Engine System Helicopter Theory Notes

8/12/2019 Engine System Helicopter Theory Notes

1/20

Aircraft Engine SensorsPressure Sensors Description: measured. High overload protection is an integral part of the design. These units arecapable of sensing extremely small changes of applied pressure and are relatively insensitive to vibration, altitudeand shock. Applications: Commercial Aircraft Military Aircraft Brake Systems, HydraulicsL VDT pressuresensors that detect and transmit vital information regarding fuel and oil p r s s u r s ~ t o the EletronicEngine Control (EEC).The all welded construction of the sensorSpeed Sensors we can measure RPM in all turbine applications. This experience of produc.ing mallY different typesof RPM sensors can solve your speed measurement needs.Temperature Sensors Temperature sensors provide output readings proportional to temperature for a variety offluid system applications. TIley also provide custom packaging to protect the sensor while allowing Hexiblc.installation into a variety of aircraft systems. Temperature measurement can be accomplished using thermocoupleor resistance temperature device (RTD) techniques depending upon system interface. temperature, or accui acyconsiderations.Pressure Transducers latest wIits Silicon on 1nsulator (SOl) technology that provides high accuracy and long IeI mstability over the widest temperature range. Pressure transducers are suitable for the tough environment found inaircraft engines as well as more benign air frame system applications.Fuel Flow Transmitters solid presence with true mass flow transmitters for higher flow requirements ofcommercial and military aircraft with flow ranges up to the highest flows found in refueling tanker applications. Forbusiness and UA V applications, new TurboMass T vf IO\v Meter; a turbine tlow meter with buUt in digitalelectronics that provides a mass Jlow output directly to the aircraft system.Engine Harnesses thelThOCouple reliability and performance means more power when needed, longer engine lifeand lower cost of ownership.

www.Vidyarthiplus.com


2/20

E i e m 0 ni t 0 r i n i n s t rum e n t sThe present day piston engine instruments used in the typical general aviation airplane are notprecision laboratory instruments.

Nevertheless, the purpose of this brief presentation is a practical approach to interpreting thereadings of your engine instruments in accomplishing a safe and efficient flight. If, for example,you were to observe an irregular reading of one engine instrument, it calls for a cross-check onall other instruments, and not relying on one instrument as a basis for a decision affecting flight.

Since the engine is dependent on fuel, the gasoline gauge is considered a related engineinstrument. f pilots are going to attempt to stretch their flight range close to limits, they shouldbe aware of the errors in the gages vs. the actual usable fueL Some modern single engine aircrafthave had the fuel gauge show several gallons remaining, when in reality the tank was empty Others have indicated a specific number of gallons when filled, but actually the tank held several. . gallons less than indicated.

Therefore, in planning for each flight, remember that general aviation engine instruments are notprecision laboratory types, so cross-check, and give yourself an extra margin for safety.More aircraft are being fitted with digital readouts. Some digital equipment can automaticallymonitor the engine functions and will sound an alarm if anything goes outside preset limits:Digital instruments can be harder and slower to read than the traditional analogue type as thebrain must take additional steps before interpreting them. An instrument reading of whatevertype is only as good as its sender unit.



3/20

This is the primary indicator that all is well with the engine. A cold engine will always show avery high oil pressure. Once hot, the pressure should remain in the green arc under nOll'lalRPMs. A low pressure may indicate a serious problem with the oil pump or engine bearings. Theacceptable ranges of pressure are stated in the aircraft operating manual. The oil pressure willdiminish if the engine becomes overheated s the viscosity of the oil becomes too thin and beginsto break dO'W11.

Oil temperature

The oil temperature gauge is also very a important device for monitoring the wellbeing of theengine. High power should not be used until the temperature has climbed into the operatingrange as damage can occur to the engine. f the temperature climbs into the red sectof, itindicates that a serious problem may have developed.Vacuum gauge



4/20

Remember that aircraft engines will continue to operate as their ignition spark is created bymagnetos which are independent of the aircraft electrical system.Aircraft are usually also fitted with a low voltage warning light which is placed in a prominentposition. f a problem arises with the charging circuit it \vill begin to flicker and then show red.The light may quite normally flicker or show dull red at very low RPM.

Cylinder temperature gauge (CHT)

Most engines are fitted with a CHT on one cylinder only. Every engine design has a cylinder thatruns slightly hotter than the rest. f the temperature climbs towards the red line it may indicate aserious problem.Exhaust gas temperature gauge (EGT)



5/20

/ .,,/

0&1n { ~ 6 n \ ' : r s i o n

O a t ~ triln$I'"r

.. k \ . . ' ~ ~ n i : : : ) 1 1 ~ J l l : : n l ~ ~ ' whlch Un j'.J.hhrc"iation 41" who.l It.: in:,': '.'tinilt ~ ' l " , Thh: r r \ ) : ~ r ; ~ m m l l i g Wilh nmemrmic insltudaon$ ito c31kuILt I1;I:/',' 'nflY:l':,::e IJt{/,t:rNtrWti,r:g b : . { ~ ) U ~ t \ aflcr Ih(: M:Y-:Jt:OCt'-.rillen, il (,.. imo t l : ~ a'i,,,mbkr p t l ) g ~ ' " "'hjch In.,hs Ihi'to:t','t'r{IOli d H',:n:h:nt cod and ; I s . . ~ t m b l e . ~ it )nIC the mcmor) :: ~ t . c

