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Tell me there is enough thread showing

V

Vlad

Well Known Member
Gents we completed landing gear install per SB. All hardware callout was by the book however we have doubts if there is enough thread showing on the middle one. Opinions please...


 
It looks a little short to me Vlad - as I bet it does to you (or you wouldn't be asking).
 
to short

To short the shank ( the grip Length ) needs to go all the way to the washer

The length of AN aircraft bolts is measured from under the head to the end of the bolt.
The Grip is the Length of a portion of the shank that has no threads.
AN960 flat washers are used under hex nuts to provide a bearing surface and as shims to obtain the correct grip length for a bolt and nut assembly.

A thin washer will not work in this situation.
 
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It looks to me like it does just meet the minimum

The requirement is 1.5 threads exposed. This refers to the end of the physical interface which is not necessarily the plane of the end of the nut but the end of the locking device. I have one or two minimum length bolts/screws in the airplane. As mentioned earlier you could substitute AN960-XXL washers for the AN960-XX washers to get a little more exposed bolt thread.

Bob Axsom
 
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Aren't the other two a little on the long side as well. It's hard to count, but it looks like 4-5 threads on both of those.
 
The nut is fully engaged! Personally though, I like to see two to three threads. I would change it.
 
FAA guidance on the number of threads required

When installing a bolt and nut, the typical rule of thumb is...you can use up to three washers and you should have one to three threads showing....but you must also consider the length of the bolt, since grip plays an important part in the equation. 43.13-1b gives us guidance on this, since the grip should extend the entire length of the hole(in a perfect world). In the following exerpt from that document, you are limited to using 1/8" of washers, not necessarily three. The typical length of threads on an AN bolt allows this much and still allows a thread to show on the nut after installation. If you can't get at least one thread, either you have more than 1/8" washers installed or the bolt is too short.

Per 43.13-1b Chapter 7-37.
GRIP LENGTH. The maximum combined height of
washers that should be used is 1/8 inch. This
limits the use of washers necessary to compensate
for grip, up to the next standard grip size.
AND
All bolt installations
which involve self-locking or plain nuts should
have at least one thread of the bolt protruding
through the nut.

The above applies only to AN bolts. Other hardware, such as an 8-32 threaded machine screw, technically does not have a limit to the number of threads that can show, although using the same rule as for bolts is a good practice.
Good luck.
 
Just finished the SB and have the EXACT same condition as shown in the photos. The bolt is too short, or a thin washer may rectify.
 
This is quite odd. Worried that mine may not be good, I just went out and photographed mine, no problem! I think Scott mentioned once during the SB talks, that extrusions are not precision, but vary from plane to plane somewhat. I had a problem of the cherry rivets being too LONG. Maybe I have a thin channel?
212beid.jpg
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I ordered thin washers because they weren't included in the kit, even though they were called up in the plans. I added the washers under the bolt head, although I could have omitted them as I ended up torqueing the nuts using a home-made tool like the one shown in an earlier thread.
 
I worked at a nuke plant where we discovered some bolts without full thread engagement in the nut. When we discussed it with the manufacturer they told us that full joint strength is attained with three threads fully engaged.

The thing that would bother me here is that everyone else seems to get two or three threads past the nut (mine too). This seems to indicate that the configuration is wrong. Possibly too short a bolt, too many washers or misaligned parts. It's usually best to look like everyone else's RV!
 
Washer mix-up?

Page 31 of 36 of the SB calls out NAS1149F0532 (thin) washers under the heads of the bolts.

The inventory on page 2 only lists the (4) NAS1149F0563 (thick) washers for under the nuts.

So, if you are using a thick washer under the head instead of a thin washer like shown on the drawing page 31, then that could account for the short thread pictures. Or, if you used no washer under the head, you might see more threads. Don, what did you use under the bolt heads?

Because the thin washers were not included in the kit, we need more exact information on what was installed on these planes.

I am starting my SB this next week, guys, so can't help yet with my results. Will post any pertinent findings...

Tony
 
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Oh Tony, you made me crawl under the plane for the 20th time today, my old body is getting sore.
As suspected, I used NO washer under the head! I cannot recall the exact reason now, perhaps since there were none to start with (35-03, figure 2), and perhaps to get enough threads showing. I don't torque nuts from the bolt head ever so maybe that was the reason.
Still, I could put a thin washer under the head, and STILL have enough threads showing though.
 
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Thin washers, thick washers, thin channels, thick channels, one thread, three threads. Variation is the enemy of Quality. I wrote the Boeing standard D1-9000 (now the Aerospace Standard - AS9100) on this, and all this makes me very nervous.

