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Helicopter PistonEngine Installations

He Wharekura-tiniKaihautu 0 Aotearoa

T H E 0 P E NP0 LYTECHN |(UF NEW ZEALAND

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CONTENTS

Piston Engine Installations 1

Position of the Engine 1

Adaption of a Horizontal Engine to aVertical Position 3

Installation of a Vertical Engine Q

Installation of a Horizontal Engine 10

Components in Common 15

Fuel Systems 15

Gravity—flow System 17

A Non—gravity System 20

Oil Systems 23

A Wet—sump System 23

A Dry-sump System 25

Engine Controls and Instruments 25

Copyright

This material is for the sole use of enrolled students and may notbe reproduced without the written authority of the Principal, TOPNZ.

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AI RCRAFT ENGll\iEERi%G

hELICGPTERS ssetsemest %

PESTON ENGINE §NST§LLAI§@fiS

The helicopter engine provides power for flight and for thevarious systems needed for the operation of the helicopter;

The piston engines used in helicopters are adaptions of fixed“wing aircraft engines. These adapted engines provide a reliablesource of power that is cheaper than would be an engine developedspecially for helicopter use.

Piston engines are now used only in the small helicopters.This is because for all but the small helicopters, small, reliablegas turbines are readily available. Furthermore, turbine fuel ischeaper and easier to produce than the Avgas needed by the pistonengine. In future, the production of piston-engined helicoptersmay well be phased out. " l

eesition at the Engine

Because of the compact mass of the piston engineg it is usuallylocated immediately beneath the main rotor mast and thus approxi~mately in the middle of the centre—of~gravity range for thehelicoptere Its installed attitude is either pointing straightupward, with the original lower half facing rearwardp {Hiller l2E§or lying horizontally, with the drive shaft facing rearward

€Hughes 269}.

Figure l shows a rear view of a Lycoming vo-see engineinstallation in the Hiller l2E. Cylinder numbering and referencesto engine parts are the same as if the engine were installed in afixed~wing aircraft. For instance? the left~hand side of the engineis still referred to as such, although in this installationfi it ison the right~hand side of the aircraft.

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l1. Engine Strut Assembly 2. Right-Hand Engine Frame Assembly3. Engine 4. Engine Air Induction System5. Earth Strap

FIG. l Vertical engine installation

Figure 2 shows the installation of a Lycoming HIO~360 enginefor a Hughes 269 helicopter. Note that the engine manufacturer'sengine locations are still used. For example, the right—hand sideof the engine is on the left~hand side of the helicopter, and theright-hand magneto is now on the left—hand side of the helicopter.Note, too, that the engine front mounts are now at the rear of theairframe, and the rear mounts are at the front of the airframe.

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1. Fuel System Installation2. Engine Mounting installation Front Mounts3. Cooling Scroll Assembly it4 Engine .

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FIG. 2 Horizontal engine installation

Adaption of a Horizontal Engine to a Vertical Position

Because the engine now has to run in a vertical position, theoil system must be modified so that the splash lubricating oil thatdrains to the bottom of the engine can be picked up by the scavengpump and returned to a separate oil tank. This is done by a sump

\ hou"ing. Used oilthat bolts directly on to the engine accessorj tsfrom the modified cylinder-head rocker box covers in carried in thenew sump through two external oil pipes. The sump may be used asthe oil tank. or the oil may be pumped from the sump to a separate

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The engforward endssubstantialbolted to thanother heavengine mount

The engbe tetheredachieved bysump to thefitted, one

direction,each directi

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ine is attached to the airframe by modifying theof the crankcase right- and left—hand halves so that a

casing designed by the helicopter manufacturer can bee two halves, {This casing, in turnt is attached toily made airframe component, which is bolted to theassembly,)

shaft end and must13;,W3 pi. "<1(Dine is now suspended from its~ <¢ .. FY77at its base to keep it steady and upright. inis is

snubbing rods joining attachment points on the specialhelicopter structurei A minimum of two rods will bein a fore—and~aft direction, and one in a lateralIn some installationsa four rods may be used, two inOils

The induction system is also redesigned so that the carburettorv*'\\,. lliiQ?

The oil

be in a level position when the engine is installed,

pressure system of the engine may be altered to provide0 I 1 n 0 ufor an oil supply to the main transmission. This is simply done by

taking an external oil line from the oil pressure pump housingdirectly to

Finallymodels of a

a connection at the top of the transmission.

