Fuel tank fwd support- one of life's little challenges :(

Desert Rat · #1 09-26-2022, 03:10 PM

Well darn.

I bought a second hand almost completed wing kit to start my build journey. Fast forward a couple of years and I did the first temporary install of the wings on my fuselage.

Wings fit good, triangulated easily, incidence and sweep set, drilled/reamed the all important aft spar hole a few thousands undersize for a AN5 bolt. Life is good.

Today I started all the cleanup tasks you do after the wings are on, and very first thing when I started looking at locating the hole for the bolt that goes through the fwd tank attach bracket to the slotted steel flange coming off the fuselage, I realized that the guys I bought the wings from had helpfully pilot drilled a #30 hole in exactly the wrong spot on the starboard tank.

I can't center the bolt hole on this because it's way to far out of the slot for the bolt to give any meaningful support to the nose of the tank, and I can't use it for as a rivet hole for one leg of the nut plate because it's a #30 hole instead of a #40.

This last part is what really sucks because one leg of a k1000-428 nutplate lines up perfectly with it.

As I see it, my options are:

1- to upsize one leg of a nutplate for a #30 rivet, which is iffy because the call out is for a skinny nutplate, so that would put the big hole and little hole uncomfortably close together.

2- to clock the nutplate vertically instead of horizontally and fill the errant hole with a double flush rivet.

3- to pull the tank off, drill out the aluminum angle from the inner end and build a new one without the offending hole, with the pro seal mess and extra time involved.

4- vans suggestion (which they just came back with while I was typing this) fabricate a new bracket and extend the ears out from the fuselage a little bit more.

curious what opinions the collective might have...

Laird · #2 09-26-2022, 03:17 PM

I'll take "what's behind door #4", Bob!

Quote:

Originally Posted by Desert Rat

Well darn.

snip

4- vans suggestion (which they just came back with while I was typing this) fabricate a new bracket and extend the ears out from the fuselage a little bit more.

curious what opinions the collective might have...

sahrens · #3 09-26-2022, 04:27 PM

Clearly the best solution.

PaulvS · #4 09-26-2022, 05:55 PM

#2 or #4 depending on whether you can get angle stock that is wide enough.
If doing #2 I think you can fill the hole with a normally set universal or countersunk rivet. It doesn't need to be double flush because there is no interference.

wirejock · #5 09-26-2022, 06:05 PM

Door #4.
Easy peasy.
Go to a metal supply and buy a piece of the same thickness and same alloy. Ask them to bend it where you need. They might charge a few bucks but it's worth it. They have the tools.
All you have to do is drill and cut.

Desert Rat · #6 09-26-2022, 06:16 PM

Just to clarify, if we're talking about extending the ears, it's not angle stock. It's a bent piece of 4130 steel.

I guess my reservation about that solution is that the bolt imparts a vertical load on what's essentially a pivot point because that bolt doesn't get torqued down to create a lot of clamping force. If you make the fuselage bracket longer, even by a little bit, it's creating more of a bending moment into the fuselage structure. I realize it's not much, but it's something.

I don't know what sort of loads are carried up there, but it seems like it has to be significant, because the structure and hardware is pretty beefy.

PaulvS · #7 09-26-2022, 06:23 PM

Ah OK! I assumed it was made from angle stock, same as the RV-6. I've recently cut those parts from 2.5" x 2" x 3/16" aluminum angle.

Honestly I don't see why #2 would not work just fine.

wirejock · #8 09-26-2022, 06:42 PM

Quote:

Originally Posted by PaulvS

Ah OK! I assumed it was made from angle stock, same as the RV-6. I've recently cut those parts from 2.5" x 2" x 3/16" aluminum angle.

Honestly I don't see why #2 would not work just fine.

Honestly, if Vans said to do it a certain way, I print the e-mail, file it and go. Why question it?

PaulvS · #9 09-26-2022, 07:09 PM

Quote:

Originally Posted by wirejock

Honestly, if Vans said to do it a certain way, I print the e-mail, file it and go. Why question it?

Maybe Vans did not think of all the options? If they said to NOT do something, then of course. There have been many many ideas from builders over the years that Vans have incorporated (generally) and I regularly (constructively) question Vans drawings because there can be errors and elements that will just not work as drawn.

Scott Hersha · #10 09-26-2022, 07:31 PM

Quote:

Originally Posted by PaulvS

Ah OK! I assumed it was made from angle stock, same as the RV-6. I've recently cut those parts from 2.5" x 2" x 3/16" aluminum angle.

Honestly I don't see why #2 would not work just fine.

Yep. Agree. Mine is a -6 with the aluminum angle, so different. No reason not to fill the errant hole with the double flush and orient the nutplate north to south. Easy to do. Make sue you drill that new hole correctly, or you’ll be using option #4. Remember, that bracket is loaded in vertical shear, protecting the positive and negative G loads on a full tank of fuel. Lateral shear loads should be close to zero, so don’t tighten that bolt too much.