789 Lt R Hampton Gray VC Squadron Ground School (2014)

789 Lt R Hampton Gray VC Squadron Ground School (2014)
Module Three: Aero Engines

789 Lt. R Hampton Gray VC Squadron Ground School 2014
In This Module: 3.1 Definitions and Configurations 3.2 The Fuel System 3.3 The Carburetor and Fuel Injection 3.4 The Exhaust System 3.5 The Ignition System 3.7 The Electrical System 3.8 The Propeller 3.9 Engine Instruments 3.11 Jet Propulsion 789 Lt. R Hampton Gray VC Squadron Ground School 2014

3.1: Definitions and Configurations

Definitions of Power The product of an engine (powerplant) is power. Power = rate of doing work. Work = heat transformed into energy. The amount of power that can be produced is based on the amount of heat that can be generated by burning gasses. The standard unit for measuring an engine’s power produced is one horsepower. The power produced within the engine is called indicated horsepower. The power available for useful work after friction and losses is called break horsepower (bhp). 789 Lt. R Hampton Gray VC Squadron Ground School 2014

PLANK P x L x A x N x K 33,000 Total Amount of Indicated HP an Engine Can Produce = P = The pressure in lb. Per sq. Inch, generated by expanding gasses. L = The length of the piston stroke, in feet. A = The area of the head of the piston in sq. Inches. N = The number of impulses, or times the engine fires in one minute. K = The number of cylinders in the engine. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Concept Check What is the definition of power? What is the difference between horse power and break horse power? PLANK / 33,000 = What? 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Types of Combustion Engines
Horizontally Opposed Radial Inline 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Horizontally Opposed Two banks of cylinders lying directly opposite each other. Both banks of cylinders operate on the same crankshaft. May have 4, 6, or 8 cylinders. Flat design and small frontal area mean reduced parasite drag. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Radial Cylinders arranged radially around a barrel shaped crankcase. Always has an odd number of cylinders (5, 7, 9, etc) due to alternate firing order (i.e ) Radial engines have a good weight to HP ratio and are easy to maintain. Large frontal area means very high parasite drag and poor forward visibility. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Inline Cylinders oriented side by side in a line along the crankcase. Each cylinder works on its own crank-throw. The practical limit is six in a row. If more are required, they will be arranged in multiple banks, i.e. in a V-shape. Single inline engines offer small frontal area an low parasite drag. Single inline engines are generally found in older aircraft, with modern aircraft favouring horizontally opposed of V-x type inline engines. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Concept Check Describe a horizontally opposed engine. Describe a radial engine. Describe an inline engine. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Parts of a Reciprocating Engine
789 Lt. R Hampton Gray VC Squadron Ground School 2014

The Four Stroke Cycle Induction/Intake Stroke Compression Stroke Power Stroke Exhaust Stroke 789 Lt. R Hampton Gray VC Squadron Ground School 2014

The Four Stroke Cycle Induction Stroke: The intake valve opens, the cylinder moves down creating negative pressure, and fuel/air mixture rushes through the carburetor into the cylinder. Compression Stroke: The intake valve closes, and the cylinder moves up, compressing the fuel/air mixture in the cylinder. Power Stroke: The spark plug fires, combusting the fuel/air mixture in the cylinder. The rapidly expanding heated gases and forcing the cylinder down with enough force to provide useful work and run the other three strokes. Exhaust Stroke: The exhaust valve opens, the cylinder comes back up and ejects the burned up gasses from the cylinder. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

