AES2

• Engine Design – Cooling

  • As the engine creates power during flight, it will start to create heat.

  • The heat of combustion inside the cylinder can reach up to 2500°C.

  • The harder the engine needs to work, the more heat that it will produce.
• Engine Design – Air Cooling

  • Engine is cooled by having air pass over the cylinders.

  • For some engines, augmenter tubes or cowl flaps may be added to create suction pulling hot air out of the engine and cowling.

  
• Engine Design – Air Cooling

  • Oil cooling, which will be covered later, must be used in addition to air cooling.

  • In some models, there may be a cooling fan mounted on the front of the engine.

  • The fan is gear driven from the crankshaft and assists engine cooling by blowing air over the engine at high altitudes where air is less dense.

  
• Engine Design – Air Cooling

  • Cylinders have fins (additional surface area) attached which helps with cooling.

  • Baffles direct the air through the fins to aid in cooling.

  • These fins look like folds on the metal portion of the cylinder.

  • The extra surface area helps dissipate heat.

  
• Engine Design - Liquid Cooling

  • A water jacket surrounds parts of the engine that produce heat.

  • Heat from the engine is absorbed by the water.

  • Pumps continually move the water from the jackets to radiators, where the water is cooled, then back to the jackets.

  • Adds weight and complexity.

  • Most often used on larger inline engines and diesel engines.

  
• Engine Design – Oil Cooling

  • While engines will be cooled by air or liquid, they will normally also be aided by oil cooling.

  • Oil primarily cools the engine through lubrication.

  • Lubrication reduces friction between moving pieces and therefore reduces the production of heat.

  
• Engine Design – Oil Cooling

  • Like the liquid cooling system, oil will absorb heat from the engine.

  • The oil is cooled using an oil cooler.

  • Oil coolers use a temperature valve which will allow oil into the cooler above a set temperature.

  • If the oil is below that temperature it bypasses the cooler and goes back to the system.

  • If oil enters the cooler, it will move through the compartments allowing cooling to occur.

  
• Engine Design – Dry Sump

  • A "dry sump" system means the oil is held in a compartment separate from the engine.

  • The oil is brought from a its tank, separate from the engine using an engine driven pump.

  • Oil will go through the engine and then settle in a sump under the crankcase.

  
• Engine Design – Dry Sump

  • A scavenge pump (different from the original pump) moves the oil through the cooler and is then returns it to the tank.

  • These are used on radial, inverted inline, and aerobatic planes.

  • It is a more complex system therefore less commonly used.

  
• Engine Design – Wet Sump

  • The wet sump is very simple and lightweight.

  • Because the oil is kept in the crankcase, we do not have the need for an additional pump.

  • Oil pressure and temperatures are monitored on gauges in the instrument panel.

  • Planes that fly inverted are unable to use an engine like this.

  
• Engine Design – Wet Sump

  • Oil sits directly in the crank case – no external tank in this system

  - A pump pressurizes oil and pushes it through a filter and a cooler.

  - The oil then moves through passageways in the crankshaft and pushrods to all bearings.

  - Oil is delivered under this pressure or is allowed to splash or both.

  • Oil can be delivered to engine parts under pressure; by splashing; or by both pressure and splashing.

  
• Engine Design – Oil Venting

  • As the engine runs a significant amount of gas (air bubbles) builds in the crankcase.

  • The crankcase is vented (air tube connected to the outside air) which allows the excess vapors and pressure to escape the engine.

  • This tube acts as an oil/air separator.

  
• Engine Design – Oil Filter

  • Captures and removes contaminants from the oil.

  • Oil will flow through this filter before entering the engine.

  • The major contaminants are:

  - gasoline

  - moisture

  - acids

  - dirt

  - carbon

  - metallic particles

  
• Engine Design – The Ignition System

  • Most piston driven aircraft have a dual ignition system.

  • This means there are two magnetos and two spark plugs in each cylinder.

  • These are installed for redundancy and performance purposes.

  
• Engine Design – The Magneto

  • The magneto provides electricity to the spark plugs.

  • They are self-exciting, meaning there is no external power source .

  • Due to the internal moving pieces, they create their own electrical charge that can be used to provide a spark inside the combustion chamber.

  
• Engine Design – The Magneto

  • A low-tension electrical current is created by having either a rotating magnet near a metal coil, or a fixed magnet with a rotating armature which holds a metal coil.

  • This converts a low-tension current into a high-tension current.

  • This high-tension current is sent to the distributor and then the sparkplugs.

  
• Engine Design – The Exhaust System

  • Expels exhaust gases from the engine.

  • Usually made from stainless steel as its lightweight and corrosion resistant.

  • Mufflers are included to help reduce noise.

  • There is often a shroud over the exhaust pipe that is used to collect the heat from the exhaust (without the carbon monoxide) for use in ancillary systems.

  
• What are the three ways to cool an engine? A

  a) Oil, air, liquid

  b) Oil, liquid, fuel

  c) Electric, oil, fuel

  d) Electric, air, oil
• What is the main advantage of operating a dry sump system? D

  a)A separate reservoir of oil allows for optimal cooling

  b) Oil is contained within the engine crankcase allowing for optimal cooling and efficiency

  c) Scavenger pumps allow for more oil flow and therefor better cooling

  d) Dry sump systems allow aircraft to operate inverted
• What is the meaning of dual ignition regarding magnetos? B

  a) The system contains two engines

  b) The system contains two spark plugs per cylinder

  c) The system contains two spark plugs per engine

  d) There are two magnetos and 1 spark plug per cylinder
• Engine Design – Ancillary Controls

  1. Carburetor heat control

  - Provides warm air to the carburetor.

