Aircraft Tech CPL

Valve timing: Benefit of certain time points:

- 25deg. spark advance = ensures peak Px. - 40deg valve lag = ensures max charge enters cylinder. - 50deg valve lead = increases exhaust release and reduces back Px. - 20deg valve overlap = both inlet and exhaust valves are open at the same time to increase weight of charge entering cylinder and inc. amount of exhaust fumes exiting.

CSU failure

- Coarse lock = no full power, if this happens shut down engine and try to feather. - Fine lock = 'windmilling', engine and propellor in same direction = runaway prop.

What does an alternator consist of?

- Conversion of mechanical energy to AC energy. - Contains a stationary loop (Stator) and a rotating magnet (rotor).

As a general rule, when is it advisable to LEAN the mixture?

- Cruise settings - ABOVE 75% max continuous pwr, mixture should be switched to RICH.

Function of current regulator and reverse current relays in generators:

- Current regulator: Prevent excessive current flow. - Reverse current relay: Prevent current in battery from flowing back into generator at a low voltage.

How to manage a 'runaway propellor'?

- Dec. throttle - Dec. airspeed by inc AoA. - pitch to FULL COARSE.

Ways to cool the engine:

- Fuel/air ratio: climb fixed pitch @ full power - Power: Dec. rpm / MAP = cooling -Vents/baffles/cowls - Prop spinner: small gap either side of cowling = inc. heat release. - Vy: best ROC = inc. airflow = cooling. - Cowl flaps - Liquid cooling - Intercooler: dec. air temp > dec. Dx > inc. engine P.

Two types of hydraulic pumps?

- Hand-operated: Ram air turbine (RAT) - drives backup generator - Power-driven (Electrical, engine-driven, bleed air from turbine)

What is a good indication of the engine losing oil?

- Inc. oil temp - Dec. oil Px.

Which configurations do the throttle and rpm have to be in to produce the greatest volumetric efficiency?

- LOW rpm - Throttle wide open

Consequences of running an engine on an 'over-rich' mixture?

- Lower than normal CHT - rough running - spark plug fouling (SPF) - possible formation of lead deposits on valves and piston heads.

Disadvantages of pneumatic system over hydraulic:

- Not suitable for larger components. - Must have effective seals

Different types of piston engines:

- Rotary - Radial - in-line - inverted in-line - V-arrangement

Advantages of pneumatic system over hydraulic:

- Safety - Availability - Lightweight - Cleaner

What are the cockpit indications following electrical system malfunction?

- The ammeter typically indicated the rate of current flowing through the battery / recharge rate. The ammeter has 2 possible indications of a fault: 1. *Insufficient current from the alternator* charging the battery = Centre-zero indicates constant negative charge, Left zero indicates abnormally LOW charge rate. 2. *Too much current* Both ammeters will indicate abnormally high positive charge rate. An alternator/generator failure will be indicated by illumination of a RED warning light

How to re-align or sychronise the DI/HI?

- Unlike the compass, the DI is easy to read in turbulence. Use the slaving/caging kno by pushing it in and turning it so it reads the same as the compass. - *Realign every 10-15min during flight*

What is pre-ignition?

- When the fuel/air mixture ignites BEFORE engines normal ignition event. Cause: - Hot spot in the combustion chamber, often created by a small carbon deposit on a spark plug, or a cracked/overheated spark plug. Result: - Engine loses power and produces high operating temperature.

A centre-zero ammeter is deflected left (-ve), what does this indicate?

- alternator output is low (or nil) and current is flowing out of the battery.

What is pre-ignition caused by?

- explosive combustion of the partly burned charge caused by glowing HOTSPOTS in a 'dirty' or overheated engine.

Why don't fuel injection systems suffer from refrigerator ice?

- fuel doesn't vaporise until it is injected into inlet port or cylinder head.

What is the principle operation of a vacuum gauge?

- i.e. Air-driven gyroscopic instruments - The vacuum gauge gives a direct indication of suction via a BOURDON TUBE. - instrument will read amount of vacuum in inches of mercury below normal atm px.

Environmental conditions for both IMPACT and GENERAL carb icing:

- impact = near / below zero degrees celsius and aircraft is flying in cloud, rain or sleet. - general = -10 to +25deg and a high humidity. REFIRGERATION / THROTTLE ice is most likely to form around 0 - -10deg.

