strut bolt torque

[flyguy]

I just noticed the strut bold torque discussion in the parts thread. Didn't see any reply or suggestions by anyone to the question of the correct torque prevent binding, but still not be too loose. Anyone out there have any numbers? I understand what the theory is, but how much is enough?
Darryl

[astjp2]

Re: strut bolt torque

It should be the standard torque for the 1/4" and 5/16" AN bolts...Tim

[flyguy]

Re: strut bolt torque

Tim,
You didn't see the discussion of lubricating the bolts and allowing the joint to "rotate" like a pin fitting?
Darryl
By the by, some of the torque numbers I see in various manuals/listings/ect. strike me as stretch the bolt, offset the thread, never use a that bolt again, kind of numbers. Excellent for bridges and skyscrapers.

[astjp2]

Re: strut bolt torque

No, and there is nothing in the manual that I read that said the bolt is supposed to rotate. If it was needing to rotate, it would have a bushing like the landing gear. Maybe there is something I dont know about but I have not heard of it yet. Mine were torqued to the standard torque for the hardware that I used. I also use cotter pined hardware in all of my wing and strut bolts except for the jury struts. Tim

[flyguy]

Re: strut bolt torque

Check Forrest's comment(s) in the sticky thread "Replacement part Sources" page 2.
DC

[astjp2]

Re: strut bolt torque

I will look, thanks. Tim

[Robert Lees]

Re: strut bolt torque

Torque on bolts in shear? Unless in the manuals (which it isn't), don't torque them up to anything like the "standard" torque used for bolts in tension. Finger tight is adequate.

How many folks have replaced struts, only to find that the wing/strut attachment fittings are so deformed by over-torquing that the new struts won't fit between the fitting ears? Or crushed the spars? Of the ten sets of struts I've been involved with here, at least half have suffered that problem.

It's basic A&P stuff. Remember, the purpose of a nut on the end of a bolt in shear is to prevent the bolt from falling out. Not to stretch the bolt.

Edit after re-reading: The only bolt that needs a cotter (split) pin is the lower strut bolt where the step is fitted (it's the only rotating part). All the other strut bolts can be nylock nuts or pinch-nuts.

Basic engineering stuff.

[astjp2]

Re: strut bolt torque

Believe it or not, there is a torque for thin nuts for bolts in Shear, it is a standard torque in the standard aircraft handbook.....Tim

[Robert Lees]

Re: strut bolt torque

For thin nuts, perhaps...when was the last time the average mechanic used thin nuts?

Most think that they need to stretch the bolt.

[N96337]

Re: strut bolt torque

AC43.13-1B, table 7-1, page 7-9 has a table for torque values for shear and tension applications of MS20365 (AN365) as well as MS20364 nuts. I use "thin" nuts alot....but I've seldom been called "normal"....
John

[astjp2]

Re: strut bolt torque

Thank Gawd someone had thier 43 handy....It saves me from having to look them up....So here is another interesting question, how does a mechanic take into affect the drag torque from a Nylock or other friction locking nut...??? I know how the USAF does it and the US Army does it differently....

[flyguy]

Re: strut bolt torque

After due consideration I think my choice of the word "rotate" may not have been quite accurate. I have a couple of better ones in mind, but they are pretty goofy sounding, (e.g. angular flexing.)

As for the bottom bolt, personally I try to avoid rotating my step at all cost, except for one SB, LOL, since the up position is likely to result in skinned shins, banged elbows and generic bruises. Seriously, my bottom strut bolts have had nylon locking nuts on them (checked regularly) for many, many years. So far , so good.

I would like to have a GOOD aircraft fastener guide book as I was just looking at a handbook at the local pilot shop yesterday and the information on bolts was scarce, and what was there was totally dumb.

Points well taken on both (sides?) of the discussion, I appreciate the input.
Darryl

[N96337]

Re: strut bolt torque

Thank Gawd someone had thier 43 handy....It saves me from having to look them up....So here is another interesting question, how does a mechanic take into affect the drag torque from a Nylock or other friction locking nut...??? I know how the USAF does it and the US Army does it differently....

Again, head to AC43.13-1B, 7-40 and there's a procedure that's acceptable data for determining final torque.
The thing I worry about with some of the "off the shelf" pilot store books is that they aren't necessarily acceptable data...they might be, but it would be up to you to prove it if something ever came up. I figure since I'm going to be using some sort of data, it might as well be what the Administrator has already found to be acceptable, and save myself a headache down the road....
Darryl, an AC43.13-1B is some of the best money you'll ever spend on books for your airplane. I've worn out a few copies already, and have taken to keeping one for the "shop" and one for my desk, as they're always in the wrong place when I need them! There's a world of knowledge and techniques in there that are priceless when needed.
John

[flyguy]

Re: strut bolt torque

Just checked my old AC 43.13. strange I had never noticed the the torque tables there before. Always looking in the rib stitching, fabric repair, wood splice sections before. Much more reasonable numbers than I have seen in other references. Five ft.lbs for a 5/16, interesting.

Yeah, John, about time I invested in a new one mine is 1-2A. I have seen one good manual in a store that had what looked like some resonable cross references between "lubricated" threads and dry ones. Didn't get the title, data is probably around somewhere on the net, but I have seen some really BIG numbers for a given bolt in some references. Assume they really were thinking about bridges or Caterpillar tractors or such. Example 348 and 140 are not quite the same. (reference was 29 ft/lbs.)
DC

[Ron Greene]

Re: strut bolt torque

Guys,

Forget dog-eared copies and buying a book. Go here and download AC43.13-1B onto your computer. For Free.

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/0/99C827DB9BAAC81B86256B4500596C4E?OpenDocument

Ron Greene