Piston Engine Principles

Question 1

what is a crankcase made out of?

Answer 1

two halves of aluminium alloy which are bolted together. to help stiffen assembly internal webs are incorporated.

Question 2

what do crankcases do?

Answer 2

provide support and housing for various components and a mounting phase for numerous accessories such as magnetos, oil pumps, fuel and vacuum pumps. also provides an oil type chamber for lubricating oil and a means of mounting the engine in the aircraft.

Question 3

what is fitted to ensure that internal pressures are equal to surrounding atmospheric pressure?

Answer 3

crankcase breather

Question 4

what is a crankshaft?

Answer 4

the backbone of a reciprocating engine at it converts reciprocating motion into rotation motion for turning the propellor.

Question 5

what is a crankshaft composed of?

Answer 5

one or more crank throws. 1 crank throw = 2 crank webs + 1 crank pin

Question 6

in addition to the crankshaft providing a drive to the propellor, it also provides a drive to what?

Answer 6

the valve

Question 7

a connecting rod is used for what?

Answer 7

to link each piston to the crankshaft.

Question 8

what does a connecting rod consist of?

Answer 8

the large end is known as the big end that attaches by a means of a two-piece bearing, a cap and attachment parts.

the opposite end is a small end bearing which is usually a bronze bush. the small end connects to the piston by means of a gudgeon pin or piston pin.

Question 9

a piston pin is usually what?

Answer 9

fully floating, that’s free to move laterally, thus preventing uneven wear. its help in place in the piston by eng plugs.

Question 10

How does a piston work and what is it made of?

Answer 10

As the fuel and the air are ignited inside the cylinder, the piston is pushed down by the resulting release of pressure. As it is connected to the crankshaft, the piston’s up and down movement turns the crankshaft.

usually made of aluminium alloy and consists of a crown, a side and a skirt. they typically have 3-4 grooves to accommodate the piston rings and are often internally thinned to provide extra strength to aid cooling.

Question 11

what is a piston ring made of and what’s its use?

Answer 11

• made of cast iron or steel incorporating an expansion gap because these materials are chosen for their self-lubricating properties and springiness.

they provide a seal between piston and cylinder during all running conditions.

Question 12

what are the types of piston rings?

Answer 12

compression, oil control and oil scraper.

Question 13

what do compression rings do?

Answer 13

prevent cylinder head gases leaking past the piston into the crankcase and help transfer heat into the cylinder wall.

Question 14

what does oil control rings do?

Answer 14

under compression rings, they prevent lubricating oil from leaking into the cylinder head and maintain the proper quantity of oil between piston and cylinder wall.

Question 15

slots in oil control rings do what?

Answer 15

allow for oil to seep through the ring and return to sump by gravity.

Question 16

what do oil scraper rings do?

Answer 16

fitted at bottom of piston skirt to remove excess quantities of lubricating oil from the cylinder walls and return it to the crankcase

Question 17

what is a cylinder barrel made out of? And what do they do? (4)

Answer 17

made of alloy steel.

provide a working surface for piston rings
a screw thread for mounting the cylinder head
a skirt and mounting flange for attachment to the crankcase
and a series of fins for cooling.

Question 18

what does a cylinder barrel do?

Answer 18

provide an opportunity to increase the efficiency of the engine cooling, whilst also simplifying the assembly, and reducing mass.

Question 19

what are cylinder heads made of and what is their use?

Answer 19

normally made of aluminium alloy they are screwed and shrunk onto the cylinder barrels with fins on it.

• for heat dissipation and lightweight assemblies while fins aid with cooling

Question 20

what is the valve operating mechanisms use?

Answer 20

the main use is to open and close inlet and exhaust valves to their respective manifolds, allowing the fuel-air charge to enter the cylinder and the burnt gases to exit.

Question 21

in a valve operating mechanism, what’s the difference between inlet and exhaust valves?

Answer 21

exhaust valves are subjected to a great deal of heat and special provisions must be made to aid cooling.

Question 22

to prevent valves rocking during their operation what is installed?

Answer 22

valve guides are fitted into the cylinder head which are usually pressed in and help to transfer heat from the valve to the cylinder where it’s dissipated into the air.

Question 23

what is required when valves are closed?

Answer 23

a tight seal. it’s achieved by having ground valve inserts fitted into the cylinder head.

Question 24

what do spark plugs do?

Answer 24

ignite the compressed fuel-air mixture in the cylinder,

Question 25

what is a camshaft?

Answer 25

It moves at half the speed of the crankshaft and its job is to open and close the valves.

Question 26

what is the inline arrangement?

Answer 26

piston engine cylinder arrangement which has a number of cylinders in a single row parallel with the crankshaft, the cylinders may be upright above or inverted below the crankshaft

Question 27

inverted arrangement for the in-line arrangement is usually for what?

Answer 27

To give pilot unobstructed forward vision.

Question 28

what is the upright v piston engine arrangement?

Answer 28

usually used when more then six cylinders are to be employed, 8 are mounted in two rows making V. angles between banks are 90, 60 and 45 degrees. arrangements reduce crankshaft length and torsional vibration.

Question 29

what is the radial piston engine arrangement?

Answer 29

have cylinders around the crankshaft. in its simplest form has a single bank of cylinders, for increased power up to 4 banks may be used. this type of arrangement has a very short crankshaft but a large frontal area.

Question 30

what is the horizontally opposed piston engine arrangement?

Answer 30

most popular for light aircraft. this type has the cylinders arranged opposite to each other on either side of the crankshaft. advantage of shorter crankshaft and also greatly improved air cooling.

Question 31

what is the most common engine for flight training? (5)

Answer 31

• horizontally opposed
• reciporicating
• air cooled
• runs on avgas
• four-stroke cycle

Question 32

What are cams?

Answer 32

The little bumps on the camshaft are known as ‘cams’ and they act to move the push rods, which are connected to the valve operating mechanism.