" , J ~ c '"mn':mN,ic codes are Mill unlike Ih" human language, .nd,o ahiBherlccl lJnguo, ,c'programming cono::pt can be adopted in wl,ienlu,tru:lions ~ . r t written in II problem-oricnled or procellure-crielllUttrt> ,r t. in theI,IS i ~ x t : " K < ' , in annloo; rQrm, and in ')rder for the Cl>mpUte,,; ID

, a ~ 1 ) ' 'YJt t l 1 c i ~ [nlerprcting fUnclir)Jl, 1he dala must be converu:;llo ab i l " ' r y , c l ) ~ e d ;)rm'll. In m 3 1 l ~ C 1 ~ < : S il is; also netessary for tU;i\ 10 be(L :, :md fn:'Jr digit.11 tf) ~ 1 t : J J ( ) g rorm:l . The (''Ollverr.ion devices 1 I ~ < X lfor , ~ , h " J r p - ; l 5 ~ , arc of the illleGF.ltcd logic circlIil typ


6/20

AlIowgoing encoded data from Ihe computers lite identified by linBduilional binary- f I - ' J p.Jf.I .r>l..td, -:-0' ontu{ntCfH/:RS'- ' - - - - - - . - . . . - - . ~ . - ~,

> . . d f f P I , ' ~ i l , , - - :~ . . . l IN:

' 1 t i f ) ~ " l r ) t " , t f -....- '". . - --1 t\ \I .""'UI WIoIU 'Strrifb tOIHl.IUQ __" __ 71lAIISI,t,TtI A ,m:CEtI/"fJl

I ~ ~I

1; : \ &IT ,..L.,. : l J \ ~ l I T )-1 en'

I " I 3 I I I G I 1 I B I , t , ~ I " I 1 I air ' I U I J ~I I I ! I I I I 1 \ I I II I 1 1 I I I I I I I !I , I I I I I I I I r I- ~ , . . I ~ ( > . 9 C L t . f ;I I I I I I I I \ ! I \I I ! I 1 I I I I ; I II 1 I v I ,I 1 I 0 I 1 I D I , i , ! ;) I I I , I 0/"',1DATA flIT WCOCl.:!;3 LQl'::

',:: ..C't : j ' C, C l l , ~ ~ t : )

1 L&.-.'-' Iff,1io ' ~ - : _ , : , ~Os (ill bits Jr to 29, con'?,-,F',xN': [0 equin:l:n: d r : d m ~ 1 1 i1 7lilcrs,IVhicll lndicarc that r h ~ DME system CO:;lpu:er is lr.msmirrifJg c[)co(toddatil correspondir.g 10 a disamc:e of 251.S nS; lj,:al m i C ~ , w ik ll:eRIIQio MtUneter com1(\ltcr i.; tt'.l.\\'.\mhur.s d , - ' ~ " 1 , - ( ) r ; c ~ \ ' C ' ; ' , \ C \ h \ " . 0 1,\\attitude of 2451).5 {tel..

llhs :,() 11 G.te l . ~ ~ \ ; U e c I . \ '",h'l.t \ . ~ ' , m ' ; . ~ d , \ ; ~' \ ~ g


http:///reader/full/manjl.edhttp:///reader/full/birl%3C.llhttp:///reader/full/manjl.edhttp:///reader/full/birl%3C.ll


7/20

I . . , f,

lv WI); (SSM), whil:h refers 10 plus, miliUS, llorth. QUilt, Idl, righl.ell:. of bin:l1')"'coded decim&lll1Jrnclic d31D. They abo rerer 10 thevalitJity.ofdata, and fanura warning.The: detection of errors in cOOts llod their correctioll J . ~ II VCI)ilnJ10rlnlll aspett ill ille tmns!nlssion of lllgillll d ~ l : l , and for thisl)urpoSC a pariry clreck rnWlod is pro\'ided whereby a compotcr callt c ~ t ",heth_r bits ill a binar), word have been accidentally changedduring transmission. The tesl is dolt, ) by a u t o r n ~ l i c summadon of thehils c o m p r i ~ i r \ g a \\,orolo oet.enl1iol' whether fhe 101,.11 number is 0011or cven. and by c d l c u l ~ t i n g w h ~ 1 is lernlcd a parity bfr: this forms theI"sl bit a word, Le. bit 32. Jf. lOf e x ~ m p ~ . therclii all odd11ulul.>t.r Df binary Is .ilmOIl& the first 31 b j t ~ , the llllrilY bit is set 101 10 I l m ~ c the w()!d of 'e\'en parit)" 'Oddwhere the p ~ r i : ) ' bit il: sellO bir..lry 0 10

