FAA AC 25.562-1B Static Interface Loads

[60NUAGE]

Let me give a question about the aircraft seat test criteria.

FAA AC AC No: 25.562-1B Dynamic Evaluation of Seat Restraint Systems and Occupant Protection on Transport Airplanes

d. Structural Tests for seats with the family design concepts (see §§ 25.562(c)(7) and (8)).
(1) Substantiation of the 16g longitudinal load condition for each family of seats:
Step 1: Determine the 9g forward static interface loads(or any other standard load) for all seats. It is generally accepted that the interface loads calculated at 0° are sufficient to determine the most critical seat. Special seat design features may require interface load calculations that would take into account the aircraft tapered sections. All occupancy variations and combinations shall be considered for each seat (from unoccupied to fully occupied).

Q1 : What is static interface loads for seat?
Q2 : What is the difference between 'static interface loads' and 'standard load' in this case?
Q3 : How the static interface loads is calculated?

Any comments or answer will be highly appreciated.

 

[WKTaylor]

How about telling-us what references YOU already have/are-using to for Your understanding of seat/restraint design/loading?

Lots of good-stuff available, already. It would be useful for us to know 'where' You've started and are now 'stuck'!

Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[60NUAGE]

WKTaylor

Thank you so much for your comment.

I can say that I don't understand the concept of 'interface loads' actually.
Could you explain me what is the 'interface loads' of the seat structure?

I think I have to start from understanding of this.

 

[Sparweb]

Make sure you follow all the sub-references in the AC. You are reading something at the top of a very wide pyramid, and to understand everything going on you have to know what's in the base.

For seats, the "interface loads" are the loads applied to each fastener that secures the seat. Seat track, wall track, etc. Every seat manufacturer is expected to determine (by test and/or analysis) the loads applied to the surrounding structure of the aircraft by the seat when it is loaded to the prescribed crash conditions.

The static load assumes no variable accelerations with time. This is usually 9g (from FAR 25.561), but that's only the forward direction. You also have to consider the side, down, up and aft load directions. Again from 25.561.

Your third question is a little hard to answer without explaining the entire Subpart C of Far 25 and making sure you have actually read and understood that - It's kind of fundamental to have a solid grip on that before you can get into specific things like seats.

Since you already have AC 25.562-1B, surely you know where to get the rest of them. Give yourself a few days of reading if you haven't already started!

https://www.faa.gov/aircraft/air_cert/design_approvals/transport/rules_acs_policy/

 

[60NUAGE]

Thank you so much for your kind answer. SparWeb.

I really appreciate it. Now I became to understand the basic concept of 'interface load' by your kind explanation. And I know I have a long way to have a solid grip on this subject as you mentioned. It is very difficult for me to understand the basic word in the this AC. Please help me to climb the top from the bottom of the pyramid.

Thank you again.

 

[rb1957]

Apologies if I'm blunt, but how much structural analysis experience do you have ?

To start, the point of 25.562 is to ensure that the seat does not collapse under a dynamic load of 16g. This is an improvement on the 25.561 9g static load. I think what they were see in plane crashes is that the seat seemed to be collapsing under loads in excess of 9g whereas the surrounding structure remained "intact". They realised this load was "dynamic" (very short duration) and the local structure responds differently to these loads (as opposed to static loads).

As I understand the dynamic (ie 16g) seat analysis you have to model the local surrounding structure as well as the seat, and run a dynamic analysis.

The dynamic test setup is very similar.

The 9g static load is a much easier thing to grasp and to analyze.

another day in paradise, or is paradise one day closer ?

 

[60NUAGE]

rb1957

Thank you for your kind comment.

I am Not a engineer and No experience for seat design. Completely layperson in the seat design. But I just what to know about test requirements of aircraft seat design.

It is hard for me to go further in AC 25.562-1B with many unfamiliar terms.

'aft fitting resultant load'
'critical seat'

Now I am stuck in the 'TEST ARTICLE SELECTION & RELATED TEST SETUP'

 

[rb1957]

I understand, but those terms should be readily understood by someone reading an AC.

Not being an Engineer makes things very difficult for you. Not be a Structures Engineer makes it damn near impossible.

I suggest you talk to your local airworthiness (whoever will be approving your test plan) for guidance,
or engage someone local who does understand these terms and this work.

good luck

another day in paradise, or is paradise one day closer ?

 

[BragiBaldursson]

For a seat to be installed on the aircraft you need to know how much loading will be transmitted to the floor seat tracks of the aircraft from the seat. This is analysed for various static acceleration load cases and for an empty seat, passenger only sitting in seat 1, passenger only sitting in seat 2 and then a fully occupied seat.

The analysis is just a summation of moments and forces and you end up with some maximum force values transmitted to the seat posts and legs. You need to check that these loads are within the aircraft limits.

If you are doing static and dynamic tests of seats there is an SAE standard for that test setup.

 

[60NUAGE]

Thank you so much for your kind comment. BragiBaldursson

Does the term "aircraft limit" in the second paragraph mean the requirements of PART 45.561?

And I presume that the "SAE Standard" in the last sentence refers to "Aircraft Seat Design Guidance and Clarifications ARP5526E."

 

[BragiBaldursson]

The standard is Performance Standard for Seats in Civil Rotorcraft, Transport Aircraft, and General Aviation Aircraft AS8049D

https://www.sae.org/standards/content/as8049d/.

25.561(b) gives you the inertia loads to work with.

 

[60NUAGE]

Many thanks for your kind reply. BragiBaldursson