, and most important, is the fact that, although allvertical engine may look alikeg there can be very

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the dampinginstalled in

fferences in their internal construction to cope withwrong engine model isrtU1 Dof torsional vibrationsi If o

a helicopter (as can be done quite easily), the resultwill possibly be a mis—match between the engine and transmission,which will rapidly lead to an engine and/or transmission failure.

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at a Vertical engine

3 shows the installation of a vertical engine into itssupport mounts, The engine is_bolted to the inner gimbal (1% whichis located and secured in thet orestrict engine movement in awhen viewedand lets the engine be tilted

xible mounts/'\ I\3 M,’outer gimbal by two bonded

r~\ C1.) \,../ /"\ 43' -../ Uand bolts The two mounts damp andclockwise and anti~clockwise direction

from above“ This allows for changes in engine torquein a fore~and~aft direction,

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1. inner Gimbai’ 2. Outer Gimbal

,\ 3. Fiexible Mount§ 4.6m:r? Q'> ? ‘*

‘\*',§/ fy ' _~ 5. Engine Mount Frame.- °\_\/ 8. Searing

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8. Engme Sump9. Snubber Assembly, Afi

10. Snubber Assembty, Lateral11. Snubber Brackets

\__/ , 12. Flexible Mounts‘ 13. Earth Strap

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FIG._§ Engine installation Q

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The outer gimbal <2} is secured in the engine frame assembly(5)which is bolted to the airframe by two bearings and bolts /'"-. O‘) \./ and(7)

The two bearings (6) allow the engine to rock laterally. Attachedto the sump (8), at the base of the engine, are the aft and lateralengine snubber assemblies <9} and (l0). The other ends of theseassemblies are attached to the engine snubber brackets (ll) an d

flexible mounts (12), which are bolted to the airframe structure.

The engine§ as it is now installed? is flexibly but firmly heldby the mounts (32 and (l2}@ The engine can be adjusted for it S

fore—and—aft and lateral tilting by the snubber assemblies (9) and

€l0>@ This adjustment is made during the rigging of the helicopter.

The engine is coupled to the driven member of the clutch by atorsion coupling bolted to the driving end of the crankshafte Inw H m Q, the torsion coupling lower section (2) is bolted directlyon to the crankshaft mounting flange (1). To the top of the torsioncoupling lower section is bolted the torsion coupling upper section(3), and to this is bolted the main drive clutch (4): which isencircled by the clutch housing (5). Finally, the main transmissionis splined directly to the clutch housing.

The engine drive torsion coupling (2) and (3) is a two-section,interlocking steel and rubber assembly positioned between theengine crankshaft and the main drive clutch. The coupling reducesengine torsional vibration loads imposed by the engine on the maindrive clutch and transmission,

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1. Crankshaft Mount Flange2. Torsion Coupling Lower Section

‘ 3. Torsion Coupling Upper SectionI 4. Main Drive ClutchK 5. Clutch Housingl 6. Bearing

7. Transmission To Clutch Spline

FIG. 4 Torsion coupling

The compact assembly of the torsional coupling, main driveclutch, and inner gimbal are shown in part section in Fig 5

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FIG. 5 Engine to transmission coupling assembly

Because the helicopter can hover and fly sideways and backwardsthe airflow over the fuselage cannot be used for engine cooling Teffect engine cooling, a fan driven by a shaft from the main trans~mission is mounted on the front face of the engine Tn's fan willalways turn when the main rotor is turning Figure 6 shows anexploded view of the engine cooling fan and shroud assemblies

Secured to the engine are the rightehand enc left-hand shroudassemblies £1) and 23 lhese tmo shrouds "box in“ the ngine and,

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Wenufacturer, direct cooling air eroird tne cylinder heads andbarrels. To these two snroocs are secured the loser the left~hand§and the right~hand transition essew lie

nellyg at the front, i _itted the shroud r;n¢ assemoly (6)which closely encircles the cool_ig far ‘ M the left—hano silS fitted the oil cooler duct essembi Q} woicl conveys air to theengine and transmission oil coolers “we cortie front of the engine end smell outlets are provided for ductingcooling air to the generator and warm air to tne ceoin neeter system

tog ther "i % the inter-cyl_nder baffles crevice CL by the engine

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tesss"'1. Right Hand Shroud Assembiy ’2. Len-Hand Shroud Assembly3. Lower Transition Assembly4. Right-Hand Upper ‘transition Assembly5. Left-Hand upper Transition Assembly