b j n ~ r ) ' h cod. This latter [')errl of pari!)' is ad:JplcdJ.n the ARJNC< 29 ' f " : ' ~ i f i c , 3 t i < l l l .D;II" Mi! mmsmiucd in h:llchc5 :II " $pccifled repclilion \.,rrefrc5r.:-:lcnt ralc ~ l o n g t h ~ approplJalc b ~ ~ s c s , and at either high"peed nOO kilobitsl",c} I l f low spo""d 02-14.5 l ; i l o b ~ I s 1 5 C C ),,,,,V; 7.\t th e e.lculnlion of true nirww:: "froll\ ~ i r I c m p e r ~ l u r e dJllll Ill:"!.ItS. The 1110dlilator a r w l l g t m ~ n : i'': .);1,\DC, i t ~ ~ ~ s a c i 3 1 c d iooi(;;Jt


8/20

-representative selection from the wide range of instruments andsystems that currently come within both areas of technology and the~ e q u e n c i n g of the relevant chapters has been arranged in such a wayall. to reflect the transition from one area to the other.

ike its predecessor, thedetails emphasize fundamental principlesand tpeir applications to civil aircraft instruments and systems, and

o v e r ~ I, are also intended to serve as a basic reference for thoseperson who, either independently or, by way of courses establishedby spec list training organizations, are preparing for AircraftMaintena ce Engineer Licence examinations. It is also hoped that thedetails wi! rovide some support to the current technical knowledgerequirement relevant to flight crew e ~ a m i n a t i o n s A large number ofself-test que 'ons have been compiled and are set out in chapter

sequence at the nd of the book.As with all boO s of this nature schematic diagrams and

photographs are of reat importance in supporting the written detailsand so it is hopedtha the three hundred or so spread over thechapters which follow ill achieve the desired objective. In reviewingsome current aircra ft ins lIations together with the contents ofAircraft Instruments, and a so of another of my booksMicroelectronics in Aircraft ystems) I found that a number ofdiagrams and photographs we still approp riate and so it wasexpedient to make further use 0 these. The diagrams relating to newsubject material have, in many ses, been redrawn from myoriginal roughs . The remaining n w diagrams and photographs(some of which are reproduced in c our) hav.e been supplied to mefrom external sources, and in this con eclion I would particularly liketo express my grateful thanks to Smith' Industries, Aer Lingus, andBoeing International Corporation for thei assistance.In conclusion, I wish to convey sincere anks to Leslie Coombsnot only for his help. past and present, in p viding material on asubject of common interest, but in particular r having accepted myinvitati on to write the Forew ord to this book, [ necessitate d hishaving to read through many pages of draft man cript, but as thisresulted in comments that required some changes 0 text, then I amsure that he too would agre e that effo rts were not w ted.

E.P.opthomeW. Sussex

\\

1 nstrument displ'ays,panels and layouts

In flight, an aircraft and its operating crew fonn a man-machinesystem loop which, depending on the size and type of aircraft, maybe fairly simple or very complex. The function of the crew within the;loop is that of controller, and the extent of the control function isgoverned by tl: e simplicity or otherwise of the aircraft as anintegrated whole. For example, in manually flying an aircraft, andmanually initiating adjustments to essential systems, the controller sfunction is said to be a fully active one. If, on the other hand, theflight of an aircraft and system's adjustments are automatic inoperation, then the controller's function becomes one of monitoring,with the possibility of reverting to the active function in the event offailure of systems.

Instruments, of course, play an extremely vital role in the controlloop as they are the means of communicating data between systemsand controller. Therefore, in order that a controller may obtain amaximum of control quality, and also to minimize the mental effortin interpreting data, it is necessary to pay the utmost regard to thecontent and format of the data displays.

The most common fonns of data display are (a) qU lmilalive, inwhich the variable quantity being measured is presented in tenns of anumerical value and by the relative position between a pointer orindex and a graduated scale, and (b) qualitative, in which the datd ispresented in symbolic or pictorial format.

Quantitative displays There are three principal methods by which data may he displayed:i) the circular scale, or more familiarly. the 'clock' type of scale,

(il) straight scale. and i i i) digital, or counter.Circular scaleThis maybe considered as the c l a s s ~ a l method of displaying data inquantitative form and is illustrated in Fig. 1.1. The scale base refersto the graduated line, which may be actual or implied, running fromend to end of the scale and from which the scale marks and line oftravel of the pointer are defined.




9/20

250

Rll '1 '5fVf?t 'Y

FiguU' r I Circul3f scaletlHc_nriUHtvc display

""..AlE(iRAQUAnON .... AtlJ;l

igure 1.2 Linear and n o n ~tineef scales. (a) Linear;(b) square-law: (c) logarithm ,

SCALE SPAClNGIN \J>4fTS Of 1

~ Implied ..:ale baseI'g o 1, -

'8 RP a { -200~ lI

1 23"f 1': 4te

Scale or graduation marks are those which constitute the scale ofan instrument. For quantitative displays the number and size of marksare chosen in order to obtain quick and accurate interpretation ofreadings. In general, scales are divided so that the marks representunits of 1, 2 or 5, or decimal multiples thereof. and those markswhich are to qe numbered are longer than the remainder.

