Airframe Design and Materials Flashcards
What are the certifying standards
Set by EASA. US=FAA
CS23=Normal Aircraft/Commuter Aeroplanes/Utility Aerobatics
CS25=Large Aircrafts.
What do certifying standards cover
Design,Quality of Material, Build quality and safety measures associated with aircraft structure and its systems.
What is safe life
Principle
Designed Life span.
Requires structure to have an explicitly stated design life within which no catastrophic structural damage can occur from normal flight.
How are cycles recorded
Various structural/system components permitted maximum number of cycles.
Recorded either by flight hours,pressurisation cycles, landings and sometimes calendar based.
Once specified limit reached component has to be replaced or extensively overhauled.
What are Fail safe multiple load paths
Multiple load paths ensure if one path fails and alternative can carry all loads through a duplicated structural component.
If a part of a structure fails it fails in a safe way-fail safe.
Critical areas are wing spars, engine fittings, cabin windows.
Disadvantage of Fail Safe
Require a lot of disassembly to inspect.
Additional weight due to duplicates leads to reduced performance and increase operating cost.
What are stress and strain
Aircraft subject to stress and strain. Stress is internal force inside structural part as a result of external loads.
Strain is deformation by actions of stress on material.
Dynamic and static loads
Forces imposed by manoeuvring are dynamic as the amount of load changes dynamically
Static loads on wing spars when on ground through landing gear.
Bending loads
Wing root experiences large bending loads. In air wing affected by upward forces produced by lift. Some relief in air by weight of fuel in wings.
On ground bending caused by upwards static force of landing gear.
