Aircraft - Airframes & Systems Flashcards
(317 cards)
1
Q
EASA standards publication for small and large aircraft
A
Small - CS 23
Large - CS 25 (>5700kg)
2
Q
Pascal’s law
A
If a force is applied to fluid in a confined space the force is felt equally in all directions
3
Q
Hydraulic calculation for force/pressure/area of surface
A
Force (N) = Area (m2) * Pressure (Pa)
F=AP [FAP]
[or pounds per square inch - psi]
4
Q
Calculation for energy of hydraulic movement (work done)
A
Distance moved * Force
This stays constant so used in calculations between two pistons.
5
Q
Assumption required for hydraulic calculations to be correct
A
Needs to be a perfect fluid with zero compressibility
[In reality we accept compressibility below 10% for 32 tons per sq in, or 70,000 psi]
6
Q
Properties of good hydraulic fluid
A
- Thermal stability (low freezing, high boiling point, range -50 to 100C)
- Corrosion resistant
- High flashpoint & low flammability
- Low volatility (does not vaporise at pressure)
- Low viscosity (not sticky!)
- Incompressible
7
Q
Hydraulic fluid description, colour:
- DTD 585 / DEF STAN 91-48
- SKYDROL
A
DTD 585 / DEF STAN 91-48: Red, refined mineral based (petroleum)
SKYDROL: Purple/Green, phosphate ester based oil, FIRE RESISTANT, less prone to cativation, synthetic based
8
Q
How to identify hydraulic fluid?
A
Colour is an indication, but specification can only be confirmed by consulting aircraft manual and using fluid from sealed, labelled containers
9
Q
Material used for seals (depending on fluid used)
A
Synthetic rubber
DTD 585 / DEF STAN 91-48: Neoprene
SKYDROL: Butyl
10
Q
Concerns around handling hydraulic fluids
A
Skin and eye irritants - wash with lots of water
Not flammable however as this would make them unsuitable (DTD 585 kerosene based so slightly flammable but high flash point)
NOT corrosive, BUT eats through paint which exposes materials to corrosion.
11
Q
Passive vs Active hydraulic systems
A
Passive has no pump, just transfers force from input to output (e.g. brakes on light aircraft)
12
Q
Open-centre vs closed hydraulic system
A
Open-centre system is simple but only allows one component to be activated at a time (more typical in light aircraft with few hydraulic systems e.g. flaps, landing gear).
13
Q
Pressure categorisation of active hydraulic systems
- Low
- High
- Typical
A
Low < 2,000 psi
High > 2,000 psi
Typical = 3,000 psi
14
Q
Advantage of higher pressure hydraulic system
A
Smaller volume required, so smaller bore pipes (easier to route, reduced fluid quantity and system weight).
15
Q
Purpose of reservoir
A
- Account for jack/actuator displacement
- Thermal expansion
- Small leaks
16
Q
How is positive pressure maintained at hydraulic pump inlet
A
Reservoir is usually pressurised, or alternatively by being located higher than the pump or being “bootstrapped”.
Non-pressurised reservoirs risk boiling at high altitudes, leading to cativation of pumps or gas in lines and actuators, so pressurised is standard.
17
Q
How is hydraulic reservoir pressurised?
A
The Pneumatic system
18
Q
Hydraulic reservoir main connection and emergency connection differences
A
Main connection will be via a stand pipe, so that in the event of a leak some volume remains.
Emergency (hand pump) connection is directly to the bottom of the reservoir to allow that extra to be used in an emergency.
[Note: Wording may say stand pipe purpose is to provide an emergency supply]
19
Q
Case drain filter
A
Filter fitted to constant pressure pumps to help monitor pump condition
20
Q
Blocked filter false warnings
A
High viscosity fluid at low temperatures can cause the block filter indicator button to trigger. A bi-metal spring can be used that inhibits the button at low temperatures to prevent this false warning.
21
Q
Filter material maintenace
A
Paper filters will be discarded.
Wire cloth can usually be cleaned (ultrasonic recommended, or trichloroethane as temporary measure).
22
Q
Hydraulic pressure & thermal release valves
A
Use a ball held in place by a spring. Opens at the cracking pressure, closes at the re-seating pressure (less than cracking).
Same device for pressure or thermal (expansion) release, thermal will be at higher pressure setting.
23
Q
Full flow relief valve (FFRV)
A
Pressure (/thermal) relief valve that can relieve the total flow of the pump if called for.
24
Q
Hydraulic filter
A
Fitted downstream of pump (sometimes to reservoir return) to filter debris greater than 25 microns.
Fluid flows into a “bowl” and must pass through cylindrical filter element in centre to exit.
Pressure relief valve may trip a red button to indicate “popped” filter.
Pressure differential will indicate clogged filter which triggers a warning light to cokpit.
25
Hydraulic filter positions
In both pressure (after pump) and return lines
26
3 (typically) backup hydraulic power unit types
Pneumatic (air turbine motor) - ATM
Ram air turbine - HYDRAT/RAT
Hydraulically driven (Power Transfer Unit) - PTU
27
Main uses of hand pumps (non emergency)
- Ground servicing without engine
- Pressure testing of joints
- Operation of cargo doors (etc.) without power
28
Constant displacement vs constant pressure pumps
Constant displacement - keeps delivering at the same rate, requires an automatic cut out valve to prevent excess pressure.
AKA fixed volume or constant delivery
Constant pressure - reduces delivery (VARIABLE VOLUME) as output pressure increases
AKA variable volume
29
How does constant displacement pump work?
## Footnote
Body of pump angled so 7 or 9 pistons get opened and closed as driveshaft rotates
30
How does constant pressure pump work?
A control (or hanger) piston is connected to pump outlet feed, which pushes a swash plate.
The angle of the swash plate adjusts the travel of the pistons, from zero with flat swash plate to maximum with it angled (creating forward and back movement as swash plate turns).
31
Constant pressure pump max/min stroke description
Maximum stroke is when output pressure is low (e.g. component just activated), control piston is not under pressure and yoke allows inlet valve fully open.
Minimum stroke when control piston pressured by outlet pressure to close the inlet valve.
32
When is automatic cut out valve (ACOV) needed?
For constant delivery pumps ACOV provides an idling flow back to reservoir when system pressure has been reached (i.e. no components in use).
33
How does ACOV work?
A feed from the system line drives a piston which opens a poppet valve when required pressure is reached ("kicked out"). This valve connects the pump outlet to the reservoir allowing an idling flow through the pump, bypassing the system.
When system demand reduces pressure the popped valve "kicks in".
34
Additional requirement for ACOV system
Need an accumulator (and NRV) in the system to maintain pressure, otherwise ACOV will continually open and close (hammering) due to leakages or use of the system.
35
ACOV diagram
36
How does accumulator work?
Contains nitrogen under pressure (added via charging point) separated via separator, floating piston or flexible diaphragm from a hydraulic liquid.
It stores hydraulic fluid under pressure, allowing for thermal expansion, dampening pressure fluctuation, providing emergency pressure and reducing ACOV activation frequency.
37
Effect of incorrect gas pressure setting in accumulator?
Hammering
Will initially be charged to minimum system pressure (around half max pressure). Gas compresses when system pressure is on and thus can push back when it reduces.
38
Blocking valve
## Footnote
Reduces engine demand on start-up and in case of fire. System pressure opens blocking valve against spring normally. When blocking solenoid is activated, pressure on both sides of blocking valve allows spring to close it, pressure builds up and constant pressure swash plate forced to neutral.
