Fixing loose rivets so they stay fixed

[Garage Guy]

Originally Posted by awm

Carefuly clean out the countersink by hand, open the hole to #30 and install a 4- rivet. Then shave or file flush. This is a common problem on many production aircraft (and is actually called out for in the Lear 24 SRM).

Just to confirm, this is called out even for .032" skins?

Originally Posted by roee

Since you'll drill the new rivet holes through the skin and spar in assembly, i.e. as one tight sandwich held together by the existing rivets, there will be no burr on the mating surfaces between the skin and spar.

But the sandwich isn't all that tight, anymore. You can feel a little relative movement between the skin and the spar. You can't see it very well in the photos, but some of the 'smoke' (aka finely divided aluminum oxide) is present in the seam.

--Paul

[roee]

Originally Posted by Garage Guy

But the sandwich isn't all that tight, anymore. You can feel a little relative movement between the skin and the spar. You can't see it very well in the photos, but some of the 'smoke' (aka finely divided aluminum oxide) is present in the seam.

In that case, I would also clamp it for drilling.

[Andrew M]

What you will end up with is a rivet head that is dimensionally some where between an AN426 and an NAS1097. The smoked rivet has removed some of the skin. .032 is not enough to machine countersink for a 4- rivet, hence clean an reshape the countersink by hand, open up to remove the knife edge, and drive a AN426AD4-rivet. Shave what sits proud and its as good as new (kinda). The determining factor on what thickness is allowed is the avoidance of a knife edge condition with rivet diameter. When a machine countersink is to deep for a rivet, the head can't fill the hole the way it is supposed to and it ends up smoking (Cessna firewall ect...)
Its a shame, I can get oversize shank, undersize head, but no oversize flush head without blowing open the hole.
Andrew

[Garage Guy]

Originally Posted by awm

What you will end up with is a rivet head that is dimensionally some where between an AN426 and an NAS1097.

OK, that makes sense.

Now reading MIL-R-47196A, it says

3.4.2 Oversize countersinks. When countersinks are enlarged beyond specified tolerances, the next larger size rivet may be used...

3.4.3 Repair limitations. The combined oversize rivet hole repairs and oversize countersink repairs shall be limited to a maximum of 20 percent of the rivets, or 10 rivets in a single rivet pattern, whichever is less. Repairs to more than two adjacent oversize rivets, or replacing more than half the rivets with oversize rivets in any 10 inch length of pattern is prohibited.

Looks like I have some thinking to do about which rivets to fix, since if I follow that, I won't be able to do them all. Wondering, does the Lear SRM say something different? Because Learjet standards would be good enough for me...!

--Paul

[Andrew M]

Hey,
I no longer have access to the Lear Manuals. I am not familiar with the purpose of the document you are quoting (type and speed of aircraft). In addition, most repairs that I have done that involve DER's the engineers are more concerned about material type for the fasteners than diameter. The thinking is how is the joint going to fail, and will one or two steel fasteners not give a little before they go and then start a progressive fail situation. The other document to check would be AC43.13-1B para 4-57 (4,b) and figures 4-9 and 4-10. Granted the tables are for protruding head rivets, the things to look at are the engineering notes about %used and will fail sheet or fastener. From the Convair 580 SRM ( I wish I had a copy) Dimpled are the strongest joints, then protruding, then machine coutersunk. My thinking is as long as you have edge distance, go ahead and open them up. If there are one or two existing fasteners in a line that are O.K. but by themselves, blow them open. What I try to imagine is what does it do, and how does it break. Can you imagine something else letting go before this joint fails? What else would have to happen?

Andrew

[Garage Guy]

A link to the MIL-R-47196A document here: http://www.vansaircraft.com/public/Specs.htm

As far as scope of the specification, it just says: "1.1 Scope. This specification covers the preparation for and installation of buck rivets." Full stop. On the other hand, it also says "approved for use by US Army Missile Command", so I guess it's possible some of its stipulations are overkill for RV's. It's referred to a lot around here, though. I was looking at it because it mentions over-countersunk repair specifically, where AC43.13-1B doesn't, as far as I can see.

--Paul

[WillyEyeBall]

I've just gone through replacing a "bunch" (not telling #) with an A&P of smoking rivets on the horizontal stabilizer, and even need to replace some of the replacements. Had assumed it was from all the acro (+5.5, -2.7 Gs typical flight), but it may be from moving the airplane around by pushing on the horizontal and vertical stabilizers at the ribs and stiffeners. Since the airplane is basically white, the smokers show up easily. I haven't seen any smokers anywhere else on the airplane. I'm planning on using a tail wheel tow bar to see if this is indeed the problem. For other than light colored aircraft tails, the smokers may not be showing up.

RV-4
Slider
485 hours, at least 350 acro hours.

[Dave62]

Just a thought....
I would mix up some ProSeal and spread between the skins if I could get a little in there and also use on the rivets as I set them. Much like a fuel tank except you dont need to cover the buck tail. This will keep the skins from moving and stop the smoking rivets. This is done on pressurized aircraft as a matter of course.
Dave (Swift Driver)

[Phil]

I'll bet the proseal is used in pressurized aircraft to "create a seal"; not to adhere anything.

A common misconception amongst the homebuilder community is that proseal is an adhesive. It's not, it's a sealant. Their purposes are completely different.

You could use something like Metalset A4 instead. It's similar to JB weld, but available in larger quantities and is stronger. It can be sanded, drilled and tapped, etc.

I would never trust any sealant to bond anything...

Phil

[Mark Burns]

Originally Posted by Phil

I'll bet the proseal is used in pressurized aircraft to "create a seal"; not to adhere anything.

A common misconception amongst the homebuilder community is that proseal is an adhesive. It's not, it's a sealant. Their purposes are completely different.

You could use something like Metalset A4 instead. It's similar to JB weld, but available in larger quantities and is stronger. It can be sanded, drilled and tapped, etc.

I would never trust any sealant to bond anything...

Phil

Phil,
So you're saying you would never use ProSeal to "bond" anything.
Gosh.

Ok, I hear you and believe you when you say it's a sealant not an adhesive.
But in my experience ProSeal is a better "adhesive" than most adhesives!!

Mark