Block 14: Induction & Exhaust - Ignition & Starting

Define Bernoulli’s principal.

The static pressure of a fluid, liquid or gas, decreases at points where the velocity of the fluid increases, provided no energy is added to nor taken away from the fluid. The velocity of the air is kinetic energy and the static pressure of the air is potential energy.

Throttle valve provides what for the engine?

The throttle valve controls the airflow to the engine.

What causes the piston head temp (CHT) to increase dramatically?

Lean mixture (air > fuel) causes too much air to enter the system which may start a fire within.

Define “Supercharger”.

Also known as a compressor, which forces compressed air into the piston engine to adjust power.

At what temp does carburetor ice form?

Between 30 to 40 degrees F.

The three types of common icing includes?

Fuel evaporation/operation ice, impact ice, and throttle ice.

(F.I.T.)

Alternate air valve purpose?

This valve is opened manually (or automatically) and takes hot air from interior engine cowling, thus sending it to components that clogged by ice.

• This valve shall always remain closed until use.

Difference between Primary and Secondary airflow?

Primary airflow is known as core air that mixes with fuel to generate power for an engine.

Secondary airflow is known as bypass air that cools the exterior of the powerplant’s components.

Would would be the compressor ratio be according to the 8083-32B?

Usually 12:1 of air to fuel mixture.

Ie:

140 cubic in of intake

20 cubic in of compression

140/20 = 7:1

Define “MAP”.

Manifold Air Pressure: The amount of fuel to air mixture within an engine's intake manifold.

Difference between internal and external compression?

Internal compresses fuel and air mixture.

External compressed air exclusively.

What type of compressor are most common in modern compressor systems?

Centrifrugal flow compressor.

Define “APC”.

Absolute Pressure Controller AKA Density Controller.

• A component that controls a turbocharged engine compressor output.

What two factors aids in engine cooling?

50% air and 50% lubricating oil.

What should be known about critical altitude?

The limit of 29.9 Hg and Hg levels increase at 40k feet altitude and above.

• Engine power reduction will occur. (Less oxygen and thinner air = increased fuel consumption)

Define “Bootstrapping”.

Bootstrapping is an indication of unregulated power change that results in the continual drift of manifold pressure.

• Not considered dangerous, prevented by differential pressure controller.

Is over boost considered dangerous?

Over boosting is dangerous to engine life as manifold pressure higher than the maximum limits set by the manufacturer.

• A pressure relief valve prevents over boost.

In a exhaust system, what areas need extra inspection?

clamps, welds, and Brackets shall be checked more carefully than other components.

• Simply because vibrations cause cracking (most common issue).

What is the purpose of a compressor stall system?

Halts compress air from entering engine, thus no thrust.

• Note that internal engine temp. will increase due to lack of intake air.

Purpose of the augmetor?

Acts as a backup for cooling engines.

Why do aircraft magnetos have a primary coil and a secondary coil?

Primary coils produce low voltage (180 of windings) with the secondary coil producing high voltage (thousands 13k of windings). Both are able to output up to 20k volts to power spark plugs.

• Magneto is driven by AC power.

What are the three types of circuits in a magneto. (In order)

Magnetic, Primary, and Secondary circuit.

The distrubutor does what?

Halves crankshaft speed, due to 4 stroke cycle engine.

Why are magnetos timed with the engine?

The spark plugs shall spontaneously spark the air to fuel mixture at the same time for max efficiency.

What is the source of magneto power?

The strength of the magnet.

Define “E-gap”.

“E” means efficiency and its where the breaker points open and create the strongest spark.

• The use of a feeler gauge can determine the optimal efficient spark.

Safety gap purpose?

Ground the secondary windings if there is a broken wire (ground to primary winding normally, primary to secondary and reversed back). Should the generated current not set off the spark plugs.

• Also protects the distrubutor from damage.

Define, “Flashover”.

Flashover is when a spark jumps (arcing in the magneto) to a wrong electrode.

• Occurs during high altitude with less dense air.

Define, “Carbon Tracking”.

Carbon tracking occurs in the distributor and acts as a conductive path to ground.

• Done by the fingers/arms that spread an extremely thin film of carbon particles around the magneto’s distributor blocks. This acts as the conductive ground.

Define, “Induction Vibrator”.

