Aircraft Technical and General - Tripod.comflyercolin.tripod.com/_files/01-ATG_ExtraNotes1v5.pdfAircraft Technical and General Supplimental Summary Notes NOTE: This is not a complete

Aircraft Technical and General Supplimental Summary Notes

NOTE: This is not a complete reference. Refer to the Avex ATG handbook and other references too.

C.Gray 2008 PPL ATG Extra Notes v1.5 1 of 18

Table of ContentsChange Control Sheet...............................................................................................................4

1THE OTTO CYCLE.................................................................................................................51.1 FOUR STROKES...........................................................................................................51.2 VOLUME DEFINITIONS................................................................................................5

2 THE OIL SYSTEM.................................................................................................................62.1 DRY SUMP SYSTEM....................................................................................................6

2.1.1 PRESSURE PUMP.....................................................................................................................................62.1.2 SUMP..........................................................................................................................................................62.1.3 SCAVENGE PUMP.....................................................................................................................................62.1.4 BYPASS VALVE.........................................................................................................................................62.1.5 OIL COOLER..............................................................................................................................................7

2.2 WET SUMP SYSTEM....................................................................................................72.3 REASONS FOR OIL......................................................................................................72.4 DETERGENT vs. STRAIGHT OIL.................................................................................7

3 Hydraulic Systems.................................................................................................................83.1 TYPES OF HYDRAULIC FLUID....................................................................................83.2 HYDRAULIC ACCUMULATOR......................................................................................8

4 IGNITION SYSTEM...............................................................................................................94.1 MAGNETOS..................................................................................................................94.2 DISTRIBUTOR...............................................................................................................94.3 IMPULSE STARTER......................................................................................................94.4 SCREENING AND CABLES..........................................................................................94.5 SYSTEM INTEGRITY....................................................................................................9

5 IGNITION AND VALVE TIMING..........................................................................................105.1 INDUCTION STROKE VALVE TIMING......................................................................105.2 COMPRESSION STROKE VALVE and SPARK TIMING ..........................................105.3 POWER STROKE VALVE TIMING.............................................................................105.4 EXHAUST STROKE VALVE TIMING.........................................................................10

6 ENGINE HANDLING............................................................................................................116.1 PRE-IGNITION vs. DETONATION .............................................................................116.2 SPARK PLUG FOULING.............................................................................................126.3 TECHNIQUE TO MINIMISE FOULING DURING TAXYING........................................126.4 FLOODED ENGINE STARTING (refer to POH for your a/c)........................................12

7 VARIABLE PITCH PROPELLORS.......................................................................................137.1 CSU AND VARIABLE PITCH NOTES.........................................................................137.2 ENGINE HANDLING WITH CSU.................................................................................13

8 VACUUM SYSTEM..............................................................................................................148.1 SYSTEM BLOCK DIAGRAM.......................................................................................148.2 SUMMARY...................................................................................................................14

9 FUEL SYSTEM....................................................................................................................159.1 SYSTEM BLOCK DIAGRAM (from Cessna 172).........................................................15


9.2 NOTES ON FUEL SYSTEM........................................................................................159.3 FUEL INJECTION vs. CARBURETTOR......................................................................16

10 GYRO INSTRUMENTS......................................................................................................1710.1 PROPERTIES OF GYROSCOPES............................................................................1710.2 TYPES OF GYROs....................................................................................................1710.3 STANDARD GYRO INTSRUMENTS.........................................................................17

10.3.1 Turn Coordinator.....................................................................................................................................1710.3.2 Attitude Indicator (a.k.a. Artificial Horison): ...........................................................................................1710.3.3 Directional Indicator (D.I.): .....................................................................................................................17

11 Electrical Systems..............................................................................................................1811.1 ALTERNATOR vs. GENERATOR..............................................................................18


Change Control Sheet

DATE CHANGE INITIAL02 Jun 2010 First Change control sheet

Add Cover and TOCOrder of chapters changedAdd Fixed timing comment for aero enginesAdd information about the three gyro instrumentsAdd Alternator vs Generator Chapter

CG


1 THE OTTO CYCLE

1.1 FOUR STROKES

Induction• Inlet valve open• Piston moving down due to inertia• Fuel Air mixture sucked into cylinder via inlet port

Compression• Both valves closed • Piston moving up due to inertia• Fuel Air mixture compressed

Ignition (Power)• Both valves closed• Spark ignites compressed fuel-air mixture• Piston moves down as result

Exhaust• Exhaust valve open • Piston moving up due to inertia• Gases from burnt mixture are expelled via exhaust port

TDC – Top dead center (piston at highest position)BDC – Bottom dead center (piston at lowest position)

