process
examples are the innumer;ibk aircraft which day after Regardless of whether we are considering a shaft
dar tlr ahove us, trailing their wakes of condensation power turbine (designed to produce mechanical power)
across the sky, but that's not all: gas turhines are at work or a jd engine. we find the same working process at the
wht'.re you might not know it: nowadays they arc used core: it is terme<l the open gas turbine procc::ss. Air is
more and more commonly in power stations, dectricity sucked into the engine an<l compressed. The comprt'ssed
generators. boat engines and much more. air then flows through a comhustion chamber in which it
Suddenly these engines are increasingly being used to is heated to a high tempentn1rc.
propel mo<lt:ls. and that is why we need to understand In their hot st;lle the gases arc c;tpablt' of performing
how they work. Unfortunately it is much more difficult to more: work than was put into them during the compres
explain how a gas turhine works than to elucidate what is sion stage:. Finally the air expands again as it is relea~d
probably the most important ent:q.ty machine of our time: into a turbine. to which it imparts a proportion of its
the piston engine. There the imnwnse pressure caused by power. 111is process sets the turhine spinning, which in
explosive combustion moves a piston running inside a rum drives the compressor to which it is connected b)' a
qlindt'.r. shaft. TI1e residual ent'rgy in tht'. exhaust gas am now he
111e principk is ckar and comprehensible. Alas. it is exploited to St'.rve the purpose of the engine. If the
just impossibk to explain in so few words how a g;1s tur exhaust stream of the hasic gas turhine is further acceler
bine works. I lere we find spinning rotors and wheels, gas ated by an t-xhaust cone the: m:tchine becomes a jct
flow an<l energy conversion, but don't kt that worry you engine.
- once we have ma<le a link headway in explaining the The resultant flow of hot gas produces a forwards-
Compressm· Combustiort cht1mber Turbfrte
0 0
C> 0
C> 0
0
0
C>
- 0
g h
Dit1gram ofa jet ei1gi11e.
a) Air irttake. b) Compressor blades, c) Ri11g ofd iffuser bla<les, d) Compressor rotor,
e) F1·011t bearing,f) Fuel injector 11ozzle, g) Combustion cbm11ber, /J) !ii/Jaft, i) Nozzle g1tide 1•cmes,
j) 1url1i11e rotor blades. k) Tm·bi11e rotor. I) Tail co11e.
Mode/jet Engim>s 11
a b c
Tj1pes oft11rlJi11e compressor.
t1) Axial compressor. b) Rt1dial comp1·ess01: c) Diago11al cm11p1·essm:
dirt:ctt:d force, i.e. there is an equal and opposite reaction (:ent in order to achieve stable <:ombustion. The sole pur
according to the familiar laws of physics. pose of the combustion (:hamber in a gas nirbim: is to
The gas turbine is dasS\:d as a heat engine as is the pi::. heat air. A':> :1 result the gas turbine is not bound strictly to
ton engine familiar to model flyers, so it will be no sur a spc::cific foe!. ln principle the engine could be made to
prise ro find that both engines share certain bask work if an electric heating element were used instead of
features. The working medium is first compressed and burning kerosene.
then heatc:d in a combustion chamber. In the piston The crucial difference hetween the gas turbine and the
engine the heating occurs by the combustion of a fuel - piston engine is in the se::quem:e of the processes within
air mixture, the combustion occurring in an explosive the engine. The piston engine completes the stages of its
form. l11e result is a tremendous rise:: in pressure inside power cycle in sequence, one by one, whereas the gas
the cylinder. In contrast, the analogous process inside the t.urbine does everything at the same time. Air is const:mt
gas turhine is isobaric in nature, i.e. the pressure remains ly sucked in and compressed, heated and expanded
constant when the working gases flow through the com again. It is this very constancy which constitutes the great
bustion chamber. ·nms in the case of the gas turbine the advantage of the gas turbine. The individual processes
increase: in usabk power is not due to a rise in pressure run continuously and in separntc:: spaces or areas of the
in the combustion chamlx'r. Quite the opposite: in prac engine.
tice we have to accept a loss of pressure of a few per Every gas turbine possesses a compressor and a tur
bine. These components are designed in the form of a
continuous tlow machine. In comparison with piston
engines they ofkr the important advantage that they are
able to produce great powc:-r in the:: smalkst possible
space::. For example, a model engine's single:: turbine::
wheel, just 6'5 mm in diameter, can drive a compressor
with a power absorption of more than 20 kW at full
throttle. In fulH;ize jet engines the power levels are
astronomic - to the point where they are difficult to
comprehend.
