Bolts and Washers and Nuts or am I "Nuts"

[gyrodeputy]

So I have a simple question to ask about bolts, nuts and washers.

I have researched at length what fasteners should be used in aviation applications.

In my kit I was supplied with 100% AN aircraft grade fasteners. :whoo:

In my research I have struggled to find an answer to a specific question about washers.

Here is what I have found (according to the FAA guide)

1. You may not use more than 3 washers total.

2. The purpose of the washer is to evenly distribute the load onto the pieces being fastened.

3. You should not have more than 1 thread inside the piece being fastened or more than 3 threads exposed outside the nut. If you encounter either of these conditions your bolt is either too short or too long respectively.

Having said all of that...here is my question:

CAN you SHOULD you or should you not place a washer under the bolt head AND the nut?

The reason why I am asking is that I don't want the BOLT head to mark up or scratch the paint on the frame when I assemble the kit. However it this is considered incorrect or improper form, I won't do it. However if I can put a washer on both the bolt side and the nut side of the pieces being fastened it would make me very happy.

I look forward to everyone's thoughts.

 

[j bird]

Washer under both, at least one thread showing past end of nylock nut, no more then four, you can add a couple washer if need be.

 

[gyrodeputy]

I must have been tired the first time I watched the kit instruction videos...

Nico clearly shows nuts on both sides...LOL!!!

If space allows I will be doing nuts on both sides to prevent paint damage.

 

[eddie]

Some bolts have a rounded area at the junction of the shank and the head, a washer

prevents that part of the bolt from being squeezed by the hole if the tolerance is tight,

it also prevents the sharp edge of the hole from cutting into the bolt where its rounded

and weakening it,The use of a washer at each end of a bolt and nut is best if possible.


Best regards,eddie....

 

[SandL]

Washer distributes load ... got that , so washer on both ends, makes sense
what is the problem if the bolt is showing more then 3 threads ?, granted it can look a little messy, but is there an engineering issue in doing that . ?

 

[bryancobb]

.. what is the problem if the bolt is showing more then 3 threads ?

Adds a fair amount of unnecessary weight, and is more likely to interfere with moving flight controls, etc.

 

[MadMuz]

Washer distributes load ... got that , so washer on both ends, makes sense
what is the problem if the bolt is showing more then 3 threads ?, granted it can look a little messy, but is there an engineering issue in doing that . ?

SandL, the threads of AN bolts are rolled in, not cut in and are a very specific length of thread compared to the width of the nut. If there is more than 3 threads showing from the nyloc nut, the nut will be contacting the portion of the bolt where the thread stops, so you may be torqueing up the nut on the bolt, but it is not clamping the material tighter, it is just the nut running into the end of the thread.... if there is 1-3 threads from the nyloc, then the nut hasn't run out of thread and the nut/bolt combo is clamping the pieces as designed.

Due to the shape f the AN bolt under the head, a washer at the head end is not 'critical' however, I like to have a washer under head and nut, because I often paint cheek plates and don't want to scratch them either... and I also believe that the washer distributes the load better.... also it stops a wrench or socket scratching the plate.... so not critical, but I prefer washer at both ends:yo:

 

[Aviomania]

Heath, use WASHERS not Nuts on both sides. We supply you with some extra bolts of other sizes, many more washers as well as thin washers so you can be sure you will finish your kit... and a lot of bolts, nuts and washers will remain so you can use them for your engine mount conversion.

A note.... AN bolt head has a built in washer at the bottom so... if need be you may not instal one under the head... but it is recommended unless otherwise stated. when tightening turn the nut... not the bolt.

 

[gyrodeputy]

Thanks Nico and everybody else for the comments.

 

[phantom]

the reason that a bolt should never turned to tighten is that it will wear the cad plating off and the aluminum around the bolt will corrode and the bolt will rust.

Norm

 

[SandL]

SandL, the threads of AN bolts are rolled in, not cut in and are a very specific length of thread compared to the width of the nut. If there is more than 3 threads showing from the nyloc nut, the nut will be contacting the portion of the bolt where the thread stops, so you may be torqueing up the nut on the bolt, but it is not clamping the material tighter, it is just the nut running into the end of the thread.... if there is 1-3 threads from the nyloc, then the nut hasn't run out of thread and the nut/bolt combo is clamping the pieces as designed.