I re-torqued (with Tony T.) these bolts on my airplane after the requisite 5 hours (or is it landings? - the S.B. is very unclear) - well it was about 7 landings and 5 hours, so we split the difference - each bolt took about 3/4 turn to bring it back up to the specified torque.

Now, I may have to go out and look at mine one more time. Don - yours look perfect to me. But, wadda I know???

On Tuesdy, we go out and start working on Tony's N577RV - we'll figure out something.....

Bob Bogash
N737G
Now with 11 Flights / 15 Landings / 13.5 hrs Hobbs
 
N124GR

Here's a marginal quality iPhone pic of mine. More thread visible than Vlad's, but not as much as Don. I used the exact hardware included from Van's. Now we have three photos of the subject area, but from what I've read, I'm not sure we've reached a general consensus as to what's acceptable?

photosbp.jpg
 
txaviator said:
I'm not sure we've reached a general consensus as to what's acceptable?
Click to expand...

In this instance, meeting the standard self locking nut rule of thumb (minimum of one thread visable) is entirely acceptable.
As Joe pointed out, having bolt shank baring on the entire I.D. of the holes would be the most desirable in high load cases. In this instance, the highest loads on the bolt are in tension (in aircraft, most high load fasteners are in shear). Also, since it is very thick material (1/4"), the bolt size installed would be fine as long as the one thread visable guideline is met.

There are a number of tolerance's interacting here. The length tolerance on a standard AN bolt is pretty loose. There is a tolerance on the aluminum C channel extrusion. Another possible issue is whether the bolts have been seated with a drift and hammer as described in the S.B. (and I believe the latest Rev. of the construction manual).

In the end, it is builders decision. The bolt called out is considered to be sufficient for the expected tolerance range of parts, but the builder is the one that has to certify that the airplane is in a condition for safe operation, so they should use their own judgement (using AC43.13 and other aircraft standards documents) in determining whether it is appropriate.
 
txaviator said:
Here's a marginal quality iPhone pic of mine. More thread visible than Vlad's, but not as much as Don. I used the exact hardware included from Van's. Now we have three photos of the subject area, but from what I've read, I'm not sure we've reached a general consensus as to what's acceptable?
Click to expand...
For whatever it's worth, mine looked just like that. I pointed it out to the FAA Airworthiness inspector (FAA, not a DAR) during my inspection and he was fine with it.
 
rvbuilder2002 said:
...
There are a number of tolerance's interacting here. The length tolerance on a standard AN bolt is pretty loose. .....
Click to expand...

The AN5 bolt has a overall length tolerance of +1/32 and -1/64.

That amount alone is 3/4 the thickness of a thick washer.

I personally would be more concerned about the two outer nuts bottoming out in the last pic posted. I would add another washer.
 
That has bothered me as well, I am considering putting another washer on them, sure look marginal at best..
az_gila said:
The AN5 bolt has a overall length tolerance of +1/32 and -1/64.

That amount alone is 3/4 the thickness of a thick washer.

I personally would be more concerned about the two outer nuts bottoming out in the last pic posted. I would add another washer.
Click to expand...
 
Once the bolt's full threads have engaged all the metal threads in the nut, it'll be as strong as it can be in tension. The threads through the nylon part are not for strength but to ensure locking, and you need to have the appropriate threads sticking out of the nylon to be sure that the nylon is doing its thing.

Also, I side with the folks who said that a thin washer is adequate. It is. Think about it - with the nut and bolt in tension, the channel will, before failure, deform and shift the load from a distribution across the bottom of the nut which tends to be greater close to the edge of the hole, to one where the nut is more strongly loaded around its periphery. That'll happen whether the washer is a thin one or a thick one.

Dave
 
Perhaps I am wrong, but I think the objections to the thin washer were that it might allow shear loads to be applied to the threaded area, if the threaded area were inside the material (bolt shank too short). Nothing to do with the washer itself.
 
My concern has nothing to do with the amount of bolt sticking out past the nut, the height of the steel part of the nut is the same as the diameter of the bolt. When the bolt is all the way in the nut, the assembly of the bolt and nut are considered the same. a thread and a half is adequate for projection.

my concern is the shank of the bolt and trying to compare it to the number of threads of projection.

The key is the shear connection of bolt shank and the last item of the connection closest to the nut.

The last item should have the shank in at least 70% of it's thickness.
The trouble with saying that it looks ok because of the number of threads showing is the layman will think is ok in all similar conditions.

The total connection may have two or three shear points and must have the shank crossing them all.

Understanding a bolt assembly is vital.
The 1/4" U Channel should have the shank in a least 3/16 of a inch (75%) to be a good connection.

my view
 
I took some quick and dirty measurments and it looks like with a minimum of one thread exposed it would leave between 1 - 1.5 threads of the bolt within the bore of the hole when using the specified washer.
With a thread pitch of 24, that would be ~ 1/16 " inside of the nominally 1/4" thick channel, which means shank baring on 70 - 75% of the holes bore ( a little variation because of the small radiused transition between the threads and full shank diameter).
 
