ENGINES EXAM REVISION Flashcards
1
Q
What is the aircraft powered by?
What do they operate at and what is this called?
A
4 Allison T56-A-15 Engines
100% RPM at all times during flight, called constant speeding
2
Q
What 3 main assemblies can the engine be broken down into?
A
- The power section
- The torque meter and tie struts assembly
- The reduction gear assembly
3
Q
What 4 components does the power section contain?
A
- 14-stage axial flow compressor
- Combustion section
- 4-stage turbine
- Accessory drive housing
4
Q
What 4 components does the torque meter and tie struts assembly contain?
A
- Torque shaft
- Reference shaft
- Torquemeter
- 2 tie struts
5
Q
Engine rated to what SHP?
A
4910SHP
6
Q
What is the Torque indicator?
A
An instrument that registers engine power, in inches per pound (not horsepower)
7
Q
What is the max allowable indicated torque?
In SHP?
A
19600LBS
4300SHP
8
Q
How much horsepower is used to drive the prop and why?
A
100HP is used to drive the reduction gearbox & accessories, leaves 4200HP to drive the prop
9
Q
What does 100% rpm equate to in rpm?
A
13820rpm
10
Q
What is the reduction ratio? To what rpm?
A
Reduction gear assy has a 13.54:1 ratio, the prop therefore rotates at 1021rpm
11
Q
What way does the prop and the core engine rotate?
A
Prop: Clockwise (from rear)
Turbine & compressor: (anticlockwise)
12
Q
What does the air inlet duct do?
What does it consist of?
A
- Ducts air onto the front of the compressor at optimum AoA
- 8 equally spaced struts, an inlet guide vane.
13
Q
What else passed through the air inlet strut?
A
the drive shaft into the accessory drive housing (6 o’clock strut)
14
Q
Describe the compressor assembly
Consists of and what does it do?
A
- 14 stage axial flow compressor with alternate rows of stator & rotor blades.
- Supplies air for combustion, internal cooling and air for the a/c pnuematic system.
15
Q
What is the purpose of Compressor/acceleration bleed valves (2)
A
- Unload compressor on start up and acceleration
- Prevent bog down & overtemp on deceleration
16
Q
Compressor/acceleration bleed valves: how many & where? What are they controlled by?
A
- 8 valves
- Mounted on the compressor casing - 4 each at the 5th and 10th compressor stages
- Controlled pneumatically by the speed sense valve
17
Q
How do the Compressor/acceleration bleed valves operate?
A
- Above 94% rpm: 14th stage (ultra compressed) air is ducted onto the top of the valves - holds them closed
- Below 94% rpm: the top side of the valves are vented to atmosphere - the compressor with then open the valve from underneath
18
Q
What does the diffuser do?
What else is mounted in the diffuser?
A
- Directs compressor discharge air into combustion section.
- The 6 fuel nozzles
19
Q
What else does the diffuser provide?
A
Air is bled off the diffuser for a/c pnuematics, eng anti ice & compressor/acceleration bleed valves via a check valve
20
Q
Describe the combustion section
A
Can-annular type
21
Q
How many ignitor plugs are there in the combustion section and where are they?
A
- 2 igniter plugs
- Located on the outer section & extend into the combustion liners (cans)
22
Q
How do the other combustion liners (cans) get ignition?
A
The six liners are connected by crossover tubes that provide flame propagation on start up
23
Q
What do burner drain valves do?
A
These draw away any left over fuel left in the combustion section after engine shutdown/failed engine start to prevent hot starts
24
Q
What is mounted on the front face of the accessory drive housing? (4: OOSS)
A
- Oil pump (power section)
- Oil filter (power section)
- Valve (speed sensitive valve)
- Switch (speed sensitive switch)
25
What is mounted on the rear face of the accessory drive housing? (4: FFFE)
- fuel Pump
- fuel Filter
- FCU
- External oil scavenge pump
26
What three functions does the TQ meter and tie strut assy provide? (TPL)
- Transmits power from power section to reduction gearbox
- Provides a reference indication of engine power
- Locates RGB to the power section
27
How is TQ measured?
Measured by an exciter wheel & magnetic pickup on both TQ and reference shafts
- The phase shift between the two signals is proportional to the amount of TQ produced by the TQ shaft.
28
What accessories are mounted on and driven by the RGB?
- Generator
- Hydraulic pump
- Oil pump
- Starter
- Tacho-generator
29
What three safety devices are fitted to the RGB?
1. NTS (negative TQ system)
2. Safety coupling
3. Prop brake
30
How does Negative TQ occur?
| Example?
When the prop tries to power the power section instead of the reverse = Uneven balance of power & a yaw motion
E.g. Air gusts, steep/rapid descent, fuel flow interruption
31
How to prevent Negative TQ?
Create aerodynamic load on prop by increasing the blade angle. (Done by the RGB)
32
When does the NTS device operate?