1.2 VOLUME DEFINITIONS

Clearance Volume : Volume remaining above the piston when at TDCCylinder Volume : Total volume when the piston is at BDCSwept Volume : Difference between Cylinder and Clearance VolumesCompression Ratio : Ratio of Cylinder volume to Clearance volume


2 THE OIL SYSTEM

2.1 DRY SUMP SYSTEM

2.1.1 PRESSURE PUMP• A gear type pump, driven by the engine• Delivers a greater quantity of oil than the system actually requires• Pressure relief valve regulates the pressure entering the engine• Oil pressure measured before entering the engine• Surplus oil used as a cooling agent and passed back to oil tank

2.1.2 SUMP• Dry sump systems utilise the sump as a form of collector tank. • Oil drains to the sump after passing through the engine

2.1.3 SCAVENGE PUMP• A gear type pump, driven by the engine• Collects oil from sump, via a scavenge filter• Scavenge pump has a greater capacity than the pressure pump• Scavenged oil is very hot so is passed to a cooler

2.1.4 BYPASS VALVE• Directs the oil flow to bypass the oil cooler when oil is cold • Directs oil flow via the oil cooler when operating temperature is

reached


2.1.5 OIL COOLER• Normally air cooled type and is cooled by ram air being allowed to pass

through the cooler fins (in a similar manner to the radiator of a car)• Oil temperature measured after (downstream) of the oil cooler

2.2 WET SUMP SYSTEM• Wet sump system consists of the same major components as the dry

sump. • Major difference: Sump also serves as the oil tank• Oil drains from engine to the sump where it collects• The wet sump system typically has no scavenge pump• Major disadvantage: when aircraft is inverted, the oil can drain into

the cylinders, Could starve vital bearings of oil whilst the aircraft is in this attitude.

2.3 REASONS FOR OIL• Lubrication• Cooling• Transport of contaminants (Cleaning)• Sealing (e.g piston rings against cylinder walls)• Protection against corrosion

2.4 DETERGENT vs. STRAIGHT OIL

Detergent oils have the ability to emulsify water, and disperse and suspend other contaminants. This keeps components free from deposits but means that contaminants must be filtered out, hence the oil filter.

Water accelerates aging of the oil. It also reduces lubricity, filterability and seal life and leads to corrosion and cavitation.

Straight oils are used during the first 50 hours of a new or newly rebuilt engine. It has less lubricating properties than AD oils in order to allow the engine piston rings to wear in and have a good seal with the cylinder walls.


3 Hydraulic Systems

3.1 TYPES OF HYDRAULIC FLUID

Type Colour Properties UseMineral (petroleum based)

Red FlammableToxicWide temp range

General in aircraft

Synthetic (Phosphate ester based)

Purple or Green

FlammableHighly CorrosiveToxic

Jet aircraft

Vegetable (Canola/Castor oil based)

Blue FlammableNon-ToxicBiodegradableOxidises easily

Not really used in aircraft.

Mixing hydraulic fluidsYou are not allowed to mix oil bases. The usefulness and range of use of the oil may be degraded, as well as damage to seals.

3.2 HYDRAULIC ACCUMULATORIn some aircraft a hydraulic accumulator is used to store hydraulic fluid under pressure. This allows a system to momentarily operate a large hydraulic load requirement, even if the pump is insufficient by itself to run all required systems. In the event of pump failure, such an accumulator system will allow the critical hydraulic systems to be operated once typically (e.g. extend flaps and gear).


4 IGNITION SYSTEM

Basic explanationMagnetos convert mechanical energy into electrical energy, by rotating a magnet next to a coil. This conversion is called electromechanical induction.

4.1 MAGNETOS• The magneto is engine-driven• Derives electrical energy from magnets • Primary coil has fewer windings on bobbin,

thus lower tension (LT)• Secondary coil has many more windings,

thus high tension (HT)• Magnet at full register induces flux and LT

flow in primary coil• As the contact breaker opens, primary coil flux field collapses• Collapsing flux field induces flux flow in magneto bobbin• Flux flow in bobbin causes electrical flow in secondary coil (HT)• HT is delivered to the distributor

4.2 DISTRIBUTOR• Distributes the HV discharge to the correct spark plug• Consists of a rotor and a distributor block• Rotor does not actually make contact with distributor electrodes• Each electrode is connected to a HT plug lead• Distributor timed to direct the HT pulse the appropriate spark plug

4.3 IMPULSE STARTER• A spring-loaded clutch device on the magneto spindle• Momentarily increases the rate of rotation of magnet, thus many sparks• As the rpm increases normal single sparking occurs

4.4 SCREENING AND CABLES• HV leads are screened to not cause interference with the radios• Magneto casing has vent holes to allow ionization products to disperse• Vent holes have flame traps to prevent sparks escaping.