Now that is the right answer

Now that is the right answer

And when you re-toque it will be little more

Thanks Scott




rvbuilder2002 said:
I took some quick and dirty measurments and it looks like with a minimum of one thread exposed it would leave between 1 - 1.5 threads of the bolt within the bore of the hole when using the specified washer.
With a thread pitch of 24, that would be ~ 1/16 " inside of the nominally 1/4" thick channel, which means shank baring on 70 - 75% of the holes bore ( a little variation because of the small radiused transition between the threads and full shank diameter).
Click to expand...
 
rvbuilder2002 said:
I took some quick and dirty measurments and it looks like with a minimum of one thread exposed it would leave between 1 - 1.5 threads of the bolt within the bore of the hole when using the specified washer.
With a thread pitch of 24, that would be ~ 1/16 " inside of the nominally 1/4" thick channel, which means shank baring on 70 - 75% of the holes bore ( a little variation because of the small radiused transition between the threads and full shank diameter).
Click to expand...

As always, thanks for the input: Scott, and everyone else that replied!
 
Bolt length

It appears that in the example the grip length of the bolt is not a critical factor, only the engagement of the locking portion of the nut is critical.
If you closely examine a large selection of AN bolts you will find that the unthreaded portion just before the start of the threads is frequently smaller in diameter than the rest of the bolt. If the bolt is engaging a thick part this is not an issue.
Lets examine a hypothetical. A strut braced wing with a single strut on each side. The wing fittings are two pieces of .063 channel with .063 reinforcements welded to the channel. The long AN6 bolt goes through the channels and the strut in the middle. In this case I firmly believe that the BEST method is to use a bolt one dash number longer than required. This insures that the relatively thin fittings are fully engaging the full size diameter of the bolt. The number of washers is a distant second in consideration. I don't really care if it requires three washers or five, this is structurally the best technique and I will argue this with any FAA Inspector or DAR.
The number of threads exposed is only a rule of thumb. This varies with the size of the bolt as the threads get courser as the bolt size increases. The critical considerations are that the unthreaded portion fully engage all parts in critical shear situations, and that the nut does not bottom out on the thread.(not enough washers)
 
Grip Length

The grip length is the smooth part of the shank not counting thread and is a critical part of a proper bolt assembly.
 
More of the same...

I had the same problem, and subsequently fitted thin washers on the bolt head and under the nut. That fixed that problem.

I planned to torque all nuts and then mark them with torque gunge "at the end" of the gear reinstallation. Big mistake. The screws and nuts that fit in the four new holes "must" be torqued up before installing the landing gear. How do I know - I just installed, removed, and reinstalled the landing gear today. Took me all day, and I then needed a glass of malt to recover my composure. Don't copy me...

Cheers...Keith
 
I miss my flights to Scotland. Cabinet is almost empty, and the bottle of delicious Islay single malt Laphroaig is empty (seems that my wife is happy, she didn't like the smell :D)

Sorry, on topic again.....

I also used thin washers under the head.
 
Longer Bolt - no

RFSchaller said:
Why not just go to the next longer bolt if you're worried about thread engagement?
Click to expand...

I decided to try the next longer bolt (an AN5-23A). Assembling the hardware on my plane with a thin washer (per plans) under the -23A bolt head the nut will bottom out on the bolt shank. Even with a thick washer under the bolt head it looks like the nut could bottom out when considering there is possible variation in channel thickness.

So I concluded that the AN5-22A bolt, thin washer under the head and thick washer under the nut as specified in the plans, is the right setup. Scott, you knew that of course. I should have been faithful.

The only issue I see is that the thin washers are not included in the kit, and some may be using a thick washer under the bolt heads which could result in only about 1 thread or less showing.

Tony
 
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Low Pass said:
Can we get 5 pages on this question??

Just sayin.
Click to expand...

Sure. I have thin under bolt head, thick under nut, and mine looks like Vlad's original photo. I'd call it marginal but OK, and will likely improve when re-torqued. If not, I may remove the thin washer, but as the forward bolt is mainly in tension, not shear, I'm not too concerned about bearing stress on the channel web.

There you go - 5 and a bit! :)
 
Tony_T said:
The only issue I see is that the thin washers are not included in the kit, and some may be using a thick washer under the bolt heads which could result in only about 1 thread or less showing.
Click to expand...

I believe this oversight has now been corrected.

It should have been caught right away but this forum is not used as the official notification point for kit an plans issues. Not all things get seen.

This just amplifies the need to also contact someone at Van's when issues are discovered.
 
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