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26-14: Difficult centre fuselage bottom skin rivets

TASEsq

Well Known Member
Patron
I have just cleco’d the bottom skin to the seat rib and aft bulkhead structure. I have a rivet partner but he’s not very confident on the bucking bar, and doesn’t want to use the gun - so as we did with the wing skins we were planning on backriveting these skins in the vertical position with my partner on a flat bucking bar on the lower skin.

However there are a number of rivets which will be impossible to backrivet - in fact some which I think would be very difficult using a gun on the outside and a bar on the rivet. These are difficult because of other structure in the way.

There are 2 holes which are called out as MK319-BS which solves 2 of the problems.

Has anyone got any tips or remember how they got these rivets? Not feeling like much of a hero, I am tending toward just using MK319-BS in all these locations.
 

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I managed to drive all four. The 2 on the spar were ok. The 2 aft are not spectacular but they’re in. I’m ok with them all but I would consider doing mk319s in the aft 2 if I were gonna do it over. Check with Vans. When I’m in doubt, I hold my tungsten or footed bar against hole and have my wife draw a dot through hole on bucking bar with fine tip sharpie. That usually tells me go or no go. I think the mk319s is likely gonna be Vans response as they are used very close by.
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Tungsten

My tungsten has an angled face perfect for those situations. Tape the bar so it won't scratch anything.
If Vans says use an MK-319-BS, then go for it.
 
So we finished the bottom skins this afternoon. The majority of them were back riveted with the double offset backrivet set. After some training my dad got on the gun with the swivel mushroom set and we set the 4 rivets on the forward and aft bulkhead flanges which were right up against the centre pair of ribs - these turned out fine. I used the angled face of the bucking bar.

The plans called for a MK-319-BS rivet on the aft gear brace on the very outboard end already. I also used one on the very inboard end of the thick doubler section - there was no way to get a bucking bar in there that I could see.

Thanks for the advice.
 

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I’m just ahead of you, some points that may help in no particular order.
Prime under side of F-01483 & 84 where side skins will overlap. Prime side skin where fairing attach angles are attached.
Check that the fwd flange of the F-01415 seat rib is inboard of the F-01404. For some reason I had mine on the outside. What a pain to fix afterward:mad:
Your call if you want to flute the F-01419s. I mounted my fluting pliers in the vice. Worked well. Both the Vans 14s are not fluted.
I use plastic syringes from the Farmers Co-Op for applying pro seal. Works well for sealing firewall.
Have some AN426AD4-8s on hand. I found the 7s way too short for sideskin to lower longeron.
Don’t fasten the 2 fwd nut plates to the F-14119s until after installed to fuse. They interfere with setting rivets, unless you have ground down your 470-3 rivet set.
I have my fuselage secured on my work bench and stood on stool, reached in to back rivet 99% of sides. Bucked the rest. Works ok if you don’t have a bucking partner.
https://www.cleavelandtool.com/products/back-riveting-bucking-bar
 
Good Info Todd - thank you.

Prime under side of F-01483 & 84 where side skins will overlap. Prime side skin where fairing attach angles are attached.
Didn't pick up that the side skins overlapped the lower skins - thanks. A pic on page 29-13 shows it well.

Check that the fwd flange of the F-01415 seat rib is inboard of the F-01404. For some reason I had mine on the outside. What a pain to fix afterward:mad:
You just set me in a panic - I assume you are talking about the F-01415-A side ribs joggled forward flange must be inside the F-01404D side angles? If so, looking at photos mins are on the inside. (Phew)

Your call if you want to flute the F-01419s. I mounted my fluting pliers in the vice. Worked well. Both the Vans 14s are not fluted.
Thanks - page 29-14 doesn't ask them to be fluted. Are they a bit bowed? I found this with the lower gear brace - but it pulled straight when i backriveted it on.

I use plastic syringes from the Farmers Co-Op for applying pro seal. Works well for sealing firewall.
So is proseal ok for the firewall? Is this the done thing? I will be up to the firewall chapter very soon. I have searched for the 3M firebarrier product i have seen in other threads, but can't find it for sale here at all. It was not in stock in the US when i was there a couple of weeks ago.

Have some AN426AD4-8s on hand. I found the 7s way too short for sideskin to lower longeron.
Will keep this in mind.

Don’t fasten the 2 fwd nut plates to the F-14119s until after installed to fuse. They interfere with setting rivets, unless you have ground down your 470-3 rivet set.
Do you mean the nutplates interfere with the 470-3 rivets which hold the root fairing attach angles to the side skins? If so that makes sense - the nutplates seem like they can be put on later once the fairing angles are attached to the side skins. Page 29-18

I have my fuselage secured on my work bench and stood on stool, reached in to back rivet 99% of sides. Bucked the rest. Works ok if you don’t have a bucking partner.
That's great info to know. We were just discussing yesterday the best height for moving forward - will probably make a low bench for use once the firewall chapter is riveted onto the centre fuse chapter then go from there.

Appreciate all the little tips - i will annotate them in my plans to make sure i don't forget. Maybe a good reference to add to the wiki as well.
 
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