Rivet spec question for the pros?

[agirard7a]

Vans refers to the mil-spec. MIL-R-47196A for riveting
guidelines. The FAA AC43.13's section on riveting spec is different.
Which is correct? Both?

Example for an 1/8" AN470-4: FAA says the shop head should
Be 1.5 the diameter min. And the min height as .5 the diam.
This is 3/16"(.1875) min diam of the shop head and 1/16" (.0625) for the min. height. (No max height)

Mil spec for the same rivet: shop head min diam: .163 and the height of
Min .050. And max .070

The mil spec is Army and DOT spec and different from FAA spec.
Why does Vans refer to the mil spec vs. FAA spec. Won't the DAR inspector
Be using FAA spec?

[David Paule]

I'd use whatever the manufacturer, in this case Van's, says. It's their design and they get to tell us what supporting documentation to use.

Dave

[fixnflyguy]

In the world of "big planes" , the MFG will often call for underdriven or overdriven rivet specs,BAC or MIL, as determined by the engineering data. In GA aircraft, we use the 43.13 as the bible, when other data is not provided. There is likely negligible difference, but Van is an engineer,and the MIL Spec is always a good reference and often the guideline for aircraft MFG. Drive on and in short time, you will forget measuring the rivet tail and your eyes will tell you its perfect or not.

[rvbuilder2002]

AC43.13 is an Advisory Circular
It is not an official book of specifications per-say. It is accept practices and guidelines.
The .5D X 1.5D is a rule of thumb for a mechanic to use when doing repairs, etc.
The Mil spec lists the absolute size limit specifications (min and max.)

Sometimes a rivet size is called out in the plans, that depending on a number of different factors might produce a shop head that doesn't quite meet the rule of thumb, but will easily meet the Mil Spec.
The reason is that the next longer rivet might just barely work but will be at a much higher risk of the rivet clinching over. Then it needs to be removed.... mistakes are often made during the removal.... in the end, the now messed up hole is compromised far more than it ever was with just a very slightly smaller shop head.

[BobTurner]

Originally Posted by David Paule

I'd use whatever the manufacturer, in this case Van's, says. It's their design and they get to tell us what supporting documentation to use.

Dave

Just to nit-pick: Unless you are building an LSA, You -not Vans- are the manufacturer. And you are ultimately responsible for the condition of the airplane.

[David Paule]

Originally Posted by BobTurner

Just to nit-pick: Unless you are building an LSA, You -not Vans- are the manufacturer. And you are ultimately responsible for the condition of the airplane.

That's the legal position. But unless you yourself ran the numbers, Van's is the authority on the structure of the aircraft.

Dave

[Z-EDD]

Originally Posted by rvbuilder2002

AC43.13 is an Advisory Circular
It is not an official book of specifications per-say. It is accept practices and guidelines.
The .5D X 1.5D is a rule of thumb for a mechanic to use when doing repairs, etc.
The Mil spec lists the absolute size limit specifications (min and max.)

Sometimes a rivet size is called out in the plans, that depending on a number of different factors might produce a shop head that doesn't quite meet the rule of thumb, but will easily meet the Mil Spec.
The reason is that the next longer rivet might just barely work but will be at a much higher risk of the rivet clinching over. Then it needs to be removed.... mistakes are often made during the removal.... in the end, the now messed up hole is compromised far more than it ever was with just a very slightly smaller shop head.

I read, and appreciated this in section 5 of the build manual. However the problem I have come across most often so far in my RV-7 build is where the plans callout is actually slightly too long! What to do then? The next full size down produces a shop head that is small, but within the mil spec, but it still bugs me that the plans called out a longer rivet, so is it really acceptable?

The most recent place this occured for me was with the majority of main rib to spar rivets, not exactly an unimportant area! I solved the problem by cutting half size rivets, and they came out great. But even my rivet cutter is not set up to cut half sizes, I have to use a home made spacer! Further evidence that half sizes should not be needed.

So, to continue the OP's question, what do the pro's do here?

[RVDan]

Choose a rivet length appropriate to give the desired result after the rivet is driven. Our drawings for certified aircraft provide the Mil-R-47196 as the standard for the bucked rivet and allow the techs to vary the length to obtain a shop head per the standard.

BTW, the structures handbook which virtually all airplane structures basic allowables come from, (either Mil-HBK-5 or the current manual MMPDS) references a tail diameter of 1.4D min and a tail height of .3D min in section 8.1.2.

From what I recall the military is concerned with long rivets and oversized tails cracking.

[Ken Martin]

As best said by Jay Pratt, "Do not build a watch!!! - we are only going to Denver; not Mars."

I agree completely.