The engine is the part of the airplane that
provides thrust to make the airplane go forward. In the Cessna 150
the engine is a four stroke, 100 horsepower Continental engine.
Four strokes means the pistons go through four different steps in
order to produce thrust.
Intake: In the intake stroke the piston is downward by the cam shaft causing fuel and air to fill the cylinder.
Compression & Ignition: When the piston is at it's lowest point a valve closes and the fuel/air mixture is compressed. once the piston reaches the highest point the mixture is ignited by the spark plug.
Power: after ignition the expanding gases push the piston downward thus turning the crankshaft.
Exhaust: once the piston has reached it's lowest point the exhaust valve is opened at the top of the cylinder and the upward moving piston pushes out all of the exhaust gases. From here the cycle is repeated.
Since the engine has four cylinders each cylinder is at a different step at any given time. this makes the engine turn because there is always a power stage going on.
The aircraft engine is made very redundant for safety reasons, for example there are two spark plugs, and two magnetos. The engine must be reliable because an airplane cannot pull off to the nearest cloud and look under the hood.
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