Fuel Lines in Composite Airplane - Glass them In or Use Clamps?

Discussion in 'Firewall Forward / Props / Fuel system' started by wsimpso1, Jun 11, 2019.

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  1. Jun 11, 2019 #1

    wsimpso1

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    I am installing hard fuel lines in my composite airplane. The ones in the stub wings will only have access to allow me to remove and install the outer wing panels (with the fuel tanks). They will be essentially sealed in once the top wing skins are bonded and taped in place. I am leaving them with a healthy zig-zag to allow reconnecting if I have to cut off a flare and redo it at some point.

    I could drill nice big holes in each surface they penetrate, then apply a bracket and an Adel clamp per AC 43.13. Or I could just drill holes with the tiniest of clearance and fiberglass them in with some dry micro and a fiberglass tape. So, which way would you do this in an inaccessable fiberglass structure and why?

    Billski
     
  2. Jun 11, 2019 #2

    Hot Wings

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    Steel or aluminum? My intuition says bond in place, but use Proseal rather than resin - especially if aluminum. I've seen both steel and aluminum lines bonded in place on ground bound vehicles wear through when the bonding fails and they start rubbing/vibrating. Most were probably due to poor prep.
    Link to Adel clamp material types:
    http://www.aeroelectric.com/articles/adel.html
     
  3. Jun 11, 2019 #3

    gtae07

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    A picture would help. However, I never see lines bonded into structure on larger aircraft.
     
  4. Jun 11, 2019 #4

    BJC

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    Avoid differential expansion issues and chafing; drill the hole with reasonable clearance and use clamps.


    BJC
     
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  5. Jun 11, 2019 #5

    don january

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    I intend to have my fuel lines in the wing and header tank area removable for future repairs if needed. With today's firewall grommets and compression fittings passing threw root ribs and Fus sides can be doable and a well planned access panel at areas where fittings connect will make easy work of it if there is such a thing. ;)
     
  6. Jun 11, 2019 #6

    plncraze

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    I believe Lancair (certified) used grounded tubes but they also had the conductive ( hopefully) mesh in the structure. The wings were wet but the hard lines went to the engine.
     
  7. Jun 11, 2019 #7

    BBerson

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    Aluminum can corrode when embedded.
     
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  8. Jun 11, 2019 #8

    wsimpso1

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    It is an airplane and NOT forward of the firewall, so it is aluminum hard lines... What difference would it make?

    What does Proseal do that epoxy and filler will not?

    I am looking for how you would do it and why ...

    Billski
     
    Last edited: Jun 11, 2019
  9. Jun 11, 2019 #9

    wsimpso1

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    There is nothing installed. What you can see is the bottom skin and a couple sandwich ribs that the fuel lines must pass through. Big aircraft like to be able to change out everything.
     
  10. Jun 11, 2019 #10

    wsimpso1

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    In most of the airplane, the fuel line are replaceable. In this location, well, let's hope they never need to be touched again.
     
  11. Jun 11, 2019 #11

    wsimpso1

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    Grounded tubes? My apologies, I must have been unclear, bonding has multiple meanings. In composites, we use the word bonding to mean "gluing it together", and that is what I meant.
     
  12. Jun 11, 2019 #12

    wsimpso1

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    Ok, and how do I prevent trapped water and corrosion at the Adel clamps?
     
  13. Jun 11, 2019 #13

    gtae07

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    I’d rather use clamps, or possibly a rubber grommet at certain locations. Either way, there’s a little cushioning for vibration and a little allowance for deflection or differential temperature expansion. I don’t like the idea of bonding lines in place.

    Movement and shifting of lines is a bigger concern in large aircraft, especially in wings. There are many places you see hydraulic lines supported by rubber blocks with two or three (or even more) lines through them.

    Disclaimer: the vast majority of my relevant experience is with hydraulic line installations on transport-category aircraft.
     