Due to the shape f the AN bolt under the head, a washer at the head end is not 'critical' however, I like to have a washer under head and nut, because I often paint cheek plates and don't want to scratch them either... and I also believe that the washer distributes the load better.... also it stops a wrench or socket scratching the plate.... so not critical, but I prefer washer at both ends:yo:

well you live and learn more every day, makes so much sense. Thank you
and other posters. So I guess that just by looking you can see the difference between an AN bolt and a shop bought bolt. I will look closer at other kit flying machines with a much more knowlagable view.

 

[bryancobb]

If you guys want to get THE WORD right from the horse's mouth, go to the FAA Advisory Circular that is the reference bible for A&P Mechanics.

AC 43.13-1B Chapter 7

 

[gyromike]

AC 43.13-1B is downloadable in it's entirety here:
http://www.faa.gov/documentLibrary/media/Advisory_Circular/AC43.13-1b.pdf

Or chapter by chapter here:
http://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.information/documentid/99861

 

[Abid]

So I have a simple question to ask about bolts, nuts and washers.

I have researched at length what fasteners should be used in aviation applications.

In my kit I was supplied with 100% AN aircraft grade fasteners. :whoo:

In my research I have struggled to find an answer to a specific question about washers.

Here is what I have found (according to the FAA guide)

1. You may not use more than 3 washers total.

2. The purpose of the washer is to evenly distribute the load onto the pieces being fastened.

3. You should not have more than 1 thread inside the piece being fastened or more than 3 threads exposed outside the nut. If you encounter either of these conditions your bolt is either too short or too long respectively.

Having said all of that...here is my question:

CAN you SHOULD you or should you not place a washer under the bolt head AND the nut?

The reason why I am asking is that I don't want the BOLT head to mark up or scratch the paint on the frame when I assemble the kit. However it this is considered incorrect or improper form, I won't do it. However if I can put a washer on both the bolt side and the nut side of the pieces being fastened it would make me very happy.

I look forward to everyone's thoughts.

Hi:
AN bolts have a flat area under the head so using a washer under the head is not necessary but advised. You should also use a flat washer under the nut. That is more important.

If you see more threads remaining on an AN bolt then it is likely that you have used a longer size of bolt than necessary which is not good because your bolt has bottomed out. However this is only true for AN bolts. Also if you use thin nuts (AN364 low profile nuts instead of AN365 regular profile nuts), that negates this rule. So the intent has to be understood.

Technically there is nothing wrong with more threads if the bolt and nut in use are different than AN bolt and nut. You do have extra weight hanging off which is useless.

AN bolts have rolled on threads where many industrial bolts have threads that are cut. Good quality bolts however can be found with rolled threads because rolling the threads on is actually a cheaper way to make the bolt in mass production. The bigger issue is Hydrogen de-embrittlement. AN bolts have higher levels of quality control to make sure that after plating the bolts are properly baked to specs to get rid of embrittlement produced during plating. The industrial bolts also follow the same specs but they are usually plated with Zinc or yellow zinc and not with Cadmium like AN bolts. Cadmium plating is bad for the environment.

On the AG-1 we use unplated bolts for certain bolts in the rotor head and grease them so as to not take a chance with Hydrogen de-embrittlement. Helicopters do that as well. AN bolts have had a go from cheap imitators as well BTW.

 

[MadMuz]

AN washers are good too, you can get thick and thin.... so especially if you have castle nuts and with a thick washer at each end and the hole is right where you cant get the pin thru, rather than leave it looser than you want or over tightening the nut, ypu can change the head end washer for a thin washer which indexes the castle around to hopefully uncover the hole at the right torque....

I find a good trick after a heavy landing or long trailer journey, it is good to run a wrench lightly over the head end of bolts... if a bolt has stretched or is loose for some reason, the bolt will turn.... you are not trying to turn it, just seeing if it is tight, where if you ddo it from the nut end, you might accidently tighten the nut and not know if it was actually loose to begin with and also I use marker paint on the nuts when tight, so that might come off if you test for loose bolts by turning the nut end..... if you do find a bolt is loose, replace it.... if it was tight before and loose now, it may have stretched :yo: