Scatter factor as per AC 23-13 A 1

[Jnnal]

Hi, as per AC 23-13 A, Eq.4 provides a scatter factor to account for the statistical variability inherent in the fatigue performance of built-up structures. As per the same, the standard deviation to be used for high strength steels like one used in landing gear are to be 25% and, the scatter factor worked out to be as high as 17. It looks very high. Generally, I see, aircraft industry uses 4 or 5 as a scatter factor for landing gear fatigue life estimation. Then, why is this discrepancy. in that case what number to be used for certification? is there any reference for the same. Thank you.

 

[rb1957]

landing gear are usually safe life. Sure they can be damage tolerant (I've worked on one that failed fatigue so used DTA) but not typical (in my experience).

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[SWComposites]

Agreed, landing gear are almost always certified as safe-life, as DT is impractical. About the only a/c structure that is now-days certified safe-life.

 

[Ng2020]

On a part 23 aircraft? Only if commuter category...

 

[rb1957]

sorry Ng, what do you mean ? most part 25 landing gear as safe life.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[Ng2020]

The OP stated they're working on a part 23 airplane. 23.571/2/3 (I'm it's assuming pre amdt 64) does not require a showing of compliance for landing gear structure, unless the airplane is to be certificated in commuter category (see 23.574).

 

[rb1957]

Wow, learn something new every day ! Makes sense.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.