Reciprocating Engines pt2

Valve Face

Creates inlet and exhaust port; 30 deg - 60 deg ground angle to form a seal against the valve seat

Valve Stem

Maintains valve alignment

Valve Neck

Joining point of stem and face

Camshaft

Pushers the lifter

Lifter

Actuates the rocker arm

Rocker Arm

Depress and open the valve

Hydraulic valve tappets (or hydraulic lifters)

Automatically adjust to maintain the correct valve clearance as the engine operates

Camshaft Rotational Speed

½ of crankshaft rotational speed; E.G. ½ rev of crankshaft = ¼ of camshaft

Radial Engine

Uses a cam ring instead of a camshaft; Cam roller instead of cam follower face

Propeller Pitch

Is the theoretical distance a propeller advances longitudinally in one revolution

Propeller Range Position

Takeoff - Low-pitch, high-rpm setting; Cruise - High-pitch, low-rpm setting

Propeller Geometry

The gradual decrease in blade angle from the hub to the tip is called pitch distribution; This is what gives a propeller blade its twisted appearance; Blade twist allows the propeller to provide a fairly constant angle of attack along most of the length of the blade

Rotational Velocity along a propeller blade segment

Example: Determine the blade velocity at a point 18 inches from the hub that is rotation at 1,800 rpm

Forces Acting on a Propeller

How does it develop “Thrust”

Angle of attack of the propeller blades; The speed of the blades move through the air; The shape of the airfoil

Temperature Effects - Hot

Structural failure of the engine components; Over temperature of the oil, could result in breakdown of its lubricating properties; Pre-ignition and detonation which result loss of power

Temperature Effects - Cold

Low thermal efficiency; Low temperature increase the internal friction of lubricants (high viscosity); The ability of the liquid fuel to change its state to a gas is reduced

Types of cooling

Air Cooling

Thin metal fins project from other surface of the walls and heads of the engine cylinders (cooling fins); Deflector Baffles are also used which are fastened around the cylinders to direct the flow of air to obtain maximum cooling

Liquid Cooling

The engine’s liquid cooling system uses ethylene glycol circulated through the cylinders by a pump, regulated by a thermostat; The heated liquid is cooled by an air-cooled radiator in the propeller’s slipstream, offering greater efficiency than air cooling

Engine Lubrication

Reduce friction and wear by preventing the moving surface coming into contact; The flow of oil through the engine helps to dissipate the heat away from the internal components of the engine

Types of Engine Lubrication

Wet Sump System

The oil is stored in the bottom or sump of the engine

Dry Sump System

Stored the oil in a remotely mounted tank. It is common in high powered, more advanced aircraft engines

Types of Engine Lubrication - Dry Sump

Pressure Pump

Oil is carried either side of the casing in the space between the gear teeth, and is made to flow

Pressure Relief Valve

When the pressure reaches predetermined figure, the valve opens and sufficient oil is returned to the inlet side of the pump to limit the maximum oil pressure

Engine Induction System

Carburetor System

Cheapest and simplest arrangement but is prone to carburetor icing and affected by flight maneuvers

Reduction gearbox

A reduction gearbox between the crankshaft and propeller slows the propeller to optimal speeds, preventing inefficiency and potential damage

Propeller

A propeller is an aerodynamically shaped blades attached to a central hub that converts the power delivered by an engine into propulsive thrust in order to propel an aircraft

Did you know?

The Maximum average CHT of a piston engine is around 400 to 450-deg Fahrenheit (204 - 232 -deg Celcius)