2 Introduction In 1903, the Wright brothers made history 1916193519551991In 1903, the Wright brothers made historywith the first powered aeroplane that could carry a man.Their flying machine was powered by a piston engine –and today, a century later,piston engines are still used,in hundreds of thousands of aircraft,all over the world.
3 External CombustionSteamCombustionAirSolid FuelPistonThere are many types of piston engine where solid fuelis burnt externally in a fire box,to turn water into steam,which is piped to the engineto drive the pistons.But these engines are much too heavy for aviation.
4 External CombustionSteamCombustionAirSolid FuelPistonConnecting RodCrankDriven WheelEven though this type of engine is heavy, it is efficient;that is, more of the energy developed (power)is available for driving the vehicle throughthe connecting rod, crank and drive wheels,compared to other forms of power generation.
5 Internal Combustion Piston Connecting Rod Crank Crankshaft With the advent of flight, power supplieshad to be more efficient - from smaller and lighter engines.Which is where the Internal Combustion Engine came to the fore.The combustionprocess takes placeinside the engine.But there are somesimilarities betweenthe two types of engine.PistonTop Dead Centre (TDC).Connecting RodCrankshaftCrankDriven WheelBottom Dead Centre (BDC).
6 Mechanical Arrangement BasicsThe piston engine and a bicycle pump are basically similar,in that both have a cylinder, inside which is a plunger or piston.Pull the piston back to force air in.Then push the piston up the cylinder,to push the air out.Air forcedoutPISTONCompressed charge of fuel and airExpanding gases force piston downAir forcedinCYLINDERPISTONCYLINDERA Bicycle PumpA Piston Engine
7 Mechanical Arrangement BasicsBLeg force in direction ‘A’gives rotational forcein direction ‘B’ on the crankAHand forcein direction ‘A’gives a rotational forcein direction ‘B’ to the nutABCrankIn both casesLinear Forcehas brought about rotation.
8 Mechanical Arrangement BasicsA piston engine has a crankshaft,which works the same wayas the bicycle pedals and crank.The force on the bicycle pedal from leg muscles is equivalentto the force supplied by burning fuel and air.Fuel and AirCylinderAPistonBCrankCrank Shaft
9 Mechanical Arrangement BasicsThe crankshaft is made-up of various parts.The piston connects to the crankshaft by a connecting (con) rod.The piston is attached to the conrod by a ‘Gudgeon’ pin.And the conrod itself is attached to the crankshaftby the ‘Big-end’ bearing.Fuel and AirCylinderPistonGudgeon PinMain BearingsConnecting RodOffset Bearing‘Big-end’Crank ShaftCounter Balance Weights
10 Mechanical Arrangement BasicsThe piston movement now causes the crankshaft to rotate,so we can use the crankshaft rotation to drive a propeller,or the wheels of a car.The rotating crankshaft also provides a means of returningthe piston to its starting point.So the piston produceslinear thrusting movementstime after time.Fuel and AirCylinderPistonGudgeon PinMain BearingsConnecting RodOffset Bearing‘Big-end’Crank ShaftCounter Balance Weights
11 Mechanical Arrangement BasicsThe crankshaft is mounted in the engine via the main bearings;on the rotational centre of the crankshaft.At the rear there is a mounting flange for a flywheel.The timing gear and ancillaries (water pump and alternator)are driven from the front of the crankshaft,which is where the aircraft propeller is mounted.Flywheel attachment flangeTiming Belt & Water Pump driving pulley locationREARMain BearingsCrankshaftFRONT
12 Mechanical Arrangement BasicsThe piston big ends are then attached to the crankshaft.They are attached on the ‘cranked’ offsets –hence the name crankshaft.The offsets are the equivalent to the pedals on a bicycle.3Pistons241Flywheel attachment flangeTiming Belt & Water Pump driving pulley locationREARMain BearingsCrankshaftFRONT
13 Mechanical Arrangement BasicsMajor Engine AssembliesThe Cylinder Head Assemblyhouses the valve gear mechanismand the top of the cylinders.The spark plugs, inlet and exhaustmanifolds are bolted to the head.The Cylinder Block housesthe cylinders and the pistons.Also the oil pump and filter (inside),and externally the water pump,and the alternator.The Rocker Box Covershields the valve mechanismand contains the lubricating oil.The Sump keeps the oil inand can double as an oil tank.‘Rocker Box’ CoverValve GearCylinder Head AssemblyCylinder BlockFlywheelPistons and CrankshaftSump(Oil Tank)
14 Mechanical Arrangement Valve OperationIn order to compress the fuel air mixture in each cylinder,first it has to be able to get in,then it has to be sealed in or compression cannot take place.This is done through the operation of inlet and exhaust valves.Inlet ValveExhaust ValveThe Inlet Valveneeds to be open,to allow thefuel/air mixture inThe Exhaust Valveneeds to be open,to allow theburnt gases out
15 Mechanical Arrangement Valve OperationPush Rod MechanismThe valve opening motioncomes from a rotating cam shaft.A cam has a raised portion that liftsthe cam follower or push rod,which either operates a rocking leveror the cam bears directlyon the top end of the valve stem,to open the valve.When the valve is forced open,the return spring is compressed,so when the cam rotates to anone raised section,the spring pushes the valve closed.RockerRocker ShaftReturn SpringValve SeatInlet ValveClosedInlet Valve OpenValve LiftPush RodCam Shaft
16 Mechanical Arrangement Valve OperationRocker ArmThe less parts there are,the more accurate the work withopening and closing times,and the more efficientthe engine.Some engines feature ahydraulic system for valve opening(closing via a return spring),but driven by a cam.Some manufacturers now fitVARIABLE valve timing;to ensure that the valvesoperate at the optimum pointat all rpm valuesto gain maximum efficiencyfrom a piston engine.Cam ShaftReturn SpringValveOverhead Cam and RockerOverhead CamNo Rocker
17 Mechanical Arrangement Valve OperationThe Cam DriveModern Enginesuse a toothedrubber belt to drivethe cam shaftsTwin Cam SystemChain TensionersPistons andCrank ShaftCam Drive Mechanism
18 Check of Understanding What, essentially, is used to drive a propellor?The con rodThe push rodThe crankshaftThe piston
19 Check of Understanding What is the purpose of a gudgeon pinin a piston engine?Attaching the piston to the conrodAttaching the conrod to the crankshaftAttaching the crankshaft to the big-endAttaching the big-end to the piston
20 Check of Understanding In the diagram belowwhich arrow points to the crankshaft?WXYZ
21 Check of Understanding In the diagram below,what is the item indicated called?The cam shaftThe rocker legThe push rodThe cam drive
22 Check of Understanding What is used to closethe exhaust and inlet valveson a piston?The return springExpanding gasesThe cylinderThe cam shaft
23 Check of Understanding In an engine, what are the spark plugs,inlet and exhaust manifolds bolted to?The cam shaftThe cylinder blockThe cylinder head assemblyThe sump
24 Check of Understanding Via what means is the crankshaftmounted in the engine?The cam drive mechanismThe main bearingsThe cylinder head assemblyThe flywheel flange