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  14. Jun 11, 2019 #14

    wsimpso1

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    There are plans for a number of fiberglass airplanes where they just cover the fuel line with flox and glass and go on. Have these birds given grief to their owners over this sort of thing?

    Billski
     
  15. Jun 11, 2019 #15

    BBerson

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    I don't know if corrosion is a big problem or not. But once the aluminum gets the powder stage it stays moist and can't get out and just rots through. Maybe a rubber tube or something.
     
  16. Jun 11, 2019 #16

    Hot Wings

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    Clean steel epoxied in place is less likely to de-bond than the aluminum. Proseal 'sticks' better, is more like a form-in-place grommet, allows for some thermal expansion and has fewer parts than the Adel clamps.

    I see nothing wrong with Adel clamps - I just think the form in place method is more elegant....But that is just an opinion.
    Ever since I cut out my first glued in windshield I've used that kind of material for all sorts of things. It is tough stuff. Proseal is similar and compatible with fuel.
     
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  17. Jun 12, 2019 #17

    Marc Zeitlin

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    You've gotten a bunch of good responses. Here's what EZ's do:

    The plans call for glassing the fuselage fuel lines (3/8" 3003 or 5002 AL) to the sides of the fuselage every 8 - 12" or so. Some folks glass the whole thing in - some use standoffs and ADEL clamps. The inside of the fuselage is accessible though, and inspectable. I've never seen, even on 40 year old aircraft, any corrosion of the AL lines, or any issue with temperature coefficients.

    If the lines are going to be permanently installed in an inaccessible area, then I'd put some service curves in them so that _IF_ there's some expansion/contraction, it can move a bit, and then glass it in. I'd make sure that there was no way for the line to touch ANYTHING other than what it's glassed into, and that there can be no wear or rubbing or chafing anywhere. I certainly don't see any problem with ADEL clamps either - it's just more complicated an install. You could also install nylon bulkhead bushings and run the tubing through that - any of these ways could work and last the lifetime of the aircraft.

    For anything that _IS_ accessible, however, I strongly recommend ADEL clamps on standoffs - maintenance capability is extremely important.

    My $0.02.
     
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  18. Jun 12, 2019 #18

    Winginitt

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    br-768-brake-line-clamps.jpg My suggestion is to glass an aluminum frame in place that you can screw an aluminum access cover to. Then use a thru bulkhead fitting in the cover. The fuel line behind the cover could have some curved excess length that would allow the cover to be unscrewed and pulled outward, or a short length of quality flexible fuel line that would also allow removal of the cover plate. I don't think I would want to install any part of a fuel system that I didn't have easy or reasonably easy access to.

    Edit to add info. One other thing you might consider is the use of some preformmed fiber/ plastic clamps. They come in sizes to fit different size hard lines and they secure the lines so they have no vibratory movement. I'm not talking about the cheap white plastic clamps with the same general shape as an Adel clamp. These are thicker and more Ridgid with no metal like an Adel has.
     
    Last edited: Jun 12, 2019
  19. Jun 12, 2019 #19

    Wanttaja

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    Guy I talked to the other day said not to make "hard" connections between wing tanks and the fuselage. If you snag a wingtip on a forced landing, the wing might displace slightly. A solid connection will break and you end up with a fuel leak. A flexible hose can tolerate some offset.

    Ron Wanttaja
     
  20. Jun 12, 2019 #20

    Victor Bravo

    Victor Bravo

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    I have no formal education on it, but my gut feel is a slip fit through rubber grommets in holes in the ribs. This allows heat/cold expansion, bending, vibration, and any other kind of movement (torsion???) to not damage or work harden anything over time. Glassing or bonding the tube creates a hard point where nothing can move even a little, which will eventually cause it to chafe against the inside of the blob of flox or cab-o-sil or glass tape or whatever. In the worst case scenario it's easier to replace the tube if something goes to s**t, you would not have to put wrenches and tools in through a large hole to un-do Adel clamps.
     
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