Systems

Question 1

What is a reciprocating piston engine?

Answer 1

The term “reciprocating” is derived from the “back and forth” movement of the piston. The engine operates on the basic principle of converting chemical energy (fuel) into mechanical energy through combustion.

Question 2

What are the two types of ignition for a piston engine?

Answer 2

1. Spark Ignition: Ignites the fuel/air mixture using spark plugs.
2. Compression Ignition: First compresses the air in the cylinder to a certain temperature necessary for automatic ignition once fuel is injected into the cylinder.

Question 3

What are the different types of cylinder arrangement designs around the crankshaft?

Answer 3

1. Radial
2. In-Line
3. V-Type
4. Opposed

Question 4

Name the two different types of operating cycles.

Answer 4

1. 2-stroke

2. 4-stroke

Question 5

What are the methods of cooling?

Answer 5

1. Liquid

2. Air

Question 6

What are some of the components of a spark ignition, four-stroke piston engine?

Answer 6

Cylinders 
Crankcase 
Accessory Housing 
Intake/Exhaust Valves 
Spark Plugs 
Pistons 
Crankshaft 
Connecting Rods 
Magnetos

Question 7

What does a four-stroke cycle mean?

Answer 7

The conversion of chemical energy to mechanical energy occurs over four separate strokes of the piston. Four strokes of the piston is considered one cycle.

Question 8

Name and explain each separate stroke in a four-stroke cycle.

Answer 8

1. Intake: Occurs as the piston starts to travel downwards in the cylinder. The intake valve opens up and allows fuel/air mixture into the cylinder.
2. Compression: Occurs when the intake valve closes. The piston starts to travel upwards toward the cylinder head, compressing the fuel/air mixture. The reason the fuel/air mixture is compressed is because it will give it a much greater power output once ignited.
3. Power: Occurs when the fuel/air mixture is ignited. Causes a tremendous pressure increase in the cylinder and forces the piston downward. This creates the power that turns the crankshaft. This specific stroke is when chemical energy is converted into mechanical energy.
4. Exhaust: After the power stroke, the cylinder is full of burned gases. This stroke occurs once the exhaust valve opens. The piston starts moving toward the cylinder head, pushing the exhaust fumes out of the exhaust valve.

Question 9

What is a propeller?

Answer 9

A propeller is a rotating airfoil. It provides the necessary thrust to pull the aircraft forward through the air.

Question 10

What factors determine the amount of thrust produced by the propeller?

Answer 10

1. Shape of the airfoil
2. AOA of the propeller blade
3. Revolutions per minute (RPM) of the engine.

Question 11

Is the blade straight or twisted on a propeller?

Answer 11

The blade is twisted so the highest pitch is at the hub while the smallest pitch is at the tip. The reason is to provide uniform lift from the hub to the tip. As the blade rotates, there is a difference in actual speed of the various portions of the blade. The tip is traveling at a higher speed than the hub.

Question 12

What two types of propellers are there?

Answer 12

1. Fixed-Pitch

2. Adjustable-Pitch

Question 13

What is a fixed-pitch propeller?

Answer 13

A propeller with a fixed blade angle. It is set by the manufacturer and cannot be changed.

Question 14

What indicates engine power on a fixed-pitch propeller?

Answer 14

Tachometer is the indicator of engine power. Calibrated in hundreds of rpm and gives a direct indication of the engine and propeller rpm.

Question 15

Which ways can a propeller be connected to the engine?

Answer 15

1. The propeller is usually mounted on a shaft, which may be connected to the engine crankshaft. This is referred to as Direct-Drive. Engine RPM & Propeller RPM are the same.
2. On some engines, the propeller is mounted on a shaft geared to the engine crankshaft. Engine RPM & Propeller RPM are not the same.

Question 16

What is an adjustable-pitch propeller?

Answer 16

A propeller where the blade angle can be changed.

Question 17

What is the most common type of adjustable-pitch propeller?

Answer 17

The most common adjustable-pitch propeller is a constant speed propeller. Pitch automatically varies in flight by a governor maintaining constant RPM despite varying air loads. A constant-speed propeller is more efficient than other propellers because it allows selection of the most efficient engine RPM for the given conditions.

Question 18

What controls does an adjustable-pitch propeller have?

Answer 18

1. Throttle: Controls the power output.

2. Propeller Control: Regulates engine RPM

Question 19

Which instrument indicates power output on a constant-speed propeller?

Answer 19

Power output is controlled by the throttle and indicated by a manifold pressure gauge. It measures absolute pressure of the fuel-air mixture inside the intake manifold and is more correctly a measure of manifold absolute pressure (MAP). As the throttle setting is increased, more fuel and air flows to the engine and MAP increases. When the engine is not running, the manifold pressure gauge indicates ambient air pressure.

Question 20

Which instrument indicates RPM on a constant-speed propeller?

Answer 20

The tachometer.

Question 21

What happens in a constant-speed propeller if you increase the propeller control?

Answer 21

When you increase the propeller control, the RPM increases. This is done by the propeller governor changing the pitch of the propeller blade to a lower pitch. This causes less resistance as the propeller cuts through the air, enabling it to increase in revolutions per minute (RPM). The tachometer will show an increase in RPM.

Question 22

What is the induction system?

Answer 22

The induction system brings the air from the outside, mixes it with fuel, and delivers the fuel-air mixture to the cylinder where combustion occurs.

Question 23

How does the outside air get into the induction system?

Answer 23

Outside air enters through an intake port normally on the front of the engine cowling. It contains an air filter.

Question 24

What happens if the intake port’s filter becomes clogged?

Answer 24

Since the filter may occasionally become clogged, an alternate source of air is available. It is usually located inside the engine cowling. Some sources function automatically while others manually.

Question 25

What are the two main types of induction systems for reciprocating piston engines?

Answer 25

1. Carburetor

2. Fuel Injection

Question 26

What are the two types of carburetors?

Answer 26

1. Float-Type

2. Pressure-Type

Question 27

How does a float-type carburetor work?

Answer 27

Outside air flows through an air filter. This filtered air flows into the carburetor and through a venturi, a narrow throat in the carburetor. When the air flows through the venturi, a low-pressure area is created that forces fuel to flow through a main fuel jet located at the throat. The fuel then flows into the airstream where it is mixed with the flowing air. The fuel-air mixture is then drawn through the intake manifold and into the combustion chambers where it is ignited.

Question 28

Why is it called a ‘float’-type carburetor?

Answer 28

Float-type carburetors acquire their name from a float that rests on fuel within the float chamber. A needle attached to the float opens and closes an opening at the bottom of the carburetor bowl. This meters the amount of fuel entering into the carburetor, depending upon the position of the float, which is controlled by the level of fuel in the float chamber. When the level of fuel forces the float to rise, the needle valve closes the fuel opening and shuts off the fuel flow to the carburetor. The needle valve opens again when the engine requires additional fuel.

Question 29

How is the fuel-air mixture regulated to the cylinders?

Answer 29

The carburetor has a throttle valve that regulates how much fuel-air mixture is sent to the cylinders depending on the power setting chosen by the throttle.