39
Power Transfer Unit (PTU)
For when the main hydraulic pump fails, NOT in case of hydraulic system fault (overheat, leak). Allows one hydraulic system to transfer power to another (can be reversible). A hydraulic pump is in the system which is driven by the hydraulic motor in that system and drives a driveshaft to the other system.
Fluid is NOT moved between the systems, just power.
40
3 types of jack (actuator)
Single acting actuator - simple piston and spring
Double actuator - fluid on both sides, can have rod on one or both sides. Either balanced (e.g. nosewheel left/right) or unbalanced with different surface area on each side, for different force in different directions (e.g. landing gear up/down).
41
Rotary actuator
This is a hydraulic motor where hydraulic flow causes rotation of a motor, which drives a driveshaft. Speed of the motor is dependent on rate of flow.
Used where rotary rather than linear motion is required as an output.
42
Hydraulic lock
When fluid is trapped between a piston and non-return valve, preventing the piston from moving.
May be used purposefully to lock an actuator.
43
Pressure maintaining valve (PMV)
AKA priority valve.
Cuts off or reduces pressure to secondary systems to ensure pressure is available for priority systems
44
Pressure reducing valve
## Footnote
Reduces main system pressure down to suitable level for certain systems (e.g. wheel brakes).
45
Restrictor valve/choke
- examples
Allows full flow in one direction and restricted flow in the other direction.
Often fitted to the "up" side of flap and landing gear to slow down retraction.
46
2 way restrictor valve
Basically a narrowing of the pipe, restricts flow in both directions (e.g. nose gear requires less force than main gear)
47
Throttling Valve
- phrase for what it aims for
Complex version of a restrictor valve. Adjusts based on the supply flow to ensure a CONSTANT FLOW RATE to a component.
48
Flow Control Valve
Similar to throttling valve. Positioned upstream of hydraulic motors to ensure an even flow rate and thus constant speed. As with throttling valve, increased flow closes the valve and slows flow down.
49
Selector valves - rotary/linear
Control hydraulic flow to activate components.
Rotary has a circular junction box arrangement which connects different lines when turned.
Linear has piston type internals which connect different inlets and outlets as they are moved. AKA spool valve or pilot valve.
50
Rotary selector valves with double/single actuators
A four port rotary selector will be used with a double actuator, providing a fluid path from or to the reservoir.
A two port rotary selector is used with a single acting actuator.
51
Shuttle valve
Connects two inlets to the system. When pressure is lost in the main supply, the shuttle will be pushed across by the secondary supply inlet which is then connected to the system to provide an alternative supply.
52
Sequence valve
Allows more than one jack to be activated in a particular sequence.
Mechanical or hydraulic!
Pressure from upstream where first jack is connected pushes a sliding piece against a spring. A second connection from the upstream flow is then opened up to the downstream flow where the second jack is found.
53
Hydraulic fuse
Limits flow of fluid so that a major leak doesn't allow all fluid to be lost, e.g. across brakes
Situated upflow of a component, fusing if flow is too high, so that component fails but rest of the system doesn't.
54
Backing ring
Hydraulic seal that prevents the seal from moving out
55
Modulator
Used for modulation in old anti-skid (maxaret) systems.
Basic sprung piston with same stroke volume as brakes. Small orifice in the piston head allows fluid through. Maxaret removes small amount of fluid upstream of modulator if it detects a skid and the orifice in modulator allows temporary brake pressure release.
56
Light aircraft power packs
AKA Open-centred
On-demand hydraulic system that powers on to do one job (eg landing gear up/down) then powers down.
Pump is operated in one direction or the other and hydraulic lock used to keep it in position (with thermal relief for expansion).
Pump is ONLY on when an actuator is travelling.
57
Pneumatic systems advantages
- Air is free
- Lighter than liquid
- No fire risk
- No viscosity change due to temp
- No return lines needed
58
Pneumatic systems disadvantages
Compressibility of air (so less precise, no good for flight controls)
Hard to detect leaks
59
2 main pneumatic systems
Air conditioning
Pressurisation
60
3 emergency systems which use pneumatics
Emergency brakes - compressed air via shuttle valve and control valve, air pressure depends on handle selection
Fixed fire extinguishers - e.g. in engine bay, use nitrogen
Emergency undercarriage - Uses nitrogen to prevent fire, backup blowdown system in case hydraulics fail
61
Other pneumatic systems
Anti-icing (hot air or boots)
Hydraulic systems (nitrogen accumulator)
Oleo legs
Door seals
Air starters (main engines started using air from APU)
Air turbine motors (hydraulic pumps or AC generators)
Jet pipe nozzle control (military after burner)
Thrust reverser control
62
Basic stress forces
- Tension
- Compression
- Shearing
63
Combination stress forces
Bending (compression inside, tension outside, shear in centre)
Torsion (tension at outer edge, compression in centre, shearing over whole structure)
64
Stress
- Description
- Units
The internal force which resists an external load (e.g. tensile load creates tensile stress).
"Force per unit area"
65
Stress corrosion linked to...
Tensile load (& corrosive conditions)
66
Strain
The deformation caused by action of stress on a material
67
Buckling
When thin sheet material is subjected to end loads, or ties are subjected to compressive forces
68
Elastic limit
The limit of stress force up to which a material will return to its original form.
Beyond this, permanent deformation is called plastic deformation.
69
Ultimate stress
The fail point for a single application of a static load.
Repeated loading and unloading at levels below this (cyclical loading) will cause metal fatigue and mean the structure will fail before ultimate stress level.
70
Design Limit Load (DLL)
Design Ultimate Load (DUL)
DLL is the maximum load the designer would expect (transport +2.5, utility +4.4, aerobatic +6).
DUL is a safety factor of 1.5x. The structure must be capable of withstanding the DUL without collapse.
71
Fail safe / damage tolerant principle
In the case of failure in a given structural component, there is another "route" through which the same loads can be withstood. The aircraft can continue to safely withstand normal loads until the next periodic inspection.
Aka redundancy.
72
Safe Life principal
Where fail safe/redundancy not practical (e.g. landing gear) instead determine a maximum number of cycles (by hours, # landings, calendar time etc) and replace the component after that number.
73
Damage tolerance principal
Components that are likely to be subject to damage should be designed to continue to function despite damage, eg wingtips, landing gear.
74
Maintenance Strategies
Hard/fixed time: Replacement of safe life components at established point
On condition: Replacing a part when it is observed to be defective
Condition monitoring: Exception to "on condition", when a component is defective but left until the next service interval. Needs to be monitored at regular intervals until replaced.
75
Table of failure types
76
Station numbers
Distances in a given plane measured from a zero datum (water line for vertical, fuselage station for longitudinal) to identify position of components.
77
Fuselage purpose
Carries aircraft payload and flight crew in suitable conditions.
Provides flight crew with effective position to operate aircraft.
78
Two types of stress due to pressurisation
Axial stress (stretches fuselage longitudinally)
Hoop stress (expands cross section of fuselage), due to pressurisation, taken mostly by the skin
79
3 types of fuselage construction
Truss/framework
Monocoque
Semi-monocoque
80
Monocoque vs semi-monocoque
Monocoque only has formers and an outside skin, with former CREATING the shape and skin taking the loads.
Semi-monocoque (aka stressed skin) has stringers (longerons) connecting the formers which spread the stress.
81
Machined skin
Profiling of the (usually) inner skin (eg corrugation) to increase strength. Can be done with machining or chemical etching, complex shapes can produce the desired characteristics. Important for semi-monocoque designs to achieve required strength.