The compressor of a gas turbine is always some fonn
of turbine machine:-; usually dther an axial or a radial com
pressor. In the case:: of the:-axial type the gas flows parallel
to the drive shaft. while the radial type hurls the gas out
wards pc:-rpendicular to the shaft. A third type - the diago·
nal c·ompressor - is used rnrely, hut it is still wonhy of
mention. As is easy to see, this represents a hybrid of the
two other types. The air arrives in the axial direction and
is pushed on in a broadly axial direction. the diameter
of the tlow increasing steadily. The axial compressor
is broadly similar co the fan of an impeller (ducted
fan). A compressor may consist of several
stages, each stage consisting of a rotating compressor
wheel and a fixed diffuser wheel. also known as the sta
Si11gle stage axial turbi11e. tor. The rotor and stator are always fitted with a particu
ll} Nozzle guicle r•m1es, b) Rotati11g bl11des. lar number of vanes or Mades. The air is initially
accelerated as it flows through the stages, then slowed
12 .Hode/.fet Engines
down again slightly. As a result of this proct:ss a propor Like the comprc:,,..,or. the power turbine can ht: con
tion of the air·s kinetic cncrgr is convcrted into prcssure Mructed in axial or radial form. lhe first successful gas
energy in each stage. Multi-stagc axial comprcssors are turbine designed b)' Pabst von Ohain ( 193-) Wa!> fittc:d
standard for full-size gas turbincs. Modem jet engines with a radial turbine. In the:- courst' of time the radial tur
have extremely complt:x compressors consisting of up to bine has been supt:rst:c.Jed almost t::ntirely hr rhe axial
17 stages and even morc. The rt:suh is an increaSt: in prc:s type. Evc:-n by the: 50s tht: radial turbine only survived
sure of up to 30 times. occ:1sionallr in low-power shaft power engines. Howcver.
The: r.tdial compressor is much simpkr in constmc for modcl jct engines this type of turhinc could still bt: of
t ion and therefore much morc suitable for model interest.
c:ngines. The air flows into thc wheel i11 the axfal dircc
tion and is then flung outward b)' centrifugal force. On it:. The question of efficiency
own this device is known as a centrifugal compressor. We will now consider the procc:sses inside:-the:-gas tur
Once again a single stage consists of a rotor and a stator, bine somewhat more closc:ly. If wt: adopt tht: prot:t:!>s
although the pressure:: incrt·aSt: per stage is much higher described here, the: engint: can <>111)' function if the tur
than with an axial compressor stage. As a result gas tur bine produces sufficient power to drivt: the compressor.
bines with radial comprt·ssors can often managc with I 'nfortunatcly turbines and compressors are not zt·ro
only one stagc. loss machines. In each stage friction and turbulence
Additional advantages of the radial comprcssor arc its absorb pan of the energy and waste it as ht:at. To mini·
robui.t nature and ih inherent rdiabilit)'. The disadvan mise friction losses there musr he a gap between the
tage" is the la~e frontal area of tht· machine. Gas turbines rotor bhtdes and the housinµ to avoid any danger of foul
with a radial compressor art' therefore always somewhat ing. This clear.met: tht:n allows a proportion of the:- f?.aS
hulkT simply to slip past the rotor.
'fhe second conunuous flow machine in thc gas tur To counter this problem and still kct:p tht: engine: run
bine: ii. the actual turbine:. This can he visualised as a com ning it is essential to kt:ep the tcmperature of thc gas -
prc:ssor "in reversc". The turbine converts pressure and thcrcfort: its power capacity - high cnough to com
energy into rhc:- !>haft power which is required to drivt: pt:nsate for the losses. However. the permissible: gas tem
the comprt:ssor. Sinct: the hot gases contain much mort: pc:raturc is not infinitely high. ·ntl' maximum tt:mpt:r.tturc
encrgy than the compressor absorbs, the:- system is self is limitt:d by the strenµth of the materials used in tht:
sustaining. If the llnal t<:mperature aftcr thc combustion engine. especially where the modt:llt:r does not have
chamber - what is known as tht: combustion gas tempt:r access to hcat-resistant steels. The only way out of this
arure - is high enough, additional power can ht: t:xtractt:d dilc:-mma is to strive: for maximum possible efficiency of
from it. the compressor and turhine. This is one of tht: mosr diffi
Like the compressor, the turbine it"elf may consist of cult probkms for the modeller to tacklt:, since: the: lawi.
one:- or more stages. Wht:n the air reaches the turbine of physics have been drawn up to thwa.n tht: t:xperi
stage it first ftows rhmugh the stator which convc:rts pan mentcr. The smaller we make the compressor and tur
of tht:: pressurt: t:nergy imo kinetic ent::rgy. As the gases binc, the le:-.'> efficient, in general terms. they becomc.
pass through the fixt:d
stator they arc accelerat A/read)' ,.ecog11i.w1bly a motlelj et e11gi11e, this desig11 p1·01l11ced 5 Newum ... of
ed in the direction of thrust 11t a 11111.ximum .~peetl of3 5.000 1p111. Tbe fuel - p11,.e diesel - w11s
rotation of the rotor. 11aporised i11 a copper t111Je c111d bur1uul i11 " 1·e11erse.flo111 combustion chamber.
The gas is accc::knucd
onct: more: within tht:
vancs of the rotor, hut
this time: in the:: opposite
dirc:ction. 111e net result
is a powerful peripheral
forct: acting on all the
rotor blades, and taking
the: form of a propulsive
torque:. This peripht:ral
force arisc:s from the
recoil which the:: rotor
blades experience. As
the cxhaust gast:s flow
through at high speed
they are accelerared in
the direction opposirt: to
that of rotation. On the
othcr hand tht: twisting
morion produced b)' the
nozzle guide vane sys
tc:-m produces an im
pulse force:- in the rotor
hlac.Jcs, varying accord·
ing to the dcsign of the
turbine stagt::.
.11odel.fet Engines 13