Spacing of marks is also governed by physical laws related to thequantity to be measured, but in general they result in spacing that iseither linear or non-linear. Typical examples are illustrated in Fig.1.2, -from which it will also be noted that non-linear displays may beof tht1 square-law or logarithmic-law type, the physical laws in thisinstance being related to i r s p e e d ~ n d rilte of altitude changerespectively.The sequence of numbering always increases in a clockwise

d i r ~ t i o i l ; thus conformili$to what is termed the 'visual expectation'of the obserVer; As in the case of marks,numbering is always insteps of 1, 20r 5 or decimal multiples thereof. The numbers may bemarked on the dial either inside or outside the scale base.

(hI

igure 1..1 H,gh range longi:cale displays. (o} Concentricscales: (b l fixed and rotating

s c . a t c s ~ (c) comrnon scale andtriple poin1ers.

- The distance between the centres of the marks indicating theminimum and max.imum values of the chosen range of measurement.and measured along the scale base, is called the scale length.Governing factors in the choice of scale length for a particular rangeare the size of the instrument. the accuracy with which it needs to beread, and the conditions under which it is to be observed.High-range long-scale displaysFor the measurement of some quantities - for example, turbineengine speed. airspeed, and altitude high measuring ranges arcinvolved with the result that very long scales are required. Thismakes it difficult to display such quantities on single circular scales instandard-size cases, particularly in connection with the number andspacing of the marks. If a large number of marks are required theirspacing might be too dose to permit rapid reading, while, on theother hand, a reduction in the number of marks in order to 'openthe spacing will also give rise to errors when interpreting values atpoints between scale marks.

Some of the displays developed as practical solutions are illustratedin Fig, l , ~ . The display shown at (a) is perhaps the simplest way ofaccommodating a lengthy scale; by splitting it into two concentricscales, the inner one is made a continuation of the outer. A singlepointer driven through two revolutions can be used to register againstboth scales. but as it can also lead to too frequent misreading. a

I , 0 /90 109 r ~ 1 1 80


10/20

igure I Reading accuracy

"

presentation by two concentrically-mounted pointers of different sizesis much better. A practical example of this is to be found in sometypes of engine speed indicator. In this instance, a lar1;e pointerrotates against an outer scale to indicate hundreds of rev/min, and atthe same time it rotates a smaller pointer through appropriate ratiogearing, against an inner scale to indicate thousands of rev/min.

The method shown at (b) is employed in a certain type ofpneumatic airspeed indicator; in its basic concept it is similar to theone just described. In this case, however, a single pointer rotatesagainst a circular scale and drives a second scale plate instead of apointer. This rotating plate, which records hundreds of knots as the

rotates through complete revolutions, is visible through anaperture in the main dial of the indicator.Scale and operating rangesInstrument scale lengths and ranges usually exceed thatrequired for the operating range of the system with which aninstrument is associated, thus leaving part of the scale unused. Thismay appear somewhat wasteful, but an example will show that ithelps in improving the accuracy with which readings may beobserved.

Let us consider a fluid system in which the operating pressurerange is, say, 0-30 Ibf/in2. It would be no problem to design a scalefor the required pressure indicator which would be of a lengthequivalent to the system's total operating range, also divided into acOllvenient number of parts as shown in 1.4(a). However, undercertain operating conditions of the system concerned, it may beessential to monitor pressures having such values as 17 or 29 Ibf/in2and to do this accurately ill the shortest possible time is not veryeasy, as a second look at 'the diagram will show.

I f the scale is now redesigned so that its length and range exceedthe system's operating range and also graduated in the manner noted

b.29 Iir(al {bl fIfi',,

earlier, then as shown at (b) the result makes it much easier to;n'''',.,..''A' and to monitor specific operating values.Straight scaleIn addition to the circular scale presentation, a quantitativemay also be of the straight scale v e r t i ~ l or horizontal) type, For thesame reason that the sequence of numbering is given in a clockwisedirection on a circular scale, so on a straight scale the sequence isfrom bottom to top or from left to right.

Although such displays contribute to the saving of panel space andimproved observatiOlNI1 ac cura cy, their application to the ,morcconventional types of mechanical and/or electro-mechanicalinstruments has been limited to those utilizing synchronous datatransmission principles. t is pertinent to note at this juncture that inrespect of electronic CRT displays (see Chapter II) there arc nomechanical restraints, and so straight scales can, therefore, be morewidely applied.

An example of a straight scale presentation of an iridicatoroperating on the above-mentioned principles is illustrated in1.5(a); it is u . ~ e d for indicating the position of an aircraft's landing

The scales are graduated in degrees, and each pointer isoperated by a synchro (see Chapter 5). The synchros arc suppliedwith from transmitters actuated respectively by left andoutboard flap sections.