82
Frame
Vertical structure which takes major loads and gives aircraft its shape, holes to reduce weight.
83
Bulkhead
Frame that is solid (although may have access doors)
84
Firewall materials
Heat resistant stainless steel or
Titanium Alloy
85
Doublers
Reinforcements around cutouts in stressed skin
86
Aeroelastic flutter
- description
- 3 components
Unstable, self-excited structural oscillation at a definite frequency where energy is extracted from air flow by the motion of the structure.
Caused by combination of 1) Inertial 2) Elastic and 3) Aerodynamic forces. Need to adjust one of the 3 to avoid oscillation at resonant frequency.
87
Adjusting inertial forces
Requires moving weight around. Heavy items resonate at lower frequency than light items.
Moving engine positions along the chord, or span wise, or fuel tanks to different places (including fuel usage during flight) have an effect. Changing CoG of control surfaces affects their flutter too.
88
Adjusting elastic and aerodynamic forces
Elastic - Adjusting stiffness of wings (resistance to bending or to torsion)
Aerodynamic - Try to design so that the speed which causes maximal flutter is outside the normal operating range of the aircraft.
89
Main requirement for avoiding flutter in flight
Stay within flight envelope, most importantly in relation to SPEED
90
Flight deck window structure
Toughened glass panels with clear vinyl interlayer.
Electrically conducting layer inside outer glass panel used for heating (to 35C)
91
Direct Vision window
Both pilots must have clear portion of windshield during precipitation.
Required opening window for first officer in case of demister failure (when depressurised).
92
Passenger window construction
Two acrylic plastic panels with airtight rubber seals
93
Window impact requirement
4lb (1.8kg) birdstrike at cruise speed
94
Eye reference position
- nominal (central) angle
- optimum and maximum ranges
Vertical: Nominal is 15 degrees below horizontal. Optimal area 15 degrees either side (so from horizontal to 30 degrees down). Maximal range is 20 degrees below nominal and 40 degrees above.
Horizontal: Nominal is centre line. Optimal range 15 degrees either side, maximal 35 degrees either side.
95
Force types on cantilever wing
Bending (weight of wing, including when on ground)
Twisting (in flight due to use of aileron)
96
Methods for reducing bending stress on wings
Aileron up-float
Engines and fuel tanks on/in wings
97
Torsion box
Formed by front and rear spars, ribs, stringers and skin in wing. Resists the bending and twisting loads in the wing.
98
Typical wing materials
Aluminium alloys for major structural components
GRP, CRP (glass/carbon reinforced plastic) or honeycomb for fairings, control surfaces etc.
99
Duralumin
Copper-based aluminium alloy - Strong, Light & Cheap.
However corrosion resistance is poor unless coated with pure aluminium (Alclad).
Can't be heated above 120C so not suited to welding or flight above speed of sound.
100
What does aluminium corrosion look like?
White or grey spots or powder
101
Common metal appearing in alloys
Copper
102
Composite materials
- description
- gradual or sudden failure
- examples
Consist of a bulk material (the matrix) with reinforcing fibres of some kind, which give strength.
Good resistance to corrosion, tend to fail gradually rather than suddenly like metals.
E.g. Kevlar, Aramid
103
Honeycomb material
Thin layers around honeycomb core.
Strong in direction of the honeycomb, light due to hollow areas.
104
Worst and best operating environments for corrosion
Tropical, industrial, marine the worst.
Arctic & rural environments the best.
105
Two types of corrosion
Oxidation - Metal reacts with environment without electrolyte (dry)
Electrolytical - Requires electrical conducting electrolyte (wet). Two differing metal surfaces become anode and cathode with material transferred from anode to cathode.
106
Max descent velocity for landing gear
10ft/sec
107
Brake fade
Reduced brake performance due to overheating (NOT carbon fibre!)
108
Brake dragging
Caused by incorrectly set brake returns, leading to small amount of permanent braking
109
What position is brake wear checked in?
With brakes applied
110
Do brakes work better when hot or cold?
Steel brake discs work better when cold
Carbon fibre brakes work better when hot
111
Taxi braking with steel and carbon fibre brakes
Steel brakes wear more with time of application, so apply a little bit regularly and try to keep a constant low speed.
Carbon fibre wear more with number of applications, so higher acceleration and a single application of brakes preferable.
Safety and passenger comfort still the priority!
112
Brake pressure dumping
Brakes designed to provide force sufficient for wet conditions, so in dry conditions force is greater than landing gear can tolerate. A brake torque limiter dumps pressure back to the hydraulic system when torque limits reached to prevent damage.
113
Brake wear adjuster
Retraction pin indicates distance between torque plate and pressure plate, which indicates level of brake wear.
Markings on the retraction pin show limits.
114
Basic anti-skid functionality
Active during take off and landing (when operative), if a wheel stops, sufficient brake pressure is removed to release brakes until wheel spins up.
Called "locked wheel skid control".
115
Anti-skid speed range
ASB not active below 20kt (taxi speeds) so aircraft can be brought to a stop
116
Maxaret anti-skid
Hydro-mechanical system that mechanically senses wheel speed and opens a valve when it is below a certain speed, releasing some of the hydraulic pressure in the braking system.
117
Electronic Anti-Skid
- Description
- Inputs (3)
Uses tachogenerator on EVERY wheel to detect rotation speed and sends a signal when it drops too low.
Either signal to a brake unit to release brake pressure, or if manually braking to maintain the appropriate "slip ratio" to maximise retardation.
- Idle wheel speed (measured)
- Braked wheel speed (measured)
- Desired wheel slip rate
118
Touchdown and bounce protection
Prevent application of brakes on touchdown. Can prevent braking even if full brake force from pilot (not recommended in any case).
Bounce protection re-engages this protection in case of a bounce to ensure wheels don't lock on second contact.
119
Impact of failed anti-skid on landing distance
Extra 50% landing distance
120
Auto-braking system (ABS)
- Description
- Factors impacting deceleration
- Requirements to work
Slows aircraft to a stop with constant G force (i.e. rate of deceleration) to maximise comfort.
Will achieve required deceleration regardless of weight, but slippery surface might require anti-skid modulation so could limit deceleration.
Needs anti-skid to work and won't work on alternative brake system.
[Note ABS not same as ASB (anti skid)]
121
Rejected take off (RTO) braking
Rejected take off results in maximum braking force, which trashes the tyres. This is a higher level of braking than the strongest setting of auto-brake.
As with auto-brake, manual braking cancels it and reverts to manual with auto-skid.
Armed during taxi, activates when speed over (eg) 70kt and thrust to idle.
122
In-flight braking
Brakes applied when wheels are up to prevent damage.
As nose wheel doesn't have brakes, a "snubber" is used to stop the wheel.
123
Emergency brake system
- required ability
- lost functionality
Must be able to stop the aircraft within 1.5 normal stopping distance.
Anti skid will not be operational.
Note that some braking will be available from the accumulator if the hydraulics system fails.
124
Typical aircraft tyres:
- Large or small
- High or low pressure
Small high pressure
125
2 wheel types
Split hub - two sides cross bolted
Detachable flange - lock ring holds tyre in place, pressure forces tyre onto lock ring
[Well type for cars not suitable as tyres too firm]
126
Tyre pressure adjustments from rated level
Add 4% to account for aircraft full weight on the tyres.
Add another 10% for heat due to taxi, take off or landing
127
Response to partial deflation of tyres
Loss of 5% pressure overnight is typical, up to this amount can be topped up.