, 6. Shroud Ring Assembly‘ 7. Oooiing Fan

8, Access Door9. Oil Cooier Duct Assembly

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FIG. 6 Engine cooling fan and shroud assemblies

Because of the rubberlike flexible mounts (3) and (12) ofP.rig, 8, the engine and transmissioncontact with the airframe, To prevent problems with the generator,the engine starter motor, and the magneto switch circuits that willarise because of this lack of contact, a heavy earthing strap isf't 'i ted between the engine and the engine mount frame (5).

are not in good electrical

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To protect the pilot and passengers in the event of an engineire, a stainless steel firewall is fitted between the engine and

the cabin enclosure.

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engine used in the Hughes 269 helicopteris an adaption of a fixed~wing 10-350 engine, the changes made being

mainly to the cylinders and pistons to enable the engine to developmore power than its fixed~wing counterpart.

centre frame (3) by two bolt, spacer, and rubber bushings assemblies,ln Fig, 7 the rear of the engine is attached to the helicopter

using the top two rear mounting lugs {M} of the engine. At the/’\ }...J \../front of the engine, two special hangers - are bolted, one on each

side of the engine crankcase. These hangers are lower attach~Pi‘W (D

ment points for two rod—and~bushings assemblies, whose top attach-ment points are lugs (2) on the main transmission. Thus, the rearof the engine is supported by the helicopter centre frame, and thefront of the engine is supported by the main transmission.

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1. Engine Front Hanger 2. Main Trasmission Engine Mtg Lug3. Centre Frame 4. Engine Rear Mtg Lug

FIG¢ 7 Engine mounting

Figure 8 shows the coupling of the engine to the transmission.An internally splined engine lower coupling adaptor (1) is bolted tothe engine starter ring gear support. Mating with these internalsplines are the front splines of the lower coupling drive shaft (l2Lwhose rear splines engage with internal splines in the lower pulleyassembly (8). The lower coupling drive shaft is made of a high-quality steel, and its splined ends are slightly convex in sectionto permit small lateral and vertical movements of the engine on itsrubber mounts. Fore-and-aft movement is catered for by the freelyfloating attitude of the shaft in the two sets of splines. Rubberbumper plugs (6) and (ll) are fitted inside the engine lowercoupling adaptor and inside the aft end of the lower pulley assemblyto cushion the floating drive shaft.

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to the airframe, as is the upper and lower pulley and Vee-beltassembly, and the engine is mounted on flexible rubber mounts. Theengine is aligned with the lower coupling by raising or loweringthe engine with the length-adj ustable mounts between the main trans-

mission and the engine front hangers (1) of fig. 7 until the align-ment ring (9) is exactly centred in the hollow lower pulley assembly.This adjustment is made with the main drive Vee belts tensioned.

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1 . Scroll Assembly 2. inlet Surface. Scroll lniet Ring 4. kmpeiler Assembiy3

57. Scroii Forward Lip

FIG. 9 Impeller and scroll

The scroll assembly direcengine shroud assembly and thrto the shroud and the scroll.assembly is shown in an explod- is mounted on the left~hand

Cooling air for the engine and

oil cooler is supplied by animpeller assembly bolted to theengine starter ring gear support.

This assembly comprises an aluminiumalloy impeller wheel with a steelflywheel weight riveted TO theouter edge of the wheel. The steelweight increases the mass of theassembly, which helps to maintainsmooth engine operation. Figure 9shows the placement of the impellerin relation to the scroll assembly.

. Starter Ring Gear Support 6. Fiy Wheei Weight.Assembiy

ts a cooling airflow through theough the oil cooler or coolers fittedIn Fig. l0, the scroll and shroud

ed view. The oil cooler —-not shownside of the scroll assembly. Various

"‘.. -1tubes from the shroud panels calternator and to the accessorThe engine is separated from tdesigned to give protection toengine catch fire.

onvey cooling air to the generator/ies mounted on the rear of the engine.

he cabin by;a firewall that is ‘the pilot and passengers should the

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All earth straps and bonding jumpers fitted between the engineand the airframe must be kept in good repair if easy engine starting,efficient electrical generation, accurate instrumentation, and asafe ignition system are to be had.

