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4 0 7 . 0 1 Basic Construction and Four Stroke Cycle

Types of Reciprocating Engines • There are three main types of piston engines in current use: • Horizontally Opposed • Radial • In-Line

Horizontally Opposed • Two banks of cylinders which lie directly opposite to each other in the horizontal plane. • Four, six or eight cylinders. • Design is flat with small frontal area (good visibility) and low drag production. • Most commonly used in general aviation.

Radial • Cylinders arranged radially. • Always an odd number of cylinders. • Crankshaft is short, compact and light. • Produces tremendous horsepower. • Poor shape increases parasite drag and reduces forward visibility.

In-Line • Cylinders are arranged side by side in a row. • Practical limit is six. • Any more cylinders and V, X or H-type in-line engines are used. • Two crankshafts side by side. • Some are inverted for better visibility. • Little drag but heavier engine and size limited.

Confirmation Stage NOTE: You must use the buttons in the Confirmation Stage

Aero Engines Basic construction and the four stroke cycle Let's try a few review questions on Aero Engines: Question #1 - What type of engine is the most commonly used in general aviation? A Radial B In Line C Horizontally Opposed D V6

Flying Scholarship Program I’m afraid that answer is incorrect Let's try again...

Flying Scholarship Program That answer iscorrect. Let's move on...

Aero Engines Basic construction and the four stroke cycle Let's try a few review questions on Aero Engines: Question #2 - What is an disadvantage of using a radial engine? Heavy crankshaft A B Poor visibility C Short crankshaft D Size is limited

Construction of a Reciprocating Engine • Piston - Cylinder shaped object that moves up and down. • Piston Rings - wrap around the piston and provide a seal between the piston and cylinder. • Connecting Rod - joins the piston to the crankshaft, which turns the propeller. • Cylinder Head - contains the inlet (intake) valve, exhaust valve and two spark plugs.

Construction of a Reciprocating Engine • Camshaft - turned by the crankshaft and operates the push rods and rocker arms. It turns at half the speed the crankshaft turns. • Magnetos - provide electrical current to ignite the Fuel/Air mixture through the distributor. • Intake Valve Ports - allow air to enter the cylinder and is connected to the carburetor where the air and fuel are mixed. • Exhaust Valve - connected to the exhaust pipe, which vents the exhaust fumes away from the cabin.

Spark Plugs Intake Valve Exhaust Valve Piston Connecting Rod Cylinder Crankshaft Major Engine Components

The Four Stroke Cycle • Most piston engines operate on the four stroke cycle. • The piston moves through four strokes, two up and two down, to complete the cycle. • The crankshaft makes two complete revolutions. • The four strokes are: • the induction (or intake) stroke, • the compression stroke, • the power (or combustion) stroke, and • the exhaust stroke.

The Induction (or Intake) Stroke • Intake valve is open. • Piston moves down. • Fuel/air mixture drawn into combustion chamber through intake valve. • Exhaust valve remains closed.

The Compression Stroke • Both valves are closed. • Piston moves up. • Mixture is compressed. • Compression ratio is comparison of volume of mixture with piston at the bottom and volume with piston at the top.

The Power (or Combustion) Stroke • Both valves are closed. • Compressed mixture is ignited by spark plug. • Burning gas expands forcing piston down. • Energy drives other three strokes as well as useful work (i.e.. turn propeller).

The Exhaust Stroke • Exhaust valve is open. • Piston moves up. • Burnt gas is pushed out through exhaust valve. • Intake valve remains closed.

Timing • The purpose of timing is to improve the performance of the engine. • Valves take time to open and close. • Therefore they are timed to open early and close late in order not to waste any of the induction or exhaust stroke.

Valve Lead • Timing the valve to open early. • Timing the valve to close late. • Allowing both valves to remain open at the same time. Valve Lag Valve Overlap

Valve Clearances • Valve clearance, or tappet clearance, is a space that must be provided between the valve stem and rocker to allow for heat expansion of the metal. • Clearances too wide cause a loss of power and excessive wear. • Clearances too close can warp the valves.

Confirmation Stage NOTE: You must use the buttons in the Confirmation Stage

Aero Engines Basic construction and the four stroke cycle Let's try a few review questions on Aero Engines: Question #3 - Name the second stroke in the four stroke engine? Intake A B Power C Compression D Exhaust

Aero Engines Basic construction and the four stroke cycle Let's try a few review questions on Aero Engines: Question #4 - During which stroke do the spark plugs fire? Intake A B Power C Compression D Exhaust

Aero Engines Basic construction and the four stroke cycle Let's try a few review questions on Aero Engines: Question #5 - What is the definition of valve lag? Valve closes early A Valve closes late B Both valves remain open C Both valves remain closed D

Aero Engines Basic construction and the four stroke cycle Congratulations!! You have now completed the Basic Construction and the Four Stroke Cycle lesson of the Aero Engines Module. Of course, this lesson is always available to you for future reference if required. You are now ready to move along to the next Aero Engines lesson you have not completed or to any other module you wish. You can advance to the Self Test Module if you feel ready to challenge the final exam. Good Luck!

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