1. FLIGHT POWER Know basic engine principles.
1. Define a list of terms related to basic engine principles.
2. Describe the mechanical, cooling, and ignition systems of the reciprocating engines.
Lesson Objective: Know basic engine principles.
Samples of Behavior/Main Points
Define a list of terms related to basic engine principles.
Define Boyle’s Law and Charles’ and Gay-Lussac’s Law.
Describe how engines evolved from the earliest version to present day.

2. Boyle’s Law
The volume of a gas varies exactly opposite that with the pressure of a gas.
A decrease in volume causes an increase in pressure
An increase in volume causes a decrease in pressure
Gas Pressure
14.7 psi
29.4 psi
58.8 psi

3. Charles’ and Gay-Lussac’s Law
The pressure and temperature of a confined gas are directly proportional
Thus, when a gas is compressed, the temperature of a gas is increased
Gas Pressure
14.7 psi
29.4 psi
58.8 psi
100
500
250
250
250
100
500
100
500

4. Internal or External Combustion?
Reciprocating Engines
Internal or External Combustion?
Reciprocating Engines
Reciprocating engines power the conventional vehicles that we use for transportation, work, and pleasure.
These engines provide power for automobiles, lawn mowers, boats, airplanes, and many other devices used in today’s modern life-style.
Most all reciprocating engines used in airplanes are alike. They have the same major systems and use similar construction materials. The differences between these engines are the number and location of cylinders they use.
The power is delivered in a back-and-forth movement of a piston. Pistons are sliding pieces within the cylinder of a reciprocating engine that move by and against the expansion pressure of burning fuel.

5. Mechanical System Cylinder Piston Crankshaft Connecting Rod Valves
Reciprocating engines used in aircraft have certain parts that are vital to their operation. These parts include the cylinder, piston, crankshaft, connecting rod, and valves.

6. Mechanical System Cylinder Known as the engine’s combustion chamber
Where the power is developed
The cylinder is the combustion chamber where the engine’s power is developed.

7. Mechanical System Piston
Fits snugly in the hollow cylinder allowing up-and-down linear (straight) motion
Fit will not allow air or fluid in the cylinder
The cylinder is the combustion chamber where the engine’s power is developed.

8. Mechanical System Crankshaft
The crankshaft and connecting rod allow for the movement of the propeller.
The cylinder is the combustion chamber where the engine’s power is developed.

9. Mechanical System Connecting Rod Attached to the throws
With the crankshaft, they change the direction of the pistons into a circular motion
The cylinder is the combustion chamber where the engine’s power is developed.

10. Mechanical System Valves
A rocker arm regulates the opening and closing of each valve.
Lobes or rings on a camshaft push the rocker arm
The cylinder is the combustion chamber where the engine’s power is developed.

11. Four – Stroke Cycle
Step one (First Stroke) is called the intake stroke.
Second step (Second Stroke) is the compression process.
Third step (Third Stroke) is near the end of the compression stroke, the air and fuel mixture is ignited by an electric spark from the spark plug.
Four-stroke cycle
The four-stroke engine cycle is intake, compression, power, and exhaust.
The piston makes four strokes-movements from top center to bottom center of the cylinder, or from bottom center to top center to accomplish the five steps in each complete cycle.
The five steps in each cycle are intake, compression, ignition, power, and exhaust. The third step, ignition, occurs just before the end of the compression step and is thus considered as a part of the piston’s second stroke.
The fourth step (Fourth Stroke) is called the exhaust stroke.

12. Four – Stroke Cycle – Stroke 1
Called intake stroke
Piston moves down the cylinder creating vacuum
Cam arrangement opens the intake valve
Fuel and air drawn into the cylinder
Intake stroke
The intake stroke begins the cycle with the pistons at top center. As the crankshaft pulls the piston downward, a partial vacuum is created in the cylinder chamber.
The cam arrangement opens the intake valve, and the vacuum causes a mixture of fuel and air to be drawn into the cylinder.

13. Four – Stroke Cycle – Stroke 2
Piston moves up the cylinder
Both valves closed
Air and fuel compressed and pressure rises
Intake stroke
The intake stroke begins the cycle with the pistons at top center. As the crankshaft pulls the piston downward, a partial vacuum is created in the cylinder chamber.
The cam arrangement opens the intake valve, and the vacuum causes a mixture of fuel and air to be drawn into the cylinder.