Components in Common

In both the vertical and horizontal installations, the exhaustsystem fitted must be the correct one for the helicopter model. Inboth installations, the system is very simple, the object being toget the exhaust gases safely clear of the aircraft without any backpressure imposed on the pistons. The exhaust system is often usedas a source of heat to prevent carburettor icing and to heat thecabin enclosure. In both cases, the heat is taken from the exhaustgases by a simple pilot-controlled exhaust gas-to-air heatexchanger.

The carburettor air intake systems are similar for bothinstallations, comprising a forward-facing air intake connected byducting to the engine. Installed in the ducting is a chamberhousing one or two paper cartridge air filters, a bypass to admitair should the filters become blocked and, if the engine is fittedwith a carburettor, a duct to bring hot air from a heat exchangerfitted to the engine exhaust assembly. All flexible ducting in anengine air induction system will be made from a wire reinforcedpetrol-, oil-, and flame~resistant material. Ducting that does nothave these qualities must ngt be used as a substitute.

<.{I51 1’

g REMEMBER

The engine retains its manufacturer's names and location At references. T

Only the correct engine model for a particular helicopter r~ may be fitted to that helicopter.

A heavy earth strap between the engine and engine mount»frame (earth) is essential for the proper and trouble-free operation of the electrical components fitted to the

L engine and transmission.

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555/3/M

_ 15 _

PRACTICE EXERCISE A

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The fuel systems used in helicopters, as in fixed-wing aircraft,

whether each of the following is true or false.

Engine—mount assemblies may be used to adjust thealignment of the engine to the transmission.

In a helicopter with a centrifugal clutch, thecooling fan will turn only when the engine isrunning.

Any type of flexible ducting may be used in thecarburettor air induction system.

The exhaust system is often used as a heat sourcefor the carburettor and for cabin air.

Because the engine is aft (downwind) of the cabin,no firewall is needed between the two.

The engine earth strap is needed only to take staticelectricity to earth in the airframe.

Some engine cooling air is distributed throughducting to cool magnetos, the generator/alternator,and the oil cooler(s).

The engine-to-transmission torsional coupling takesup acceleration and deceleration loads when thethrottle is opened and closed.

Engine cylinder numbering remains the same whateverits installed attitude.

A fixed—wing aircraft engine with an unmodifiedwet~sump oil system cannot be installed in avertical position.

(Answers on page 23;

FQEL SYS?E I3 6/J

can be divided into two types:

l. Gravity~flow systems, and

2. Non-gravity systems.

555/3/Q

_ 17 _

The fuel tanks in the gravity~flow system are mounted aboye,and in the non-gravity system, below, the level of the carburettoror fuel injector unit. A gravity-flow system may or may not need afuel pump, but a non-gravity system must have one or more pumps.Generally, only the smaller of the helicopters and fixed-wing air-craft utilise gravity—flow systems.

Gravity-flow System

Figure 11 shows a gravity~f1ow system from the tank to theengine, and Fig. 12 shows a rear view of the tank. Because theengine has a fuel injector or fuel metering, an electrically drivenfuel boost pump has to be fitted to the system so that the fuelinjector and the engine cylinders can be primed with fuel to enablethe engine to be started. To ensure that the necessary fuelpressure exists at the fuel injector all the time the engine isrunning, an engine—driven fuel pump is also fitted, with the fuelboost pump being available should the engine—driven pump fail. Thefuel boost pump is controlled by the pilot through an on/off switchin the cockpit. l

Referring to Fig. 11, fuel is housed in the fuel tank (1)mounted on the right-hand side of the helicopter, aft of the cabin.It is attached to the airframe by two strap assemblies (2) and (17)and separated from the engine by a firewall pan (7). Mounted on therear-sloping face of the tank is a filler cap neck (10) of Fig. 12,a fuel quantity sender (8) of fig. 12, and a low-level switch (3),of Fig. 12. At the top of the tank is a tank vent (2) 12,o W w |-I. mto let air out of the tank when the fuel expands and to let airinto the tank as fuel is consumed by the engine. At the bottom ofthe tank is the tank sump (Q). The fuel outlets to the engine andto the fuel drain valve (16) are taken from this sump. The fueldrain valve is readily accessible, and from its outlet, a pipe (12)

—-acarries the drained fuel clear of the helicopter. fitted to theinside of the tank is a baffle assembly (Q) of Fig. 12 thatprevents fuel from "sloshing". The tank is bonded electrically tothe airframe. The filler cap neck is sited below the top of thetank, thus providing an airspace for expansion of the fuel when itbecomes heated.