A single-engine a/c w/ a flat battery is started with the master switch OFF. if the aircraft is fitted with an alternator, how will this affect the electrical power of the a/c?

- when the master switch is ON, the alternator will NOT come 'online' and provide electrical power.

Reverse Thrust

-20 deg. Turning blades beyond fine pitch stop. - Typically used just after touchdown to decrease speed. - ground use only.

Load type differentiation:

1. Bending 2. Tensile - stretching of structure AWAY fro fuselage. 3. Compression - TOWARDS fuselage. 4. Torsional - twisting 5. Shear - sliding of SFC (ie. bolts or rivets).

Types of weight and bal questions:

1. CoG shift - weight add/subtract --> use WxA = M table *Moving weight to bring CoG into legal limit formulas:* 2. Weight shifted [*b/w two known points*] --> x = weight to move. 3. Weight shifted [*distance to move known weight*] --> x = dist. weight is moved. 4. Weight added or subtracted [*weight to be removed from known point to bring CoG into limit*] 5. Weight added/subtracted [*known amount of weight to bring CoG into limit*]

Types of airframe loads:

1. Manoeuvring 2. Gust 3. Control SFC 4. Pressurisation 5. Landing and t/o

Symptoms of carb ice formation:

1. Power loss (indicated by rpm drop, dec. MAP and/or poorer performance). 2. Rough running.

3 functions of a landing gear:

1. Support a/c weight 2. Provide directional control. 3. Absorb shock

Types of airframe structure:

1. Truss - tension/compression only. 2. Monocoque - resists bending in all directions --> circular. 3. Semi-Monocoque - blend of Truss and pure monocoque.

Essential features of a retractable landing gear:

1. Uplocks 2. Safety lock - prevents on-ground raising. 3. Overcentring strut - ensures gears are down on landing. 4. Position indicators 5. Warning horns - sounds when gears are not down. 6. Emergency lowering system - if hydraulics are lost.

3 types of accumulators

1. Weight charged 2. Spring charged 3. Gas charged (Bladder, diaphragm, piston)

Dispersal of energy in an engine:

30% = mechanical energy 40% lost via exhaust gas 30% runs engine.

How does a generator work?

A generator uses motion in a magnetic field to produce current.

EQ: if an aircraft has a dry sump oil system it requires:

A separate oil tank / reservoir

EQ: how would you confirm that the ELT is activated and operating correctly?

A series of short red flashes on the red annunciator light used for ELT transmission

Advantages and disadvantages of Turbo and Supercharging:

ADV: - Compensates for a dec. Dx at high alt. - Sea level engine efficiency can be increased to higher altitudes. DIS: - risk of 'overboosting' - caused by significant temperature increases in fuel-air mixture = Detonation.

Function of oil and air in an oleo-pneumatic strut:

Air: shock absorption Oil: damping, heat absorption, lubrication

How does a pitot-static system work?

All three pressure instruments (Altimeter, VSI and ASI) rely on static pressure to operate. ASI requires a source of total (pitot) pressure. Pitot system is arranged in either: - combined pitot-static head - Pitot tube on the wing + static vent on fuselage. *Must be positioned where airflow is not greatly disturbed - otherwise errors will occur*. - Can also be fitted w/ electrical heating elements incase of pitot icing.

Causes and prevention of detonation?

Causes: - Using lower octane rating - high Px - Lean mixture - high temp Prevention: - reduce power - rich mixture - increase airspeed to increase cooling.

What are the indications of damage or airframe failure?

Composite structures - stiffer and less prone to fatigue and corrosion = more durable. - This means hail or small stones would barely damage the exterior. - MOST COMMON cause of failure = *delamination* or separation of plies via bonding matrix failure. - Delamination can be identified by: - discolouration compared to surroundings - cracked surfaces - areas with exposed fibres via high heat or due to fretted/abraded through rubbing.

EQ: what is the function of a fuel vent?

Designed to keep px above fuel in the tank equal to ambient air px

What are the types of gyro and their associated planes?

EATDRT - Earth (A/H): freedom in 3 planes, kept in one plane by gravity. (*vertical*) - Tied (DI): freedom in 3 planes, kept in one plane by outside force. (*Horizontal*) - Rate (T/C): freedom in 1 plane only (other than plane of rotation) --> movement in 3rd plane used to measure precession.

EQ: What does a centre-zero ammeter indicate in an aircrafts electrical system?