  2. Primer Pump

  - May be electrical or mechanical.

  - Primer will push raw fuel directly into the cylinder.

  - In the case of mechanical primers, it draws directly from the fuel line. Leaving it open after engine start may starve the engine leading to engine failure.

  
• Engine Design – Ancillary Controls

  3. Mixture controls

  - Allows the adjusting of the fuel/air mixture from full rich (more fuel) to full lean (less fuel).

  - This is used to compensate for the reduced air density at altitude and improves fuel economy.

  4. Alternate Air

  - Provides a backup source of air for the engine.

  
• Engine Design – Ancillary Controls

  5. Cowl Flaps

  - Attached to the rear of the engine cowling.

  - Can be opened and closed from the cockpit.

  - Opening the cowl flaps increases engine cooling by allowing hot air to quickly exit the cowling.

  
• Engine Design – Ancillary Controls

  6. Environmental controls

  - For cabin air there are air intakes or scoops on the exterior of the plane. This provides cool air inside the cabin.

  - For heat, a shroud (covering) is placed over the exhaust. Radiant heat is taken and directed in the cabin.

  - The same heat may also be used to defrost the windshield.

  
• Engine Design – Ancillary Controls

  6. Environmental controls

  - In most cases, the cabin heat is supplied by radiant heat from the exhaust system.

  - This means we don’t use exhaust gases directly, but the air that it warms.

  - We must be careful to monitor the carbon monoxide card inside the cockpit to ensure exhaust gases are not getting into this airflow.

  
• Engine Design – Ancillary Controls

  6. Environmental controls

  - If there is a crack or break in the exhaust system, it will allow burnt gases into the cockpit.

  - This is extremely hazardous to pilots as carbon monoxide is odorless and toxic.

  
• Engine Operations – Turbocharging

  • Normally aspirated aircraft use the atmospheric pressure outside to supply air for combustion and power.

  • As the aircraft climbs, the atmospheric pressure decreases, leading to a loss of air and therefore a loss of power.

  
• Engine Operations – Turbocharging

  • Turbochargers provide the engine with more dense air by compressing it. This allows the aircraft to be flown at higher altitudes.

  • This compression of air also allows higher power values at low altitudes.

  
• Engine Operations – Turbocharging

  • If the turbocharger provides higher pressure than atmospheric pressure in the inlet manifold this is referred to as “boost”

  • Boosted engines are very powerful but require appropriate engine management techniques

  
• Engine Operations – Turbocharging

  • Exhaust gases (shown in red) that are normally expelled, are now used to drive a turbine wheel (or impeller).

  • This wheel is spun at a very high rpm.

  • The turbine wheel is mounted on a shaft which is connected to a centrifugal air compressor.

  • The compressor, therefore, spins at the same speed as the turbine wheel.

  
• Engine Operations – Turbocharging

  • The compressed air provides additional power by increasing the fuel:air mixture.

  • Exhaust gas is controlled by a “waste gate” to keep pressures within limits.

  
• Engine Operations – Turbocharging

  • Adjusting the turbocharger speed can be done automatically or manually.

  • The turbocharger is a particularly efficient system since it uses engine energy to maintain horsepower without using any engine horsepower as its source.

  
• Engine Operations – Turbocharging

  
• Engine Operations – Supercharging

  • Like the turbocharger, the supercharger provides denser air to the engine through means of an impellor (or compressor).

  • The big difference is that the supercharger is geared directly to, and therefore is powered solely by, the engine itself.

  
• Engine Operations – Supercharging

  • As the engine turns the compressor, this can draw up to 16% of the engine’s power.

  • Although supercharging will result in a reduction of engine power, the benefits of the compressed air at higher altitudes is worth the loss.

  
• Engine Operations – Fuel Systems

  • The engine will have either a carburetor or fuel injection system that supplies and controls the mixture of fuel and air.

  • Both systems have their pros and cons.
• Engine Operations – The Carburetor

  • Fuel is drawn through a passageway (darker blue line from the float chamber) by the venturi because it creates a lower pressure and pulls the fuel into the airstream.

  • As the fuel passes through the venturi, the low pressure will also vaporize the fuel into a gas creating the fuel/air mixture we need for combustion.

  
• Engine Operations – The Carburetor

  • Once the fuel & air is mixed, the mixture will be sent to the intake manifold. The throttle valve will control the flow of the fuel/air mixture.

  • As the fuel level lowers in the float chamber, the float drops and allows more fuel into the chamber (system controlled).

  • There is also a mixture control valve or needle that alters the amount of fuel going to the discharge nozzle (pilot controlled).

  
• Engine Operations – Carburetor Ice

  • Carb icing is caused by the cooling effect of the carburetor, vaporization of fuel and moisture in the air.

  • Can occur at outside temperatures between -15 degrees Celsius up to +32 degrees Celsius.

  • Most severe carb icing occurs between -2°C and +15°C.

  • Can block the intake system and cause engine failure.

  
• Engine Operations – Carburetor Ice

  • Can be recognized by a loss of power or in extreme cases,sudden engine stoppage.

  • Pilot awareness of the conditions that are conductive to carb ice and the carb heat system are the only defense.

  • When carb heat is selected on, the ice in the carburetor will melt. The water will be ingested by the engine, causing roughness. Once the ice is gone, the engine roughness will smooth out and you will see an increase in RPM or manifold pressure.