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FIG. l2 Fuel tank

Fuel from the tank passes through an elbow/strainer assembly(5), whose coarse mesh stops large pieces of foreign matter fromentering the fuel system, and passes through the pilot-controlledfuel shut—off valve (15) to the external fuel boost pump (13) andthen to the fuel strainer assembly (ll).

The fuel strainer houses a fine—mesh filter inside a largefilter bowl, to which is attached a fuel drain valve (not shown).The filter bowl and filter are easily removed for inspection andcleaning, and the fuel drain valve is easily reached to obtain afuel sample after refuelling. from the fuel strainer assembly, thefuel goes through the engine—driven fuel pump (8) (which operateswhenever the engine is running) and then into the fuel injector(10), where it has to pass through another fine—mesh strainer beforebeing metered to the engine, .

The fuel quantity sander unit, which consists of a variableresistor controlled by an attached float arm, is connected to a fuelquantity gauge on the instrument panel. The fuel low—level switchoperates a fuel low warning light on the instrument panel. This

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light comes on when the fuel remaining in the tank falls belowl§ to 2 gallons. Injector fuel pressure is measured at the injectorby an electrical fuel pressure sender and displayed on a gauge onthe instrument panel.

A son-gravity System

Figure l3 shows a nonegravity fuel system, where a bladder~type,rubber nylon reinforced, fuel cell is installed and secuzifi by tabsin a specially prepared cavity in the lower section of the fuselage.lnstalled immediately above the fuel tank are the engine,transmission, and main rotor, so the fuel is carried almost exactlyat the c.g. position of the helicoptert Thus, as fuel is burned?there is very little change in the c.g. position,

1. Fuel Cell Assembly 2. Filler Cap 3. Scupper Drain4. Drain Valve 5. Fuel Strainer 6. Shut-off Valve7. Supply Hose 8. Auxlllary Pump 9. Fuel Strainer

10. Supply Hose To Engine Driven Fuel Pump 11. Fuel Quantity Tank Unit 12. Vent Lines13. Overboard Drain 14. Shutfoflvalvo _(§gnt_r_ol' _ _ A _ H

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fuel is drawn through the coarse mesh strainer (5)5 the fuelshutoff valve (6), and the fine meshed strainer assembly (9) by theauxiliary pump (8) and then sent under pressure to the engine—drivenfuel pump £2) of Fig. ls. Both the fuel shutoff valve and theauxiliary pump are controlled by the pilot from the cockpit,

555/3/H

_ 21 _

When the engine is running, the engine~driven fuel pump is used tosupply fuel to the engine, with the auxiliary pump being used forengine starting and during take—off and landing as a precautionarymeasure. The auxiliary fuel pump has its own relief valve and aninternal bypass so that it will offer no restriction to the fuelflow when it is not in use.

Fuel is added to the tank through a conventional filler capsited in a drained scupper. The tank assembly is vented by forwardand aft vent pipes (12), which join with a drain from the auxiliarypump seals and go overboard through the drain (l3).

A drain valve (4) is fitted to the bottom of the fuel tank sumpimmediately below the strainer (5).

Another fuel drain valve (not shown) is fitted to the auxiliarypump (8) and fuel strainer assembly (9), and an air relief valve (notshown) is fitted to the top of the fuel strainer (9). The fuel drainvalves are used to obtain fuel samples after each re—fuelling andbefore the first flight of each day. The air relief valve is openedto release air that may be trapped in the strainer assembly.

Fuel quantity gauging is done by either two capacitance unitsor two float-operated resistance units sited at position (ll). Thefuel quantity is shown by an indicator mounted on the instrumentpanel. t

Figure ls shows the continuation of the fuel system fromFigg l3. The fuel arrives through the hose (l) at the engine-drivenpump (2), where its pressure is increased. From the pump, the fuelis taken to the carburettor(s) and to the solenoid priming valve(4), which is normally closed, being used only for engine startup.This valve is controlled by a switch on the cabin console and, whenenergised, allows fuel under auxiliary pump pressure to pass throughthe priming line (5) and into the inlet manifold of the engine,where it is readily available for the cylinders.

A drain valve and drain line are fitted to the base of thecarburettor(s) for taking fuel samples. Drain lines (6) are fittedto the base of the air filter assembly and to the engine—drivenfuel pump seal chamber to drain away any fuel and oil that may haveaccumulated.