Automatically at -ive 1260 +/- 600 in lbs
33
How does the NTS work? (3)
- Negative TQ condition exists; rotation causes the RING GEAR to move forward
- This overcomes the spring force & moves plungers & actuator rods forward.
- Actuator rod is mechanically connected to the prop & positions prop linkage to increase blade angle
34
Why safety coupling?
If NTS device fails, safety coupling is backup to prevent excessive -ive TQ
35
What does the safety coupling do when what limit is reached?
- Intermediate member will overcome the springs & move aft due to action of helical splines.
- power section decouples from RGB, then the prop
- negative TQ exceeds 6000 in lbs
36
What are the three purposes of the prop brake
- increase rate of deceleration on shutdown
- Prevents windmilling
- Prevents reverse rotation in feather
37
What are the 3 positions of the prop brake & general functions
- Released: during engine ops, held disengaged by RGB oil pressure above rpm >23%
- Applied: as rpm <23% & oil pressure drops, prop brake is applied
- Locked: Attempt to rotate prop backwards induces a lock
38
Run through the basic flow of the oil system
Diagram (for understanding)
39
Oil tank location & capacity
- On top of the engine
| - total capacity 20 US gallons, but limited to 12 gallons. The rest is breathing space
40
What is Nacelle preheat & what is its power source?
28V ISOL DC
| Allows hot air from bleed air system to warm engine nacelles prior to start
41
Requirements for Nacelle preheat (3)
| Source of Bleed Air
- A/C on ground
- Condition lever in ground stop or feather
- Only used below -18deg C
APU only source of bleed air
42
Oil section: what regulates the oil output pressure?
| To what limits?
A pressure regulating valve
| 50-60psi
43
Limit for RGB oil pressure?
| What is the rule for adjusting?
150-250psi
| A pressure adjusting valve should only be adjusted to INCREASE pressure as the system wears
44
What are the two main scavenger pumps? Purposes?
Main scavenge
- Scavenges oil from RGB
Nose scavenge pumps.
- Scavenges oil from prop shaft bearing & other areas when a/c is in low nose attitude
45
What is the component that controls oil temp?
| Powered by?
Oil cooler flap controls air flow passing through (controlled by a thermostat to maintain oil temp at 80deg C)
Powered by LH DC
46
If the oil cooler flap is left OPEN, what component then regulates the temperature of the oil when it gets too cold/pressure?
A thermostatic bypass valve that bypasses oil around the oil cooling matrix when oil temp is below 68deg C. OR when oil pressure is 50psid across the matrix
47
Major engine controls (3)
- Power levers (LH side)
- Condition levers (RH side)
- Fire handle
48
How does the power & condition levers work
Connected mechanically to a degrees coordinator. Lever positions are measured from a pointer on the coordinator
49
Significant throttle positions (4)
- Max reverse
- Ground Idle
- Flight Idle
- Take off
- Max reverse: 0deg
- Ground Idle: 18deg
- Flight Idle: 34deg
- Take off: 90deg
50
```
Significant throttle ranges (3)
- Ground (Beta) range
- Flight (Alpha) range
- LSGI range
- Temp limiting range
- Temp control range
(what is the position between the last two ranges)
```
- Ground (Beta) range: 0-34deg
- Flight (Alpha) range 34-90deg
- LSGI range: 9-30deg
- Temp limiting range: 0-65deg
- Temp control range: 65-90deg
Crossover (65deg)
51
How does the condition lever work?
| Positions and what each one does? (4)
connected mechanically to the coordinator & has four positions
- Feather: Mech/Elec feathers prop & closes fuel shutoff valve
- Ground stop: Elec closes fuel shutoff valve
- Run: arms engine start circuits
- Air start: arms engine start circuits & energises prop aux pump
52
What electrical functions will occur if a fire handle is pulled? (FOFFFEEPEE)
- Fuel shutoff valve on FCU closes
- Oil shutoff valve closes
- Firewall hydraulic pressure shut off valve closes
- Firewall hydraulic suction shut off valve closes
- Firewall fuel shutoff valve closes
- Engine bleed air shut off valve closes
- Engine start circuits de-energised
- Prop feathered
- Extinguisher directional valves positioned
- Extinguisher agent discharge switch armed
53
General function of the start cycle
Almost completely automatic;
1. Engine start button depressed
2. Pneumatic starter motor cranks the engine
3. Automatic sequence of electrical operations causes engine to accelerate to self-sustaining RPM
54
What is the speed sense switch & what are the 3 positions?
Driven by accessory drive housing, consists of three switches that are actuated by flyweights at 16, 65 and 94% RPM to auto control fuel and ignition during the engine start cycle.
