FAA/EASA Ultimate Test 3 seconds requirements : What is the rationale behind it!

[AeroStructAnalyst]

What is rationale behind holding structures under Ultimate load test for 3 seconds accroding to FAR 25 or EASA CS25 Aircraft certification requirements? In terms of structural failures, what is the 3 seconds no failure at ultimate load testing requirement meant to demonstrate? I have asked this question from 'seasoned' Airframers and no satisfactory response was provided, so I am hoping someone out there perhaps can give more insight behind this requirement.

 

[SWComposites]

It's to ensure it is a "static" test, rather than a dynamic test where the ultimate load is only applied for a millisecond and the dynamic strength increase is used to pass the test.

 

[AeroStructAnalyst]

Thanks SWComposite,
I have always thought that was the main reason but I thought there was more justification behind the 3 seconds.

 

[SWComposites]

It was could have something to do with the capabilities of the instrumentation systems long ago and the time required to record data ( or write down the data manually, long, long ago).

 

[rb1957]

long ago someone picked a number ... count to three, that'll do.

and that became the standard ...

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