14. Four – Stroke Cycle – Stroke 3
Air and fuel ignited by electrical spark
Rise in temperature forces piston down
Intake stroke
The intake stroke begins the cycle with the pistons at top center. As the crankshaft pulls the piston downward, a partial vacuum is created in the cylinder chamber.
The cam arrangement opens the intake valve, and the vacuum causes a mixture of fuel and air to be drawn into the cylinder.

15. Four – Stroke Cycle – Stroke 4
Piston moves up forcing burned gas out of cylinder
Burned gas transmitted to exhaust system
Intake stroke
The intake stroke begins the cycle with the pistons at top center. As the crankshaft pulls the piston downward, a partial vacuum is created in the cylinder chamber.
The cam arrangement opens the intake valve, and the vacuum causes a mixture of fuel and air to be drawn into the cylinder.

16. Four – Stroke Cycle – Process
Intake stroke
The intake stroke begins the cycle with the pistons at top center. As the crankshaft pulls the piston downward, a partial vacuum is created in the cylinder chamber.
The cam arrangement opens the intake valve, and the vacuum causes a mixture of fuel and air to be drawn into the cylinder.

17. Four – Stroke Cycle – Process
Occurs at the same time in all cylinders, but not on the same step
Ignition sequence of the cylinders called the firing order
The four-stroke cycle occurs at the same time in the other cylinders of the engine, but no two cylinders are at the same stage of the cycle at the same time.
The cylinders are timed to fire in sequence to turn the crankshaft smoothly, transmitting power from it to the propeller.
The sequence of ignition of the cylinders in the engines is called the firing order.

18. Cooling System Engine produces vast amount of heat
Modern aircraft engines use an air cooling system
The liquid cooling system on an aircraft works the same as does the cooling system on most automobiles.
The coolant flows through the engine block and around cylinders.
The liquid circulates through a system of pipes to a radiator.
Cooling System
All reciprocating engines produce a tremendous amount of heat through the burning gases within the cylinders.
Without having some method of cooling, the continued operation of these engines would not be possible. The metal become so hot they would fuse together.
Modern aircraft reciprocating engines use an air cooling system.
During World War II, some aircraft used a liquid cooling system. The liquid system is actually more efficient than the air type, but its components are heavy and easily damaged.
The air cooling system is simple, lightweight, and it requires very little or no maintenance.
The air cooling system involves moving the internally generated heat to an outside-the-engine surface where the air can carry the heat away.
The most efficient way of doing this is to expose as much as possible of the conducting metal’s surface to the air by using cooling fins.
These fins are a part of the cylinder and expose a broader surface to the cooling effects of the air. If all the cylinders were to protrude into the airstream where they would be exposed to the airflow, cooling would not be a problem. However, as much streamlining as possible is needed to reduce drag, so a cowling (cover) is used to enclose all modern aircraft engines.

19. Ignition System
Must receive an electrical spark originating in the magneto
Ignition System
To supply power, the fuel and air mixture in the chamber must receive a hot electrical spark. This spark begins in an electric generator called a magneto. A magneto is used in aircraft because it is very reliable.
As a safety factor, all aircraft engines have two magnetos. Both magnetos produce electricity while the engine’s crankshaft is turning. This is because the magnetos are linked mechanically to the engine’s crankshaft.
Since the propeller is linked to the crankshaft, it is possible to start the engine of a small airplane with a person spinning the propeller by hand: this is called hand propping.
In the early days of aviation, hand propping was the way aircraft engines were started.
Some of the older aircraft still flying continue to be started by the hand propping method.

20. Types of Reciprocating Engines
In-line Engines
Cylinders are located in a row, one
behind the other
Two classifications:
Upright
Inverted
Types of Reciprocating Engines
A constant concern of engine manufacturers is how to get more horsepower from an engine. One solution is to increase the number of cylinders and another solution is to increase the size of each cylinder.
The limitations for increasing the size of cylinders are so restrictive that manufacturers have concentrated on the other design method, development of multi-cylinder engines.
This method adds smoothness to the power supply because of the added number of power strokes per revolution of the crankshaft.
To accommodate additional cylinders, the crankshaft must be lengthened and its number of throws (bends in the crankshaft) must be increased.
Manufacturers have come up with several different designs to accommodate the addition of cylinders. The most common designs are in-line, opposed, V and X, and radial.

