Piston Engines Flashcards
Radial Engines
- Circular
- Cylinders arranged around the crank case
- Odd number of cylinders (Usually 9 max)
- Odd so that no cylinder fires twice in a row
- Good cooling, relatively good power
- Easy to maintain
- Poor forward visibility and excessive drag
In-Line Engines
- Cylinders side by side in a row
- Usually a maximum of 6 due to vibration
- Engine may be inverted for better visibility
- Greatest weight to horsepower ratio
- Less drag and better visibility
Horizontally Opposed Engines
- Most common in small aircraft
- 2 rows of cylinders arranged horizontally
- Even number of cylinders
- Small frontal area
- Less drag
- Automatic system if air intake gets blocked, uses unfiltered air already inside the cowling
Parts of the Reciprocating Engine - Intake Valve
Provides fuel-air mixture to cylinder
Parts of the Reciprocating Engine - Exhaust Valve
Parts of the Reciprocating Engine - Spark Plugs
Parts of the Reciprocating Engine - Cylinder
Parts of the Reciprocating Engine - Piston
Parts of the Reciprocating Engine - Combustion Chamber
Parts of the Reciprocating Engine - Crankshaft
Parts of the Reciprocating Engine - Connecting Rod
Parts of the Reciprocating Engine - Piston Pin
Parts of the Reciprocating Engine - Piston Rings
Parts of the Reciprocating Engine - Cylinder Flange
Parts of the Reciprocating Engine - Camshaft
Opens and closes intake and exhaust valves
Parts of the Reciprocating Engine - Valve Lifter
Parts of the Reciprocating Engine - Push Rod
Parts of the Reciprocating Engine - Rocker Arm
Parts of the Reciprocating Engine - Crankcase
Where crankshaft is located
Four Stroke Cycle
- Intake
- Compression
- Ignition
- Exhaust
Compression Ratio
Volume of the cylinder above the piston at the bottom of the compression stroke compared to the top of the compression stroke
Power Calculation (BHP)
BHP = PLAN / 33000
- P = Mean pressure in PSI
- L = Length of stroke in feet
- A = Area of piston in square inches
- N = Number of impulses per minute
Engine Timing
- Timing of opening or closing of the intake and exhaust valves and the ignition of the fuel/air mixture
- Can lead to better performance is valves open early or close late so there is no waste
- Valve lead, valve lag, valve overlap
Two Stroke Cycle
- One rotation of the crankshaft
- Intake and compression stroke, then ignition and exhaust stroke
Engine Cooling
- Air Cooling (Fins and Cowl Flaps)
- Liquid Cooled (Coolant)
4 Functions of Oil
- Cooling
- Sealing
- Lubrication
- Flushing
Requirements of Oil
- Proper Viscosity (Resistance to flow)
- High flash point (Ignition point)
- Low carbon content (deposits)
- Low Pour Point (Freezing point
Types of Oil - Mineral Oil
- No additives
- Used to break-in engine
- Granular
Types of Oil - Ashless Dispersant
- Contains Dispersants
- Suspends Contaminants such as carbon and lead
Additives - Detergents
Cleans inside of engine
Additives - Oxidation Inhibitors
Improves oil stability
Additives - Anticorrosion Additives
Deter Corrosion
Additives - Pour Point Depressants
Lowers pour point temperature
Methods of Lubrication - Splash Oil
- Oil contained in sump or reservoir
- Revolving crankshaft splashed down into oil
- Droplets spray over various engine parts
- Cheap, simple, effective, lightweight
- No aerobatics
Methods of Lubrication - Force Feed (Dry Sump)
- Oil forced under pressure from a pump through the hollow crankshaft
- Oil exits crankshaft through tiny holes directed at critical parts
- Oil contained in a seperate tank
- Oil drained from pump through a scavenging pump
- Oil goes through a cooler and then back into tank
Methods of Lubrication - Forced Feed (Wet Sump)
- Oil forced under pressure from a pump through the hollow crankshaft
- Oil exits crankshaft through tiny holes directed at critical parts
- Oil contained in a pan (sump) under crankcase
- Pumped to crankshaft, pushrods, bearings, etc.
- Some parts splashed lubricated as well
- Oil then drains back into sump
- Oil cooler may be installed in return line
Venting
- Allows changes in pressure within the tank
- Temperature changes cause density changes
- Can be in the cap of oil tank
Filters
- Have bypass valves in case of clogging
- Dirty oil is better then no oil
Pumps
Also have bypass valves to allow oil to return to tank if excessive pressure
Oil Cooler
Same as a radiator, heat dissipated into the air
Octane
- Ignition Inhibitor
- Used to prevent detonation of fuel and promote smooth controlled burning of the mixture
- Type determined by compression ratio of engine
Heptane
Ignition Promoter
Fuel Grades
- IE 80/87
- 80% Octane at Lean mixture
- 87% Octane at Rich mixture
- Above 100 expressed as performance number
- Always use higher fuel grade
Anti-Icing Additives
Prevents formation of ice crystals which may clog filters
Lead Scavenging Additives
Helps reduce plug fouling due to lead and carbon deposits
Turbocharger
- Fools the engine into thinking it is working at sea level
- Uses the energy of the hot exhaust gases to power a compressor
- Boosts intake air pressure
Supercharger
- Fools the engine into thinking it is working at sea level
- Uses rotational energy of the crankshaft to power a compressor
- Boosts fuel/air mixture pressure