5 to 10% top up and make a note in the tech log (if it happens twice, replace tyre).
If a deflated tyre is found on a bogie, partner is also replaced. If 2 or more are deflated, all tyres on the bogie are replaced.
128
Ply rating
NOT the number of plys in the tyres, more of a strength rating
129
Radial vs cross ply
Radial ply go radially from one side of tyre to the other, cross ply wrap over each other diagonally.
130
Remoulding
Aka retreading
Adding more rubber to outside of tyres when they are worn out, can be done several times.
131
Taxy speed limit for tyre wear
20kt (22mph)
132
Tyre wear limits
- grooved
- block
Grooved tyres need 2mm depth.
Block tyres need pattern to be discernible.
133
Fire extinguishant for wheels
Dry powder only
Liquid extinguishant can cause heavy steel brake discs to explode
134
Minimum aquaplaning speed
V (kts) = 9 x sqrt(pressure in psi)
[7.7 x for a non-rotating wheel]
135
Fusible plug
Explode at given temperature to allow controlled deflation of tubeless tyres, preventing the tyres from blowing
[Tubeless tyres only]
136
What gas are tyres filled with?
Nitrogen
Max 5% oxygen
137
Tyre cover
This is the tyre outer shell itself, NOT a removable cover!
138
Tyre cover parts
Crown, Shoulder, Sidewall, Bead
139
Tyre pressure levels
Low pressure: Up to 200psi
High pressure: 200 to 315psi [typical for jets]
140
Tyre creep mark sizes & limit on movement
[For tubed tyres only!]
1" for up to 24" tyres
1.5" for over 24" tyres
Creep limit when left edge moves past right edge of the other mark (for example).
141
Chined tyre
Shaping on the shoulder of the tyres deflects water back down towards the runway, to reduce water ingestion by engines
142
Green or grey dots on tyre
Awl vent positions (these let air out of tyre carcass to prevent expansion at altitude)
143
Red dot/triangle on tyre
Lightest part of the tyre, position opposite to the valve
144
Wing growth
This refers to the unexpectedly wide arc of outer wing on swept back wing aircraft when turning during taxi
145
Reversible/irreversible controls
Reversible controls means it is possible for force on the control surface to create a force on the controls.
Fully powered controls are irreversible, power assisted controls are reversible.
146
Cable tension - tools for checking and adjusting
Turnbuckles control the tension in the cable.
Tensiometers measure the tension (with ambient temperature considered)
147
Turnbuckle safety
Check enough thread is in the turnbuckle by checking inspection holes are filled, or if none, check # threads exposed.
Lock the turnbuckle with a wire or other device to ensure no movement.
148
Control stop types
- primary vs secondary
Primary - Restrict the control surfaces
Secondary - Restrict the controls
149
Backlash
Free or ineffective movement of controls when direction is reversed - not acceptable.
150
Take off configuration warning
Similar to landing config warning (alarm if landing gear is up).
Alarm is sounded when on ground, thrust is opened up and config is incorrect (e.g. flaps, trim, doors open, controls locked)
151
How are leading edge devices set?
Usually based on trailing edge device settings, might activate before or after trailing edge are deployed or retracted
152
Leading edge or trailing edge retracted first?
Retract trailing edge first, then leading edge.
153
Load Limiting Devices
Restricts power to hydraulic (or other) systems to extend devices (eg flaps) if speed is too high. This is an example of a blowback system.
More sophisticated systems can retract flaps at high speed and re-deploy when speed reduces again.
154
2 types of spoiler
Flight - linked to ailerons to assist roll
Ground - Require "weight on" status to arm [This is the main requirement for their automatic operation]
Can act in combination on the ground
155
Alpha/speed lock
Prevents retraction of leading edge slats if aircraft is at high alpha or below a minimum airspeed.
156
Flap/slat asymmetry
Sensors detect any asymmetry, which can be catastrophic, and lock devices in place until landing. Capabilities reduces but this is better than being asymmetrical.
157
Autoslat system
Automatically extends slats at high AoA
158
Pitch trim on large aircraft
Typically control wheel controls elevators and trim adjusts the entire tailplane. This ensures that full range of control is available on the elevator, whereas if elevator itself is trimmed its range is reduced.
159
Spoilers on go-around
Sense wheel spin up and automatically retract
160
Adverse aileron yaw solutions (3)
Frise type ailerons
Differential ailerons
Aileron/rudder coupling
161
Inboard ailerons
Less effective as shorter moment arm, but less stress caused when speed is high.
So might have 2 sets of ailerons with inboard being used in clean configuration.
162
Mixer unit
Balance use of ground/flight spoilers or ailerons/spoilers
163
Speed brakes
Achieve high levels of deceleration, for example during turbulence or if quick descent requested by ATC
164
Preventing excessive rudder deflection (2 methods)
Rudder ratio changing - Pedals move fully but reduced rudder range as IAS increases
Variable stop systems - Over 165kts the range of the rudder pedals reduces
165
Mach trim
Automatically trims above a certain speed level to offset nose down effect of mach tuck
166
Q-pot system
Artificial feel system which uses pitot and static pressure to create a force on controls related to EAS (or EAS^2 or EAS^3 depending on importance of high speed vs low speed feel).
167
Spring feel system
Simple artificial feel system which uses springs to create a resisting force on deflection of controls.
No relation between aerodynamic loads on the surfaces and feel on the controls.
168
Artificial feel systems fitted in-line or parallel with control runs?
Parallel
169
Gear change
AKA ratio changing
This is gearing related to IAS such that full deflection of controls leads to full control surface deflection at low speed, but less at higher speed. Rudder is good example.
Related method is blowback (blowdown) where control surface force is constant, but deflection is less at high speed due to higher aerodynamic force.
170
Datum shift
Adjustment of relationship between control column range and control surface range, to ensure full deflection is available. For example in case of stall, full pitch down needs to be available.
171
Power Control Unit (PCU)
Closed loop, servo controller for powered controls.
Pilots control moves a spool type valve. When the valve is moved the hydraulic force moves the control surface AND the body of the spool valve, so as to re-centre the spool valve and remove forces. This allows gradual movements to be instructed and powered via hydraulics.
In case of failure the spool valve body locks to the controls to give direct control of the control surface.
172
Fly-by-wire control modes
Normal
Alternate
Direct
Mechanical back-up
173
Fly-by-wire control path
Analogue signals from controls sent to the Actuator Control Electronics (ACE).
Signals combined with other sources (eg autopilot) and digital signal sent to another ACE.
The second ACE converts to an analogue signal to be sent to the PCU which makes the control movement.
Analogue signals sent back from control surface to the second ACE in a feedback loop.
174
Fly-by-wire redundancy
Entire system redundancy. So failure of a wire means a separate computer can use separate wires to power separate actuators, not just using alterantive wiring.
175
Irreversible flight controls
- Effect of trim (elevator/aileron/rudder) on zero force position of control wheel
- Effect on the control surface
Elevator trim: Zero force position does NOT change (control doesn't move)
Aileron/rudder trim: Zero force position moves "in the direction of the trim". Control surface also moves
176
How dual side sticks interact
Airbus side sticks arithmetically add the forces from each control.
It is possible to LONG PUSH a takeover button to deactivate the other side stick.
The sticks are sprung to neutral and no mechanical connection exists between them.