Another variation of this type of display is shown at (b) of1.5. t is known as the moving tape or thermometer display and wasoriginally developed for the measurement of parameters essential tothe operation of engines of large transpbrt aircraft. Each unitcontains a servo-driven white tape in place of a pointer, which movesin a vertical plane and registers against a seale in a similar manner tothe mercury column of a thermometer. As will be noted, there is onedisplay unit for each parameter, the scales being common to eachengine in the particular type of aircraft. When such arclimited to only one or two parameters then, by scanning across theends of the tapes, or columns, a much quicker and more accurateevaluation of changes in engine performance can be obtained ascompared to 'clock' type displays. This fact, and the fact that pandspace can be reduced, are clearly evident from the diagram.Digital displayA tll!!1tai. or counter, type of display is one that is 0 be

in conjunction with the circular type of display; twoexamples are shown in Fig. 1.6. In the application to an altimeterthere are two counters: one presents a fixed pressure value which can

:;




11/20

F i ~ U F ( ' J 5 Straighl ~ c a l ed l p l a y ~ . b) g i Y ~ ~ s acomp : tns on between moving-t::lpe and cl cular scale displays.

(a)

(b)

4050

Figure 1 6 Application ofdigital counter displays.

G

ffIcI,rt,,kIIf

DYNAMIC O U N T E ~OISP\.AY

be set as and when required, and is known as a st ticwhile the other is geared to the altimeter mechanism

as a ayllatmc counter in altitude, and is therefore knownpresentation of altitude data by means of a scale and COunter is yetanother method of solving the long-scale problemon page 3. The counter of the turbine gas temperatureindicator is also a dynamic display since, in addllion to the mainpointer, it is driven by a servo transmission system (see also page

3 6 : ~ .

Dual indicator displaysThese displays are designed principally as a means of conservingpanel space, particularly where the measurement of the variousquantities related to is concerned. They arc normally of twobasic forms: in one, twoseparate indicator mechanisms and scales arecontained in one case, while in the other, which also has twomechanisms in one cas e, the pointers re gister agaill" a commOnscale. examples of display combinations are illustrated in Fig1.7.Operational range m a r k i n o ~

take the form of coloured arcs, radial lines andto the scales of instruments, their p u r p o ~ e heing to

iJmits of operation of the systems with which theinstruments are associated. The definitions of theSe marks are asfollows:RED radial line Maximum and minimum limitsYELLOW arc Take-off and precautionary rangesGREEN arc Normal operating rangeRED arc Range in which operation is prohibited

EXHAUSTGAS

i. RPM

EngineNo.

EGTc %RPM .I S 892 470 903 480 884 520 90

7


http:///reader/full/comp.:.tns.onhttp:///reader/full/OISP/.AYhttp:///reader/full/comp.:.tns.onhttp:///reader/full/OISP/.AY


12/20

Figure 1 8 Operational rangeigure 1" 7 Dual-indicator GREENdispiays. Ttl


13/20

Director displays

Fi; ;iil< /.10 DirccWf UISP'Y( ~ J T O horizon).

These displays are associated priricipally with the monitoring of flightattitude and navigational data, and present it in a manner thatindicates to the flight crew what control movements must be made,either to correct any departure from a desired flight padt, or to causean aircraft to perfonn a specific manoeuvre. It is dtus apparent thatin the development of such a display there must be a closerelationship between the direction of control movements and theinstrument pointer, or symbolic-type indicating element; in otherwords, movements should be in the natural sense in order that thedirectives or command s of the display may be obeyed.Displays of this nature are specifically applied to the two primaryinstruments which comprise conventional flight director systems andelectronic flight instrument systems (see Chapters 9 and 12). One ofthe instruments (referred to as an Attitude Director Indicator) has itsorigins in one of the oldest of flight attitude instruments,namely the gyro horizon .(see Chapter 4), and so it serves as a basisfor understanding the concept of director displays. As will be notedfrom Fig. 1.10, th ree clements make up the display of theinstrument: a pointer registering against a bank-angle scale, anelement symbolizing an aircI;llft, and an element symbolizing thenatural horizon. Both the bank pointer and natural horizon elementare stabilised by a gyroscope. As the instrument is designed for the

of attitude angles, and as also one of the symbolic elementscan move with. respect to the other, then it has two referenee axes,that of the case which is f i ~ e d with respect to an aircraft, and that ofthe moving element.Assuming that in level flight an aircraft s pitch attitude changessuch as to bring the nose up, then the movement of the horizonelement relative to the fixed aircraft symbol will be displayed as indiagrdJl1 (a). This indicates that the pilot must get the nose down .Similarly, if an aircraft s bank attitude should change whereby theleft wing, say, goes down, then the display as at (b) would direct thepilot to bank the aircraft to the ril:rht'. In both cases the commands

8AN4( SCAJ..

co (h)

