AN bulkhead fitting torques

[grjtucson]

I'm using the Standard Aircraft Handbook table for torques for my flare fittings. Dry, 37 deg scotch-brited flares.

However, it is not clear what I should use for torque values for the nuts that hold the bulkhead fitting to the rib. It seems reasonable to use the same. Both searching here, the SAH, and AC43.13 returned no other thoughts.

Am I good doing that, am I over-obsessing (very much not like me), or have I missed the right answer?

Also, any pitfalls/gotchas in sealing these fittings and spacers to the rib? I was just planning to wet-seal the fittings in there and fillet around each side.

One tank is nearly done

George

[az_gila]

George.... you could try using the Aluminum column in this chart. I presume you are using the blue anodized aluminum fittings....

http://dodgeram.org/tech/specs/bolts/SAE_bolts.html

The only gotcha is that sometimes there is a minimum thickness that the bulkhead (rib) must have since the fittings are not threaded all of the way. An aluminum washer or spacer may be needed if this is the case.

gil in the other end of Tucson

[grjtucson]

Originally Posted by az_gila

George.... you could try using the Aluminum column in this chart. I presume you are using the blue anodized aluminum fittings....

http://dodgeram.org/tech/specs/bolts/SAE_bolts.html

The only gotcha is that sometimes there is a minimum thickness that the bulkhead (rib) must have since the fittings are not threaded all of the way. An aluminum washer or spacer may be needed if this is the case.

gil in the other end of Tucson

Gil,

Thanks for the chart. If I use those values based on thread size, I end up with REALLY high torques - beyond my little 20-200 in lb wrench for a few, and all a bit much for aluminum AN fittings I'm thinking...

Of course I ended up doing these late last night and by the time I had seal everywhere I went for the "Gutten-teit" precision German torque value. I did use spacers on all three bulkhead fittings (draw, vent, and return) and ended up with enough seal that they look leak-proof without being embarassingly gobbed up. I doubt they'll come loose either

George

[Kevin Horton]

Originally Posted by grjtucson

Thanks for the chart. If I use those values based on thread size, I end up with REALLY high torques - beyond my little 20-200 in lb wrench for a few, and all a bit much for aluminum AN fittings I'm thinking...

I think that chart is for bolts, where you need a minimum torque to allow the bolt to perform its structural function of holding things together. The nut on an AN fitting only needs to be tight enough to hold the fitting in position, with enough load on the nut so it won't loosen up. The torque values are not critical.