26-04-2011, 10:54 AM
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Aircraft Systems
Engine Types
Turbine Engine
– Found in transport Category aircraft
– Relatively costly but extremely powerful
Reciprocating Engine
– Found in general aviation
– Economical, but still very reliable
Cessna Engine
Horizontally Opposed
Direct Drive
Air Cooled
4 cylinder
Engine Operation
What are the four strokes of an engine?
Four Strokes on an Engine
Intake
When the piston moves away form the cylinder head
Intake valve opens
Fuel/Air mixture is drawn into the combustion chamber
Compression
Piston moves back toward the cylinder head
Intake valve closes
Fuel/Air Mixture is compressed
Power
Compression nearly complete
Spark plugs fire
Compressed mixture is ignited
Rapidly expanding gases drive the piston, providing the power that rotates the crankshaft
Exhaust
Expels the burned gases through the exhaust valve, which opens at the end of the power stroke
Induction System
Brings outside air into the engine, mixes it with fuel in the proper proportion and deliver it to the cylinders where combustion occurs.
Throttle
Mixture
Intake Port
Throttle
Controls Engine Speed
Regulates the amount of fuel/air mixture that flows into the cylinders
Mixture
Controls the fuel/air ratio
Intake Port
Where outside air enters the induction system
Normally contains an air filter to keep out dust and FOD
Carburetor
Mixes the incoming air with fuel and delivers it to the combustion chamber
Carburetor
Air passes through a venturi, increases velocity and decreases pressure
Fuel enters from a float chamber where it is maintained at a nearly constant level by a float device
Discharge nozzle is located in an area of low pressure created by the venturi
Fuel is forced through the discharge nozzel by the higher atmospheric pressure in the float chamber
Overly Rich Mixture
What does it mean to have a “Rich” mixture?
– As altitude increases, the mixture will get progressively richer due to the decrease in air density.
– Can result in engine roughness: excessive carbon buildup on the spark plug will cause them to foul.
– High elevation airports, climb or cruise at high elevation
Overly Lean Mixture
What does it mean to have a “Lean” mixture?
– May result in high engine temperatures causing excessive wear or even failure
– Enrichen Mixture on descents from high altitudes
– Watch engine temperature
Carburetor Ice
Occurs due to the effect of fuel vaporization and decreasing pressure in the venturi which causes a sharp temperature drop in the carburetor
If water vapor in the air condenses when the carburetor temperature is at or below freezing, ice may form on internal surfaces of the carburetor, including the throttle valve
Likely below 21C (70F), humidity above 80%
Carburetor Ice
Carburetor Ice
Carburetor Ice Indications
Why can Carburetor Ice be dangerous?
What are some indications of Carb Ice?
– Drop in engine RPM
– Engine Roughness
– Fuel starvation
What can we do to get rid of carburetor ice or even prevent it from happening in the first place?
– Carburetor Heat
Carburetor Heat
Carburetor ice is especially dangerous when operating at low power settings, may go unnoticed until power is added
– How does carburetor heat work?
– Carburetor heat routes air across a heat source before it enters the carburetor
– How will carb heat affect engine performance?
– Causes a slight decrease in engine power (heated air is less dense)
– If ice is present, there will be a decrease followed by a gradual increase in rpm
Carburetor Heat
Fuel Injection
What is the benefit of a fuel injected fuel system?
– No carburetor
– More precision in metering and distributing fuel/air mixture
– Injects the fuel directly into each cylinder separately
– Lower fuel consumption, increased Horsepower, lower operating temperatures, longer engine life
Fuel Injection
High Altitude Flight
Supercharger
– Compresses the incoming air to the engine using a pump driven by the engine
Turbocharger
– Pressurizes the air into the engine using a mechanism driven by exhaust gases
Turbocharger
Ignition System
What does the ignition system do?
– Provides spark that ignites the fuel/air mixture in the cylinders
List the parts of the ignition system.
– Magnetos
– Spark Plugs
– Interconnecting wires
– Ignition Switch
Magneto
What is a Magneto?
– Self contained, Engine driven
– Supplies electrical current to the spark plugs
– Uses permanent magnet for electrical current that is completely separate from the electrical system
– Begins when you engage starter
– Operates whenever the crankshaft turns
– Normally two for redundancy/ improves combustion
If you lose your battery/alternator in flight, will your engine stop working?