Systems Flashcards
How likely is a minor failure
Probable
How likely is a major failure
Remote
How likely is a hazardous failure
Extremely remote
How likely is a catastrophic failure
Extremely improbable
What is “safe life”
Life given to a aircraft in which it will not suffer a catastrophic failure
What is fail safe
A failure of a particular part is compensated by an alternative part for a limited time
Limited time is until next periodic inspection
Disadvantage is it’s heavy
What is a damage tolerant structure
Spreading load over a large area
Damage can be detected during normal inspection cycles before failure occurs
What is a stress
Internal force per unit area inside a structural component as a result of external loads
What is strain
Deformation caused by stress on a material
% dimension of original
What are the 4 types of stress
Tension (traction)
Compression
Torsion
Shear
What strain is placed on a component during bending
Compression inside of bend
Tension outside of bend
Shear in middle (@spar)
It is a combined load
What is torsion
Twisting
Tension is at outer edge
Compression in the centre
Shear cross structure
What is elasticity
A material can elongate then return to original shape
What is plasticity
Material permanently reform
What is a stringer used for
To prevent compression load on outside of skin buckling
What is buckling
Occurs to thin sheet materials when subject to compressive forces
What are dynamic loads
Built up quickly due to changes in flight conditions
What are static loads
Usually Constant and build up slowly
I.e loading up with fuel
Where experiences the largest bending moment
Wing root
On ground = static force is main gear on wings
In air = upward forces by lift
Max on empty wings
How to reduce wing loading / stress
Outboard ailerons locked it at same time as flap retraction
Aileron upwards = pushes wing down at High speeds
Fuel in winds
Engines on wings
What is a cyclic load
Repetitive load placed on and off
Causes structure to fail quicker than static load
What determine the number of cycles to failure
Amplitude of the load
What is design load limit
Max load designer expects the aircraft to experience in service
Based on 2.5g for transport aircraft
Design ultimate load
Safety factor applied to design load limit
Must withstand design ultimate load without collapse
Safety factor of 1.5 added to design load limit
If aircraft is at ultimate load what is the impact
Should remain largely intact for at least 3 seconds
What is failure
Fail of a structure which is subjected to continual reversals of load
What does the S-N diagram / wohler curve represent
The relationship between fatigue and amplitude
What type of load is failure more likely under
Tensile (tension / traction)
What is a alloy
2 or more metals together that give properties not had before
Good weight to strength ratio
What qualities but a material contain
Elasticity
Plasticity
Stiffness
Strength
What are common materials used in aircraft
Aluminium Titanium Magnesium Alloys Steel
What is the most common aluminium alloy used
Daralumin
What is daralumin
Copper based aluminium alloy
Magnanese, silicon, magnesium
Very god thermal / electrical conductivity
Excellent strength to weight ration
Susceptible to corrosion
What is Alclad
Sheets of duralumin with pure aluminium coating on its surfaces
Duralumin = strength Aluminium = protects the duralumin
What is a composite material
2 or more elements to produce w material with different properties to those of the original
What does a composite material consist of
Matrix usually a thermosetting polymers or eproxy resins
Fibres = carbon / Kevlar / glass
What is a radar dome made out of and why
Fibre glass and it is radar transparent
What is carbon fibre good for
Strength to weight ratio
But doesn’t like big impacts
What is Kevlar (aramid) good for
Impact resistance
What is a matrix used for
Spread the load to each fibre
Also protect the fibres
What is a honeycomb / sandwich construction
Typically used for flight control surfaces, flooring, fuselage panels
Has good strength to weight ratio + really strong in direction of honeycomb openings
What is corrosion
Disintegration of a engineered material
Oxidisation = when metal is exposed to air
Electrolytic = am electric current between two metals
Degree of corrosion is proportional to level of moisture
What is stress corrosion
Integration between fatigue and corrosion
Combination of corrosive conditions and tensile loads
Causes quick, unpredictable failure
What is stress corrosion (cracking) (SCC)
Unexpected failure due to stress fatigue
What is hard time maintenance
Definite time limit for individual components and structures
Item is removed from service before scheduled maintenance period for inspection of repair
what is on condition maintenance
Inspection or check that can be done without disassembly or overhaul, to assess the performance and then if required will be removed for maintenance
What is the fuselage
Pressure hull between forward and rear bulk heads
What is the main structural member of framework / truss
Longeron
Frame take all the loads