4.5 SYSTEM INTEGRITY• Two entirely independent ignition systems on aero engines• Advantage 1: is redundancy (safety)• Advantage 2: Ensures more efficient ignition of the charge• A small drop in rpm occurs when one magneto is switched off (run-ups)


5 IGNITION AND VALVE TIMING

5.1 INDUCTION STROKE VALVE TIMING• Occurs after the exhaust stroke• Inlet valve opens before TDC (valve lead)• Valve stays open past BDC during the compression stroke (valve lag)

Using the IntertiaThe mixture that is sucked into the cylinder has momentum, and continues to flow even after the piston starts moving up for the compression. Thus the charge is increased, thus increasing volumetric efficiency.

5.2 COMPRESSION STROKE VALVE and SPARK TIMING • Inlet valve closes after BDC of induction stroke. Both closed.• Spark occurs before TDC of compression stroke• Pressure build-up reaches a maximum early in the power stroke

Advancing and Retarding the Spark• As the rpm increases the spark is advanced to ensure complete

burning. This is called advancing of the spark• Conversely, as the rpm decreases the spark is retarded• The spark always occurs before TDC (even at lowest rpm)• NB: Typical aircraft engine has FIXED timing

5.3 POWER STROKE VALVE TIMING● Mixture already ignited ● Rapidly expanding gas increase pressure and pushes the piston

downward ● Exhaust valve opens before BDC on this stroke (valve lead)● This allows pressure scavenging of the combustion chamber

5.4 EXHAUST STROKE VALVE TIMING● Inlet valve opens before TDC● Exhaust valve remains open after TDC into the induction stroke● Exiting burnt gases induces the fresh charge to enter before the

induction stroke

Octane Rating of Fuel and Leaded Fuel● Octane rating is a measure of how resistant fuel is to the abnormal

combustion phenomenon known as detonation.● Lead is added to fuel to boost the octane rating, so that a higher

compression ratio can be used.● Lead also helps to protect the valve seats from corrosion on older

engine designs.


6 ENGINE HANDLING

6.1 PRE-IGNITION vs. DETONATION

PRE-IGNITION DETONATIONDEFINITION Progressive burning that commences

before ignitionExplosive, spontaneous combustion

INDICATORS • Rough running• Possibly backfiring• Sudden rise in the cylinder

head temperature

• Rough running • A decrease in power • High cylinder head

temperature

RESULTS • Severe damage to the pistons, valves and spark plugs

• Very possibly complete engine failure

• Severe damage to the pistons, valves and the spark plugs

• Very possibly complete engine failure

CAUSES • e.g. a carbon deposit becoming red hot and igniting the mixture

• Carboned-up engine• Too hot a spark plug type• Use of high power when the

mixture is too lean (hence no extra for cooling).

• May occur in one cylinder only, where a hot spot exists

• Too low an octane of fuel• Detonation will normally

appear in all cylinders.

TREATMENT /HANDLING • Enrich the mixture (to help

cool engine)• Throttle back (Reduce

pressure in the cylinders)

• Increase airspeed (to help in reducing cylinder head temperatures)

• Throttle back (Reduce pressure in the cylinders)

SUMMARY Function of the condition of a particular cylinder or cylinders

Function of the fuel/air mixture and temperature being supplied to all cylinders.


6.2 SPARK PLUG FOULING

● Typically occurs when engine is run at low RPM for long periods, when spark plug tip temperature is insufficient to burn off deposits

● Deposits can be carbon, unburnt fuel, oil or other (e.g. lead/chemical additives)

● Leads to misfiring due to spark to leaking to metal shell instead of sparking across plug gap

● Wet-fouled (oil) spark plugs stop firing and must be cleaned or changed

● Dry-fouled spark plugs can sometimes be cleaned by bringing engine up to operating temperature

Normal Dry fouled Wet fouled

6.3 TECHNIQUE TO MINIMISE FOULING DURING TAXYING1. Start engine normally2. Throttle 1200-1300 RPM3. Lean the mixture until engine runs roughly, and starts losing RPM4. Move mixture forward just enough so engine runs smoothly again5. Throttle ~1200 RPM for idle

Fouling during long, low power descentsWhen doing long glide descents, the plugs can get fouled up too. There is a directive out that says to cycle the engine to full power every 1000ft of descent. A five second cycle to full power in back normally minimises the risk of fouling and the chance of a heart stopping moment during the go-around!

