Bulkhead Cut Outs 1

[swilkins2]

Greetings-

My customer would like to make cut outs to the nose bulkhead. They are trying to put more more avionics into their nose cone. Therefore, after the cut outs are made, they will put cannon plugs, usb and ethernet plugs into a piece of sheet metal and rivet that into the where the cut out is. What sort of analysis is appropriate? The bulkhead is a pressure bulkhead. The max pressure is 8 psig. Since it is a nose bulkhead, the pressure is applied to the flat shear web. The thickness of he bulkhead .025" and it is 2024-T3. I am planning on analyzing the riveted joint to make sure that it doesn't fail. The load that I will look at is the Pressure (8 psi)*Surface Area of repair area. Also, I will make sure that I recommend that that the material that my customer mounts their connectors into is the same thickness as that of what they removed. Any suggestions woudl be appreciated.

Thanks,
-SW

 

[40818]

8 psi seems a little low to me to be honest. Normally pressue bulkheads are analysed to twice the max oeprating pressure differential (2psid).The fwd bulkhead at 0.25 is really quite thick, there must be no bulkhead curvatrue i take it?
Again, i must question the operating pressure you quote for the OEM to make it that thick.
You must asertain whetehr the bulkhead carries the load in bending (most probably by the size) or by membrane tension.
You need to re-evaluate how your going to analyse the structure, as the way your going isn't the right way.
Remember that you really dont want that bulkhead to fail....

 

[der8110]

Calculate your stresses by either ESDU 71013, “Elastic Direct Stresses and Deflections for Flat Rectangular Plates under Uniformly Distributed Normal Pressure”, or equation 19 on page A17.6 of Bruhn. Or FEM would be even better. If civilian (FAA) the regs are 25.365 and the usual 25.3xx series. Look at your rivet loads, fatigue, crack growth and such just like any other skin repair or mod.

 

[GBor]

This is a pressurized bulkhead with apparently no curvature and it is 0.025" think...general aviation? I'm guessing twin engine something that exceeds 18k feet?

Get a professional...this won't be as easy as it seems. der8110 summed it up in one line, but I'm guessing you won't follow the nuiances in what he/she stated.

Garland E. Borowski, PE
Engineering Manager
Star Aviation

 

[inertia4u]

Fatigue will be your main problem.

My first stab at reinforcement would be as follows:
I would up the gauge to 0.032". Install minimum of 3 1/2 rivet rows around the cutout. Allow for generous radius for the cutouts.

-----
Nert

 

[thruthefence]

And after the design is finalized, before cutting metal;

http://www.faa.gov/aircraft/air_cert/design_approvals/field_approvals/field_approv_proc/

http://www.faa.gov/about/office_org/field_offices/fsdo/lit/local_more/media/FA_Checklist.pdf

http://www.faa.gov/about/office_org/field_offices/fsdo/lit/local_more/media/FA_Instruct.pdf

 

[swilkins2]

Thank you all. The advice given has been very helpful.