Engines and fuel

Question 1

Engine stages overview

Answer 1

EA:
LP compressor Fan (N1) driven by LP turbine
HP compressor (N2) driven by HP turbine
Combustion chamber with 2 igniters (A and B)
Accessory gearbox driven by HP rotors

RR:
Same but has intermediate compressor driven by intermediate turbine as well

Question 2

Accessory gear box

Answer 2

Both:
Driven from HP rotor drives:
1 engine driven generator
2 engine driven hyd pumps
Pneumatic starter
FADEC dedicated alternator
Oil pumps
Engine fuel pumps

Question 3

FADEC controls

Answer 3

Both:
1 per engine:
Engine envelope
Power management
Ignition and starting
Engine parameters and display

Both:
Normal (THR is primary engine parameter)
Degraded (N1 primary parameter)

RR also has ALt mode where N1 Pri computation but THR displayed on EWD

Question 4

Reverse thrust

Answer 4

Both:
Only on inboard engines; powered electrically (not hydraulically)

3 protections exists to stop deployment in cruise

Question 5

Starting

Answer 5

Both (in flight or on ground):
Fadec controls system as follows:
Bleed air supplied from another engine, APU of HP ground air, drives air turbine starter
Starter drives HP rotor via accessory gearbox
Fuel supplied to combustion chamber which is ignited by igniters

In flight, FADEC automatically chooses between windmilling start or starter assisted (APU/other engine)

Question 6

FQMS (Fuel Quantity and Management Systems)

Answer 6

2 systems manage fuel

Question 7

11 Fuel tanks

Answer 7

5 on each wing:
* 2 feed tanks (feed APU and engines)
* 3 transfer tanks (1 outer, mid and inner; enable fuel transfer between wings)

The systems are considered separately

1 tank in THS

Question 8

Fuel feed system - Collector tanks

Answer 8

Each of the 4 Feed tanks has a Collector tank (1300-1500 kg capacity), always kept full (prevents cavitation), each of which has 2 identical fuel pumps

Each pump operates continuously and supplies its own engine
* all pumps can supply all engines via X-feed

Gravity feeding is all pumps fail

Question 9

APU fuel feed

Answer 9

Usually via Fuel feed tank 4, but can be from other feed tanks or APU feed pump

Question 10

Fuel transfer system

Answer 10

Uses wing (inner, mid, outer) and trim (THS) transfer tanks

4 automatic transfer types:
* Load alleviation (reduces structural load after TO/before landing)
* Main transfer (fills FEED TKs)
* CG transfers (to control the CG)
* Cold fuel transfers (to avoid fuel freezing in the outer tanks

2 additional transfers may be selected:
* Refuel/defuel on ground
* Jettison in flight (only transfer fuel can be dumped, not feed fuel)

2 galleries (sets of pipes - FWD and AFT) link the transfer tanks - Trim pipes join Trim tank to these galleries

XFR (transfer) pumps transfer the fuel between tanks

AFT and FWD galleries can be used simultaneously and independently

Question 11

Main transfer sequence

Answer 11

1. Feed tanks feed Feed collector tanks which supply engines
2. After TO, to alleviate load, inner (mid if inner empty) fuel transfers to completely fill outer tanks
3. Inners supply Feed tanks when Feed tanks get to certain threshold (maintain these from threshold to threshold + 1000 kg)
4. When Inner empty, Mids supply Feed tanks
5. Main transfer from Trim to Feed Tanks when any Feed Tanks reaches 6 000 kg with Inner and MID Tanks empty (continues until TRIM empty)
   * Alleviation transfer from Trim FWD if CG becomes too AFT
6. Finally OUTER transfer which can be:
   * Load alleviation (transfer fuel to INNER/MID/Feed tanks before landing)
   * Main (to supply FEED tanks - maintains Feed tanks 4000-4500 kg when INNER/MID and TRIM tanks empty)
   * Cold fuel transfer (happens if any OUTER tank fuel temp <-35 degrees)