Aircraft Engines

Question 1

How many types of engines can we find ?

Answer 1

Radial ( 7 to 36 cylinders )
In Line, In V ( 6 to 12 Cylinders )
Opposed ( 4 to 6 cylinders )

Question 2

What is the PLANK formula ?

Answer 2

PLANK/33000 
This means one horse power is the force needed to raise 33000 Lbs for 1 foot in 1 minute.
P (mean Pressure in lb. per  sq.inch) 
L (Length of the stroke in feet) 
A (Area of the piston in sq.inches)
N (Numer of power strokes per minutes)
K (Number of cylinders)

Question 3

What are the 4 strokes ?

Answer 3

• Induction : The intake valve opens, the piston is going down. The air/fuel mixture enters into the cylinder.
• Compression : The two valves are closed, the piston goes up and compress the mixture.
• Power : The spark plug ignite the compressed mixture, the burning gases, expanding under tremendous heat, create the pressure which drives the piston down with terrific force.
• Exhaust : The intake valve is closed, the exhaust valve opens. The piston moves up pushing the burned gases pas out the exhaust valve.

Question 4

Where the energy from the combustion goes roughly ?

What is the Break Horse Power ( BHP ) ?

Answer 4

30 % Useful work
45 % Exhaust
20 % Cooling
5 % Friction

BHP = power available for useful work after friction and losses

Question 5

What are the 4 functions of oil ?

Answer 5

• Cooling : Remove excessive heat produced by the engine.
• Sealing : Prevents pressure loss between the cylinder wall and piston segments.
• Lubrication : It forms a light film between the moving surfaces to reduce wear.
• Cleaning : Removes contaminants entering the engine or produced by the combustion and retains them in the filter.

Question 6

What are the 4 criterias needed for oil in a plane ?

Answer 6

• Visvosity
• High Flash point ( the temperature beyond which a fluid will ignite )
• Low content of carbon and good resistance to oxidation
• Low pour point ( The temperature at which liquid solidifies )

Question 7

What are the 2 methods of lubrication ?

Answer 7

Wet sump : The oil is splashed on all the parts inside the crankcase thanks to the crankshaft rotation. Sometimes a pump and a filter may be added so that the bearings are directly lubricated. The crankcase is used as the oilt tank.

Dry sump :
The oil is directly provided to the bearings thanks to a pump. The residual oil in the crankcase is sucked by the scavenge pump and and redistributed to an outside oil tank.

Question 8

What are the 3 types of fuel ?

Answer 8

• Avgas : Piston aircraft fuel.
• Mogas : car fuel ( approved on some aircraft in accordance with a Supplementary Type Certificate).
• Jet fuel ( jet A1 ) : Kerosene for turbine and diesel engines.

Question 9

What is the Octane ?

Answer 9

A Substance which possesses minimum detonating qualities.It Slows down the combustion.
An high octane index will slow the combustion, making air/fuel mixture igniting at higher temperature and burn slowly.
A low octane index makes the mixture igniting even before the sparks plug ignite causing the cylinder temperature to increase dramatically.

Question 10

What is the Heptane ?

Answer 10

A Substance which possesses maximum detonating qualities. An high heptane index will accelerates the combustion.

Question 11

What are the two types of fuel feeding to the cylinders ? How does the fuel goes from the tank to the fuel injectors or to the carburetor ?

Answer 11

By Carburetor or fuel injectors.

By gravity or thanks to a pressure pump.

Question 12

What is Detonation ?

Answer 12

The fuel burns too fast because the octane index is too low or the mixture is too poor.
It results in high cylinder and exhaust gas temperature.
To solve this issue an appropriate fuel must be chosen and the mixture might be used at full rich.

Question 13

What is Pre-Ignition ?

Answer 13

It is a premature ignition of the mixture before the piston is in correct position. It is caused by the carbon deposit due to a rich mixture. It may results in backfire, piston surface damage and crack.

Question 14

What is Vapour Lock ?

Answer 14

It is caused by the gas bubble formed inside the fuel lines which will block the fuel circulation in the lines. It usually happens when there is a high ambient temperature.
This results in a hard engine start.

Question 15

What are the 5 main Fuel / Air ratios to remember ?

Answer 15

• Richest : 1/8
• Best power : 1/14
• Chemically correct : 1/15
• Low consumption : 1/18
• Poorest : 1/20

Question 16

What happens if there is a too rich mixture ?