Figure I JJ Attitude directordisplay. (a) Aircraft straight00 level; I .ircrafi nose up;e) aircraft banked left; d) ' f ly

up command; k 'Ily leftcomn-uuxt

Iti

i .,.II (d)

would be satisfied by the pilot moving the appropriate flight controlsin the natural sense.The display presentation of a typical Attitude Director Indicator isshown in Fig. I. II (a), and as will be noted it is fundamentallysimilar to that of a gyro horizon. Details of its operation will becovered in a later chapter, but at this juncture it suffices to note thaFixed bankpoInter

tronr ,Ii ~ _CommandJaB

-aircraftsymbol I I (b) I I Ila)

01

~ C ~ ~I I I '

(e)10

11




14/20

Electronic displays

1:!

the horizon symbolic element is driven by servomotors that receiveappropriate attitude displacement signals from a remotely-locatedgyroscope unit. Thus, assuming as before a nose-up displacement ofan aircraft, the signals transmitted by the gyroscope unit will causethe horizon symbolic element to be driven to a position below thefixed element symbolizing the aircraft, as shown at (b). The pilot istherefore directed to 'fly down' to the level flight situation as at (a).lf a change in the aircraft's attitude produces, say, a left bank, thenin response to signals from the gyroscope unit the horizon symbolicelement and bank pointer will be driven to the right as shown at (c).The pilot is therefore directed to 'fly right' to the level flightsituation.In addition to displaying the foregoing primary attitude changes, anindicator also includes .what istenned a command bar display thatenables a pilot to establish a desired change in aircraft attitude. If, forexample, a climb attitude is to be maintained after take-off, then bysetting a control knob the command bars are motor-driven to a 'fly

position as shown at (d) of Fig. 1.11. During the climb thehorizon symbolic element will be driven in the manner explainedearlier, and the corrunand bars will be recentred over the fixedelement so that the display will be as shown in diagram (b).Roll attitude, or turn commands, are established in a similarmanner, the command bars in this case being rotated in the requireddirection; diagram (e) of Fig. 1 11 illustrates a 'fly left' command.As the aircraft's attitude changes the aircraft symbolic element moveswith the aircraft, while the horizon symbolic element and bankpointerare driven in the opposite direction. When the command hasbeen satisfied, the display will then be as shown in diagram (c).. The scales and pointers shown to the left and bottom of theindicator also form a director display that is utilized during the fapproach and landing sequence under the guidance of an Instmment tLanding System. Details of the operation of this display and of the fifsecond indicator involved in a Flight Director System will be given in fChapter 9. fWith the introduction of digital signal-processing technology into the \field colloquially known as 'avionics', and its application of microelectronic circuit techniques, it became possible to make drasticchallges to both quantitative and qualitative data display methods. Infact, the stage has already been reached whereby many of theconventional clock type instmments which, for so long, haveperfom1ed a primary role in data display, can be replaced entirely hya microprocessing method of 'painting' equivalent data displays onthe screens of cathode ray tube (CRT) display units.In addition to CRT displays (see Chapter II), electronic display I

Table 1.1 Applications of eleclronic displaysDisplay technolog y Operating mo4e Typi( (l/ applicationsLight-emilling diode Active Digital counter displays of engine pcrfom)anccLiquid crystal Passive monitoring indicators; rndio frequency sciecwr

indicatofs;rdist.ance measuring indicators: contrf.J1d ~ s p l a y t n ~ of inertiai na igatlon ~ y s t e m ~Eleclron CRT beam Active Weather radar i n d i c a t o r s ~ display of navigationaldata; engine performance data; system status;check lists.

techniques also include those of light-emitting diode and liquid crystalelements. Typical examples of their applications are given in Table1.1. The operating mode of these displays may be either active orpassive the definitions of which are as follows:

Active: a display using phenomena potentially capable ofproducing . ight when the display element s areelectrically activated.

Passive: a display which either transmits light ft;om an auxiliarylight source after modulation by the device, or whichproduces a pattern viewed by reflected ambient

Display configurationsDisplays of the light-emitting diode and liquid cryst.al type arc usuallylimited to applications in which a single register of alphanumericvalues is required, and are based on what is termed a seven-segmentmatrix configuration or, in some cases, a dot matrix configuration.

Figure 1.12(a) illustrates the seven-segment configuration, theletters which conventionally designate each of the segments, and thepatterns generated for displaying each of the decimal numbers 0--9.A segmented configuration may also be used for displaying alphabeticcharacters as well as numbers, but this requires that the numher ofsegments be increased, typically from seven up to 13 and/or 16Exanlples of these alphanumeric displays are illustrated at b) of Fig1.12.

In a dot matrix display the patterns generated for each individualcharacter are made up of a specific number of illuminated dotsarranged in columns and rows.[n the example shown at c) of1.12, the matri x is designated as a 4 x 7 configuration, i.e. itcomprises four columns and seven rows.Light-emitting diodes (LEDs)An LED is a solid-state device comprising a forward-biased p-njunction transistor formed from a slice or chip of gallium arsenide

i3


http:///reader/full/cryst.alhttp:///reader/full/cryst.al


15/20

~ ; P ; ; ' S 5 f M

Figure 1.12 Ek (,lfOnic Aa(plUloumeric d i ~ p l a } : : ; .a) S e v e n ~ s c g r n e n t : 18b) 13- and 16-scgment; F_* Gc) a 4 x 7 matrix.

