Lemmingman

Lemmingman

Well Known Member
I'm doing research on safetying bolts and fittings and AC43.13 does a good job of describing the basics, but I still have a question on the types of wire that I should keep in my shop and when one diameter of stainless steel wire should be used vs. another.

On the topic diameter for double twist 43.13 says:

When using double-twist method of safety wiring, .032 inch minimum diameter wire should be used on parts that have a hole diameter larger than .045 inch. Safety wire of .020 inch diameter (double strand) may be used on parts having a nominal hole diameter between .045 and .062 inch with a spacing between parts of less than 2 inches.
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The way I read this is that if I have a hole of .045 I can use SS wire above .032 and I should be good. How do I know what size the hole is short of getting out the micrometer and loupe?

I guess a better question might be what do you stock and what do you use for what purpose?
 
Lemmingman said:
The way I read this is that if I have a hole of .045 I can use SS wire above .032 and I should be good. How do I know what size the hole is short of getting out the micrometer and loupe?

I guess a better question might be what do you stock and what do you use for what purpose?
Click to expand...

Typically I probably use 4 times as much .032 as all other sizes put together. Easiest way to check hole diameter is with a drill bit.
 
question

On this same subject, I have noticed through looking at pics here and elsewhere, that a lot of b-nuts on fuel systems are not safety wired. I have read a lot of fuel leaks causing fires also because of loose fittings. So, when I install my fuel lines from tank all the way to carb. what do I do to insure these fittings do not back off? thanks.

bird
 
Bird,

Generally, most folks don't safety b-nuts, which is something I always wondered about as well. Apparently these nuts don't back off easily. However, you can purchase a drill jig and drill your own holes for safety wires:

http://pitposse.com/nutdrilljig.html

I've been thinking of doing this for my fuel lines, just for the extra margin of safety.

There are some other threads about this in the archives.

cheers,
greg
 
Lemmingman said:
...
The way I read this is that if I have a hole of .045 I can use SS wire above .032 and I should be good. How do I know what size the hole is short of getting out the micrometer and loupe?

I guess a better question might be what do you stock and what do you use for what purpose?
Click to expand...

As a reference, AN3 and AN4 bolt heads have a nominal hole diameter of 0.045 and can be used as a visual check for a smaller hole...:)

The Mil-Spec (now a NASM spec) also uses essentially the same text as AC 43.13 saying to use 0.032 wire as a general default.

http://www.everyspec.com/MS+Specs/MS3/MS33000-MS33999/download.php?spec=MS33540J.014934.pdf

Note that manufacturers data overrides as always, and most props call for 0.040 safety wire.
 
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thanks

Thanks Greg, I am going to either drill and safety wire or use some type of method lock them. Its just too many leaks and fires that I have read and seen.
Hoping more info like from Mel or other advisors on here will have some input on this.

bird
 
Safety wire

You will find .032" will be the most widely used wire on the aircraft, with a few .040" tasks like prop bolts.Rule of thumb is, if it doesnt fit through the hole in the bolt/nut, drop down to next size. Anything over .050" is a pain to even use. Get a can of .032" and .040" and you will have enough for life. As far as "B" nuts, very few ever have safety wire needs. I have made my living for 31 years as an AP/IA in heavy aircraft overhaul, and find that properly torqued fittings seldom if ever come loose. I always utilize "torque seal"(bright orange) or as the military calls it, sabotage paint on the "B" nuts and self locking nuts all over my plane after I have torqued them. It is very easy to see when looking over during pre-flight or inspection if a joint has loosened,as the torque seal will crack and crumble. Remember, safety wire does not maintain torque,it just keeps a loosened nut from comming all the way off...good luck!
 
fixnflyguy said:
As far as "B" nuts, very few ever have safety wire needs. I have made my living for 31 years as an AP/IA in heavy aircraft overhaul, and find that properly torqued fittings seldom if ever come loose.
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I agree with Bill, I've never seen a torqued 'B' nut come loose, they are not normally safeted in all the aircraft I've ever seen (includes GA and heavy iron).

Just tighten em down and you should never have a problem.

However, on every RV I do a condition Inspection on (including my own) I check every fuel line 'B' nut with a wrench, just looking at them does nothing. A common fitting I find loose is the ones in the fuel pump, be sure to always check the jam nuts on these fittings at they are subject to loosening from the tension and flexing on the hoses.

Using torque seal is ok, but the only way to really check that a fitting is tight is by using a wrench, eyeballs cannot check torque!
 
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