AGK Systems Flashcards
Minor failure conditions ?
May be probable
Major failure conditions ?
Must be no more frequent than remote
Hazardous failure conditions ?
Must be no more frequent than extremely remote
Catastrophic failure conditions ?
Must be extremely improbable
Safe life concept ?
Requires structures to have an explicitly stated lifespan within which no catastrophic structural damage may occur under safe operation
Safe-life concept can be measured in ?
Flight hours
Pressurisation cycles
Landings
Calendar duration
Fail safe design ?
Critical areas have multiple load paths, designed to provide redundancy. This ensures if one fails an alternate path can carry all load through duplicate.
Fail safe design examples
Wing spar attachments
Tail plane attachment
Engine fittings
Cabin windows
Fail safe design disadvantages ?
Weight penalty consumption
Corrosion
Fatigue
Damaged tolerance design?
Some excess weight can be avoided if the are damage tolerant, these structures have crack arresting features.
What is load ?
An external force applied to a component that causes stress, which leads to deformation, know as strain
4 main stress types ?
Tension
Torsion
Compression
Shear
Dynamic loads are ?
Imposed by manoeuvring and can change very fast.
Rapid build up can cause severe stresses on materials.
Static loads … ?
Build up slowly or remain constant
Cyclic loads ?
During flight loads change and alternate rapidly, components experience compression and tension changes.
Can cause metal fatigue which can lead to structural failure
Overstress ?
Can lead to structural failure and any suspected OS must be investigated.
Areas prone to stress ?
Spar lines
Wing horizontal and vertical attachments
Roots
A/C skin
Load limit on transport A/C
2.5 g
Ultimate load limit is (+50%)
So 3.75g
Risk of fatigue increases with ?
Corrosion
High number of flight cycles
Hard manoeuvring
Poor maintenance practices
How is fatigue detected ?
Visual inspection during walk around
Corrosive conditions and steady tensile load can produce metal fatigue, also known as ?
Stress corrosion
Max ramp mass ?
Max mass authorised for manoeuvring on the ground
Max take off mass ?
Mass at which the pilot is allowed to take off
Max zero fuel mass ?
Mass of A/C and all it’s contents excluding the weight of useable fuel onboard
Max landing mass ?
Maximum mass at which A/C is permitted to land
Fatigue can be reduced by ?
Reduced cycles
Avoiding coarse manoeuvres
Avoiding turbulence
Not flying with excess fuel/payloads
Corrosion ?
Disintegrates the smooth surface of metal.
Creates a natural starting point for fatigue cracks
Corrosion is more likely ?
Over warm, salty water
How should corrosion be dealt with ?
Repaired, primed and re-painted
Corrosion indicators ?
Brown/reddy discolouration
Aluminium forms a grey powder
Potential Al mixes ? (Alloy)
Cu
Mg
Mn
Composite Mats are made from ?
Two or more materials with different chem of physical properties, combined to produce the best of both, components remain separate
Composite fibres can comprise ?
Kevlar (aramid)
Carbon (graphite)
Glass bonded with
Resin
Filler
Matrix is ?
Material the supports the fibres, and bonds them together.
Composite mats adv ?
Better power to weight ratio
Lighter
Fibres can be aligned to provide best load qualities.
Corrosion resistant
Composite mats disadv ?
Hard to inspect flaws
Doesn’t conduct well
Expensive
Less damage tolerant
Lighting impacts on composite mats ?
Can result in explosion of material at exit point
Lighting strikes on alloys ?
Tend to leave pinholes at entry and exit (little damage)
Hard time maintenance ?
Is predictable
A definite time limit in component before it has to be replaced
(Could be-
Calendar time
Landings
Cycles
Flight hours)
On condition maintenance is ?
Periodic inspection of components, post check a component is either replaced or continues in service.
(Checked once an issue arrises)
Fuselage structure type is ?
Monocoque (she’ll)
Or
Semi-monocoque (shall over frames and ribs)
How are structure components fixed ?
Bolting
Riveting
Bonding
Welding
Frames … ?
Define the shape
Stiffeners, stringers and longerons …?
Provide the base for the skin
Cross beams …?
Support floor panels
A secondary overlapping material layer is called a …?
Doubler
Where are pressurised bulk heads ?
Eitherend of the fuselage
Structural and non structural ones are in between
Fuselage shapes include ?
Circular
Oval
Double-bubble
Rectangular
What stress does the pressure hull experience …? (Everything in between pressure bulkheads)
Hoop and axial stress
What can cause unseen potentially catastrophic damage to the rear pressure bulkhead/epanage ?
Tail strike
Key structural component of the wing is ?
Main spar
How is wing shape achieved ?
Shaped skin mounted on ribs and longerons
What do large A/C use for the main spar ?
