Factor of safety

[Simon Chaddock]

Aircraft are normally designed with a factor of safety of 1.5.

In other word it should survive 1.5 times the maximum designed load which I believe for commercial airliners is 2.5g sustained.

On test the A380 wing apparently failed at 1.45 maximum load so Airbus incorporated a mod weighing just 30kg to satisfy the EASA & FAA.

Given the total weight of the A380 wing this does show the extraordinary level of design detail they have to go to on these big aeroplanes.

 

I hope they got it right!

[Erfolg]

I do not understand where this thread comes from.

 

The factor of safety, may be reassuring.

 

The real challenge is defining the maximum design load, justifying and supporting the contention. After all, not all aircraft have a rating for 6g normal max. operation.

 

Although there are many examples of commercial aircraft suffering extreme issues and surviving, which I would be surprised were envisaged by the engineers when formulating the design parameters.

 

Yep, re-assuring.

[Martin Harris - Moderator]

The factor is applied to the design load e.g. +4 -2 would be tested to fail at more than +6 -3  ... the placard speeds are based on these factors to establish maximum manouvering speeds etc. (although to hit 1.5 times design loads only requires exceeding the placarded speed by 1.22 times)

[Erfolg]

What I am hinting at are such issues as sink rate for landing, and many other parameters. Where designers start with a all up weight, with weight allocations and duty requirements, for the sub assemblies. As the design process progresses, there are variance between allocations and anticipated outcome, which need approval, feeding back into the weight and design, load calculations etc. 

 

Like many things, in principal easy, in practice needs management and control. I guess that is why the design process can be expensive.

Edited By Erfolg on 19/08/2010 12:41:54