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Engine fuel pressure is tapped from a carburettor and led viatubing to the fuel pressure gauge on the instrument panel. Thisgauge is a direct~reading instrument.

Figure l5 shows this fuel system in schematic form.

555/3/Q

_ 23 _

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10. Caburetior 11. Drain Valve

FIG. l5 Schematic fuel system

OIL SYSTEMS

Aircraft piston engines have either a wet sump or a drg sump.The wet—sump engine carries its oil supply in its sump, and thedry—sump engine uses a separate oil tank to hold its oil. We shalldiscuss the helicopter airframe part of the lubrication system foran engine of each type.

A Wet-sump System

_Figure l6 shows a wet-sump engine and its external oil system.The system is a simple one and consists of an oil cooler inletline (6), an oil cooler (7), an oil cooler return line (5), acrankcase breather (4), an oil temperature sender unit (2), and,not shown, an electrical oil pressure sender unit clamped to theengine mount and connected to an oil pressure tapping on the enginewith a flexible hose. The oil temperature and pressure aredisplayed on the instrument panel in the cockpit. The oil systemis vented to atmosphere through the crankcase breather tube (Q).

555/3/4

....2l.,L..

Cooling air for the oil cooler is ducted from the scrollsurrounding the engine~driven fan assembly. In later versions of,the installation shown, another oil cooler is added, in series, withthe existing oil cooler. This cooler also takes its air supplyfrom the engine cooling air.

Temperature control and filtration of the oil are done by thethermostatic oil cooler bypass valve (3) and an oil pressure screen

(l). This combined unit is part of the engine assembly, not partof the airframe. .

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FIG. 16 Wet~sump engine external oil system

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A Dry-sump System

The dry-sump system shown in Fig. 17 comprises an oil tank, acooler, and connecting hoses between the engine, the cooler, and theoil tank. The cooling air for the oil cooler is tapped from theengine cooling air supplied by the engine cooling fan. A breatherhose between the oil tank and the engine allows the oil in the tankto expand or contract without bursting the tank. The enginebreathes to atmosphere through a breather line attached to the topof the engine.

Oil under pressure is taken from a tapping on the engine oilpump by small tubing to an indicating gauge on the instrument panel.Engine oil temperature is measured electrically and displayed on thesame gauge. This gauge, sometimes known as a triple gauge, is acombined fuel-pressure, oil-pressure, and oil—temperature gauge.

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REMEMBER

The oil system is vented to the atmosphere.

A thermostatic valve controls the flow of oil throughthe cooler.§

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The three basic engine controls used are

1 .

_. A hand—operated twist grip mounted on the end ofthe collective control lever to open and closethe carburettor/injector throttle valve;

2. A lever-operated mixture/idle cutoff controlsited near the instrument panel and used foradjusting the strength of the fuel/air mixtureengering the engine and for stopping the engine;an

3. A lever~operated hot air control to regulate thetemperature of the air in the air intake. Thiscontrol is fitted only when a carburettor isused to meter the fuel.

Other controls needed for controlling and starting the engine

l. A lever- or knob—operated fuel supply valve On/Offselector;

2. A starter button used to energise, through a relay,the engine starter motor and the starter vibrator;

3. An on/off switch for each magneto, for testing themagnetos only when the helicopter is on the ground

’ é.and for making the engine dead when it is not running.In some aircraft, two separate switches may be used,but a combined magneto/starter switch is usuallyfitted;

A. An on/off switch to operate the fuel priming valve.This switch is not needed if the engine is fittedwith a fuel injector and not a carburettor;

S. An on/off switch to operate the fuel booster pump; and

6. An on/off switch to bring the generator/alternator onto line.

S55/3/Q

._2']..

The engine and engine-related instruments used are

1. An oil pressure gauge, which measures the regulatedoil pressure as it leaves the engine oil pressurePUmP5

2. An engine tachometer, which is usually housed in thesame case as the rotor tachometer, with the needlesof the two instruments lying one above the otherwhen the drive from the engine to the rotor is madeand is not Slipping;

3. An oil temperature gauge that shows the temperatureof the oil as it enters the engine oil pressure pump;

H. A cylinder head temperature gauge, which shows thetemperature of the hottest running cylinder (thehottest running cylinder is determined by the aircraftmanufacturer);

5, A carburettor air temperature gauge that gives thetemperature of the induction air at or close to thecarburettor venturi;

6. An induction manifold gauge, which shows the pressureof the air/fuel mixture in the induction system;

7. A fuel pressure gauge, which shows the pressure of'the fuel at the inlet to the carburettor or fuelinjector;

8. A voltameter to show the voltage and current outputof the generator/alternator, or

9. A warning light that will light up when the generator/alternator output falls below that of the battery;

l0. A fuel quantity gauge to indicate the amount of fuelheld in the fuel tank; and

t ll. A fuel low—level light, which will light up when thefuel quantity remaining in the fuel tank(s) fallsbelow a certain minimum.