Torsion box, attached to a centre wing box
Flutter is ?
Oscillation caused by interplay between aerodynamic forces and torsional stiffness
Where can flutter occur ?
Wings and Horizontal stabiliser
Flutter countermeasures ?
Forward mounted engines
Forward CG
Good torsional stiffness
What forces are imposed in asymmetric flights ?
Lateral
Fin can be over stressed by unnecessary rudder inputs
Semi-monocoque structure contains ?
Formers/frames
Stringers
Longerons
Stressed skin
What is the pressure hull pressure ?
Max 8 or 9 psi
Purpose of stringers in fuselage construction is to ?
Assist the skin in absorbing longitudinal compressive loads
Wing box is ?
Main structure component of the wing
How is vertical empennage attached ?
3 or 4 lugs and pins, relatively weak point
Hydraulic systems that require more or less human effort ?
more human effort - passive system
more hydraulic effort - active system
Closed centred system
Open centred system
Closed - Constant hydraulic pressure all the time
Open - Pressure only delivered when demanded
Air craft with high pressure active system operating range ?
3000-4000 psi
Hydraulic fluid ideal properties ?
Low viscosity
Resistance to foaming
Lubricant
Heat resistance
Chemically stable
Low FZ point (-70)
High boiling point (80)
Non-flammable
Good storage properties
Two types of hydraulic fluid ?
Mineral : DTD585
-is red
-has synthetic rubber seals and hoses
Synthetic : Skydrol
- 500A is purple
-used in systems with butyl rubber/ teflon seals
Danger of hydraulic fluids ?
Types cannot be mixed or will cause serious damage to parts.
It is very corrosive and irritating to human skin, gloves and eye protection must be worn around it.
Advantages of hydraulic systems ?
Good way to provide very large amounts of power
Very little energy loss
Leaks are easy to spot
Lighter than mechanical equivalent
Dis-advantages of hydraulic systems ?
Highly corrosive
Require strong structures
Susceptible to fluid contamination and damage
hydraulic fluid is a health and environmental hazard
Primary components in a hydraulic system ?
Reservoir
accumulator
double acting cylinder
non-return valve
pump (usually EDP)
selector valve
Actuator role ?
Turn hydraulic pressure into movement.
Role of actuators non-return valve ?
Allow fluid to flow in one direction only.
fluid pressure in one direction unseats the ball and if the pressure falls the spring re-seats closing the valve preventing reverse fluid flow
Selector valves operation ?
Mechanically or electrically operated
Difference between an open and closed centre hydraulic system ?
Open centre can only operate one system at a time
Closed can operate multiple systems at a time
Why does pressurisation happen in hydraulic reservoirs ?
To stop boiling of hydraulic fluid at altitude, known as self bleeding.
It also provides positive pressure at pump inlet
A relief valve protects it from over pressurisation
Accumulators role/operation
Comprises pressurised gas and fluid, acts as a store of hydraulic fluid under pressure.
It provides a limited supply if the pump fails, often used for emergency brakes
Hydraulic pumps + alternatives ?
Pumps provide flow and pressure. primary are usually driven but the engine.
Alternatively they can be-
Electrically powered
Hand operated
Driven by a RAT
Driven by a hydraulic motor (PTU)
Constant delivery pumps ?
Have a fixed volume
Requires an ACOV (Automatic Cut Out Valve)
Constant pressure pumps ?
Have a variable volume, are more fuel efficient and rate of delivery is not dependant on RPM, but still driven by the engine.
It self regulates and only supplies that required to maintain constant working pressure.
The pump is lubricated by hydraulic fluid
When is a constant pump at nil stroke ?
When the swash plate is perpendicular to the input of the drive shaft.
Hydraulic Motors ?
Use hydraulic pressure to generate rotary motion.
useful for operating screw jacks to drive the flaps
Hydraulic filters ?
Filtration and hydraulic circuit protection keep fluid free of contamination. Typically these filters trap particles larger than 25 microns.
What does pressure release valve do ?
Protects from over pressurisation
What does restrictor valve do ?
Restrict fluid flow to slow speed of operation
What does priority valve do ?
Ensures sufficient fluid flow at all times to the primary flight controls and wheel brakes
what does a Shuttle valve do ?
Allows one service to be operated by two independent supplies
- Allows most appropriate pressure- Exam answer
Hydraulic fuse is ?
Located upstream of major components and to shut off flow and prevent total fluid loss in the event of a major leak. Once shut off anything downstream will be isolated
hydraulic systems main requirements ?
Redundancy
Instant response
Ability to operate multiple at once (closed centre)
Prioritise supplies to flight controls and wheel brakes
Provide emergency sources of pressure
Hand driven pump ?
