divan arm loads 2

[mila888]

I'm trying to find which loads do I have to use for a side-facing divan arm stress analysis.
Thank you

 

[rb1957]

is it occupied for landing ? (that'd be unusual)

is it placarded "not to be occupied in event of a crash" (i do think that one !) ?

if not, then it'd be the standard crash loads for the divan alone (9g fwd, 3g side).

then there'd be the case when it's occupied in-flight (weight = divan + occupyant(s)) to ult flight inertia up/down

 

[mila888]

We have some situations when the divan is occupied - having a seat belt I don't know if we have to consider the whole weight of the occupant - some suggestions are to use an inertia load of 70lbs from occupant applied on the upper part of the cabinet (the divan arm) during the forward load case - any idea from where could come the 70 lbs or if there is a way to calculate this load.
thank you
Sorry I just subscribe to this site and I didn't find yet how to reply to your post or if this the way to reply.

 

[bf109g]

I'm with rb. You need to look at emergency landing conditions (FAR 25.561).

I would also look at TSO-C39 and SAE Aerospace Standard AS8049.

As an aside, I worked on a project several years ago for sideways facing seats and saw a video from the Civil Aeromedical Institute. The video showed sled tests of dummies in foward/side and aft facing seats. The human body is not designed to take 9g's in it's side.

 

[rb1957]

usually these divan's aren't occupied at take-off (or landing), this is usually a limitation in the FMS; for the reasons bf109g gives.

it's your divan, so you can limit it if you want.

if it is occupied for take-off, then the crash cases apply to the divan and it's occupants (185 lbs now). i suspect that allowing some load to be reacted by nearby structure was required becuase the divan alone wasn't able to handle the load.

if it is to be occupied, i'd chat with your airworthiness people, in case they want some special consideration for the side orientation (FAR25.785 doesn't give much insight !).

remember, the up/down loads from from the ultimate flight envelope (the local fuselage acceleration where the divan is placed).

 

[GBor]

Should we ask the seemingly obvious first: Is this a US tail number? Also, I know divans USUALLY go in to VIP jets, but is the a FAR 25 aircraft?

 

[epeus]

bf109g,

That study/video was probably:

DOT/FAA/AM-07/13
Office of Aerospace Medicine
Washington, DC 20591

Assessment of Injury
Potential in Aircraft Side-
Facing Seats Using the ES-2
Anthropomorphic Test Dummy

It is a very interesting read, let me know if you can't find it in the public domain....it will put you off sitting in a sidefaceing seat anyway

Regarding Sidefacing seats, my only experience has been in rotorcraft and not typically analysing the seat structure, however I do recall it very imporatant to have the correct type of harness installed, ie a standard 4 point harness is not really suitable, something like a TARC harness is better. I also recall armrests are not that crash-hot for divans - I would definitely agree with rb1957 that the divan should be placarded "not for takeoff/landing".

to the OP, I suspect that report may have some loads in it which may indicate whether your heading in the right direction - its been awhile since I have read it!

 

[mila888]

Thank you so much - it's the first time I'm using this forum and it is incredible - I found the FAA report - I looked also for AS8049/1 for side facing seats but it's still in WIP - it's a US tail A/C - FAR25 - VIP with the divan occupied during landing and take-off - the divan arm is a small cabinet attached to the divan - for this reason I don't know if the occupant weight is applied only on the divan - as per FAA test we can see that some weight from occupant (upper torso, left leg, arm) could be applied towards the divan arm for forward 9g case. As per AC 25.562 the side facing seat dynamic test is different - they suggest to use the automotive solution but they don't say how.
Thank you very much for your help - it's an amazing experience for me to receive so much help from people I don't know, from people having so much knowledge.

