Extra Shit

Question 1

What is TDC and BDC

Answer 1

Piston at max distance from crank shaft.

Piston at minimum distance from crankshaft

Question 2

What is clearance volume and swept volume

Answer 2

Clearance - the volume remains above the piston of an engine when it reaches top dead centre

Swept - the volume through which a piston moves as it makes a stroke.

Question 3

What is compression ratio?

Answer 3

Swept volume + clearance volume

Question 4

What is firing interval?

Answer 4

How often you can have a power stroke.

The number of degrees per cycle/number of cylinders.

Question 5

What is valve lead and lag

Answer 5

Lead - early opening of exhaust valve on power stroke to assist in scavenging burnt gases.

Lag - late closing of inlet so allows more charge to get in meaning increased pressure.

Question 6

What is valve overlap and its advantage

Answer 6

Both valves being open at same time.

Increase amount of charged induced into cylinder, helps with scavenging and cooling.

Question 7

What is spark advance?

Answer 7

Supply of the ignition spark on the compression stroke earlier than TDC. Done so highest pressure is developed before con rod and crankshaft are at 90 degrees.

Question 8

What is crankthrow

Answer 8

Radius of camshaft

Question 9

Where is brake power measured

Answer 9

Propellor hub

Question 10

What is engine torque

Answer 10

Turning force

T=fd

Question 11

What is brake horsepower

Answer 11

Actual power output at crankshaft

Question 12

What is indicated power

Answer 12

Total power developed within the cylinders by the combustion process. (What the engine manufacturer says engine has)

Question 13

What is friction power

Answer 13

Power lost due to friction and other things.

Question 14

Brake power formula

Answer 14

BHP = IP - FP

Question 15

What is rated power?

Answer 15

The brake power that can be continuously maintained by an engine at a stated rpm (and manifold pressure if with a CSU)

E.g 112hp at 2600rpm

Question 16

What is rated/critical altitude

Answer 16

The altitude at which engine will develop its rated power.

As altitude increases, density decreases so engine develops less power. So for non supercharged engines it’ll be close to sea level.

Question 17

What is full throttle height?

Answer 17

The altitude at which a given manifold air pressure set can be maintained at a given RPM.

Lower the map selected, the greater the altitude to which it can be maintained.

Question 18

What is brake thermal efficiency.

Answer 18

The overall efficiency of the engine. Losses are due to cooling, exhaust gases and friction.

Can also be expressed as how much fuel is being used at any one point in time (brake specific fuel consumption)

Question 19

What is mechanical efficiency.

Answer 19

Part of the overall thermal efficiency of the engine. It’s the ratio between indicated power and brake power.

Most efficient rpm it is 90%

Question 20

What is volumetric efficiency

Answer 20

How efficient the engine is at breathing or taking in the induction of the fuel air mixture.

100% efficiency, volume drawn into the cylinder must be equal to volume displaced by piston.

Factors reducing it is drag from walls of pipes/manifold, inertia of the charge and rate of inflow.

Question 21

How are the efficiency equations remembered.

Answer 21

Thermal efficiency = fuel flow/brake power (To Fly Bravely)

Mechanical = brake power/ indicated power (Means Being Into)

Volumetric = volume of charge/piston displacement (Vicious Vibrating Planes)

Question 22

What are the ideal conditions for an engine?

Answer 22

Low temp, high pressure, low humidity

Throttle butterfly valve wide open

Low rpm

Cool induction manifold temperature.

Question 23

What is manifold pressure?

Answer 23

The measure of the pressure in the intake manifold which is made up of the fuel air mixture and ambient air temperate

Question 24

What is the relationship with manifold pressure and ambient pressure?

Answer 24

Ambient air pressure decreases with altitude so manifold air pressure must also decrease. So efficient also decreases and power output.