Electrical current discharging from or charging the battery, where -ve = discharging, +ve = charging. A SLIGHTLY positive charge is indicative of *normal operation*.

Mechanical efficiency

Engine efficiency to produce power. - ~ 80-90% for most engines. - PLANK P = pressure (PSI) L = length of stroke (inch) A = Area plan (inch^2) N = Number of strokes K = number of cylinders. - brake hp/indicated hp

EQ: if you attempt to take off with less than recommended takeoff flap setting, acceleration will be:

Faster and ground roll distance will be longer.

Basic operation principles of GNSS:

Global Navigation Satellite System - 24 satellites orbiting earth w/ at least 3 extra as operational spares. - Each sends a signal w/ nav message and unique pseudo-random code (which is used for ranging). - Ranging = measurement of time period b/w transmission and time received. - *The receiver is located on earth*

Conditions for most efficient engine operation:

High performance achieved at: - Low temp - High Px - Lean mixture - Low rpm - High MAP

What is the purpose of valve overlap?

Improve volumetric efficiency of the engine.

Further problems that may arise when you are required to hand swing a propellor due to a flat battery:

Insufficient charge to bring the alternator online.

Lead-acid vs. Nickel-cadmium cells:

Lead-Acid: - Most common - 2.2v per cell - ventilation required - Charge/discharge cycle may release explosive gas. NiCAD: - Plates covered w/ electrolyte solution - 1.2v per cell - thermal blanketing insulation against fire. - Many advantages over Lead-acid (cheap, faster start, more efficient, high power:weight ratio, high recharge rate).

When is spark plug fouling likely to occur?

Long periods of HIGH rpm. - Rich mixture / engine oil leak

On a Brake power/Prop PA vs TAS graph what does the difference between the two reflect?

Losses due to prop inefficiency

What is MAP?

Manifold Px - the pressure of the mixture in the intake manifold.

Rated Horsepower

Max power produced in favourable conditions. - i.e. Low temp, high atm. Px

Do the magnetos require power from the aircraft battery/electrical system?

NO - magnetos operate separately from each other - do not require aircraft electrical power to operate.

EQ: How is nose attitude affected if flap is lowered in a descent, if you are maintaining airspeed?

Nose attitude will be lowered to maintain airspeed

The AVGAS fuel available in NZ is given a grade of 100/130. What do these numbers mean?

Power obtained before detonation = given a rating of 100 at a lean mixture, and 130 at a rich mixture.

Primary vs. Secondary cell batteries:

Primary: - Not rechargeable - Immediate current - Portable device use - Disposable Secondary: - Rechargeable - Charge before use - Components may reverse chemical reactions.

What is volumetric efficiency?

RATIO of weight of the charge in the cylinder, to weight of the charge in the cylinder at ATMOSPHERIC PRESSURE.

Volumetric efficiency

Ratio of actual weight charge into cylinder : total possible weight of charge able to hold.

Thermal efficiency

Ratio of useful work done via Engine:heat energy ratio of fuel used. - Depends on compression ratio. - Best T.E = Lean mixture, low rpm, high MAP.

Principle of operation of TAWS:

Reduces CFIT (controlled flight into terrain). - receives info from a/c GPS to determine a/c position/altitude/configuration and flight path - will then compare this to database of terrain/obstacles etc. - generates both a *visual and aural warning* - 3 classes: 1. CLASS A - cautions and warnings, display, imminent contact w/ ground indications. 2. CLASS B - no display 3. CLASS C

What does a 'wide open throttle' mean?

Refers to an internal combustion engine's maximum intake of air and fuel that occurs when the throttle plates inside the carburettor or throttle body are "wide open", providing the least resistance to the incoming air.

Aquaplaning speeds:

Rotating wheel: 9 x Squareroot PSI of tyre. Non-rotating wheel: 7.7 x SR PSI of tyre. - higher tyre Px = less chance of aquaplaning.

EQ: Magnetometer:

Senses the direction of the earths magnetic field

How to determine pressure altitude using an altimeter?

Setting 1013 hPa on the subscale. - If using this method in the air, *don't forget to re-set the QNH* once pAlt has been obtained.

EQ: what inputs does an ADC (air data computer) receive?

Static px, pitot px and OAT

Stress vs. Strain

Stress = Extraneous force acting on a/c structure. Strain = Amount of shape distortion.