The Two Stroke Cycle The two stroke engine (found on some small ultra light aircraft) uses only two strokes and one camshaft rotation. It does this by combining the intake and exhaust actions into one stroke of the piston. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Concept Check What are the four stages of the four-stroke engine cycle? What is the difference between a four-stroke cycle and a two-stroke cycle? What kind of aircraft might a two-stroke engine be found in? 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Turbocharging At higher altitudes air is thinner, resulting in decreasing engine performance due to lowered air density as a plane climbs. A turbocharger supplies the engine with denser, compressed air to compensate for the thinner outside air, allowing the aircraft to perform more efficiently even at high altitudes. The turbocharger will provide the engine with near sea level performance up to a certain altitude, the critical altitude, at which point the turbocharger is at maximum capacity and any further climb will result in lowered engine performance 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Turbocharging Escaping exhaust turns an impeller which drives a compressor. The compressor takes in air at atmospheric pressure and compresses it to a higher density. The higher density air is then sent to the intake manifold. The speed of the impeller/compressor can be either fixed or adjustable. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Supercharging While turbochargers are powered by exhaust gasses exiting the engine, and thus do not require engine power, superchargers are powered directly by the engine’s power output. Superchargers compress the fuel/air mixture after it leaves the carburetor, whereas turbochargers compress the air before it is mixed with fuel. When engine power is increased at low altitudes using a supercharger, it’s called boost. At high altitudes it’s called supercharging. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Engine Cooling Engines generate a tremendous amount of heat which must be dissipated to prevent overheating. Some engines use liquid cooling, but air cooling is the most common method by far. Fins are added to engine cylinders to increase surface area to allow the air passing to carry away more heat. Air is allowed in through openings in the cowling and directed over engine parts using shrouds and baffles. Higher performance aircraft may have cowl flaps which can be opened at low speed/high power settings to increase cooling airflow. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Concept Check Describe how turbo-charging works. What is the benefit of turbo-charging? What is the main difference between turbo-charging and super-charging? Describe how air cooling works. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Oil and Lubrication Engine lubricating oil has four major purposes: Cooling: Carries away some of the excessive heat generated by the engine. Sealing: Provides a seal between the piston rings and cylinder walls, preventing “blow-by” loss. Lubrication: Maintains an oil film between moving parts, preventing wear through metal on metal friction. Flushing: Cleans and flushes the interior of the engine of contaminants. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Dry Sump Lubrication 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Wet Sump Lubrication Lighter weight and less complex than dry sump system. Can not be used for aerobatic planes that fly inverted without special modification. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Concept Check What are the four main purposes of engine oil? Describe dry-sump lubrication. Describe wet-sump lubrication. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

What Makes Good Oil? Viscosity: Viscous (resistant to flow) provides proper distribution and ensures the oil film lubricating parts isn’t broken. Oil with a high viscosity index is resistant to changes in viscosity due to temperature changes. High Flash Point: Flash point is the temperature beyond which fluid (the oil) will ignite. This must be well above the highest engine temperature. Low Carbon Content: Low carbon content ensures that should the oil burn it will not leave carbon behind. Low Pour Point: Pour point is the temperature at which a fluid will solidify. This must be low to facilitate cold weather starting. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Oils with different additives can not be mixed!
Oil Additives Detergents: Improve engine cleanliness. Oxidation Inhibitors: Improve oil stability. Anticorrosion Additives: Deter corrosion. Pour Point Depressants: Lower oil pour point. Oils with different additives can not be mixed! 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Grades of Oil Saybolt Viscosity S.A.E. Number U.S. Grade Summer 120 60 1120 Fall or Spring 100 50 1100 Winter 80 40 1080 Arctic 65 30 1065 The grade of oil recommended for use changes with season. Grades are designated by S.A.E. Number of Saybolt Viscosity. In the U.S. it is common practice to add 1000 to the Saybolt Viscosity. To eliminate the need to change oils seasonally, companies have developed synthetic “multi-viscosity” oils, that remain thin in extremely cold weather but have the same viscosity as traditional summer grade oils in high temperatures. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Oil Temperature Oil temperature is very important because temperature affects viscosity. At too high a temperature, oil is too thin, may burn, and will not coat and seal properly. At too low a temperature, the oil is too thick and will not flow properly. Oil temperature is monitored in the cockpit using an oil temperature gauge on the instrument panel. Manufacturers specify operating limits for oil temperature which must be strictly adhered to. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Concept Check What are the four main qualities of a good oil? Name four types of oil additives. What happens when oil is at too high a temperature? Too cold? 789 Lt. R Hampton Gray VC Squadron Ground School 2014