5§ REMEMBER =

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Fuel drain valves must be opened, and the fuel must be Fchecked for contamination, after every refuelling andbefore the first flight of the day. é

5 Magnetos must never be tested while the helicopter is5 airborne.

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ERACTECE EXERCISE B

State whether each of the following is true or false.

l. To prevent flooding of the carburettor in agravity—flow system. the fuel tanks are sitedjust below the level of the carburettor.

2. A fuel booster pump must be running wheneverthe engine is running.

3. A fuel injector houses a fine—mesh fuel filter.

4. The fuel outlet from a tank houses a fine~meshfuel filter.

5. A fuel tank must be bonded to the airframe.

6. The main purpose of a baffle is to strengthenthe fuel tank.

7. The fuel tank vent incorporates a one-way checkvalve. '

8. An engine oil system breathes to the atmosphere.

9. The oil temperature gauge shows the temperatureof the oil as it leaves the engine.

l0. A hot air supply is needed only when a carburettoris used to meter the fuel to the engine.

(Answers on page 29)

ANSWEQS T9 PRACTECE EXE%CZSE$

EXERCISE A

Statements l, 4, 7, 9, and l0 are true.

2. False: Because the cooling fan, in this installation,is driven by the transmission, the fan will turn when-ever the rotors are turning.

3. False: The flexible ducting used must be fire-resistant....-..._.,...._....-.-.-_......-._-._---.------

and impervious to oil and fuel.

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5. False: The position of the engine makes no difference.A firewall must be installed between the engine and thecabin.

6. False: The engine earth strap must be capable ofcarrying, with little resistance, the heavy returncurrent from the starter motor.

8. False: The torsional coupling damps the torsionalvibrations of the engine, due to the power impulsesof the cylinders, to an acceptable level for thetransmission.

EXERCISE B

Statements 3, 5, 8, and 10 are true.

l. False: If the tanks were mounted below the levelof the carburettor by even a small amount, thecarburettor would never fill with fuel and wouldnot function properly. In practice, the carburettormanufacturer gives a minimum fuel pressure for thecarburettor. This pressure translates to a minimumheight for the tank above the carburettor.

2. False: The fuel booster pump is needed to start theengine and as a safety precaution during take-offand landing. In normal flight, this pump is notusually required.

H. False: The fuel outlet from a tank houses a coarse-mesh filter. Fine filtration is done by the mainfuel strainer/filter assembly.

6. False: The main purpose of a baffle is to stop thefuel from sloshing around in the tank during changesin flight attitude.

7. False: Air must be free to enter and leave the tankduring changes of atmospheric pressure and fueltemperature, when fuel is taken from the tank duringengine operation, and during fuel draining. Thismeans that the vent must be unobstructed, and sono one-way check valve is fitted.

9. False: The oil temperature gauge shows the temperatureof the oil as it enters the engine.

555/3/Q

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TEST PAPER /-I N a

Give reasons for the small helicopter having its enginelocated immediately under the main rotor mast.

How is fore-and—aft and lateral alignment of the verticalengine and transmission installation achieved?

Make a schematic sketch, including the fuel tank and fuelinjector, of the fuel system shown in Fig. ll and l2.Label all the components.

Why must the magnetos not be tested while the helicopteris airborne? (Hint: the main rotor can never drive theengine.)

What are the three basic engine controls needed for anengine fitted with a carburettor? Which of thesecontrols is not needed for an injected engine, and why?

Suggest how a horizontally opposed engine may be modifiedso that it can be installed and run in a vertical position.

State why a heavy earthing strap is used to electricallybond the engine to the airframe. If the strap becomesdisconnected and the starter motor is energised, whatcould happen to

(a) The shielded ignition switch leads, and

(b) The fuel lines to the carburettor/injector.

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