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  #1  
Old 02-10-2019, 07:01 PM
Stockmanreef Stockmanreef is offline
 
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Default Torquing Vert Stab Attach Castle Nut Question

So I am attempting to torque down the bolt (AN4-5) for the front of the vertical stabilizer. It would not torque down to any range (50-70 in lb) to line up the hole for the cotter pin. the call out is for two 463P washers. So I added a third thin washer (1/32"). I put them all on the nut side and I can torque down and slide in the cotter pin. I was advised that I should not have all the washers on one side. So I moved one of the 463P washers to the head side. For some odd reason, I can't get the nut to torque down with any combination of washers on the nut side now that I have one washer on the head side.

I moved them all back to the nuts side and torqued down fine.

Any thoughts?

Is it unsafe to have three washers on the nut side?

thanks
ken
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  #2  
Old 02-10-2019, 07:55 PM
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jcarne jcarne is offline
 
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I think the general rule of thumb is no more than three washers before changing bolt size. I also don't know why someone told you not to have all three on the nut side, I can't think of any reason why it would be a problem. The only thing I can think of trying is to try playing with different combinations of thick and thin and finally to try a different AN4-5 if you got it, the threads and hole may be in different positions allowing for the cotter pin to go in. I also find cotter pins fight me more on Mondays so maybe wait a day.
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  #3  
Old 02-10-2019, 11:54 PM
Tommy123 Tommy123 is offline
 
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Acceptable practice is no more than two washers. Use a shorter bolt. A lot of fastener call outs in the plans are off, every plane is different. Use the bolt size that fits correctly don't just blindly follow plans.
I've seen fastener call outs on Boeing aircraft that were incorrect. I like to have one washer under nut to prevent scuffing the aluminum. Also never met a castellated nut I've ever put a toque wrench on unless it was specifically called for in forty years of airline aviation.
You would probably blow the torque range by just lining up the hole.

Last edited by Tommy123 : 02-10-2019 at 11:59 PM.
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  #4  
Old 02-11-2019, 05:55 AM
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snopercod snopercod is offline
 
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Quote:
Originally Posted by Stockmanreef View Post
Is it unsafe to have three washers on the nut side?
No. On the space shuttle, the specs allowed 3 washers on one side. If it's good enough for NASA, it's OK for you.

Edit: I agree with Jereme that you should try different AN-5 bolts. The tolerance on the grip is +/- 1/64" for an AN5 bolt. The tolerance on the length is +1/32" - 1/64" Source: Skybolt.
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Last edited by snopercod : 02-11-2019 at 06:05 AM.
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  #5  
Old 02-11-2019, 06:03 AM
Freemasm Freemasm is offline
 
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Default Basic torque rule of thumb

From my Space Shuttle Engineering days (I learned those old North American Aviation/Rockwell International/NASA specs before I learned any FAA related specs): There's a reason there's a range for torque values. I'm sticking to shear applications only.

- You torque to the mid value above the running torque (self locking nut) when you torque from the nut side. (preferred method)

- You torque to the high side when you have to torque from the bolt side as friction in the stack will add to the perceived (not actual/applied) torque

- You torque to the minimum value when utilizing a castellated nut then align the next hole (only for a non-specifically engineered application).

There is a lot margin in the fastener as the values for tension are typically ~ 90% higher. Don't forget about "Lite" washers when they make sense.

For the Aircraft Structural Engineers that may read this; yes, I simplified this and there are exceptions. I won't get into any back and forth. Remember the audience and application. I'm talking good shop practice here.
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Old 02-11-2019, 10:01 AM
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JonJay JonJay is offline
 
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Quote:
Originally Posted by Freemasm View Post
From my Space Shuttle Engineering days (I learned those old North American Aviation/Rockwell International/NASA specs before I learned any FAA related specs): There's a reason there's a range for torque values. I'm sticking to shear applications only.

- You torque to the mid value above the running torque (self locking nut) when you torque from the nut side. (preferred method)

- You torque to the high side when you have to torque from the bolt side as friction in the stack will add to the perceived (not actual/applied) torque

- You torque to the minimum value when utilizing a castellated nut then align the next hole (only for a non-specifically engineered application).

There is a lot margin in the fastener as the values for tension are typically ~ 90% higher. Don't forget about "Lite" washers when they make sense.

For the Aircraft Structural Engineers that may read this; yes, I simplified this and there are exceptions. I won't get into any back and forth. Remember the audience and application. I'm talking good shop practice here.
Should make this a sticky. Best answer I have heard.
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  #7  
Old 02-11-2019, 05:29 PM
pilotkms pilotkms is offline
 
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I agree Jonjay.
I just printed it for my maintenance logbook.
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  #8  
Old 02-12-2019, 05:05 AM
Stockmanreef Stockmanreef is offline
 
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what is the protocol for torquing down nuts that use a star washer like those on the grounding plates?
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  #9  
Old 02-12-2019, 11:04 AM
gasman gasman is offline
 
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Book torque...... but never reuse the star washer.
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  #10  
Old 07-03-2019, 01:15 PM
Stockmanreef Stockmanreef is offline
 
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Another random question: I am about to mount engine and the plans say that a washer may or may not be needed under the castle nut. So it is OK to have NO washer under the castle nut on the engine mount bolt?
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