3.2: The Fuel System

Fuel Systems The purpose of the fuel system is to deliver fuel, at the correct pressure, to meet the engine’s needs. Most aircraft have multiple fuel tanks, most commonly in the wings. Each tank has a line leading to a selector valve in the cockpit that allows the pilot to choose which tank is used. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Fuel Pump Fuel System Fuel pump systems use an engine driven pump to supply the engine with fuel. Fuel pump systems are used in all low wing airplanes and high performance planes. A fuel pressure gauge in the cockpit tells the pilot the pressure of fuel entering the carburetor. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Gravity Feed Fuel System
Gravity feed is the simplest type of fuel system and is used on many high wing and low power aircraft. Fuel from the tanks is fed using gravity. A strainer and drain allow water and sediment to be removed before the carburetor. The primer pumps raw fuel into the intake manifold or cylinders to aid with starting. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Concept Check What is the purpose of the fuel system? Where are the fuel tanks in most aircraft? Describe a gravity feed fuel system. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Parts of the Fuel System
Fuel Tanks: Most commonly found in the wings and wingtips, but can be located elsewhere. Made from materials that won’t react with aviation fuel. Vented to the outside to maintain atmospheric pressure in the tank. Fuel Selector Valve: A selector valve in the cockpit allows the pilot to select which tank is in use or to cut off the supply of fuel entirely. Fuel Lines and Filters: Aluminum alloy tubing and synthetic rubber or teflon hose connect the different components of the fuel system. A series of strainers collect water or debris that may make it into the fuel lines. Strainers should be drained prior to flight to remove water from the fuel system. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Parts of the Fuel System
Fuel Quantity Gauge: Fuel quantity gauges located in the cockpit tell the pilot how much fuel is in the fuel system. In addition to these gauges, pilots should manually check fuel levels before departure to ensure gauges read accurately. Fuel Primer: The primer is a hand pump located in the cockpit that allows the pilot to manually pump fuel into the cockpit. Priming is normally only necessary in cold weather. Over-priming can flood the engine with fuel. Carburetor: The function of the carburetor is to measure the correct amount of fuel, vaporize it, and mix it with the correct amount of air to feed into the engine. Carburetor is not present in aircraft with fuel injection systems. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Concept Check Describe the function of each of the following components: Fuel Tanks Fuel Selector Valve Fuel Lines Fuel Quantity Gauge Fuel Primer Carburetor 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Fuel Types Fuels for modern engines need to burn slowly and expand evenly rather than explode quickly. Fuels that have this quality are called high octane fuels. Fuels contain both octane, and heptane: Octane possesses minimum detonating qualities. Heptane possesses maximum detonating qualities. A fuel’s octane rating describes its proportion of octaine to heptane. I.e. 80 octane fuel is 80% octane and 20% heptane. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Fuel Types Fuels are often described with two octane numbers. For instance, 80/87 describes fuel that is 80 octane at lean mixture, and 87 octane at rich mixture. Low Power Output Grade 80 (80/87) Red Med. Power Output Grade 100LL (low lead) Blue Grade 100 (high lead) Green Jet Fuel Kerosene/Diesel Clear or Straw MOGAS P87-90 P84-87 Undyed Common fuels Pilots must be sure to use the correct fuel for their aircraft. If the correct fuel is not available for refuelling, the next higher grade must be used. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Fuel Related Problems Detonation: Describes the inability of a fuel to burn slowly and is characterized by abnormally rapid and instantaneous combustion. Detonation causes cylinder pressure and cylinder head temperature to rise quickly and violently and can be very damaging to the engine. It is caused by use of incorrect fuel, engine overheating, or over-leaning the mixture. It can be temporarily remedied by putting the mixture to full rich, and permanently remedied by using the correct fuel as specified in the POH. Pre-Ignition: Pre-ignition is premature ignition of fuel, usually due to trying to start a hot engine, and normally results in a backfire through the intake manifold. Pre-ignition can cause very serious damage to the engine. Vapour Lock: Vapour lock occurs when high atmospheric temperatures cause gas to vaporize, thereby blocking flow of the liquid fuel in the lines. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Concept Check What are the two components of fuel and which one is more resistant to detonation? What does a fuel’s octane rating describe? Describe detonation. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