Answer 16

Mixture too rich results in lower cylinder head and exhaust gas temperature and possibly in spark plugs fouling.

Question 17

What happens if there is a too lean mixture ?

Answer 17

Mixture too lean results in high cylinder head and exhaust gas temperature.

Question 18

What are the main carburetor icing factors ?

Answer 18

The vaporization of the fuel and the venturi effect.

Question 19

How to prevent carburetor icing ? How do we know in a case of a constant speed propeller ?

Answer 19

We can recognize it with a loss of RPM. The carburetor icing may be prevented thanks to use of the carburetor heating system.
In a case of a constant speed propeller there is loss in the manifold pressure.

Question 20

Why there is a double ignition system ?

Answer 20

• Safety : redundancy , if one magnetos fails there is still the other.
• Performance : Better combustion with two plugs.

Question 21

What are the main components of the electrical system ?

Answer 21

Battery, Starter, Alternator, Ammeter, Voltage regulator,

Bus bar, Breakers.

Question 22

What is the Pitch ?
What is the Geometric Pitch ?
What is the effective pitch ?
What is the propeller efficiency ?

Answer 22

Distance, in feet, travelled by a propeller in one revolution.
Distance covered by a propeller in one revolution, if air was a perfect fluid.
The real distance covered by a propeller in one revolution, since the air is not a perfect fluid.
Geometric pitch – Effective pitch = Propeller efficiency

Question 23

What is the use of the propeller ?

Answer 23

It transforms the rotary motion from the engine into forward thrust.

Question 24

What is the Propeller pitch ?

Answer 24

The angle between the direction of the rotation and the chord of the blades.

Question 25

When do we use a Fine pitch ?

Answer 25

Used for ground circulation , take off, climb and approach.

Question 26

When do we use a Coarse pitch ?

Answer 26

Cruise

Question 27

How works a constant speed propeller ?

Answer 27

The Propeller maintains the selected speed in all flight conditions by automatically changing the blades angle.

Question 28

What are the assets and drawbacks of the Turbocompressor and the Supercharger ?

Answer 28

The Supercharger uses engine power ( up to 16%) and it's noisy. The Turbocompressor use exhaust gas energy so there is no loss of power.

Question 29

What are the oil additives ?

Answer 29

o Detergents ( improve engine cleanliness ) o Oxidation Inhibitors ( Improve oil stability ) o Anticorrosion additives o Pour Point Depressants

Question 30

Where is located the fuel tank , how it is designed ? What about the fuel lines ? What is a fuel heater ?

Answer 30

Fuel tank : It is mostly found in the wings and the wingtips. The chosen material must not react with aviation fuel. It is vented to the outside ambient to maintain atmospheric pressure in the tank. Fuel lines : They are made of aluminum alloy tubing and synthetic rubber or Teflon hose. A series of strainers collect water or debris that may make it into the fuel lines. Fuel heater : The fuel heater can use engine bleed air or engine lubricating oil as a source of heat. The bleed air type is called an air-to-liquid exchanger and the oil type is known as a liquid-to-liquid heat exchanger. The function of a fuel heater is to protect the engine fuel system from ice formation.

Question 31

What are the advantages of fuel injection ?

Answer 31

* More even distribution of fuel to all cylinders due to individual metering. * Better cooling due to elimination of leaner, hotter mixtures to distant cylinders. * Savings on fuel through more uniform distribution. * Increased power over carbureted engines. * Elimination of carburetor icing problem.

Question 32

What can a too rich mixture induce ? A too lean mixture ?