 

[rb1957]

let's assume that this relatively minor component of your interior wasn't focused on when your company started its discussions with the FAA about certification of the project. in that case, now is the time. occupying a side-facing seat for take-off (and landing) is reasonably unusual in FAR25 a/c, so they may want to see something special with it. distributing the load is the relatively easy bit ... you can distribute the load in anyway that is reasonable and can be rationalised. you say a report has put 70lbs on the adjacent unit, is not another (certified) instance similar to yours (justification) or are you vetting someone else's analysis ?

i scanned 25.562, didn't see any reference to "automotive". what about all the other requirements of 562 (beat tension loads, HIC, ...) ?

is it possible to add an airbag to the adjacent unit ? (following on from the "automotive" comment)

 

[mila888]

01/10/2006 AC 25.562-1B
page 38

d. Side-facing Seats.
(1) General. All seats occupiable for takeoff and landing are subject to the
specified dynamic test conditions. Included are side-facing seats and both single
occupancy and multiple place seats, such as divans. Compliance with the structural
requirements should be demonstrated for side-facing seats, using the same conditions for
the test and pass/fail criteria as for fore- and aft-facing seats. The seat should be loaded
in the most critical case structurally. Means of restraining the ATDs may need to be
adapted to ensure adequate retention during the test. The application of floor distortion
will need to be assessed on an individual basis, depending on the design of the fixation of
the seat. The injury criteria of § 25.562 are not adequate to demonstrate equivalent safety
of side-facing seats when compared to fore- and aft-facing seats.

To demonstrate equivalent safety fully in the absence of such specified criteria, the applicant must use other injury criteria which may be derived from the automotive industry, which uses side-impact ATDs.

(2) Assessment criteria. Research into side-facing seats is ongoing. As
research proceeds, the FAA will work toward establishing a more definitive policy with
respect to the acceptance of side-facing seats. Until then, in the absence of specific
compliance guidance, the FAA is prepared to assess side-facing seats on the following
basis:
(a) The seat must demonstrate compliance with the structural requirement.
(b) If an acceptable side impact ATD has not been used with assessment of
the corresponding injury criteria, it must be shown that the occupants are restrained in a
manner that prevents substantial energy absorption by body to body contact (on a
multiple occupancy seat) and which, using the best available engineering judgment,
minimizes injury to the occupant(s).

 

[bf109g]

No matter how you restrain the torso, I have a major concern about the occupant's head. The neck just can't take these side loads without serious damage to the spinal cord.

Sideways facing is just not a safe idea for takeoff/landing unless there's support for the head. And such support would probably not be aesthetically pleasing. IMHO.

 

[der8110]

First to answer the original question: divan end arm cabinets typically are analyzed with just their own inertial loading, occupant loads are carried separately through the restraint system (belts) and divan frame. Beyond 25.561, there are abuse loads listed in SAE ARP's (Aerospace Recommended Practices, not AS8049) for seating systems: for arm rests, I think it is 300 lbs. vertically and 150 lbs. sideways. They also have food tray loads you could also use. Now, if the divan is certified as a berth for take-off and landing, that is a different situation, it now has to take the forward occupant inertial load (the "diaphragm or padded end board"). As a practical matter, I have never seen a divan arm or end cabinet so designed. Full bulkheads, yes.

If 25.562 is part of your cert basis, then the end cabinet will have to be there for test - of the occupant interaction, not its strength (I have never seen a crash pulse accepted totally in lieu of 3 second static). But for the cabinet itself, to show 25.561 compliance you do not have to include the loads an occupant places on it, because in .561 the occupant and cabinet are separate masses. If your cabinet attaches to the divan frame, the the frame needs to be strong enough to take those loads too. So unless the seat belts attach to the cabinet - analyze them separately.

As to some of the, well, ignorance - side facing divans are quite common. And safe. 9g's is next to nothing, 16g's too in comparison to the 30-40g's in a frontal car crash and 60-some g's in a side collision. As a matter of fact automotive side impact dummies are specified for these tests. Unfortunately there is nothing convenient and completely codified yet for 25.562 like AC25.562-1B and AS8049, go to the various exemptions and Equivalent Level of Safety findings. Areas of interest are torso trauma index, occupant-to-occupant contact, and leg loads (though not femur loads; I never saw any that amounted to much). And there are no side facing TSO-C127a products yet, they are to TSO-C39b but have been dynamically tested. Belt geometry is critical, and looks "odd", the lap belt on the leading hip anchors behind the middle of the back.

Divan vendors will help you to a limited extent, but they do not know anything about your particular installation. And one last item, you still need to show compliance to 25.785 so any nearby items would need to be padded.

 

[bf109g]

der,

Sounds like you have experience in this area. Admittedly, I haven't done much bizjet work.

Thanks for keeping me straight.