AGK - Airframe Flashcards
What are the two major certification standards?
CS23 - Light aircraft
CS25 - Turbine powered large aircraft
What is the safe life concept?
No catastrophic damage to occur during normal operation over the life of the product.
What 3 ways can safe life be measured in?
Landings
Flight hours
Calendar duration
What is the fail-safe multiple load path concept?
Multiple load paths ensure if one fails, others can carry the load
What are the advantage of fail safe?
Inspections ensure failures are noticed
What are the disadvantages of fail safe?
Heavier aircraft leading to increased costs
What is stress?
Internal force per unit area in component
What is strain?
Deformation caused by stress as a change in dimension as percentage of the original.
What are the 4 types of stresses?
Tension
Compression
Torsion
Shear
What is the ultimate load?
1.5 * Design load
What is the design load?
2.5 g for Transport aircraft
What is elasticity?
The ability of an object to return to it’s shape under stress up to the elastic limit where permenant deformation occurs.
What 2 types of corrosion are there?
Oxidisation - exposure to air
Electrolytic - current between two metals
What affects the rate of corrosion?
Level of moisture
What is the relationship between increasing weight and fatigue?
1% increase in weight
5% increase in fatigue life consumption
What are composites?
Combination of two or more organic or inorganic components.
What is a composite matrix?
Holds composite together
What is a composite fibre?
Provides reinforcement
What are 6 advantages of composites?
Light Strong Stiff Durable Resistant to corrosion/fatigue Excellent strength/weight ratio
7 Disadvantages of composites?
Hard to find flaws May absorb water, freeze and delaminate Expensive to produce Difficult to repair Not damage tolerant Non conductive Heats up and delaminates when struck by lightning
What is hard time maintenance?
Set a definite limit for components after which it must be removed.
Failure preventitive method
What is on condition maintenance?
Inspect components to determine performance against a known standard.
Removal before failure in service.
What probability term for a minor failure?
Probable - 10^-3
What probability term for a major failure?
Remote - 10^-3 to 10^-5
What probability term for a hazardous failure?
Extremely remote - 10^-5 to 10^-7
What probability term for a catastrophic failure?
Extrememly improbable - 10^-9 or less
What is a truss structure?
Frames covered in fabric and doped
Internal bracing frames prevented buckling
Used in old type aircraft
What is a semi-monocoque construction?
Series of aluminium frames joined my longerons
Metal skin around the entire assembly
It no internal framework or truss
What is the skin used for in a semi-monocoque design?
Provides a smooth outer cover
What are formers and frames used for in a semi-monocoque design?
Defining the structure’s shape
Disadvantage of semi monocoque design?
Surface damage weakens the structure
What are the 6 principal components of the semi-monocoque design?
Aircraft skin
Formers/Frames
Stringers
Longerons
Bulkheads
Firewall
What do stringers do (semi-monocoque)?
Run logitudinally and bonded to skin to help withstand buckling
What are longerons?
Main logitudinal load carrying members of the fuselage which withstand banding loads
What are bulkheads?
Provide structural partitions within the fuselage to secure pressure.
Also provide structural support
What is a firewall?
A fire resistant bulkhead
What is a machined structure?
A single piece of aluminium forms skin and stringer like structure through the use of acid to dissolve unwanted metal
Advantage of a machined structure?
Dispenses of rivets and other attachment methods saving weight
What two reasons are fuselage cross sections circular?
Ensures airflow will not separate at moderate angles of attack or sideslip
Easily withstand loads of pressurisation
2 Advantages of double bubble fuselage?
Higher cruise critical mach number
Efficient, waste less space
3 Advantages of Oval cross section fuselage?
Lower cost
Greater capacity
Better options for cargo loading
What is the pressurisation differential maximum value?
9 psi
What is the pressure hull?
Entire fuselage section between the forward and rear bulkheads
What are the two forms of stress on the pressure hull?
Axial stress along the longitudinal axis
Hoop stress radially
3 Components of wing construction
Semi-monocoque with refinements
Main spar/front spar
Rear spar
Held together with ribs
What are the 3 types of wing design?
Cantilever
Semi cantilever
Externally braced
What defines a cantilever wing?
It is support at one end so the structure supports all the load internally
Why do all fast jet transport aircraft have cantilever wings?
External struts cause too much drag
What defines a semi cantilever wing?
It has some supporting struts like a cessna 172
What defines an externally braced wing?
Supporting struts and bracing wires, common on old biplanes
What is a wing spar?
Main spanwise structural member designed to withstand bending moments and weight of wing on the ground.