What is a monocoque construction
Formers just give the shame
Skin takes all the loads
Extra strength (Doublers) needed to be built around holes (window etc)
Heavier
Only suitable for small aircraft
What is a semi- monocoque construction (stressed skin)
Main structural member = longeron = goes nose to tail
Stringer = prevents buckling = gives fuselage shape
Skin takes majority of the load but is supported and assisted by frames, longeron, stringers
Good weight / strength ratio
What are stiffeners
Additional lengths of metal between frames riveted to the skin to provide additional support
What are different attachment methods
Riveting Welding Bolting Bonding Pinning
What is a firewall made out of
Stainless steel/ titanium alloy
What is a rectangular fuselage
Many non pressurised
High weight / strength ratio
Cheaper to build
What is a circular fuselage
Ideal shape for pressurised
Stress spread evenly
Relatively easy built
Sometimes space is wasted when pax and cargo has to be accommodated
What is a double bubble fuselage
Figure of eight
Can carry more pax
Will save fuel
Will be slightly slower
What is designed to oppose hoop stresses
Frames
What are hoop stresses
Outward stress in shape of s hoop round fuselage
What is the max difference of pressure between inside and outside
9 psi
What is the main spar of a wing
Front spar
What gives the shape of a wing
Ribs = front to back
What goes spanwise of a wing
Stringers
What structure is on the leading edge of s wing
Honeycomb structure
What is a externally braced wing
Usually older aircraft
Like a biplane
What is a semi cantilever wing structure
Mostly light / high wing aircraft
Like Cessna
What is a cantilever wing
Fully self supporting
No external bracing
What is the middle of a main spar called
web
What is the torsion box
2 spars with skin on upper and lower side
With rilo inside
What is the empennage
Tail section
Provides longitudinal / directional stability
Horizontal and vertical stabiliser
Rudder
Elevator
Supporting structure underneath
What load does a wing NOT want
Twisting
Can cause flutter
Where is the max bending moment of s wing
At the root
Reduces by fuel in wings
Engines as mass balance (forward of cg)
What is floor venting
Blow out panels = open automatically to equalise pressure across floor structure
Prevent distortion during rapid decompression
Aircraft doors are what type
Plug type
What is a cargo door operated by
Hydraulic power pack
Not s plug type door
What do windows need to withstand
Airflow Precipitation Birds Insects Pressurisation
What is the typical window construction
Glass
Heating element
Vinyl (polycarbonate)
Glass
= like a sandwich
What is a DV window
Direction vision window
= can open
= pilot must have a window that can open when cabin not pressured
What is a eye reference position
To set seat at correct position
What is the difference between a heavy landing and a overweight landing
Heavy = too much vertical descent rate
Overweight = too heavy
What is the primary damage of overweight / heavy landing
Landing gear
Support structure in wings / fuselage
Wing / tailplane attachments
What is secondary damage of a heavy and overweight landing
Fuselage structure
Fuselage upper and lower skin
Wing structure
Wing upper / lower skin
What is the damage of s nosewheel landing
Front pressure bulkhead
Nose wheel drag / shock struts
Possibility of nose wheel collapse
What is the damage / risk or tail strike
Higher risk on flapless landing
Over rotation
Damage to:
Empennage structure
Rear pressure bulkhead
What is sea level pressure
14.7 psi
1 bar = 14.5psi
What is hydrostatic pressure
Pressure generated by height
What is pascals law
Pressure will be felt the same everywhere 90° to surfaces
What is bramah press
Force = pressure x area
Small piston = small force
Large piston = large force
For the same pressure
What is a passive hydraulic system
No pump
If air in brakes = feel spongy
Solution = bleed breaks normally
What is a active hydraulic system
Pump is used to ensure pressure
Typically 3000psi
= size of actuators can be reduced = needs less fluid = pipes can be smaller = easier to fit
Reduces weight
What is a O-ring seal
With high pressure = night leak
Acts both directions
What is a chevron seal (v seal)
Only seals one direction
Better for very high pressure
What is the purpose of a backing ring
Prevents extrusion
What is mineral oil
DTD 585 = Def Stan 91-48 super clean
Red
Seal material = synthetic rubber
Flammable
What is synthetic oil
Skydrol
Green or purple
Butyl rubber seal
Irritant to both skin and eyes = fire resistance = less prone to cavitation
What happens if wrong oil is used
Eats away at seals
What is a single acting actuator
Hydraulic pressure moves piston in one direction
Spring returns pressure when released
= undercarriage door locks
What is a double acting balance
Hydraulic pressure moves piston in both directions
Equal pressure on both sides
Nose wheel steering
What is double acting unbalanced actuator
Pressure either side
One side has a ram shaft = less pressure that side
= more force going one way
= Landing gear / flaps
What are the 2 types of selector valve