May be used for emergency back up power on some lighter a/c but mainly used for maintenance
Used on ground system to operate doors, flaps, brakes anything linked to the system
RAT is ?
Ram Air Turbine-
Deployable turbine to produce emergency hydraulic power to essential systems.
Used to drive an auxiliary hydraulic pump or electrical generator
Types of landing gear ?
Fixed
Retractable
Tri-cycle
Conventional
(+) and (-) of fixed landing gear ?
(+)
Lighter and less prone to failure
Ideal for training a/c as checklists and actions are reduced
(-)
It does suffer from increased drag
Which landing gear must touch down first ?
Main landing gear must touch down first, landing on the nose wheel will cause the whole assembly to collapse
Bogeys and trucks ?
Have at least 4 wheels per landing leg
The wheels are attached to a bogey beam, which is attracted to the leg via a pivot
more wheel allow better weight distribution and this reduces ground pressure.
Requires a lot of internal space to store it
Oleo strut make up ?
They are Hydro-pneumatic shock absorbers that reduce and absorb the stresses encountered during landing.
Fluid (oil) is the dampening medium, and controls compression and extension through the shock absorber.
Compressed nitrogen in the upper section acts as a spring.
Oleo compression may be caused by ?
Low gas pressure
fluid leak
When does greatest torsional strain on the bogle occur ?
On the ground making tight turns when taxiing
Visual indication of gear status ?
Wheels up - Lights out
Wheels down - 3 green
Wheels transitioning - Red lights
Down locks are for ?
Ensuring accidental gear reduction can’t happen
A mechanical device is required to break the lock prior to Gear retraction.This means In emergency operation the gear will still be locked and safe in the down position
Ground locks are ?
Ground locks will be installed when the a/c is on the ground.
They will always be fitted with a “remove before flight” tag
Failure to remove will cause gear to remain down until locks are manually removed
How is the landing gear controlled ?
The landing gear is controlled by the ‘gear handle’ on the main instrument panel, its fitted with a wheel on the end for a tactile reminder in low light conditions.
Under what conditions is the gear handle locked out ?
When already up, the handle will be locked above a certain TAS/Mach number
When down, the handle will remain locked when weight on wheel signal is present.
VLO and VLE are ?
VLO- velocity landing gear operating
VLE- velocity landing gear extended
Emergency LG extension designs ?
Manual hand crank system
Compressed nitrogen to bow gear down
Gravity free fall system (most common)
Methods of nose wheel steering on a light a/c ?
Differential braking- Applied to the main wheels, it causes the nose to sing left or right
Rudder pedal steering- Mechanical link between nose wheel and rudder wheel
Tiller operation at low speed
Nose wheel steering on larger a/c ?
Tiller can be used to steer nose left or right of centreline. this provides 75º steering each direction.
Tight radius turns at low speed when combined with differential breaking can cause significant tire damage.
What is a shimmy ?
A lateral oscillation along the longitudinal axis
Alternative shimmy causes ?
May also be the result of faults on the a/c such as -
Worn or broken torque links
Wear in wheel bearings
Low or uneven tire pressure/wear
Ply rating ?
Indicates tyre strength
Tire creep ?
Caused by the movement of the tire around its rim
creep marks should be-
1” wide for 24” or less
1.5” wide for 24” or more diameter
Tire speed rating ?
Often in MPH, tire speed rating dictates the limiting speed on the ground.
Optional faster tyres may be available
Tire wear -
Tire inspection points of interest ?
Cuts- any cut to the cords or sidewall require tyre replacement.
Bulges- indicate weaken structure and potential failure.
Flat spots
FOD
Contamination- Fluid spillages onto tire
Creep check
Wear
Pressure- Over inflation leads to excess wear and possible blowout, Under inflation leads to creep, excess heat, wear and failure
What tyre pressure do large a/a use ?
Relatively high
Low- up to 200
high- 200-315
Two types of brakes ?
Fixed disk floating calliper
Floating calliper fixed disk
How do the brakes work ?
Both types use hydraulic pressure to clamp brake friction pads tightly against a steel disk. pressure must be applied evenely
When should brake wear indicator pins be checked ?
When the brakes are applied.
Brake pads should be replaced when the pin is flush with the adjuster housing.
Automatic Brake wear adjuster ?
Ensures correct clearance between rotating assembly
Advantages and dis-adv of carbon brakes ?
(+)
Lighter
Better performance- can absorb twice as much heat as steel equivalent
Durability- Carbon brakes last 30-175% longer
(-)
They are more expensive than steel alternatives
Hydro-plaining speeds formula ?
Spin up 9x√tP = (kts)
Spin down
If a control surface can be wiggled and something moves within the a/c moves it must be ?
Reversible
Manual/conventional
Modes and laws ?
Modes - Boeing
Laws - Airbus