177
Warnings/signals for:
- Sidesticks both being used
- Sidestick priority selection
If both sidesticks used together get:
- "DUAL INPUT" aural alert; and
- flashing warning light
In case priority is selected get:
- "PRIORITY LEFT/RIGHT" aural alert; and
- lasting visual indication (eg red light)
178
Fluids in oleo pneumatic landing gear system
Nitrogen gas - supports the load of the aircraft and ABSORBS loads
DTD 585 - Controls speed of expansion and contraction (DAMPING of landing load and recoil)
179
Oleo pneumatic gear w/o separator
An orifice allows oil in the bottom to enter the top part when compressed. A metering rod in the bottom part goes through the orifice and is shaped so that it restricts oil flow with more compression.
The variable restriction prevents the aircraft springing back upwards.
180
Oleo pneumatic gear with separator
In large aircraft a separator prevents the oil from mixing with the nitrogen. This is free-floating to allow volumes of oil and gas to change. There are orifices in the oil section between incompressible and compressible sections to slow recoil action.
181
Landing gear stays
Main gear (sideways retracting) require sidestays and forestays (drag stays) to prevent collapse sideways or rearwards collapsing of gear.
Nose wheel requires drag stay if forward retracting, push stay if rearward retracting (I.e. drag forward or push forward from the bay).
182
Anti retract latch
Prevents landing gear being brought up on the ground.
CAN be overridden in an emergency.
183
Geometric vs Hook landing gear locks
Geometric (aka "OVERCENTRE") are mechanical locks only used for down position, which require mechanical force to unlock.
Hook locks engage automatically but release with hydraulic pressure. Normally used as up-locks but can be used as down locks too.
184
Landing gear cockpit ights
Green - Gear locked down
Red - Gear unlocked or position disagrees with lever
No light - Gear locked up
Red and green - Gear lowered by emergency means
Truck light - Bogey out of position for retraction (lever disabled)
185
Emergency landing gear methods (and which is typical)
Typical system is gravity
Can also have backup hydraulic, mechanical, pneumatic (blowdown)
186
Steps in emergency landing gear extension (via gravity)
1) Release hydraulic cut-off valve which holds hydraulic pressure
2) Release locks holding undercarriage doors
3) Release mechanical uplocks holding the gear up
187
Straightening of nosewheel on retraction
Nosewheel (especially) must be straightened on retraction. Upper and lower cams can be used (lower linked to aircraft, upper to the wheel assembly) which mate together in the right direction when weight is off and oleo at full extension.
188
Shimmy
Sinusoidal movement of wheels (especially nosewheel). Need shimmy damper to prevent issues. Also MARSTRAND tyres, which are a dual contact type of tyre (each side resists oscillation).
189
Steering systems on large aircraft
Tiller allows nosewheel up to 75 deg movement (rudder steering only 7 deg to each side).
Main gear also turn (can be automatically activated after 20 deg) in opposite direction to nosewheel.
Tight turns should be avoided though and only very low speed, can damage bogie type gear torque links.
190
Engine Bleed Air System
High pressure and low pressure feeds bleed hot air from 2 stages of jet engine, mixing to achieve required pressure.
Separate feeds from left and right can be mixed via isolation valve.
Hot feeds used for de-icing systems and passed through air conditioning pack for cabin air.
Bleed air comes from COMPRESSOR not turbine.
191
Bleed air from compressor considered to be:
- high or low pressure?
- high or low volume?
Low pressure
High volume
192
Turbo-compressor (bootstrap) system
- Flow (diagram)
193
Bootstrap system
- Effect of compressor and turbine on air
The turbine drives the compressor.
So the compressor adds energy to the air (higher temp and pressure) which is then ready for its major cooling in second pass of the heat exchanger.
It then enters the turbine where it does work to turn the turbine, giving up energy so temperature and pressure reduced.
Most temperature loss is from the second heat exchanger though.
194
Bootstrap system
- Water separator and humidifier
Water separators used to extract excess water from cooled air, preventing issues.
Consists of wool sock over a metal frame, swirling air uses centrifugal force to move water particles to the outside.
Humidifiers can be used to add moisture to very dry air (1-2% at 40,000 ft), but not a major concern.
195
Bootstrap system
- Cold Air Unit (CAU)
This refers to the compressor and turbine of the bootstrap system.
196
Air conditioning on ground
Bootstrap system can be run via the APU ("pack fan" instead of ram air for the cooler).
Alternatively the aircraft can be connected to a ground conditioned air source.
197
Advantage of electric-pneumatic systems vs bleed air
Increased efficiency and thus range
198
Pressurised areas of aircraft
Cockpit
Passenger cabins
Cargo holds
Other areas (radome, tail cone, undercarriage bays) not pressurised.
199
Aircraft pressurisation
- Pressure valves (4)
Outflow/discharge valve: Controls rate of flow of air outwards to manage pressure
Safety valve/positive pressure relief valve: Allows excess air out if max pressure differential (7-9 psi) is exceeded by 0.5 psi
Inwards relief valve: Simple valve preventing excess negative pressure diff (0.5 to 1.0 psi) e.g. in rapid descent.
Dump valve: Allows excess cabin pressure to be dumped in emergency.
200
Discharge valve positions
- Cruise
- Descent
Cruise: Partially open (to balance inflow of air conditioned air)
Descent: Partially closed
201
Blow Out Bung
AKA pressure equalling panels
Plastic bungs between underfloor cargo bay and cabin, ensuring floor stays intact in case of depressurisation event (in either direction).
202
Pressurisation controller phases
Taxi: Switch from ground to flight mode, pre-pressurised to 0.1 psi
Climb: Change to proportional control, outflow valve managed to achieve cabin altitude ROC 300-500ft/min
Cruise: Isobaric control maintains pressure differential (constant flow through outflow valve as new air being brought in through air con).
Descent: Back to proportional control for 300ft/min down to 0.1 psi on touchdown.
Ground: Outflow valve fully open to equalise pressures.
203
How is pressurisation controlled?
Cabin pressure controller
Duplicated and secondary will take over if primary has a problem.
Can go to manual control of the outflow/inflow valves if needed (DC motors)
Dump valves may also be linked to weight-on-wheels switch to ensure zero pressure differential on ground.
204
Different type of pressurisation control system
Pneumatic are older. Rate of change of pressure is set on controls and pressure sensors adjust valves to achieve that target.
Electronic are the newer version.
Both default to an automatic mode but can go manual if necessary.
205
Electronic pressurisation system failure response
- controller failure
- air con failure
There is a standby system which negates the need for a dump valve.
Manual mode available if standby fails, giving control over the outflow valve only.
There is a ram air inlet available in case air conditioned supply fails.
206
Recycling of cabin air
Air drawn from cabin (other than toilets or galleys) is recycled to limit demands on the air con system.
Excess air needs to be flowing out of outflow valve as new air introduced through air con.
207
Decompression rates
- Explosive
- Rapid
- Normal
Explosive: 0 to 3 seconds
Rapid: 4 to 6 seconds
Normal: 6 to 10 seconds
[explosive leads to mist and dust in the air]
208
Result of depresurisation (cabin heights and what happens)
10,000ft cabin alt: Visual and aural cabin alt warning
13,850ft: AUTO FAIL light
14,000ft: Passengers automatically presented with oxygen masks (half hung)
209
Typical and maximum cabin altitude climb rates
Typical: 500fpm
Max: 1800fpm
210
Cabin temp range
18-24 C
211
Cabin humidity range
NO TARGET - not maintained
212
Duct Relief Valves
Allow excessive pressure in the air con ducts to be released
213
Ditching cocks
Close outflow/inflow valves when aircraft ditches in water to limit ingress of water into the aircraft.