Linear or spool
What is hydraulic lock
Nothing in / nothing out
What hydraulic system do some small planes use
Self contained package system
Or
Basic open centre system
When nothing selected = oil goes round and round
Simplest
Only one service can be operated at a time
What is a constant delivery pump
Gives same flow of hydraulic fluid
Requires automatic cut out valve to stop exploding pipes = senses pressure downstream
What happens if there isn’t enough pressure in accumulator
Hydraulic pressure will fluctuate
Can get chattering
What does a content delivery pump require
ACOV
accumulator
What is a constant pressure pump
Makes sure sufficient pressure to maintain 3000psi
Can simultaneously operate multiple services
Why is a hydraulic reservoir sometimes pressurised
Prevents cavitation
Or
Prevents boiling
How should a hydraulic reservoir be checked for level
When all system components are at correct setting
Accumulators are fully charged
What is a stack pipe
Stops fluid becoming too low so can be used for emergency system
Where is a hydraulic fluid temperature sensor found
In reservoir
Where does the air for a hydraulic system come from
Compressor stage of turbine
What are baffles for
Stop hydraulic fluid moving round too much
What are accumulators
Filled with nitrogen
Should be at half system pressure
But when main hydraulic system is fully charged should be 3000psi
Acts as a store of hydraulic fluid under pressure
damps our pressure fluctuations
What is a brake accumulator for
For operation of brakes if hydraulic pressure lost
Gives a limited number of applications
What happens to the ACOV if there is a leak
Cut in and out frequently
What happens to the swash plate in a constant pressure (variable volume) pump when at low pressure
Swash plate = acute angle = max deflection
What is a quill drive
Drive shaft necked so that if pump stops the drive shaft snaps to stop damage to engine
What is a drain case for
Small amount of fluid is let through holes in a hydraulic pump for lubrication
Collected in drain case
Purpose of a drain case filter
Monitor condition of pumps
If 2 pumps that deliver 3000psi @ 10 gals/ min each
What is the combined output
3000psi @ 20gals/ min
If one pump fails = services work slower / operating times extended
Not half speed!!
What are the 2 types of hydraulic filter element
Paper (replaceable)
Metal ( washable)
What is a full pressure full flow relief valve
Excess pressure acts against a spring causing the ball to unseat at cracking pressure
Dumps flow of pressure
What is a thermal relief valve
Relieves excess pressure caused by expansion of trapped fluid as ambient temperature increases
Senses pressure not temperature!!!
What does a mechanical overload protection do
Fitted in flap circuits and some spoiler circuits
Prevents damage caused by aerodynamic forces
Eg flaps at High speed
What is a restrictor valve
Used for undercarriage down
Flaps up
Restricts fluid flow to slow speed of operation
Found in up lines
What is a pressure maintaining valve (priority valve)
In event of system supply reducing
Ensures pressure is provided to essential services
What is a pressure reducing valve
Reduces pressure for use on some systems
What is a modulator
Specific to brake system = helps anti skid
Basically a flow control valve
What is a shuttle valve
Provides a method of having both emergency and normal supplies of pressure to a single source
What is a hydraulic fuse
If massive leak downstream = stops you leaking all your fluid
System upstream still operates normally
If there is a slow external hydraulic leak what happens to contents pressure and temperature
Contents slowly decrease
Pressure no change
Temperature no change
What happens to a fast external hydraulic leak in terms of contents pressure and temperature
Contents rapid loss
Pressure nil
Temperature n/a
What happens for a internal hydraulic leak in terms of contents pressure and temperature
Contents no change
Pressure no change
Temperature increases
What is a hand pump
Hydraulic pump
Double acting
What are sequence valves
Males systems work in right sequence
Can be mechanical or hydraulic
What prevents landing gear being selected up
Patched pin on leaver
What is the steps of landing gear retraction
Doors fully open
Inflight braking to stop wheels spinning usually around 400psi ish
Break the down lock
Main retraction jack starts to rotate
Doors shut
Cockpit indicator lights off
What are the steps of landing gear extension
Doors fully open
Undercarriage down
Over centre geometric device locks
Doors shut
Green cockpit indicators
What happens if landing gear doors are in incorrect position
Orange light
What are the characteristics of spring steel cantilever leg and rubber chord / bungee
Nothing to stop recoil / bounce
Typically used on small aircraft
What prevents the sliding / plunger or a oleo pneumatic strut from rotating in the leg
Torsion torque
What is a bogey
4 or more wheels would
In a shock absorber what acts as a damper
Oil
In a shock absorber what acts as the spring
Gas
In a shock absorber what happens when flutter plate is open
Oleo can compress easily