What is a torsion box?
Torsion box resists wing twisting adding to strength
What are wing ribs?
Wing ribs provide the wing aerodynamic shape allowing the stressed skin to be attached to the wing structure and transfer loads into the spars.
What to wing stringers do?
Same function as fuselage combine with ribs and transfer loads to the spars
What is the wing stressed skin? (2 points)
Provides a smooth aerodynamic cover
Designed to withstand tension and compression stresses
What is a wet wing construction?
Where internal wing space can form an integral fuel tank
Construction of the empennage?
Similar to wing with main spar to carry main bending loads and ribs to define the structure shape with skin covering
Benefit of a T-Tail?
Keep tail out of turbulent airflow of the wing
Smoother air flow
Disadvantage of a T-Tail?
It’s stuck in turbulence from the wing at high angle of attack could develop into superstall/deep stall
What 5 properties must flick deck windows have?
- Excellent optical qualities
- Be sealed securely to withstand cabin pressure
- Withstand stresses from temp differences
- Withstand significant impacts without breaking
- Have de ice/anti ice properties
What is inside a flight deck window? (2 piles)
Made of two transparent piles
Clear-vinyl interlayer absorbs impact forces and stops fragmenting
Electric conducting coat for anti-icing
Window set in pressure seals
What does CS25 require direct vision windows to do?
2 things
Designed to slide back or open inwards
Large enough to be used as an emergency escape
What are the CS25 regulations for a birdstrike? (Windshield and fuselage)?
Windscreen/Fuselage must be able to withstand penetration by a 4 lb bird at Vc at sea level or 0.85 Vc at 8000 ft.
What is the eye refernce position?
CS25 requires aircraft to be fitted with one so flight crew seats can be adjusted to the correct position to achieve optimal viewing angle
What is Pascal’s theorem?
Conservation of static pressure
The pressure is transmitted undiminished in all directions
What is the conservation of energy formula in a hydraulic system?
Input force * input distance = output force * output distance
What is a passive hydraulic system?
Human powered
What is an active hydraulic system?
Use one or more pumps
What is a closed centre hydraulic system design?
Constant pressure all the time
What is a open centre hydraulic system design?
Pressure only when needed
What are the types of hydraulic fluid?
Synthetic - Used where butyl/teflon seals
Mineral - only synthetic rubber seals, red colour
DO NOT MIX DIFFERENT TYPES
What is an open hydraulic circuit?
Series flow
Can only select one thing at a time
Spur gear (constant flow) pump used
Used on small to medium aircraft
What is a closed hydraulic system
Systems provided flow in paralell
Can operate multiple systems simultaneously
ACOV provides idling when no systems are used
Uses variable volume pump
What is the purpose of a stack pipe?
Ensures an emergency supply of fluid is avaliable in event of fluid loss.
Why do we pressurise the top of a hydraulic reservoir? (2)
To prevent cavitation in the pump
To prevent evaporation
What is the purpose of a hydraulic accumulator?
Piston with nitrogen above
Stores hydraulic pressure
If hydraulic pump fails can provide limit emergency pressure for essential services
Can damp out pressure pulses caused by the pump
What does the pressure gauge read on an accumulator with no power?
The pre charged nitrogen gas pressure
What does the pressure gauge read on an accumulator with power?
The system pressure
What do we have to use in conjunction with a constant delivery pump in a hydraulic system?
An ACOV (Automatic cut off valve)
What is a constant delivery pump?
Spur gear pump
Dump pump
Provides a constant volume of fluid supply
What is a constant pressure pump?
Through use of a swash plate and pistons we get no flow when it isn’t required (swash plate at 90 degrees)
No ACOV required for this type of pump as it can provide a variable volume based on needs.
In a constant pressure pump at what angle of the swash plate do we get no flow?
90 Degrees
How do we make a hydraulic motor?
Like a constant pressure pump but use a fixed angle swash plate and force fluid in the other way
How do we know if a hydraulic filter is blocked?
Red tag comes out the top if relief valve activated
When pops out can also activate a warning light
What is the purpose of relief valves?
To help prevent excessive system pressure
What does a restrictor valve do?
Restricts flow to slow speed to operate slower service
One way allows full flow in one direction but restricted in other
What is a pressure maintaining/priority valve?
Closes off non essential systems once pressure drops below set point
Allows other circuits to continue
What is the purpose of a shuttle valve?
Allow to use the most appropriate pressure to operate a service (EASA)
Uses differential pressure to guarantee supply if either system fails.