55
speed sense switch, what occurs at 16% (5)
- Fuel shutoff valve in FCU opens
- Fuel enrichment valve (if selected) opens
- Paralleling valve opens
- Drip valve energised closed
- Ignition energised
56
speed sense switch, what occurs at 65% (3)
- Paralleling valve opens
- Drip valve de-energised (held closed by fuel pressure)
- Ignition de-energised
57
speed sense switch, what occurs at 94% (2)
- TD control switches from 'start limiting' to 'normal limiting'
- TD valve max take stop switches from 50% to 20%
58
Fuel flow diagram - be able to explain;
| - Series
- Series: paralleling valve is de-energised in "open" position, normal engine operation. (sec pump - paralleling valve - primary pump - high pressure filter)
59
Fuel flow diagram - be able to explain;
| - Parallel
- Parallel: paralleling valve is energised closed between 16-65% = higher pressure & flow for engine start. (sec pump-check valve = higher pressure - activates pressure switch - turns on SEC FUEL CAWS- primary pump draws fuel from check valve-outputs from sec & primary pump join prior to high pressure filter
60
Fuel flow diagram - be able to explain;
| -Enrichment
Allows for unmetered fuel to bypass the FCU during start = initial burst of fuel during start to aid in light-off during cold wx operations
61
Purpose of fuel heater strainer
| What meters fuel temp
- Uses oil to heat the fuel to prevent ice crystals from forming from water in the fuel. Also lowers fuel viscosity
- Thermostatic bypass valve bypasses oil as necessary to keep fuel temp at 75deg F
62
What is the FCU & what does it do? (4)
Hydromechanical device that schedules fuel flow to the engine for;
- Throttle position
- Compressor inlet temperature
- Compressor inlet pressure
- Engine speed
63
What percentage of fuel will the FCU schedule to send into the engine? (what is excess for)
120%
| Excess is used to power the TD valve
64
What is the purpose of LSGI (3)
| How is it achieved?
- Reduce noise
- Reduce thrust
- Reduce fuel flow
Achieved by resetting the FCU governor spring tension to reduce rpm to 69-75.5%
65
What is the TD valve & what is its purpose
| What does it respond to?
The temperature datum valve is a spring loaded motor operated bypass valve that controls the amount of fuel going into the engine from the FCU. (responds to inputs from the electronic fuel correction system to take or add more fuel as required)
66
TD valve; NULL position
The de-energised position of the TD valve that bypasses 20% of the fuel back to the inlet side of the fuel pumps.
67
TD valve; TAKE
Bypassing more fuel is known as TAKE and can take up to 20-50% more fuel
68
TD valve; PUT
Bypassing less fuel is known as PUT and can add up to 15% more fuel
69
Temp limiting range; <94% RPM
- TIT
- TD valve limit
- 830deg TIT
| - Up to 50% Take
70
Temp limiting range; >94% RPM
- TIT
- TD valve limit
- 1067 to 1083deg TIT
| - up to 20% TAKE
71
Temp controlling range; >94% RPM
- TIT
- TD valve limit
- 1067 to 1083deg TIT
- Up to 20% TAKE
- up to 15% PUT
72
What is the temp limit for crossover?
TIT change to 820 +/- 20deg when advancing through crossover
73
Systems controlled by the ice detection system; (3)
| What is the limit for the ice detection switch?
- Engine inlet Air duct anti-icing
- Prop anti-icing
- Radome anti-icing
74
What is the limit for the ice detection switch?
do not hold in the No.2 or No.3 position for longer than 5 secs.
Can be repeated but only after a 5min wait (to allow detector to cool)
75
What does the extinguishing system run off of?
The BATT BUS
76
```
EGT (Exhuast Gas Temp) limits;
Continuous Temp
Max Temp
Max RPM
Extra rules x 2?
```
Continuous Temp: 620deg C
Max Temp: 663deg C
Max RPM: 109%
Warm up for 3 mins before applying bleed air load
Cool down with no bleed air load for 2mins prior to shutdown
77
APU starter cycle limits
1min ON, 6min OFF
1min ON, 6min OFF
1min ON, 30min OFF
78
APU Sequencing switch: Percentages & what happens at each?
```
- 35%
De-energises starter
De-energises amber light
-95%
De-energises ignition system
Energises on-speed green light
Arms the load control circuit
-110%
De-energises all electrical circuits causing fuel shutoff solenoid valve to close
```
79
Methods of Cooling APU compartment (3)
- Electric cooling fan
- Accessory cooling fan
- Exhaust eductor
80
What does the ADV flag on the EIDS indicate?
Will illuminate when one screen only is being displayed due a fault, and the current display detects that the other display is unable to display data & out of limits events
81
Engine shutdown list (11)
Run Lieutenant FOT on the piss
RUN LT FOT OTP
- Roughness/Vibe
- Uncontrollable power
- Nacelle overheat
- Leak (excessive visible fluid leak)
- Throttle control failure
- Fire (engine fire)
- Oil pressure (uncontrollable drop in oil pressure)
- Turbine overheat
- Oil Temperature (uncontrollable rise in oil temp)
- TIT (uncontrollable rise)
- Propeller (certain malfunctions)