Answer 32

``` Too rich mixture : • Wasted unburned fuel being expelled • Spark plug fouling • Combustion chamber deposits • Rough engine operation • Loss of power or engine failure ``` ``` Too lean mixture : • Rough engine operation • Sudden cutting out/popping back in of engine • Overheating and detonation • Loss of power of engine failure ```

Question 33

What are the benefits of leaning ?

Answer 33

* Economy of fuel for lowering operating costs. * A smoother running engine. * A more efficient engine giving higher cruise performance. * Extended range at cruise speeds (due to lower fuel consumption). * Less spark plug fouling and longer spark plug life. * More desirable engine temperatures. * Cleaner combustion chambers resulting in less likelihood of pre-ignition.

Question 34

What are the 3 types of ice that can be generated in the carburetor ?

Answer 34

Fuel vaporization ice: The heat to make the vaporization of the fuel from liquid in the carburetor is absorbed from the air. The temperature of the air drops and any significant amounts of moisture can condense on the carburetor surfaces and freeze into ice. Throttle ice: The drop of pressure due to the venture effect makes the moisture of the air freeze on the back side of the butterfly valve. Impact ice: The moisture in the atmosphere in the form of snow and sleet can build up on the outside of the carburetor air intake. This blocks the air and cause a subsequent loss of power.

Question 35

What are the advantages and disadvantages of a metal propeller ?

Answer 35

The disadvantages of metal propellers include: * Heavier than wooden propellers * Harder to manufacture * Increased tendency to vibrate * Cost more The advantages of metal propellers include: * Ease of maintenance should the prop be chipped * Resistance to weathering * Low drag * Low service requirements * Ease of storage

Question 36

What is the solidity ?

Answer 36

Solidity is the ratio of the propeller disk at a given radius to the circumference of a solid disk : (Number of blades * Chord at radius ) / Circumference at radius

Question 37

What is the asset of having a variable pitch propeller ?

Answer 37

By varying the pitch of the propeller we are able to operate the propeller at the optimum AofA over a wider range of RPM and TAS setting. ( A propeller blade will be most efficient at an angle of attack around 4 ° )

Question 38

How does the propeller blade Angle of Attack vary according to the TAS and RPM ?

Answer 38

If the RPM increases the AofA will increase. If the TAS reduces the AofA will increase. If the RPM decreases the AofA will decrease. If the TAS increases the AofA will decrease.

Question 39

What is Fuel Grounding ?

Answer 39

Always ground the airplane and the hose nozzle when refueling, owing to the danger of fire from static electricity. The hose nozzle should make metal to metal contact with fillet neck of the fuel tank that is being filled. Plastic containers, funnels or other devices of non conductive material should not be used for the transfer of fuel to an airplane.

Question 40

What is the difference between diesel and gasoline engine ?

Answer 40

Whereas the air/fuel mixture used in gasoline engine require a spark to be ignited, the air/fuel mixture used in diesel engine is ignited by heat resulting from the piston compression of air ( compression ratio from 15-1 to 20-1 with operating procedures between 500°C to 700°C ) The air is directly injected in the cylinder as well as the fuel which is sprayed. The diesel engine have therefore fewer moving parts (no carburetor).

Question 41

What are the main fuel management considerations ?

Answer 41

* Check your fuel supply visually to be sure to have the correct type of fuel * Check the fuel vent is cleared ( fuel tanks must be vented to allow air to enter the as the fuel is used and maintaining the atmospheric pressure ) * Learn how to use the mixture control properly * Drain fuel sumps on all pre flight checks

Question 42

What are the possible propeller failures ?

Answer 42

* Over Speeding –Increased centrifugal forces resulting in excess stress on the propeller hub * Lightning Damage –Can result in burn damage * Vibration –When the propeller is producing thrust, aerodynamic and mechanical forces cause the blade to vibrate. * Nicks and fatigue cracks –Chips in the propeller may lead to a fatigue crack and eventual failure. * Fatigue of the hub –It can be hard to detect fatigue in the hub due to its size.

Question 43

What is the procedure in the event of a backfire ?

Answer 43

Any fire resulting from a backfire can be quenched by continuing to crank the engine since this action will suck the flames and explosive vapours into the cylinder where they will do no harm.

Question 44

What are the engine operations that must be performed in cold weather ?

Answer 44

The oil temp must be in green before going for the flight. Check if the breather is not blocked by frozen moisture. We can use a winter kit which consists in baffle plates installed on the engine cowling. Check the fuel sumps if they are not freezed. If the engine doesn’t start it can be explained by the presence of frozen moisture on the spark plug. A battery that is not fully charged is apt to freeze at below freezing temperatures. In cold weather the electrolyte will break down and change to water. The water may then freeze and possibly bursts its case.

Question 45

What is shock cooling (thermal stress) ?

Answer 45

Shock cooling occurs when the pilot closes the throttle to idle thereafter immediately entering a high speed descent. This generates thermal stress on the engine and reduce the cylinder head durability.