Temporary vs Permanent magnets:

Temporary: - Soft iron - Easily aligned and magnetised - Bad retention Permanent: - Hard iron - Hard to align and magnetise - Good retention (once magnetised, remain magnetised)

How does the Butterfly valve (i.e. WASTEGATE) prevent a turbocharger from overboosting the engine?

The BV opens, allowing more gas to bypass the turbine wheel.

EQ: what does a zero-left ammeter indicate?

The electrical load being supplied from the alternator. +ve = alternator is producing electrical current.

EQ: what happens to a vacuum operated turn indicator if the vacuum is reduced below limits in a turn?

The turn indicator will UNDER-read due to REDUCED gyroscopic rigidity at a LOWER rpm

What happens to a vacuum operated turn indicator if the vacuum is reduced below its limits in a turn?

The turn indicator will UNDERREAD due to REDUCED gyroscopic rigidity at the lower rpm

Because the temps to be measured are quite high, a CHT gauge sensor will normally be a:

Thermocouple

Why does the DI have to periodically be synchronised to the compass?

To account for *REAL DRIFT* error (real wander), cause by friction forces leading to unwanted precession.

Power v TAS curves - what do the lines represent?

Top curve = BRAKE power from ENGINE. Bottom curve = thrust power available from PROP.

Three types of hydraulic oil:

Vegetable: - Blue - Causes corrosion - Used in natural rubber seals Mineral: - Red - General aviation - Petroleum based Skydrol: - Purple - widely used in aviation (high alt. A/c) - Attacks plastic / vinyl

vol --> weight calculation:

Vol = weight / S.G

When will fuel flow from the main jet of the float carburettor?

When air px in carb > main jet outlet.

In normal S+L flight in calm air, do the wings bend?

Yes - UPWARD, because their centres of lift are about the CoG.

What is a bourden tube?

a curved hollow tube, which responds to an increase in internal pressure by DECREASING its curvature.

Before starting the engine, what should the MAP gauge read?

around 30 inHg. atm px. is ~29.92 inHg.

To obtain an unambiguous position on the SFC of earth, a GNSS receiver must determine the range from how many satellites?

at least 3. 4 for RAIM.

Selector valve (hydraulics)

directs flow of fluid

A Watt is a measurement of:

electrical power

Semi-monocoque consists of:

formers and longerons, attached via a light skin and stabilised where necessary with stringers.

What is the primary cause of icing in a float-type carburettor?

heat absorption from the airstream as the discharged fuel changes from a liquid to vapour. - i.e. liq-gas requires heat.

A turbo/supercharger is designed to:

inc. MAP above what a normally aspirated engine can develop, therefore inc. power AVAILABLE. - in other words, functions to maintain a constant power output w/ changes in altitude w/o decreasing engine efficiency.

What is the effect of increasing the cylinder stroke?

inc. compression ratio

Function of pendulous unit in A/H:

keep spin axis of gyro aligned w/ vertical

What is the function of a voltage regulator?

maintain voltage within its limits

Accumulator Function

provide a ready store of hydraulic pressure, which reduces peal demand on the pump - smoothing out variations in pressure.

The first indication of a blocked static vent will occur:

right after t/o, when the airspeed would appear to operate normally, but a ROC and inc. in altitude would fail to be registered.

How is mixture controlled in a fuel injection system?

throttle butterfly and metering unit

Correct action to take following illumination of a generator warning light at high rpm:

turn all non-essential electrics off > land at nearest suitable aerodrome.

What is the compression ratio of an engine w/ unswept volume of 115cubic cm, and a swept vol of 460 cubic cm.

use formula: [SWEPT + UNSWEPT / UNSWEPT] = 5:1

Using an a/c with and without a Cylinder head temperature (CHT) guage:

w/o: - Be aware of cause of overheating (i.e. high power, low airspeed) Avoid: - Running engine w/ fully closed throttle - Climbing @ high power, low A/s - Descending w/ closed throttle for long periods. with: - easier to detect cooling system function. - monitor CHT guage. If inc. temp, open cowl flaps (vice versa).

If an a/s is heading 260 degM and rapidly accelerates, what will the compass do?

will read less than 260 (i.e. 255). - Due to ANDS and SAND - SAND (southern hem.) = *Apparent* turn SOUTH when ACCELERATING, and *Apparent* turn NORTH when DECELERATING.