21. Types of Reciprocating Engines
Opposed Engines
Two rows or banks of cylinders on each side of the crankshaft
Rows directly opposite each other called horizontal opposed
Opposed Engine
Opposed engines have two rows or banks of cylinders, one row on each side of the crankshaft.
The rows of cylinders are directly opposite each other, and the engine type is called horizontal opposed.

22. Types of Reciprocating Engines
V Engine
“V” engine features two rows of cylinders set
at an angle of about 45°
V and X Engine
The “V” engine features two rows of cylinders set at an angle of about 45°.
The “X” engine, which is not as common, is essentially an opposed “V” engine.

23. Types of Reciprocating Engines
Radial Engine
Crankshaft with only one throw
Odd number of cylinders in each bank or row
Maximum number of cylinders in each bank is nine
Radial Engine
Features a crankshaft with only one throw.
The cylinders are arranged around the crankshaft in a circle so that all the cylinders and connecting rods contribute their power through a single throw. The cylinder whose connecting rod from the piston in this cylinder is designated as the master cylinder. The connecting rod from the piston in this cylinder is called the master rod, and attaches to the throw of the crankshaft.
Other connecting rods, called articulating rods, connect the other pistons to the large end of the master rod. The master rod, however, is the only rod that is connected directly to the crankshaft itself.
The radial engine always has an odd number of cylinders in each bank or row.
The firing order of the four-stroke cycle requires this feature to assure an even delivery of power to the crankshaft. To keep the crankshaft turning smoothly, the radial engine’s cylinders are designed to fire not in numerical order, but according to the best firing order for each engine. By staggering the firing, the engine makes the best use of the power from each cylinder. The maximum number of cylinders in each bank is usually nine. Where more power is needed from an engine, additional banks of cylinders may be added behind the first bank. If more banks are added, the crankshaft must be lengthened to accommodate the master cylinders in each additional bank.
These extra banks operate in the same manner as does the original. In effect, a radial engine with two banks of cylinders is two engines working together, one behind the other.

24. Fuels Used in Reciprocating Engines
Most common form of fuels is hydrocarbons
derived from petroleum
Gasoline and kerosene offer several advantages:
They are volatile
Evaporate quickly
High heat content which means high potential energy to be converted to kinetic energy as the fuel burns
Do not deteriorate when stored over long periods of time
Fuels used in reciprocating engines
The most common form of fuels is hydrocarbons derived from petroleum. Petroleum is a natural oil pumped out of the earth. The principle hydrocarbon fuels used in aircraft today are gasoline and refined kerosene. Diesel fuel, fuel oil, and lubricating oils are also distilled from petroleum.
The gasoline and kerosene used as aviation fuels offer several advantages. They are volatile. They evaporate quickly. They can be mixed easily with air to form a combustible mixture. Gasoline and kerosene have a relatively low flash point.
Petroleum-based fuels have low freezing points. This is important when an aircraft is operating in the low temperature of high-altitude flight.
Gasoline and kerosene have a high heat content. This means there is much potential energy within these fuels that may be converted to kinetic energy as the fuel burns.
Both fuels are relatively stable and can be easily handled using fairly simple safety precautions.
They do not deteriorate when stored over long periods of time and are available at reasonable costs.
The petroleum from which gasoline and kerosene are derived is found primarily in the United States, Venezuela, the former USSR, Kuwait, Saudi Arabia, Iran, Iraq, and the United Kingdom.

25. FLIGHT POWER Know basic engine principles.
1. Define a list of terms related to basic engine principles.
2. Describe the mechanical, cooling, and ignition systems of the reciprocating engines.
Lesson Objective: Know basic engine principles.
Samples of Behavior/Main Points
Define a list of terms related to basic engine principles.
Define Boyle’s Law and Charles’ and Gay-Lussac’s Law.
Describe how engines evolved from the earliest version to present day.