EI Ie 1 ] ~ 2 3 Y S 6 1 8 9D NQ. of segmontS 6 6(a)1\1/1i l/l- \1 17i\1

I I IJ 1- TI ,- 1- ,- I I-I C] TI r- TI r: C r: LJ T Ir-, JJ ,_ JJ C r 1-= r-I _ I_I I I _0 L JJ C_' U 1 1 _L tJl I 1\/1 1\ I 1- CI -I - j -I I I 1\11 1\ I r-I CI r- r-I r -I \ - I I I \I U I 1 \ f\ t_ I I I \I tJ I - r ;: : ]11/11\1\1 7 11//11\/\1 -7-I \ \ 1 1 LJ \ \ Ie

I LJ C L- CI LJ III 1 1 ] ] IJ C - 1 0 [I n 1I , ~ L U _I IL.I 1 II_J IJUI UJUIb) Trows

. t-4 m ; ~ ? ? ~ f : ; r 6 1 f l : : : ~ l f i I E F ] I ~ f l E I [ : lJ ~ ~ ~ ~ ~ ~ ~ f : ~ _ _ _ ..dLJ(c)

phosphide (GaAsP) Inoulded into a tra l1sparent covering as shown inFig. 1.13. Whefl :current f l o ~ s t ~ r o t l g h tlj:echip it emits light whichis in direct proportion to the cqrrent .flow J.jght emi;;sion in differentcolours of the spectrum dn, where t ~ u i r e d , be obtained by varyingthe proportionsqf m; ele ments. emilpi-i?ing the chip, and also bv atechnique of 'doping' with o t l i e r e J e ~ e n t s . e.g. nitrogen.

In a typical seven-segment display format it is usual to employ oneLED per segment and mount it within a reflective cavity with a

14

Figure I. 13 U g h c ~ e m ; u i n gdiode.CRYSTAt.. C ~ t U : t

Oilfuser pia e

~ rReflectiv< Cl\l I l t i t s

EffE.ctl1 e:wg(nent_ __ 'lgh'

--.-

Plastic Q ~ r l a .

P[ 'Sllt: overtay

COHHEC1lOHS

plastic overlay and a diffuser plate. The segments are formed as asealed integrated circuit pack, the connecting pins of which aresoldered to an associated printed circuit board. Depending on theapplication and the number of digits comprising the appropriatequantitative display, independent digit packs may be used, orcombined in a mUltiple digit display unit.

LEOs can also be used in a dot-matrix configuration, and anexample of this as applied to a type of engine speed indicator isshown in Fig. I .14. Each dot making up the decimal Ilumbers is anindividual LED and they are arranged m a 9 x 5 matrix. The counteris of unique design in that ils signal drive circuit causes an apparcm

of the digits which simulates the action of a mechanicaldrum-type counter as it responds to changes ill speed.Liquid crystal display (LCD)The basic structure of a seven-segment LCD is shown in Fig. 1.15. Itconsists of two glass plates coated on their inner surfaces with a thinfilm of transparent conducting material (referred to as polarizing film)such as indium oxide. The material on the front is etched toform the seven segments, each of which farms an electrode. A mirrorimage is also etched into the oxide coating of the backbut this is not segmented since it constitutes a common rctum for allsegments. The space between the plates is filled with a liquid crystal

15




16/20

Figure 1 14 Engine s p t . ~indicator with a dot matrixLED. (Courtesy of Smith ,industries Ltd.)

Figure 1 5 Strucwre 01 anLCD

UQuid clystal {l yeftYPIcal spacing' 10 tntcrons)

cOIllPound, and the complete assembly is hermetically sealed with aspecial thermoplastic material to prevent contamination.When a low-voltage, low-current signal is applied to the segments,the Iiolarizatioit of theeompound is 6hanged together with a changein its optical appearance from transparent to reflective. The

Figure 1 /6 Application 01LCD.

magmtude of the


17/20

Fig t 7 Head-up display.WlNDSCftH~ ~ ~ _ . . . . . . - ~~

~ ~ R TUBE

Oats _ I PROCESSOR ANDi n p u t s - - ~ ~ O ~ GENERATOR I-----------------J(al

Altituoo

Aircraftsymbo

Airsped

-Vertical sped

Horizonbars 21 22

Headingb)

The aIT 0unt. of data required fordispJay is gove(1led by therequirementf. o thc varioijs:fligh(phliSes and operational role of anaircraft, i.e:, militaryor civil, but the parameters shown in diagram(b) are common to all. Theforma[ and disposition of the displayscorresponding to required parameters can vary between systems; forexample, a heading display may be in the form of a rotating arc at

Panels and layouts

Instrument grouping

the upper part of the renec/or plate, and altitude may he indicated bythe registering of moving dots with a fixed index at one side of theplate instead of the changing digital counter readout located as shownin the diagram. Additional data such as decision height, radio altitudeand runway outlines may also be