6.4 FLOODED ENGINE STARTING (refer to POH for your a/c)1. Mixture lean 2. Engage the starter3. Open throttle4. When engine fires, move mixture forward, and retard the throttle


7 VARIABLE PITCH PROPELLORS

7.1 CSU AND VARIABLE PITCH NOTES• RPM is controlled by adjusting the tension on the flyweight spring

(speeder spring)• The blade position is controlled by hydraulic pressure• Hydraulic pressure is supplied to the propellor hub by a booster pump• Hydraulic fluid used in the system is engine oil.• With pitch control set, any change in throttle will result in no change in

RPM.• When entering an accelerating descent or decelerating climb the RPM

will remain constant.• With the pitch fully fine, you're dealing with a constant pitch propellor

7.2 ENGINE HANDLING WITH CSU

To Increase power : Engine control order as Mixture, Pitch, PowerTo Decrease power : Engine control order as Power, Pitch Mixture

Power is often referred to as MAP (Manifold Pressure). This is the pressure as measured in the inlet manifold of the engine.


8 VACUUM SYSTEM

8.1 SYSTEM BLOCK DIAGRAM

8.2 SUMMARY• Air is drawn through a filter intake behind the instrument panel• Next through the vacuum instruments and gage in parallel• The vacuum line then enter the engine compartment• Air passed a relief valve upstream of the pump (in case of blockage)• Then through the pump • Exit through a vent pipe in the engine bay

NotesVacuum pump is an engine driven centrifugal air pumpSuction level displayed on gage: 3-5”Hg (inches of mercury)


9 FUEL SYSTEM

9.1 SYSTEM BLOCK DIAGRAM (from Cessna 172)

9.2 NOTES ON FUEL SYSTEM• Fuel pressure is supplied by an gravity an/or an engine driven pump• Additional pressure can be supplied by an electrical booster pump• Mixture control regulates the flow of fuel into the carburettor throat• Vent is located higher than the full fuel level• Fuel tank outlet is located slightly higher than the lowest point• Fuel drains are located at the lowest points in the tanks• Some fuel filler caps also have a vent valve incorporated• Engine primer injects fuel dircetly into one of the cylinders


9.3 FUEL INJECTION vs. CARBURETTOR

FUEL INJECTED CARBURETTOR

● More accurately metered fuel flow, correct amount metered for each cylinder

● Does not suffer from carb icing (no carburettor)

● Vapour locks in fuel lines when engine is hot

● Easy to start when cold

● Less accurate. Fuel mixed before the inlet manifold. Distribution not accurate.

● Suffers from Carburettor and fuel evaporative icing

Fuel injection “spider” (6 cylinder engine)


10 GYRO INSTRUMENTS

10.1 PROPERTIES OF GYROSCOPESRigidity - axis will maintain alignment with fixed point in spacePrecession - Force acting on gyro is executed 90 deg in direction of spin

Rigidity ∝ vROTOR x MassROTOR x dMASS-FROM-AXIS

10.2 TYPES OF GYROsSpace Gyro - Free in all planes of movement No practical applicationEarth Gyro - Axis remains aligned with Center of Earth (Attitude Indicator)Directional Gyro - Axis is tied to a direction, a.k.a. directional gyro (D.I.)Rate Gyro - Axis tied to lateral axis of aircraft (Turn Coordinator)

10.3 STANDARD GYRO INTSRUMENTS

10.3.1 Turn Coordinator

• Type: Rate Gyro

• Tied to Lateral Axis

• Gyro Slow = Lesser Rate of Turn = Over bank

10.3.2 Attitude Indicator (a.k.a. Artificial Horison):

• Type: Earth Gyro

• Axis kept vertical by mass at bottom and controlled by exhaust vanes

• Errors act 90o out due to precession!!!

• Pendulous Error (Heavy) = Acceleration = False Turn Right

• Erection Error (Exh. Vanes) = Acceleration = False Climb

• Markings and AoB = kts/10 +7 (,or AoB = mph/10 + 5)

10.3.3 Directional Indicator (D.I.):

• Type: Directional Gyro (aka Tied Gyro)

• Axis horizontal (can topple)

• Suffers from Wander/Drift: Real and Apparent Wander

• Cage Locks on some to prevent damage when manoeuvring


11 Electrical Systems

11.1 ALTERNATOR vs. GENERATOR

ALTERNATOR GENERATOR

Has an electromagnet, so needs a battery Has a permanent magnet, so no battery needed

Produces Alternating Current (AC) Produces Direct Current (DC)

Comparatively light weight Comparatively heavy

Produces good output at all RPM Must run at higher RPM

Uses a rectifier to produce DC from AC Uses a commutator to produce it's DC output


Documents

Aircraft Technical and General - Tripod.comflyercolin.tripod.com/_files/01-ATG_ExtraNotes1v5.pdfAircraft Technical and General Supplimental Summary Notes NOTE: This is not a complete