3.3: The Carburetor and Fuel Injection

The Carburetor and Fuel Injection
The purpose of the carburetor is to measure out the correct quantity of fuel, vaporize it, mix it with air in the proper proportion, and deliver it to the engine cylinders. Proper fuel air mixture is very important to ensure the engine runs properly, and an incorrect mixture can be very damaging. Running Mixture ~ 1 to 8 Best Power Mixture ~ 1 to 14 Lowest Fuel Consumption Mixture ~ 1 to 18 Leanest Running Mixture ~1 to 20 . Example fuel to air ratios. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Rich Mixture vs. Lean Mixture
Mixture has a significant effect on engine temperature. A lean mixture (lower fuel:air) will generate more heat than a rich mixture (higher fuel:air) because it burns slower. Too Rich Mixture May Result In : Wasted unburned fuel being expelled. Spark plug fouling. Combustion chamber deposits. Rough engine operation. Loss of power or engine failure. Too Lean Mixture May Result In : Rough engine operation. Sudden cutting out/popping back in of engine. Overheating and detonation. Loss of power of engine failure. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Float Carburetor 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Concept Check What is the purpose of the carburetor? What is mixture? What are some properties of a rich mixture? A lean mixture? Describe how a float carburetor functions. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Mixture Control Carburetors are generally calibrated for sea level, so the best mixture at sea level will be full rich. As an airplane climbs, the air becomes thinner, so an equal volume of air will weight less, and if left at full rich, the fuel:air ratio will become too high. To correct for this, a mixture control allows the fuel:air mixture to be modified as necessary. This control can be automatic, or as it frequently is in smaller aircraft, a manual control in the cockpit. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Manual Mixture Control
Most commonly, the mixture control is manual and is operated with a sliding knob or lever in the cockpit. This mixture control controls the mixture needle in the carburetor. When advanced fully, the needle moves fully out of the discharge nozzle, allowing full fuel flow. When pulled back fully, the needle fully blocks fuel from flowing into the discharge nozzle (idle power). Rich Mixtures – High Power Settings Lean Mixtures – Cruise Power Settings A common method to lean is to move the mixture control from full rich towards lean. When the maximum RPM is reached, this is called rich best power. Further learning will result in stable RPM to a point, after which, RPM will drop. This point is called lean best power. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Benefits of Leaning Proper leaning of the engine will result in: Economy of fuel for lowering operating costs. A smoother running engine. A more efficient engine giving higher cruise performance. Extended range at cruise speeds (due to lower fuel consumption). Less spark plug fouling and longer spark plug life. More desirable engine temperatures. Cleaner combustion chambers resulting in less likelihood of pre-ignition. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Concept Check What is the benefit of having a mixture control in the cockpit? Rich mixtures should be used at ____ power settings, lean mixtures at ____ power settings. What are some benefits of leaning the mixture? 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Carburetor Icing Carburetor ice can form in certain moist atmospheric conditions in temperatures ranging from approximately -5 degrees Celsius to 30 degrees Celsius. Carburetor icing may be the single biggest cause of accidents in general aviation. It is very serious and very dangerous if left unchecked. Carb icing is normally indicated by a loss of power (drop in manifold pressure with constant speed prop or drop in RPM with fixed pitch prop). In severe cases it can cause complete engine failure. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

How Carb Icing Happens Fuel Vaporization Ice: Fuel must be vaporized from liquid form to be sent to the engine. This is done in the carburetor. The heat to make this vaporization happen is absorbed from the air in the carburetor. The temperature of this air in the carburetor can drop by as much as 30 degrees. Due to this low temperature drop, any significant amounts of moisture in the air can condense on the carburetor surfaces and freeze into ice. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

How Carb Icing Happens Throttle Ice: Air rushing around the throttle butterfly valve causes low pressure and a resulting small drop in temperature. Moisture in this low pressure area will freeze on the back side of the butterfly valve. A small amount of throttle ice can cause a significant reduction in airflow (and this power. A large amount of throttle ice can jam the throttle entirely. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

How Carb Icing Happens Impact Ice: Moisture in the atmosphere in the form of snow and sleet can build up on the outside of the carburetor intake screen or scoop during flight. This blockage of the intake can cause a loss of air flow and a subsequent loss of power. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Concept Check Describe fuel vaporization icing. Describe throttle icing. Describe impact icing. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Temperature/Humidity and Carb Ice
Carburetor icing can happen anywhere from ~ -5 degrees Celsius to 30 degrees Celsius At very low temperatures (< -5C), risk of carburetor icing is very low. The most suspect temperature for carburetor icing is around 15 degrees Celsius. A relative humidity of around 50% is generally required for icing to occur and the risk of icing goes up as the humidity does. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Carburetor Icing Chart