214
In flight icing conditions
TAT < 10C and
Either visible moisture OR visibility <1500m
215
Runback icing
-3C to +10C
Warm rain hits cold airframe.
Aircraft speed prevents freezing so water runs back and freezes as a clear glaze.
216
Rosemount (Vibrating Rod) Ice Detector
1 of 2 Mechanical Ice Detector types
Small rod is vibrated at 40kHz. If ice builds up on it the frequency changes due to the mass change, which is detected and leads to a warning.
It is heated with an element every 6 seconds to allow detection of the rate of ice build up.
[Constant light means ERROR]
[AKA Piezo-electric]
217
Pressure operated ice detector
- description
- order of heating
AKA Smiths ice detector
Hollow aerofoil with 4 small holes on leading edge, 2 larger on trailing. If leading edge holes cover with ice static pressure (from trailing) rises relative to pitot pressure (from leading edge) which is detected.
Heat SMALL HOLES FIRST then large holes to remove accumulated ice.
218
Rotary (Napier) Ice Detector
Electric motor rotates a serrated shaft 0.002 inches from a knife edge. When ice builds extra torque is required as the shaft slices off layers of ice, which affects the flexible shaft mounts and drives a warning. The warning sounds until ice is no longer fouling the blade.
219
Visual ice detectors
Hot rod or black rod is oldest. Mounted near pilot it is lit and has a heater. Can heat it then see how long it takes ice to re-form.
Ice detection lights light up wing leading edges for inspection.
220
De-icing paste
Actually more anti-icing. This paste can be used on GA craft with no other systems. Put it on the leading edge to prevent ice build up.
221
Mechanical de-icing
Rubber boots, or overshoes fixed to leading edges (span or chord wise) with alternate flat rubber and inflatable tubes. When activated over 34 seconds the tubes are inflated by the pneumatic system then allowed to deflate. A vacuum system ensures complete deflation during the cycle and also when the system is not active.
It's possible to adjust how often the system activates, but not the cycle time.
Need 0.5 to 1.5cm thickness, too thin and ice may form on expanded boot, too thick and may not break.
222
Thermal anti/de-icing
A thin inner skin inside leading edges, slats (not flaps), tail units, leaves a gap through which a LARGE amount of HOT air can be sent. Air supply can be from compressor stage of engine or a combustion system. Or an electric system using heater mats under surfaces (e.g. to protect high risk gas turbine engine entry) which cycles on and off depending on OAT.
If selected on the ground will stay off until 12 seconds after TO to prevent overheating.
223
Fluid anti-de icing systems
Freezing Point Depression (FPD) fluid pumped from central reservoir through porous metal strips in leading edges.
Can activate for variable periods up to 8 minutes.
Warnings sounds when 30 minutes fluid left.
224
Jet Engine anti-icing
Hot air exits through perforated ducts at the front of the nacelle. Performance impact (due to hot air taken from engine and less dense air entering it) but minimal enough that it is sometimes left running all the time and may be no performance calculations.
225
Turbo prop intake anti-icing
Turbo prop intakes (open mouth for ram air under the prop) use thermal anti-icing. The lip around air intake has a stagnation zone at proudest point prone to icing. Some parts have intermittent, some continuous anti-icing.
226
Ice diverter
Panel in turbo prop intake which diverts broken off pieces of ice away from the engine intake.
227
Windscreen cleaning/rain systems
Windscreen wipers: Don't operate on dry windows
Windscreen washers: As with cars, sprays fluid on windows for use along with wipers
Windscreen rain repellent system: Two nozzles to each screen with repellent fluid sprayed using aerosol. Sprays for up to 15 seconds and works in conjunction with wipers.
228
Windscreen anti/de-icing
Fluid system
Electric system - Thermostatically controlled for 35C temperature. Have low and high settings (turn on low first to prevent thermal shock). High only for visible icing.
229
Propeller anti/de-icing
- Electric
First third of the blade de-iced, sometimes a double boot to cover first 50%. Second 50% only needs centrifugal force.
Idea just to loosen ice then centrifugal force gets rid of it.
Can switch between even numbered blades, but if odd numbered need all on at same time.
230
Propeller anti/de-icing
- Spinner
The spinner is anti-iced as ice tends to stay there once built up
231
Propeller anti/de-icing
- Electric cockpit indications
Light aircraft just an ammeter jumping between zero and full power (which should fall in a set range).
Turbo has a steady green light when anti-icing (windscreen & air intake) on and flashing light when de-icing cycle (prop or full air intakes) on.
232
Propeller anti/de-icing
- Fluid
For smaller prop aircraft, slinger ring distributes fluid to base of prop and centrifugal force spreads it.
233
Cabin crew required protected breathing equipment endurance
15 minutes
[Means smoke hood]
234
Continuous demand oxygen system
Usually for light aircraft, need to be plugged in.
Adjustable type can have the amount of flow adjusted.
Flow indicators show oxygen is flowing but not how much (or if it is enough).
Flow doesn't depend on breathing of the user, flows as long as the mask is plugged in.
235
Diluter demand oxygen system
Have "on" button to turn on.
"Normal/100% oxygen" button. Normal means aneroid allows outside air to be mixed with oxygen (will go 100% oxygen @ 32,000 ft), 100% oxygen cuts off external air (e.g. fumes in cockpit).
"Emergency" will provide continuous flow of 100% oxygen regardless of demand.
Only for flight crew as complex to operate.
236
Flight crew oxygen mask features
Activate when removed with two red toggles, have face mask with goggles (optional demister). Button to push for 100% oxygen and an emergency button too.
Contain R/T facilities and test mode.
Must be able to put on with one hand.
237
Walk around oxygen sets
1800psi 120 litre oxygen tanks.
Different flow settings (e.g. 2l for 60 mins, 4l for 30 mins or 10l for 12 mins).
238
Passenger oxygen system
Passenger Service Units (PSUs) can be opened barometrically over 13,300 to 14,000ft or at any altitude from flight deck.
Oxygen will be continuous flow type supply, from either high pressure gas system or chemically generated.
Masks drop in half-hung position and flow initiates when check valve is tripped.
Deliver mix of cabin air and oxygen.
239
Chemical Oxygen generators
Uses sodium chlorate and iron, produces oxygen continuously for min of 15 mins.
Temperature regulated to max 10C above cabin temp.
5 year shelf life.
Require 10% more masks than seats. (for infants/children).
Generator has a white stripe on it which turns black to show it has been fired.
Uses 28V DC to activate the chemical reaction, no power required for tank systems.
240
Portable oxygen systems
- Pressures
- Flow rate (2 modes)
Stored at 1800psi, reduces to 100psi intermediate, 8-10psi mask pressure.
Normal rate - 2 litres per minute
High rate - 4 litres per minute
241
Oxygen Cylinder Thermal Compensator
Tube with copper wire bristles in it which even out temperature as gas flows over them through conduction.
The purpose is to adjust the charging pressure for temperature.
242
Oxygen cylinder pressure relief
A bursting or safety disk prevents oxygen cylinders exploding.
When activated a green disk will pop out, showing a red bowl instead (similar to fire extinguishers).
243
Other crew oxygen systems
Need training to use smoke hoods and crew portable oxygen, which use cylinders or 15 minute chemical oxygen generators.
244
Oxygen cylinder colour
USA/Europe: Green
Britain: Black with white neck
245
Oxygen safety factors
Not flammable but supports combustion.
Heavier than air so will pool at lower areas.
