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  #1  
Old 08-12-2021, 12:30 PM
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KatieB KatieB is offline
 
Join Date: Jun 2010
Location: Belton, MO
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Default Finishing kit lock nuts- nyloc or metal?

Hi all. A friend of mine is building an RV-14, his 3rd or 4th RV project. He noticed that most or all of the self-locking nuts included in the kit are metal instead of the usual nyloc. Normally, one would use metal lock nuts firewall-forward to guard against heat, and nylon lock nuts firewall-aft. He's worried the metal nuts are more likely to damage the cad plating and invite corrosion on the bolts aft of the firewall, so he called Van's, but didn't get a very detailed answer as to why they ditched the nylocs. Do you all know of a good reason to use metal lock nuts on the airframe aft of the firewall?

Thanks!
Katie
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  #2  
Old 08-12-2021, 12:46 PM
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rvbuilder2002 rvbuilder2002 is offline
 
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Two reasons
They are lighter, and cheaper.

I would think that if there was concern about what they do to the surface finish of a fastener, that they wouldn't meet stringent design requirements in place for MS hardware, but I agree, they do disturb the plating on the threads slightly.
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  #3  
Old 08-12-2021, 06:02 PM
Aluminum Aluminum is offline
 
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Although I stuck to the plans on my -14A, I too dislike intensely the MS21042 metal replacements for AN365s for a number of reasons:

- The drag torque is much higher and more variable than nylocs, so I keep having doubts if I put enough strain on the bolt. Some folks try to measure the drag torque with a small analog torque wrench to add to set value, but I find batches to differ quite a bit in the amount of "squeeze", so I just grudgingly follow Ch.5 guidelines for nylocs figuring they aren't falling out of the sky.

- Different wrench size for bolt and nut. Need four instead of two wrenches/sockets lying around when figuring out how to access a difficult bolt.

- Most 1/4" sockets can't reach all the way down--they bottom out on the bolt so the top of the nut gets mangled, must add washers etc.

- Much more difficult to handle with gloved fingers, starting the thread blind and so on.

- Open 1/4" wrenches feel too loose on the squeezed flats, likely to strip if not careful.

- Not immediately obvious if the nut has already been used and should be thrown out (but it matters less than with nylocs I suppose).

- More expensive to replace, $0.22 vs $0.13 apiece from Spruce.

- The aforementioned corrosion doubts.


For firewall-forward stuff AN363s don't suffer from most of these issues, but they are more expensive for some reason and a bit heavier.
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  #4  
Old 08-12-2021, 07:26 PM
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RV6_flyer RV6_flyer is offline
 
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To save weight when I built my RV-6, I replaced almost all the Nylocs with MS21042 nuts because they were lighter.

Next month with be 24-years since first flight and there are just shy of 3,500 flight hours.

I do not have any signs of corrosion that others think this substitution will cause.
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  #5  
Old 08-13-2021, 05:53 AM
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Bill Boyd Bill Boyd is offline
 
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How much weight do you estimate it saved?
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  #6  
Old 08-13-2021, 06:46 AM
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bjdecker bjdecker is offline
 
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IIRC the weight savings in an F1 rocket was ~4lbs. or so --- F1Boss can provide correct data.

Of note, I started down this path with my RV-7 a few years ago and ran into a couple of issues --

1. The nut isn't the same size as the bolt -- @#*&()! -- another socket/wrench combination needed for installation/removal. PITA.

2. There are differences between the MS21042s, Lubed/non-lubed. Then I looked at the data sheet for the MS21042 "L" and see that they are NOT an equivalent for the AN364/5...Oh my...

3. Then there was the hydrogen embrittlement issue from a few years back (2014)...no way to tell which ones were going to break until they broke. (https://ms21042.info/failures.html)

I decided to revert to tried/true -- AN364/365 aft of the firewall and AN363 (MS21045) ahead of the firewall..
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Last edited by bjdecker : 08-13-2021 at 07:01 AM.
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  #7  
Old 08-13-2021, 08:07 AM
BoydBirchler BoydBirchler is offline
 
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I can truly say, that with 22 owned planes and over 49 years of experience: I have yet to observe any corrosion problems on bolts or machine screws caused by the use of metal locking nuts.
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  #8  
Old 08-13-2021, 12:29 PM
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KatieB KatieB is offline
 
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Thanks for the info!
If it were my plane, I'd stick with nylocs...
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EAA Homebuilt Aircraft Council
Rebuilt most of SNF tornado victim RV-3B Tony Boy II (had to sell him, but he's flying!)
RV-9 93281 tail kit has arrived... here I go again!
VAF Dues Paid 2021!
Thoughts & opinions expressed here are my own, and not those of my employer.
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  #9  
Old 08-13-2021, 12:54 PM
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Toobuilder Toobuilder is offline
 
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Just about every nylock nut I see in my shop automatically goes in the trash whether new or not. I use the MS21042's on almost everything.
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