NAS bolt torque?

13brv3 · #1 10-21-2006, 07:07 PM

Greetings,

Years ago, I built an RV-8, and I recall that Van had a chart in the manual that gave the torque specs for each combination of bolt type, and nut type. When it came time to torque my wing bolts, I don't recall having any doubt about what was correct, since I had the chart to look it up on.

I just installed the wings permanently today on my current RV-8 project, and I DO mean permanently. MAN were those bolts tight

Anyway, I found that Van has a different chart now, and it doesn't mention NAS bolts at all.

Next step was to go to the handy dandy AN43-13, and I can't find NAS torque specs in there either. There's a nice chart for normal bolts, but I didn't see any chart for NAS bolts.

I seem to recall that NAS bolts have higher torque ranges than normal bolts, but so far, I can't find anything to prove that. My other local RV buddy has loaned his builders manual out, but had a note that the torque for the NAS1304 bolts was 80-100 in-lbs, and the NAS1307 bolts was 520-630 in-lbs. So far, I haven't found these specs printed anywhere.

The other point that nags me is the nuts that we're using. Van calls out for AN365 nuts, which are just common tension type friction nuts. When using these with NAS bolts, would you use the torque value for a common bolt, or for an NAS bolt?

For now, I have the NAS1307's torqued to 40 ft-lbs, and the NAS1304's torqued to 70 in-lbs. These are the common bolt specs.

Do I need to go up to NAS bolt specs, and if so, what are they? I would also need to see the source of the spec for myself to be sure.

Thanks,
Rusty (DAR's paperwork on my desk)

rvbuilder2002 · #2 10-21-2006, 07:23 PM

NAS torque values are the same as for the equiv. size AN bolts.

The nuts used on NAS bolts are the same nuts used on AN bolts and the torque values in large part are related to the strength of the fastener threads, not the strength of the faster shank.

Bob Axsom · #3 10-21-2006, 07:46 PM

Scott, My plans book shows them close but the NAS 1303 through 1320 bolts with the AN365 nuts are shown with a little higher torgue limit range than the AN3 through AN 20 bolts with the AN365 nuts.

10-32 AN 20-25ins-lbs vs. NAS 25-30
1/4-28 50-70 vs. 80-100
5/16-24 100-140 vs. 120-145
3/8-24 160-190 vs. 200-250
7/16-20 450-500 vs. 520-630
1/2-20 480-690 vs. 770-950

This is from a table in the RV-6A book that identifies the source as AC43.13-1A dated 1972.

Bob Axsom

Quote:

Originally Posted by rvbuilder2002

NAS torque values are the same as for the equiv. size AN bolts.

The nuts used on NAS bolts are the same nuts used on AN bolts and the torque values in large part are related to the strength of the fastener threads, not the strength of the faster shank.

13brv3 · #4 10-22-2006, 07:23 AM

Well, it's clear as mud now

After some more thought, I rememberd that I still had my preview plans book from the earlier -8 that I built. Sure enough, there's my old friend the torque chart, and it very clearly shows a higher torque spec for NAS13XX bolts when used with AN365 nuts.

As Bob mentioned, the chart does show a reference of "AC 43.13.1A", which appears to have been cancelled in 1998 when the current "1B" version was released. This may at least explain why I can't find this info in the current "1B" version.

I guess the question now is why did the FAA remove the NAS bolt torque info from AC 43.13.1B. Did they decide it was wrong to use the higher torque, or did they just omit the info because they didn't think it was commonly needed?

This is important enough that I'll call Van's Monday to double check, but it's clear that there are planes out there that are using two different torque specs for their wing bolts. This almost sounds like the beginning of another AD.

Thanks,
Rusty

mlw450802 · #5 10-22-2006, 12:51 PM

Quote:

Originally Posted by 13brv3

Well, it's clear as mud now

After some more thought, I rememberd that I still had my preview plans book from the earlier -8 that I built. Sure enough, there's my old friend the torque chart, and it very clearly shows a higher torque spec for NAS13XX bolts when used with AN365 nuts.

As Bob mentioned, the chart does show a reference of "AC 43.13.1A", which appears to have been cancelled in 1998 when the current "1B" version was released. This may at least explain why I can't find this info in the current "1B" version.

I guess the question now is why did the FAA remove the NAS bolt torque info from AC 43.13.1B. Did they decide it was wrong to use the higher torque, or did they just omit the info because they didn't think it was commonly needed?

This is important enough that I'll call Van's Monday to double check, but it's clear that there are planes out there that are using two different torque specs for their wing bolts. This almost sounds like the beginning of another AD.

Thanks,
Rusty

Doing a google search on 'nas bolt torque' gave these hits on the first page:

http://www.coastfab.com/torque&fastener.html
http://www.sacskyranch.com/mechanic_contents.htm

-mike

rvbuilder2002 · #6 10-22-2006, 03:40 PM

Quote:

Originally Posted by Bob Axsom

Scott, My plans book shows them close but the NAS 1303 through 1320 bolts with the AN365 nuts are shown with a little higher torgue limit range than the AN3 through AN 20 bolts with the AN365 nuts.

Bob Axsom

Hmmmm...

Been a couple of years since I mounted any wings. Thats what I get for working from memory which seems to "work" more poorly as time goes on.

Thanks. I will have to go look at my charts again to do a "refresh".

Bob Axsom · #7 10-22-2006, 06:14 PM

You and the rest of Van's staff in 1996 taught me how to build an aluminum airplane in October of 1996. I still owe you.

Bob Axsom

13brv3 · #8 10-23-2006, 09:03 AM

I just talked to Ken at Van's, and he told me that everyone just uses the normal AN torque specs. Naturally, he also said that was all they ever used, but I pointed out that the old manual showed a higher spec, and I know for a fact that people were using that spec.

Overall, he wasn't concerned by the fact that planes are flying with different torque specs, and I have to admit that this lack of concern does bother me a bit. I wonder if Van or one of the other engineers at Van's would treat this so casually. On the other hand, they should know this already, so perhaps there's really no reason to worry.

For now, the choice isn't too difficult. I'm torqued at the high end of the AN specs, which is very close to the low end of the old (?) NAS specs. This is also what virtually all builders do now, and it hasn't been a problem, so I should quit worrying about it and move on.

Cheers,
Rusty