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Old 28th Jul 2016, 09:24
  #242 (permalink)  
swh

Eidolon
 
Join Date: May 2001
Location: Some hole
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I had downloaded the pdf before posting.

Components have multiple load cases they are designed to under the certification requirements. They are designed for the ground loads, vertical load factor, braking, bumps, turns, rejected takeoff, incomplete gear extension, ground winds, and break away. In flight they are designed for maneuver, gust, control deflection (normal and failure abnormal cases), buffet, inertia, vibration, aeroelastic/flutter loads. Additionally there are the other requirements such as jacking, pressurization, crash-worthiness, bird strike, lightning strike, hail, power plant failure, fire, fatigue, damage tolerance, fail safety, acoustics, and ground handling/towing.

Aircraft are designed so that the most limiting design case has 150% safety margin. Other non-limiting load cases at ultimate design load can have a additional margin of safety from a different load case which overlaps that component. For example the skin on the wing may need a ultimate load of X for bending moment, however requires 10 times X for crash worthiness. If the skin sees 2 times X bending moment load is is not going to fail as it still has significant margin for the crash worthiness requirement.

If we only had to look at 5 load cases when designing an aircraft we could do that in the afternoon, in reality it takes years because the task is a smidge more complicated.
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