Airframe Design and Materials Flashcards
Minor Failure
Probable
10^3
Major Failure
Remote
10^5
Hazardous Failure
Extremely Remote
10^7
Catastrophic Failure
Extremely Unprobable
10^9
Safe Life
The life of an aircraft which it will not suffer catastrophic failure.
May be used during a declared number of cycles or flight hours.
Fail Safe
The load is carried by other components if a part of the structure fails.
The limited amount of time that an aircraft can carry a failed load.
Can be carried until the next periodic inspection.
“PARALLEL LOAD PATHS”
Damage Tolerant structure
Load is spread over a large area.
Bending
The total combination of tension, compression and shear.
Tension
The outer edge stresses.
Can cause pulled rivets.
Compression
The inner edges squeezing together.
Shear
Occurs across the structure as forces try and tear it.
Stress
The internal force per unit area inside structural part, as a result of external loads
Strain
- The quantifiable effects of stress
- The Deformation caused by the action of stress on a material
Buckling
Deformation occurring to a thin sheet after compressive forces.
What is a Stringer used for?
L shape metal that is bonded to skin.
Will PREVENT BUCKLING
Design Limit Load CS25
The maximum load the designer expects the aircraft to experience in service.
2.5g
Ultimate load = 2.5g x 1.5 = 3.75g
Dynamic Load
Builds up quickly due to changes in flight conditions.
Produced when manoeuvring
Can be severe.
Static Load
Build up slowly, fairly constant
When does maximum stress occur at the wings?
Maximum stress occurs with empty wing tanks
What provides bending relief at the wing roots?
Ailerons
Fuel in wings
Underslung engines.
What does the Wohler Curve exhibit?
Relationship between stress and cycles to Failure
Stress Corrosion
Combination of stress & corrosion.
Causes by fatigue.
Unpredictable and quick
What determines the number of cycles to failure?
The amplitude or size of load
Define an Alloy
A combination of two or more metals providing properties we didn’t have previously
Properties of an alloy
Elasticity
Plasticity
Strength
Stiffness
Most common materials for alloys
Aluminium
Titanium
Magnesium
Steel
What is the most common alloy used in today’s modern manufacturing?
Duralumin
Properties of Duralumin
A copper-based aluminium alloy
Good strength to weight ratio
It’s more susceptible to corrosion difficult to weld however
Alclad
Improvement to Duralumin
Aluminium coating on its surfaces
Duralumin gives it strength; Pure aluminium protects the Duralumin
What is steel composed of?
Iron and carbon
What are composite materials?
Two more materials with properties that are different to the original elements
Consist of matrix, bulk, reinforcement
The reinforcement is fibre.
Properties of composite materials?
Light weight
Rigidity
Strength
Why is the nosecone made from glass fibre?
Allows for radio waves to pass through, transparent.
Properties of Aramid/Kevlar
Impact proof
What is fibrelam used for
Flooring
Disadvantage of a honeycomb/sandwiched flooring
Not suitable for concentrated loads, loads must be spread.
Hard Time Maintenance
A component that is overhauled or replaced after a set number of hours, cycles or operations.
On Condition Maintenance
Visually check if performance is acceptable.
Without disassembly, or removal from service.
Framework / Truss Fuselage
Frame takes all the loads
