1. PISTON ENGINES
Part 1
Introduction

2. Introduction In 1903, the Wright brothers made history
1916
1935
1955
1991
In 1903, the Wright brothers made history
with 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 Combustion
Steam
Combustion
Air
Solid Fuel
Piston
There are many types of piston engine where solid fuel
is burnt externally in a fire box,
to turn water into steam,
which is piped to the engine
to drive the pistons.
But these engines are much too heavy for aviation.

4. External Combustion
Steam
Combustion
Air
Solid Fuel
Piston
Connecting Rod
Crank
Driven Wheel
Even though this type of engine is heavy, it is efficient;
that is, more of the energy developed (power)
is available for driving the vehicle through
the 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 supplies
had to be more efficient - from smaller and lighter engines.
Which is where the Internal Combustion Engine came to the fore.
The combustion
process takes place
inside the engine.
But there are some
similarities between
the two types of engine.
Piston
Top Dead Centre (TDC).
Connecting Rod
Crankshaft
Crank
Driven Wheel
Bottom Dead Centre (BDC).

6. Mechanical Arrangement
Basics
The 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 forced
out
PISTON
Compressed charge of fuel and air
Expanding gases force piston down
Air forced in
CYLINDER
PISTON
CYLINDER
A Bicycle Pump
A Piston Engine

7. Mechanical Arrangement
Basics B
Leg force in direction ‘A’
gives rotational force
in direction ‘B’ on the crank A
Hand force
in direction ‘A’
gives a rotational force
in direction ‘B’ to the nut A B
Crank
In both cases
Linear Force
has brought about rotation.

8. Mechanical Arrangement
Basics
A piston engine has a crankshaft,
which works the same way
as the bicycle pedals and crank.
The force on the bicycle pedal from leg muscles is equivalent
to the force supplied by burning fuel and air.
Fuel and Air
Cylinder A
Piston B
Crank
Crank Shaft

9. Mechanical Arrangement
Basics
The 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 crankshaft
by the ‘Big-end’ bearing.
Fuel and Air
Cylinder
Piston
Gudgeon Pin
Main Bearings
Connecting Rod
Offset Bearing
‘Big-end’
Crank Shaft
Counter Balance Weights

10. Mechanical Arrangement
Basics
The 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 returning
the piston to its starting point.
So the piston produces
linear thrusting movements
time after time.
Fuel and Air
Cylinder
Piston
Gudgeon Pin
Main Bearings
Connecting Rod
Offset Bearing
‘Big-end’
Crank Shaft
Counter Balance Weights

11. Mechanical Arrangement
Basics
The 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 flange
Timing Belt & Water Pump driving pulley location
REAR
Main Bearings
Crankshaft
FRONT

12. Mechanical Arrangement
Basics
The 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. 3
Pistons 2 4 1
Flywheel attachment flange
Timing Belt & Water Pump driving pulley location
REAR
Main Bearings
Crankshaft
FRONT

13. Mechanical Arrangement
Basics
Major Engine Assemblies
The Cylinder Head Assembly
houses the valve gear mechanism
and the top of the cylinders.
The spark plugs, inlet and exhaust
manifolds are bolted to the head.
The Cylinder Block houses
the cylinders and the pistons.
Also the oil pump and filter (inside),
and externally the water pump,
and the alternator.
The Rocker Box Cover
shields the valve mechanism
and contains the lubricating oil.
The Sump keeps the oil in
and can double as an oil tank.
‘Rocker Box’ Cover
Valve Gear
Cylinder Head Assembly
Cylinder Block
Flywheel
Pistons and Crankshaft
Sump
(Oil Tank)

14. Mechanical Arrangement
Valve Operation
In 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 Valve
Exhaust Valve
The Inlet Valve
needs to be open,
to allow the
fuel/air mixture in
The Exhaust Valve
needs to be open,
to allow the
burnt gases out

15. Mechanical Arrangement
Valve Operation
Push Rod Mechanism
The valve opening motion
comes from a rotating cam shaft.
A cam has a raised portion that lifts
the cam follower or push rod,
which either operates a rocking lever
or the cam bears directly
on 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 a
none raised section,
the spring pushes the valve closed.
Rocker
Rocker Shaft
Return Spring
Valve Seat
Inlet Valve
Closed
Inlet Valve Open
Valve Lift
Push Rod
Cam Shaft

16. Mechanical Arrangement
Valve Operation
Rocker Arm
The less parts there are,
the more accurate the work with
opening and closing times,
and the more efficient
the engine.
Some engines feature a
hydraulic system for valve opening
(closing via a return spring),
but driven by a cam.
Some manufacturers now fit
VARIABLE valve timing;
to ensure that the valves
operate at the optimum point
at all rpm values
to gain maximum efficiency
from a piston engine.
Cam Shaft
Return Spring
Valve
Overhead Cam and Rocker
Overhead Cam
No Rocker

17. Mechanical Arrangement
Valve Operation
The Cam Drive
Modern Engines
use a toothed
rubber belt to drive
the cam shafts
Twin Cam System
Chain Tensioners
Pistons and
Crank Shaft
Cam Drive Mechanism

18. Check of Understanding
What, essentially, is used to drive a propellor?
The con rod
The push rod
The crankshaft
The piston

19. Check of Understanding
What is the purpose of a gudgeon pin
in a piston engine?
Attaching the piston to the conrod
Attaching the conrod to the crankshaft
Attaching the crankshaft to the big-end
Attaching the big-end to the piston

20. Check of Understanding
In the diagram below
which arrow points to the crankshaft? W X Y Z

21. Check of Understanding
In the diagram below,
what is the item indicated called?
The cam shaft
The rocker leg
The push rod
The cam drive

22. Check of Understanding
What is used to close
the exhaust and inlet valves
on a piston?
The return spring
Expanding gases
The cylinder
The cam shaft

23. Check of Understanding
In an engine, what are the spark plugs,
inlet and exhaust manifolds bolted to?
The cam shaft
The cylinder block
The cylinder head assembly
The sump

24. Check of Understanding
Via what means is the crankshaft
mounted in the engine?
The cam drive mechanism
The main bearings
The cylinder head assembly
The flywheel flange

25. PISTON ENGINES
End of Presentation