Oil and grease can catch fire spontaneously in the presence of oxygen.
Moisture present will react and cause corrosion and freezing of valves.
Approved lubricant only (e.g. graphite).
246
First aid oxygen
Provides oxygen in mask at 3l per minute for medical use
EASA requires at least 2 bottles, and enough for 2% of passengers for time above 8000ft
247
Types of smoke detector
Optical (Labyrinth) - Light directed at a photo-electric detector cell with block in-between. Smoke will refract light around the blockage (test button operates a separate bulb to activate alarm).
Ionization - Radioactive material bombards oxygen and nitrogen causing ionisation => current detected. Smoke attaches to oxygen/nitrogen and reduces current flow.
248
Areas requiring fire detection
Jet engine bays
APU bays
Wheel/main gear bays
249
Fire Detection Systems
- Melting Link
Melting link detectors are an old version where a fusible plug holds apart a pair of contacts. The plug melts at a specific temperature.
They can't be reset, will continue to provide warning after fire is out.
250
Jet engine fire risk zones
Zone 1 - Surrounds hydraulic pumps, gearbox, FCU, engine lubrication (etc) so most likely place for fire to start and needs fire detection.
Zone 2 - Where compressor blades could touch engine casing causing metal fire (hotter than zone 1).
Zone 3 - Hottest zone, aft of the rest, surrounds combustion chamber and engine. Separated zone 1 with stainless steel bulkhead.
251
APU & wheel bay fire detection
APU can be left running on its own so fire detection and response is automatic.
Wheel bay has no fire suppression so if fire is detected will need to (follow SOPs) slow down to a speed where gear can be dropped. Fire would be caused by overheated brakes.
252
Fire Detection Systems
- Resistive
- Resistance and current in case of fire
A wire detection loop (in pairs for duplication) has a resistive filler around the core that allows current to flow when burned. This connects a wheatstone bridge to earth, with wheatstone bridge voltage output being detected by the alarm.
Fire => resistance LOW, current HIGH
253
Fire Detection Systems
- Capacitance
- (Advantage vs resistive)
- Capacity in case of fire
Uses same continuous wire loop as resistive, but instead of wheatstone bridge a charging unit and measuring unit sense the capacitance. Increased temperature increases capacitance, so a crushed wire won't produce a false alarm (unlike resistive).
Fire => capacity HIGH
254
Fire Detection Systems
- Systron Donner detector
Helium (averaging gas) at 7psi detected by integrity pressure sensor (pressure reduction causes failure warning). Titanium Hydride gives off hydrogen gas in a fire, increasing pressure to 40psi which triggers the alarm.
Can still function if crushed, assuming gas route still exists.
255
Fire Detection Systems
- Overheat sensors
Use differential expansion.
Some sprung (open) contacts are inside a tube which expands quickly under heat. This brings the sprung outward contacts together and closes a circuit.
Primarily for overheating (eg bleed air), if used for fire detection need a delay to deal with vibration.
256
Fire Detection Systems
- Practical arrangement of detectors
Continuous Fire Detectors or Gas Filled Detectors usually arranged in a double loop around a sensitive area (e.g. engine). Only if both loops detect fire will the actual fire warning be given.
Failure of one of the loops may or not prevent aircraft from being used.
257
Delayed fire warnings
Fire warnings may be supressed in critical stages of flight (just after rotation or before landing).
258
General engine fire drill steps
1) Cancel the aural warning
2) Sequence to shut off fuel, bleed air, electrics and hydraulics to the engine
3) Discharge fire bottles into engine fire zones
259
Process for engine fire
All relate ONLY to the affected engine!
1) Close throttle
2) Turn off fuel
3) Turn off ignition
4) Pull fire handle (this cuts off fuel)
5) Turn fire handle one way to let off one extinguisher (30 secs, enough to stop fire)
6) Turning handle the other way (if fire ongoing or as a precaution before landing) fires second extinguisher
260
Process for cargo bay fire
Need to pull and turn the arming switch to arm squibs.
Then lift guard on one of the extinguisher switches and push it.
If second one needs to be fired it is already armed.
261
Physical indications fire extinguishant bottle has been fired
Zero reading pressure gauge
Ejection of green disc under which a red disc is now visible.
Indicator pin on the bottle head
262
Toilet fire system
Automatically deployed fire extinguishant system aimed into disposal receptacle in toilet, required for aircraft with capacity of 20 or more passengers.
Melting of fusible plus sets them off.
263
Cabin fire zone classes
Class A: Populated cabins in passenger craft.
Class B: Accessible cargo area.
Class C & D: Not accessible.
Class E: Cargo only planes.
264
Detection of fire in different compartments according to class
Class A (flight deck/cabins) use visual detection of smoke.
Class B, C, D & E need their own separate fire or smoke detection system to give warning on flight deck.
265
Fire suppression in different compartments according to class
Class A &B: hand extinguishers
Class C: approved fire extinguishing system and ventilation control.
Class D: allowed to burn out due to increased fireproofing.
266
Smoke/fire detection duplication
Sensors are duplicated in parallel.
BOTH sensors have to detect fire to trigger a warning.
Detection wire connection to ground will inhibit the sensor.
267
AVGAS
- Types available
- Colour
- Specific Gravity
- Flash point & freezing point
80, 100, 100LL
Red, Green, Blue
[Specific gravity: 0.72 need this?]
Flash point: -47C
Freezing point: -60C
268
Meaning of octane rating/performance
This is resistance to detonation. The higher the resistance to detonation, the higher working pressure is possible in the engine.
269
OK for piston engines to use fuel with higher or lower octane rating?
Higher is ok
270
Use of MOGAS
- Safety considerations and restrictions
Not possible for commercial flight.
- No flight above 6000ft
- Not fly if fuel temp over 20C
- High risk of carb icing and fuel vapour lock (due higher volatility and water content)
- Can affect seals and hoses so record use in maintenance log
271
AVTUR
- Basis
- Types available
- SG
- Flash point & freezing (waxing) point
Kerosene, for turbine engines
Mixed with additives to make JET A1 and (in USA) JET A with lower waxing/freezing point
[SG: 0.8 @ 15C need this?]
Flash point: 38C
Waxing point: -40C Jet A1, -47C Jet A
272
Wide cut fuels
- contents
- types
- temperatures
- approval
e.g. Jet B
Mix of 70% gasoline, 30% kerosene to overcome ignition problem.
Flash point: -23C
Freezing point: -60C [same as avgas]
[Lower than Jet A/A1]
Not approved in EASA.
273
Cloudy fuel
Can mean air if the cloudiness rises or water present if it falls to the bottom.
274
When to check fuel for water
At the start of the day (not before every flight or after refuelling).
275
Fuel System Additives
Fuel System Icing Inhibitor (FSII) - Icing inhibitor to prevent the small amounts of dissolved water from turning to ice crystals and blocking engine.
Biocide - Fungal suppressant to combat Cladasporium Resinae (present in turbine fuels) which can block fuel systems and produce corrosive by products.
276
Combatting water in fuel (3 methods)
Water drains
Fuel heater - Used in turbine craft to prevent water present from freezing. Either use heat exchanger or hot oil (cools oil while heating fuel).
Atmosphere exclusion - Fill up the tanks with fuel to displace moist air.
277
Waxing
When heavy hydrocarbons are deposited from the fuel at low temperatures.
Refinery should limit amount of heavy hydrocarbon present, then fuel heating helps prevent issues.