This supplies pulsating direct current to the primary winding of the magneto coil, then current is induced into secondary winding.

What occurs when a Induction Vibrator breaker point is closed or open?

Closed = Current is grounded

Open = DC flows through primary windings, thus high voltage is produced

What is common in dual magneto?

Rotating magnet and the cam.

What is the purpose of impulse coupling?

Momentarily give high rotation.

What is full register position?

When the North and South Pole is fully aligned with the shoe.

_ (2nd coils)

| | - (soft iron pole shoes)

N S

What is neutral position?

North Pole or South Pole is 45 degrees off the shoe.

_ (2nd coils)

| | - (soft iron pole shoes)

S S

Why are magneto vented?

To let out corrosive gases and moisture.

Condenser purposes?

Provides alternative points for the breaker points.

Where is the secondary coil in a low tension magneto?

Near to each spark plug.

When replacing spark plugs, should you use the same washer?

No, some washers are work-hardened and reusing the same washer may not seat the spark plug properly. Even if servicing/inspecting the same spark plug multiple times, always use a new washer.

Difference between hot and cold spark plug?

Hot spark plug: Pre-ignition can occur due to hot spot = Denotation (that’s bad).

• Longer ceramic insulator nose.

• Dissipates heat slower

Cold spark plug: Shorter, thicker insulator nose with more direct contact with the metal plug body.

• Dissipates heat faster

Purpose of varying reaches of a spark plug?

The length of the threaded ends of a spark plug is used for proper seating and proper ignition of the fuel end charge.

If you drop any sort of spark plug once, should you still use it?

No, the ceramic shell (or any sort of shell ie: aluminum oxide ceramic) may be cracked and if used, denotation may occur.

Why might a spark plug not cause to spark, even if there is oil present?

Valve guide or piston rings is worn out. Thus, no oil is able to circulate around the entire spark plug and conduct the electricity fully.

How to prevent seizing of a spark plug?

A specialized grease that is used around the threads. A thin film will suffice.

Purpose of neoprene in a spark plug?

Neoprene can resist abrasion and engine chemicals.

Purpose of a internal resistor?

To resist capacitance.

Most harness size are usually?

5, 7, 9 mm.

Is it true turbine engines use spark plugs?

False, they use igniters.

Aux ignition units are usually connected to?

Connected to the left magneto or the distributor.

Induction vibrator unlike distributors have what difference?;l\

Does not produce high ignition voltage within itself.

Reciprocating engine are how efficient?

25% to 30%. Turbines are far more efficient, but more expensive.

Which is more dangerous to the plane, preignition or denotation?

Preignition is more dangerous as it can shear the crankshaft.

Purpose of sonic venturi?

Determines how much air goes into cabin.

How do you know when to replace a spark plug based on the electrode wear?

When the plug’s center electrode is worn down to half or less of its original thickness.

Why are turbine engine igniters less susceptible to fouling?

The igniter discharges a high-intensity, high-energy spark that self-cleans the firing end every time the plug discharges.

• Simply, this spark is powerful enough to blast away any contaminate inside the chamber.

Low tension magnetos are special for what reason?

Transformer at each secondary coil?

The safety device for high-pressure manifold would be?

Pressure relief valve that is placed before throttle.

If the aircraft speed is increased, what will happen to voltage?

Voltage will increase as well.

Magnetos consist of what parts?

1. Housing

2. Multiple magnets

3. Shaft connected to engine

4. Pole shoes

5. Soft iron core

6. Primary winding/secondary windings

7. Contact points

8. Distrubutor

What is a magneto generate?

A magneto is a AC generator.

When does breaker points open?

Start to open when magneto is moving away from Pole shoe (full register).

When contact point opens, what occurs?

When closed, grounded to magneto body, but when open, its parallel to capacitor (prevents arcing in contact points).

How fast does the camshaft spin?

Half the speed of the crankshaft.

Purpose of the augmentor tubes?

Aids in cooling.

Purpose of density controller?

Only functions when full throttle.

Purpose of differential pressure controller?

Prevents bootstrapping by delaying the action of equilibrium.

VAPC purpose?

Variable Absolute Pressure Controller allows for raising the upper-deck pressure for full turbocharger boost.

Slope controller purpose?

Maintain discharge pressure from compressor.

APC purpose?

Controls the speed of the turbocharger.