What is a reciprocating piston engine?
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.
What are the two types of ignition for a piston engine?
- Spark Ignition: Ignites the fuel/air mixture using spark plugs.
- Compression Ignition: First compresses the air in the cylinder to a certain temperature necessary for automatic ignition once fuel is injected into the cylinder.
What are the different types of cylinder arrangement designs around the crankshaft?
- Radial
- In-Line
- V-Type
- Opposed
Name the two different types of operating cycles.
- 2-stroke
2. 4-stroke
What are the methods of cooling?
- Liquid
2. Air
What are some of the components of a spark ignition, four-stroke piston engine?
Cylinders Crankcase Accessory Housing Intake/Exhaust Valves Spark Plugs Pistons Crankshaft Connecting Rods Magnetos
What does a four-stroke cycle mean?
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.
Name and explain each separate stroke in a four-stroke cycle.
- 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.
- 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.
- 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.
- 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.
What is a propeller?
A propeller is a rotating airfoil. It provides the necessary thrust to pull the aircraft forward through the air.
What factors determine the amount of thrust produced by the propeller?
- Shape of the airfoil
- AOA of the propeller blade
- Revolutions per minute (RPM) of the engine.
Is the blade straight or twisted on a propeller?
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.
What two types of propellers are there?
- Fixed-Pitch
2. Adjustable-Pitch
What is a fixed-pitch propeller?
A propeller with a fixed blade angle. It is set by the manufacturer and cannot be changed.
What indicates engine power on a fixed-pitch propeller?
Tachometer is the indicator of engine power. Calibrated in hundreds of rpm and gives a direct indication of the engine and propeller rpm.
Which ways can a propeller be connected to the engine?
- 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.
- On some engines, the propeller is mounted on a shaft geared to the engine crankshaft. Engine RPM & Propeller RPM are not the same.
What is an adjustable-pitch propeller?
A propeller where the blade angle can be changed.
What is the most common type of adjustable-pitch propeller?
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.
What controls does an adjustable-pitch propeller have?
- Throttle: Controls the power output.
2. Propeller Control: Regulates engine RPM
Which instrument indicates power output on a constant-speed propeller?
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.
Which instrument indicates RPM on a constant-speed propeller?
The tachometer.
What happens in a constant-speed propeller if you increase the propeller control?
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.
What is the induction system?
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.
How does the outside air get into the induction system?
Outside air enters through an intake port normally on the front of the engine cowling. It contains an air filter.
What happens if the intake port’s filter becomes clogged?
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.