Concept Check What temperature range can carburetor ice develop in? What is the most likely rough temperature at which icing may happen? Why is icing unlikely at very cold temperatures below -5 Celsius? 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Preventing Carb Icing Carburetor Heat: Most carbureted airplanes come with a carburetor heat control in the cockpit. Activating the carburetor heat directs air heated by the engine exhaust into the carburetor to melt any ice. It takes significantly more heat to melt away existing ice than to prevent ice from forming. Carb ice should always be applied before reducing engine power. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Preventing Carb Icing Carburetor Heat Con’d: Activating carb heat after significant ice has already formed may be too late (due to insufficient engine heat). If ice is suspected at low power settings, engine power may need to be increased to generate sufficient heat. Activating carb heat partially can be worse than no carb heat at all. Carb heat should never be used on take-off or go-around, but can be left on for the remainder of a flight if serious icing is suspected. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Preventing Carb Icing Using Carb Heat: Apply carburetor heat and watch for the manifold pressure or engine RPM to drop due to reduced power. If no ice is present, the power will not drop any further, and carb heat can be disengaged. If icing is present, the melting ice will cause a further reduction in power and rough running of the engine while the water passes through the engine. Once the manifold pressure or RPM stabilize, the ice has been cleared. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Concept Check How does carburetor heat combat icing? When should carb heat always be applied? Why might carb heat not work if left too late? What might indicate carb ice developing? 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Fuel Injection Note: Throttle attached to fuel/air control unit. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Advantages of Fuel Injection
More even distribution of fuel to all cylinders due to individual metering. Better cooling due to elimination of leaner, hotter mixtures to distant cylinders. Savings on fuel through more uniform distribution. Increased power over carbureted engines. Significant reduction/elimination of carburetor icing. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Concept Check How does a fuel injection system differ from a carbureted engine? What are some benefits of fuel injection? 789 Lt. R Hampton Gray VC Squadron Ground School 2014

3.4: The Exhaust System

The Exhaust System 789 Lt. R Hampton Gray VC Squadron Ground School 2014

3.5: The Ignition System

The Ignition System Magnetos: Use magnetism to send current to the spark plugs. Spark Plugs: Provide spark to engine cylinders to fire combustion. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Dual Ignition System Most modern engines have a dual ignition system with two spark plugs for each cylinder and two magnetos each powering one spark plug per cylinder. The magneto switch in the cockpit can be set to the left magneto, right magneto, both, or off. It should always be set to “both” for normal flight. If one magneto fails in flight, the airplane can still be flown on the other magneto with a slight loss in overall power (~ 75 rpm). If one magneto fails, the engine will likely run rough if both magnetos are left active, and better if run on the working magneto only. After landing, the magneto switch MUST be turned to the off position or the engine may fire inadvertently. NEVER touch an airplane’s propeller unless you’re certain the magnetos are switched off. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Concept Check What is the purpose of a magneto? What is the purpose of a spark plug? What is the main benefit of a dual ignition system? Why should you never touch a propeller unless you’re certain the magnetos are off? 789 Lt. R Hampton Gray VC Squadron Ground School 2014

3.7: The Electrical System

Components of the Electrical System
Battery: Provides stored electricity to operate the electrical system when not being supplied by the engine. Master Switch: Connected to a solenoid which connects the battery to the rest of the electrical system. Starter Motor: Turns over the engine so it will begin firing and operate. Alternator/Generator: Supplies current to the electrical system and recharges the battery. Bus Bar: Receives the current from the alternator/generator and distributes it among the electrical system. Circuit Breakers: Protect the components from excessive voltage or current. Ammeter: Shows the rate of current flow in the system. Should always be on the + side of 0. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Components of the Electrical System

Concept Check What does the master switch do? What does the alternator do? What do circuit breakers do? What should the ammeter be reading to indicate a properly functioning electrical system? 789 Lt. R Hampton Gray VC Squadron Ground School 2014

3.8: The Propeller

The Propeller The function of the propeller is to push a large volume of air backwards, creating thrust. (Newton’s Third Law) A propeller is an airfoil. The twist in the propeller is to ensure equal lift across the entire propeller blade. A propeller’s lift creates the airplanes thrust. Propellers attached ahead of the engine are called tractors, and propellers attached aft of the engine are called pushers. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Propeller Pitch Fine Pitch: Low blade angle. Takes “small bites” of air. Has less drag, and allows the engine to develop greater power. Best suited for take-off. Coarse Pitch: High blade angle. Takes “big bites” of air. Airplane moves forward more for any given RPM. Best suited to cruise flight. A propeller’s pitch is the distance that it moves forward for one full revolution. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Types of Propellers Fixed Pitch: Fixed blade angle, set by manufacturer, that can not be adjusted. Blade angle chosen to give best overall performance for all flight conditions. Must balance trade off between take-off and climb performance and cruise performance. Variable Pitch: Blade angle can be changed to suit differing flight conditions. Adjustable pitch propellers allow blade angle changes on the ground. Controllable pitch propellers allow blade angles to be adjusted from the cockpit during flight. Constant speed propellers adjust automatically to maintain a constant RPM as set by the pilot in the cockpit. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Propeller Feathering Feathering refers to turning the blades “full coarse” so they are 90 degrees to the airflow and do not turn. If an engine dies, feathering reduces drag, stops the propeller from windmilling, and reduces vibration. Not all airplanes with variable pitch propellers have the ability to feather the prop. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Concept Check What is the function of a propeller? What is a propeller’s pitch? What is the difference between a fixed pitch propeller and a variable pitch propeller? What is feathering? 789 Lt. R Hampton Gray VC Squadron Ground School 2014

