New job, need some hints from the experts

[MrStupidQuestons]

Hello all, this may be my first post on eng-tips but I've been a lurker for years. I just started a new job with an aero-startup and I was originally assigned to stress on secondary structure for systems but I am currently needed for design work on the secondary structure. The plane is a mostly composite structure VLJ. This is the first time working on a general aviation plane and I need to get off to a good start but I've never done design work.

My question is: What are some of the most important things I should consider as I begin work on secondary structure (brackets, clips, etc.) for the hydraulic systems? I realize this may be the most vague question ever posted here, but any constructive advice would be greatly appreciated. More specific questions are: What are the faa certification documents I should be following, are there off-the-shelf composite brackets I should consider, what can I do to better understand the load paths in a 3000 psi system, and what are the less obviuos failure modes of a composite hydraulic system bracket?

Thanks

 

[rb1957]

one red flag to me is protecting the composite/metal interface. i know that Al and Carbon don't like each other (that's why they use Ti fittings or other isolation means). a pet quibble ... i don't think i'd label hydraulic bracketry as 2ndary structure. Obvious loads are associated with big heavy pieces (accumulators, etc). I'm not a systems guy but i can't see significant loads on brkts supporting the tubing. two things i would be looking for would be how are deflections accounted for (like along the wing) and consideration of hydraulic pulse loads.

good luck

 

[HANDCALC]

Let's assume you are not designing the hydraulic systems, but only designing the attachment to the aircraft. Decide whether you are going to mechanically fasten your brackets to existing structure, build in the supports, or bond new attachments using CLICK-BOND products. Consider: wing-flexing and physical clearances around hydraulic lines, electrical bonding provisions for lightening protection, and fire protection issues. Review FAA advisory circulars like AC43.13-1B and industry standards like SAE ARP4752 to make sure you understand some of the basic issues. Calculate your loads, draw your free-body diagrams and physically test representative samples to determine design allowables. Talk to any AME's on site, and try to incorporate their experience and knowledge into your design. As they say, "the only stupid questions are the ones you didn't ask". Anyone else?

 

[MrStupidQuestons]

rb,

Good point, the structure holding up the heavy components will act more like primary structure in many cases. I am starting with the fuselage components but I would imagine there will be deflections to consider there as well. The pulse loads are yet TBD - any suggestions for documentation on this...? Thank you for your comments and suggestions.

HC,

Again, thank you for taking the time and for the great suggestions. The documentation suggestions are espeacially helpful. You are correct, I only have the bracketry for the systems, some simple Click-Bonds, clamp block brackets P-clips, and others that will need more detailed analysis. What type of substantiation is needed to use Click-Bond products? Buy all means, feel free to elaborate on the lightening and fire issues.

One other thing that comes to mind is thermal expansion loads. I would imagine that it would not be that big of a deal if the total length of an assembly were small, but long length of steel or aluminum tubing would be an issue.

You guys are really great to take the time to discuss this with me.

Thanks

 

[SkyPunk]

MIL-H-5440 hydraulic systems, design, and installation for aircraft may provide a great deal of answers.

MIL-W-5088 has considerations for clearance with electrical.

Should you elect to use aluminum brackets most common protection I have seen is last ply of composite stackup should be fiberglass extending at least .25 all directions from aluminum component footprint. Both surfaces epoxy primed, fay, and fillet sealed with 870, ac665, or MIL-PRF-81733 whatever known as in your neck of the woods. Fasteners wet installed, and cap sealed on aluminum side of stackup with same.

Hope I didn't fly in from left field on this one.



Skypunk

 

[aeromatt]

Skypunk,

That helps a lot, probably how most of the major bracketry I have should be installed.

Does anyone have any experience certifying Click-Bond products on carbon/epoxy composites?

Thanks