278
How is fuel heated
Heat exchangers heat fuel in wings (fuselage tanks don't get cold) from oil primarily (Fuel Cooled Oil Coolers (FCOC)) or from returning hydraulic fluid. Prevents waxing.
Jet aircraft ONLY.
279
Fuel boiling
At high altitude, low pressure causes boiling temp of fuel to fall and can get vapour lock.
Fuel booster pumps can overcome the problem by pushing fuel to the engine rather than being sucked from the tanks by pumps.
280
3 types of fuel tank
Integral tanks - Areas of the aircraft (e.g. wings) designed to hold fuel. Saves weight.
Rigid tanks - A solid tank inside the aircraft, adds weight.
Flexible tanks - Made of sealed rubberised fabric, used in military as self sealing in battle damage.
281
Fuel tank expansion space requirement
Minimum of 2% of tank volume as vent space.
282
Fuel tank venting
Needed to replace used fuel with air. May use a ram air system to provide POSITIVE pressure and aid fuel flow.
Can vent to a vent surge tank to capture fuel loss. Situated in wing tips, fuel is redirected back to main tanks and they are usually empty.
Ram air entry on UNDERSIDE of wing.
283
Fuel tank pressurisation
- 2 methods
To prevent vapour locks engine bleed air can be used to pressurise fuel tanks to 5psi above ambient. Or ram air system in some cases.
284
Pressure-fed fuel system
For multi-engine aircraft, allows fuel tanks to be mounted lower than the engines but "pressure-fed" also implies connection between tanks.
Any engine can be fed from any tank, a leak can be isolated by feeding both engines from the working tank.
285
Trim tank
Tank in horizontal stabiliser that allows CoG to be managed. Fuel pumped into it (rearwards) in the cruise to increase stability, pumped forwards before descent to improve longitudinal control.
286
Low pressure (booster) pumps
Fitted in pairs (redundancy) in high altitude aircraft to prevent cavitation in engine driven pump.
Centrifugal pumps (impeller), induction driven, AC, low pressure (20-100 psi) high volume.
In case both fail, minimum equipment list will limit maximum operating altitude to prevent fuel starvation.
Multiple power sources for redundancy.
287
High pressure pumps
Engine driven, part of the engines not in the fuel tanks
288
Collector tank
Aka feeder box
Contains the low pressure pumps and a measured quantity of fuel to ensure the low pressure pumps are always submerged.
Also allows low pressure pump replacement without draining entire fuel tank and KEEPS PUMPS COOL.
289
Fuel pressure warning lights
"Low pressure" amber lights to show loss of pressure down route of low pressure pumps, out of fuel tanks.
290
Suction (bypass) valve
Allow LP pumps to be bypassed in case of failure, so HP pumps can draw fuel from the tanks. Can achieve 75% of normal flow, but aircraft may be altitude limited.
291
Jet pump
Used to move fuel between tanks or keep booster pump box full of fuel.
Uses venturi principle, small spray of fuel into the outlet created pressure which sucks high volume of fuel from surrounding area with it.
292
High and low level fuel float switches (or level sensors) - purpose
High level to prevent overfilling with fuel.
Low level to prevent over-draining of fuel (e.g. fuel jettison).
293
Baffles
Used in fuel tanks to dampen rapid movement of fuel (surging or sloshing) during manoeuvres. May be one directional (allow fuel towards centre of craft but not to head towards wing tips).
294
Crossfeed valve
Used to transfer fuel between tanks. Typically closed for takeoff and cruise, opened in a specific process to move fuel.
295
Spar valve
Valve that shuts off fuel as it leaves the tank system (engine shut off valves are separate and sit just before fuel enters the engines).
296
Cockpit fuel indications (4)
Fuel quantity (mass or volume)
Fuel flow
Fuel temperature
Fuel filter status
297
Fuel jettison system
- Why is it needed?
- Minimum fuel that must be kept
Fuel dump system required if MLM is much lower than MTOM. Need to be able to dump enough fuel to land within 15 minutes.
CS-25 stipulates minimum fuel to allow climb to 10,000ft and cruise at max range speed there for 45 mins.
298
Functionality of fuel jettison system
Uses low pressure booster pumps usually
299
Capacitance of fuel vs air
Impact of density on capacitance
Fuel has twice the capacitance of air
Capacitance increases with density
300
Effect of water in fuel tank with capacitive sensor
Water has 40 times capacitance of fuel so will increase reading massively. Water falls to bottom of tank where reference unit is so likely to read full tanks.
301
Dripstick
Pulled out through bottom of fuel tank in fuel proof aperture, fuel starts running out when the top of the tube goes below fuel level - markings indicate how much fuel at that point.
302
Dropstick
Aka "Magnetic Level Indicator" (MLI).
Uses a magnetic float and magnet on the end of the dropstick to determine the fuel level in the tank (measure protrusion of rod under bottom of wing).
303
Position of fuel flow meter and flow control unit
HP pump ->
Flow Control Unit ->
HP valve ->
Fuel flow meter ->
Engine
304
Minimum size of fuel zones
6m (20 feet) radially from filling and venting points.
305
Rules for fuel zones (4)
No smoking
If exhaust of an APU required for fuelling discharges into the zone, must be started before caps are removed or connections made. Must not be restarted if it stops, until fuelling has stopped.
Ground power units located as far away as practical.
Fire extinguishers to hand.
306
Plastic funnels and pipes in fuelling
Should never be used
307
Maximum pressure for pressurised refuelling.
And defuelling.
Max 50 PSI.
Max -5 PSI for defuelling
308
Refuelling gallery
Used for refuelling, defuelling and fuel dumping
309
Grounding before refuelling
Need to ground the aircraft (can't rely on conductive hosing).
Overwing (light aircraft) fuelling, should ground the nozzle to aircraft, also funnels, filters, cans etc.
Underwing pressure refuelling uses hose-end bonding cable for this purpose.
Don't remove grounding until fuel caps refitted or pressure hose disconnected.
310
Risks related to full or empty fuel tanks
Full: Fire risk
Empty: Explosion risk
[and condensation]
311
Precautions during refuelling
Passengers embarking/disembarking should be supervised by airline official and routed away from fuel zone.
Move steps, jacks (etc.) from under aircraft in case it settles on landing gear.
Don't operate main engines.
No strobe lights.
Torches/lamps certified flameproof or 'intrinsically safe' type.
Only authorised personnel and vehicles in fuelling zone.
312
Rules for having passengers on board during refuelling
NOT allowed if less than 20 seats, if wide cut (e.g. JET-B) or AVGAS being used.
Seat belt signs off, non-smoking signs on, lighting on.
Warn crew, staff & passengers (no smoking, seatbelts off).
Need 2 exits, one of which can be an automatic chute if they're available.
Need 1 staff at designated point suitably trained, sufficient other staff to carry out evacuation.
313
Special refuelling hazards (4)
No refuelling within 30m of working radar station.
No refuelling if landing gear is overheated until cooled down (fire service should be called).
Extreme caution in electrical storms.
No flash photography within 6m of fuelling or venting points.
314
Fuel markings
- AVTUR
- AVGAS
AVTUR: Marked AVTUR and JET A or JET B with white text on black background.
AVGAS: Marked AVGAS and grade with white text on red background.
315
Load factor limits
Normal
CS23: 3.8g
CS25: 2.5g x 1.5 safety factor = 3.75g
[CS23 reduced mass 4.4g, aerobatic 6.0g]
316
Drain valve (fuel tank)
This is where you take your fuel sample
317
Primary flight controls
Ailerons
Elevator
Rudder
ROLL SPOILERS!
