Bolts provided by Beringer for brake caliper too short?

I'm currently working on bolting my Beringer brake calipers onto the main wheel fairing brackets for my RV-10. All 5 bolts provided by Beringer seem to be too short because the shank does not extend all the way through the parts. For some of the bolts (maybe all of them) I could go up to the next length bolt and the shank would just barely make it to the other side of the parts. I'd like to think that Beringer wouldn't get this wrong and I can't find any other posts about it so I figured I would check if this is actually ok.

AC 43.13 says:


But "in general" doesn't necessarily mean always, so does the shank need to extend all the way through all of the parts being bolted together or is it ok if only threads are visible exiting the hole as long as there are enough threads for the nut?

Someone usually corrects me but if there are three threads showing when the nut is torqued you are in good shape. How many threads show with washers and nuts on?

Bolts

tims88 said:

I'm currently working on bolting my Beringer brake calipers onto the main wheel fairing brackets for my RV-10. All 5 bolts provided by Beringer seem to be too short because the shank does not extend all the way through the parts. For some of the bolts (maybe all of them) I could go up to the next length bolt and the shank would just barely make it to the other side of the parts. I'd like to think that Beringer wouldn't get this wrong and I can't find any other posts about it so I figured I would check if this is actually ok.

AC 43.13 says:

In general, bolt grip lengths of a fastener is the thickness of the material the fastener is designed to hold when two or more parts are being assembled​

But "in general" doesn't necessarily mean always, so does the shank need to extend all the way through all of the parts being bolted together or is it ok if only threads are visible exiting the hole as long as there are enough threads for the nut?

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I vaguely remember replacing bolts with longer ones.
Been a while and I've slept since then.

I know what you mean about the shank going through the assembly, and not having the threads in there, but that’s not always the way it works out. One example is the rear spar, they don’t want the threads in the parts, so they specify a longer than normal bolt, then a stack of 3 washers to keep the nut from running out of threads. I’ve seen more than one plane where the builder didn’t understand this, and substituted a shorter bolt, I since replaced it with the correct stack (and cotter pin).
I would venture to say on your brake application, as long as you get some threads through the nut, it’s fine.

In a thick assembly / item where there will be a lot of bolt shank baring load, it is acceptable to have a few threads inside of the body of the part as long as the rules for proper nut engagement are still met.

The overriding issue is to make sure the nut doesn't bottom out on the shank of the bolt. When that happens, the torque wrench will show the correct torque, BUT the bolt is essentially un-torqued.

That's why washers are stacked in some instances.

Thanks everyone. I've ordered some longer bolts but I'm feeling a lot better now about the bolts Beringer calls out so I'll likely just stick with those unless responses to my follow up questions below change things.

JDA_BTR said:

How many threads show with washers and nuts on?

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I think most of the bolts will only have 1 thread showing past the nut but I did find that 7-37 in AC 43.13 says at least 1 thread should be showing so I think it might be ok.

rvbuilder2002 said:

In a thick assembly / item where there will be a lot of bolt shank baring load, it is acceptable to have a few threads inside of the body of the part as long as the rules for proper nut engagement are still met.

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Thanks, that's good to know. Is this still true if the last part in the assembly only has threads in it? The shanks of the bolts I've circled in the attachment end inside of the AV-VANS-016 part so only the threads extend into U-1010.

Follow up question: Is it ever ok to not put a washer under a nut? I thought washers were required to distribute the clamping force a little and to prevent the nut from damaging the part underneath while tightening it. However, the two bolts circled in the attached picture do not use washers under the nuts and I believe that if they had washers underneath (even the thin .032" washer) that there would not be any threads showing past the nut.

tims88 said:

Thanks, that's good to know. Is this still true if the last part in the assembly only has threads in it? The shanks of the bolts I've circled in the attachment end inside of the AV-VANS-016 part so only the threads extend into U-1010.

Follow up question: Is it ever ok to not put a washer under a nut? I thought washers were required to distribute the clamping force a little and to prevent the nut from damaging the part underneath while tightening it. However, the two bolts circled in the attached picture do not use washers under the nuts and I believe that if they had washers underneath (even the thin .032" washer) that there would not be any threads showing past the nut.

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Having a component part within an assembly baring only on the bolt threads ( such as a thin flange, etc) is not allowed. Sometimes it is possible to just turn the bolt around so that the bolt shank is coming through the thin material.

Washers are used under nuts to distribute load, but since most bolted joints in aircraft are loaded in sheer, this is not a very important purpose. More important is the protection of the component from the rotating nut. Particularly when the nut is bearing against aluminum. it is for this reason that sometimes a thin washer is specified under a bolt head. In instances where the bolt is going to have to be rotated when being torqued.

Thanks Scott, that all makes sense. Based on that I think I'll replace those two bolts with longer ones so that I can get the shanks into/through U-1010 and add a washer to protect the aluminum from the nuts.

I think the rest of the bolts are acceptable since those shanks do extend at least part way into the much thicker Beringer parts and will have at least one thread showing through the nut.

I'll probably also torque the bolt on the inboard side of U-1010 from the bolt head because I think reaching the nut with a torque wrench could be very difficult (a crows foot adapter might work but there's still just not much room for the adapter to rotate the nut). In that case I'll move the washer from the nut side to under the bolt head. I won't replace the washer on the nut side since it sounds like one isn't required as long as the nut isn't rotating, and if I did leave a washer on the nut side too then I would have to use a longer bolt.

tims88;1677289 I think most of the bolts will only have 1 thread showing past the nut but I did find that 7-37 in AC 43.13 says at least 1 thread should be showing so I think it might be ok. [B said:

Follow up question:[/B] Is it ever ok to not put a washer under a nut? I thought washers were required to distribute the clamping force a little and to prevent the nut from damaging the part underneath while tightening it. However, the two bolts circled in the attached picture do not use washers under the nuts and I believe that if they had washers underneath (even the thin .032" washer) that there would not be any threads showing past the nut.

View attachment 40370

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You're probably overthinking this one but that's fine.

There's no real general requirement for bolt thread protrusion. One full thread (discounts chamfer/thread relief) past the locking feature of any fastener is a very typical requirement.

As stated, (at least one) washer under the rotating fastener unless it places threads in critical bearing. This does not sound like the case here. If the OEM instructions call for one washer, a lite washer one each side would be preferred here IMO.

If torqueing the male fastener versus the female, torque to the high limit (plus running torque) of the fastener per released OEM torque level. If not provided, then use the high limit for the fastener size per the appropriate VANs sect, AC, etc.

The subject OEM here is respected and the product mature. Always good to question stuff but give any advice to deviate from OEM instructions some serious scrutiny. Stay safe

Freemasm said:

You're probably overthinking this one but that's fine.

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It is my super power

Freemasm said:

If the OEM instructions call for one washer, a lite washer one each side would be preferred here IMO.

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That is what I would prefer too but the washers used are already the thinnest I can find on Aircraft Spruce for AN4 bolts at .032". I'll look around a little more to see if I can find something thinner but that may be my only option unless I go to a longer bolt.

Freemasm said:

The subject OEM here is respected and the product mature. Always good to question stuff but give any advice to deviate from OEM instructions some serious scrutiny. Stay safe

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That is exactly why I figured my understanding of nuts and bolts must not be quite right. I really appreciate everyone taking the time to help educate me on a simple topic that I thought I understood already.