All instruments essential to the operation of an aircraft areaccommodated' on panels, the number and disposition of which varyin accordance with the number of instruments required for theappropriate type of aircraft and its cockpit or flight deck layout. Amain instrument panel positioned in front of pilots is, of course, afeature common to all types of aircraft since instruments displaying

data must be within the pilot's normal line of vision. Thepanel may be mounted in the vertical position or, as is now morecommon practice, sloped forward at about 15" from the vertical tominimize parallax errors. Typical positions of other panels a r ~overhead, at the side, and on a control pedestal located centrally

1.18 illustrates the foregoing arrangementto the Boeing 737-300 series aircraft. Where a flight

is required as a member of an operating crew, thenwould also be located at the station specifically provided on the nightdeck.

Flight instrmncntsthere are six night instruments whose indications are so

ordinated as to create a 'picture' of all aircraft's flight condition andrequired control movement s: are the airspeed indicator,altimeter, gyro horizon, direction indicator, verrical spec:d indicatorand IIlrnand-bank indicator. It is, therefore: most impo rtant hH thescinstrumcnts to be properly grouped maintain co-ordination ;lfld )assist a pilot in obscrvltlg them with the minImum of effort.The first real attempt at establishing a standard method ofwas the 'blind flymg panel' or 'basil' six' 1;IYOU{ shown in Fig,I 19(a). The gyro horizon occupies trl : top c.:ntre posllion. and s l n c ~it provides positive and direct indications of attitude, and alliwciechanges in the pitching and rolling planes, it is lltiliz.ed as the masterinstrument. As control of airspeed and altitude arc directly related 1attitude, the airspeed indicator, altimeter and vertical speed indicatorflank the gyro horizon and support the interprClalion of pitch attitude.Chan'?,cs in direction are initiated by banking an aircraft. and {hedegree of head'ng change is obtamed from the direction Indicator:this instrument therefore supports the intemrct31HHI of roil altitude

1819


http:///reader/full/lltiliz.edhttp:///reader/full/lltiliz.ed


18/20

Figmc 18 FiighllilY(u BoeIng 737 - ]00 e m ~ ~;;ircl'afl

FiXi.n j _ } High ifl;,truuh:lltg(()Uptng_ a) a ~ k

lMsir 'T' (with fhg 1IdirectOr sysum Hldt.:-ators)

{bl

and is positioned directly below the gyro horizon. The tum-and-bankindicator serves as a secondary reference instrument for headingchanges, so it t ~ s u p p r t s the interpretation of roll altitude.

With the development and introduction of new types of aircraft,and of more comprehensive display presentations afforded by theindicators of flight director systems, a review of the functions ofcertain of the instruments and their relative positions within the groupresulted in the adoption of the 'basic T' 'arrangement as the currentstandard. As will be noted from diagram (b) of Fig. 1.19, there arenow four key indicators: airspeed, pitch and roll attitude. an altitudeindicator forming the horizontal bar of the T , and a horizontalsituation (direction) indicator forming the vertical bar. As far as thepositions flanking the latter indicator are concemed, they are taken upby other less specifically essential flight instruments which, in theexa.'l1ple shown, are the vertical speed indicator and a radiomagncticindicator (RMI). In some cases a turn-and-bank indicator. or anindicator known as a tum co-ordinator, may take the place shownoccupied by the RMI. In many instances involving the use of flightdirector system indicators andlor electronic flight imtnlment systemdisplay units, a turn-and-bank indicator is no longer used.

IIn the case of electronic flight instrument systems, the two CRT

display units (EADI and EHSI) are also used ill conjunction wilh fourconventional-type indicators to form the basic 'T', as shown in Fig.1.20(a). In displays of more recent origin, and now in use in suchaircraft as the Boeing 747-400 (see also Fig. 12.11), the CRTscreens are much larger in size, thus making it possible for the EADlto display airspeed, altitude and vertical speed data instead ofconventional indicators. The presentation, which also corresponds tothe basic 'T' arrangement is illustrated at (b) of 1.20.Power pl nt instrumentsI The specific grouping of instruments required for the monitoring ofpower plant operation is governed primarily by the type of powerplant, the size of aircraft, and therefore the space available forlocation of instruments, In asinglc-engined aircraft this does notpresent too much of a proble'm since the sllIall number of instrumentsrequired may flank the flight instruments, thus keeping them within al small canning range'.

21




19/20

I'('

igure 1,20 Dasi


20/20

Figur 1.12 Po\ver pl.llll1f l. \ (fUrnenldl5,f1 ays

The earth'satmosphere

pattern of a panicular power plant. Another advantage of thismethod is lhat all the instrllments for one power planl are

more associated with the controls for that power plan .Figure 1.22 illustrates the gwuping arrangement currclI ly

III Boeing 737 --400 series aircraft for the display of theparall1e ers associated with its power pl:Plt5.

The numer ie values corresponding to each parameter arc in

Documents

Engine System Helicopter Theory Notes