Cap 9 Piston Engine Power ,efficieny And Control

Question 1

Power

Answer 1

~The mass of charge
~ the number of times per second that the charge is put into the cylinder

POWER= (froce X distance)/ time

Answer 2

Power = P L A N E 
P=pressure mean effective pressure
L=lenghth
A=area
N=number of cyclinders
E= rpm/2

Question 3

Volumetric efficiency

Answer 3

80 % is the volumetric efficiency

Question 4

Mechanical efficiency

Answer 4

Measures the effectiveness of an engine in turning the input power into a useful output power.

Taking into account friction and vibration losses it can be determined that mechanically most enigines are aroun 90-95% mechanically efficeint

When factoring in thermal efficiency the result falls to around 80% as a maximum

Question 5

Thermal efficiency

Answer 5

Closely linked to mechanical efficiency
Defines how effective the engine is at converting the energy contained within the fuel to producing mechanical work

The efficiency in only around 25 25% for standard engine.

Thermal efficiency is increased as the compression ratio increases

Question 6

Rpm gauge

Answer 6

Measures crankshaft RPM

Question 7

Manifold prssure gauge

Answer 7

Measures manifold pressure in HG in

Question 8

Boost pressure gauge

Answer 8

Measures manifold pressure in PSI relative to sea level pressure

Question 9

Oil pressure gauge

Answer 9

Measures the oil pressure just after the pressure filter

Question 10

Oil temp gauge

Answer 10

Measures the oil temp in the oil return line

Question 11

CHT guage

Answer 11

Temp of the hottest cylinder

Question 12

EGT

Answer 12

Measures the temp in the exhaust gas stream

Question 13

Fuel pressure gauge

Answer 13

Measures fuel pump output pressure

Question 14

Induction temp gauge

Answer 14

Measures the temp at the carburettor inlet

Question 15

Pre start inspection

Answer 15

On inverted or radial engines ,the propeller should be pulled through to prevent hydraulicing

Question 16

Starting procedure precautions

Answer 16

Starting procedure:
~shut down if warning light remains on for 30sec after engine start
~positive oil pressure should be indicated within 30 sec of eng start
~in very cold conditions increased oil viscosity may make starting more difficult

Question 17

After start checks and testing

Answer 17

~individually check magnetos to ensure both ignition circuits are working normally
~carburettor heat should be off when the engines is running on the ground
~prolonged idling should be avoided to avoid plug fouling

Question 18

Procedure for changing power settings

Answer 18

~slow smooth throttle movement to reduce engine stress
~reduced to max continuous as soon as is safely possible after take off
~constant speed propellers : rev up ,throttle back

Question 19

Shutdown procedure

Answer 19

~allow engine to cool at low RPM before shut down

~do a dead cut check to confirm that both ignition circuits are properly earthed

Question 20

Engine running faults

Answer 20

~excessively weak mixture could cause excessive CHT
~rough running could be caused by carburettor icing ,moisture in the ignition circuit ,problems with fuel delivery or uneven compression in the cylinder
~black exhaust smoke indicates an excessively rich mixture
~blue exhaust smoke oil is burning (worn or broken pistons)
~ high CHT on the ground ( cowl flap could be closed)