3.9: Engine Instruments

Oil Pressure Gauge Indicates the oil pressure supplied by the oil pump to lubricate the engine. Usually located with the engine temperature gauge and fuel gauge. May be colour coded to ease reading. Must be checked immediately after engine is started. Engine must be shut down if oil pressure doesn’t register within 10 seconds. Oil pressures high or low of the normal operating temperatures can damage the engine. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Oil Temperature Gauge Indicates the temperature of the oil in the engine. An abnormal drop in oil pressure and rise in oil temperature is an indication of malfunction. A rise in oil temperature on it’s own to a point above normal is an indication of increased friction in the engine. Overly cold oil does not circulate properly and is therefore also very undesirable.. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Tachometer Indicates the speed at which the engine crankshaft is spinning. Also normally shows total engine time in hours. In an airplane with a fixed pitch propeller, the tachometer is the sole source of information on engine power. In an airplane with a constant speed or controllable pitch propeller, the tachometer works in conjunction with the manifold pressure gauge. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Manifold Pressure Gauge
Indicates the pressure of the fuel/air mixture in the intake manifold at a point between the carburetor and cylinders. In airplanes with constant speed or controllable pitch props, manifold pressure is controlled by the throttle and is used to monitor engine power. Manifold pressure and RPM are intimately connected. Charts for proper matching of manifold pressure and RPM for different speeds at different altitudes are published in the POH. Opening the throttle increases manifold pressure. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Other Engine Instruments
Cylinder Head Temperature Gauge: Records the temperature of one or more cylinder heads, gives a good indication of engine cooling effectiveness, and helps avoid potential problems like detonation. Carburetor Air Temperature Gauge: Indicates the temperature of the fuel:air mixture entering the manifold, allows a pilot to maintain an efficient temperature, and warns against icing conditions developing. Outside Air Temperature Gauge: Indicates ambient temperature. When corrected to get true air temperature, gives the pilot information that can assist with calculating true airspeed, true altitude, and warns of conditions that may cause icing. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Concept Check Describe the oil pressure gauge. Describe the oil temperature gauge. Describe the tachometer. Describe the manifold pressure gauge. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

3.11: Jet Propulsion

Jet Propulsion Jet propulsion uses hot gasses ejected from the rear of the engine to produce forward thrust (Newton’s 3rd law). Whereas propeller move a large volume of air backwards at slow speed, jet engines move a smaller volume of air backwards at very high speed. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Ramjet Engine The ramjet is the simplest form of jet engine. High speed ram air is forced through the front of the engine and compressed by the diffuser section. It is then mixed with fuel, combusted, and the exhaust is expelled through the nozzle. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Turbojet Engine The turbojet engine is a more complex jet engine that was used in many earlier jet aircraft. It uses a series of compressor blades driven by a turbine to compress the air entering into the engine. Turbojets produce very high power output. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Turboshaft and Turboprop Engines
Turboshaft and turboprop engines are variations on the turbojet in which engine power is used to drive either a propeller a geared power shaft in order to turn the expelled exhaust gasses into rotational power. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Turbofan Engine The turbofan engine is a development of the turbojet in which a ducted fan is used to send cool bypass air around the main power section to be mixed downstream with the hot jet exhaust. This results in reduced power put significant fuel efficiency. The amount of bypass air will determine drop in power and fuel efficiency. 789 Lt. R Hampton Gray VC Squadron Ground School 2014

Concept Check What are the four types of jet engine discussed? What are the four main stages of a jet engine? How does a turbojet differ from a turbofan? 789 Lt. R Hampton Gray VC Squadron Ground School 2014

End of Module 3 789 Lt. R Hampton Gray VC Squadron Ground School 2014

789 Lt R Hampton Gray VC Squadron Ground School (2014)

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