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Landing Gear SB Question...

Piper J3

Piper J3

Well Known Member
I need to do both the Fuel Tank and Landing Gear SB?s on the RV-12 I recently bought. I want to do the fuel tank first and I?m considering buying a new completed tank directly from Van?s.

I have a question? If I install the new tank now, can the tank remain in position during the landing gear upgrade or does the tank need to be removed for that SB? I think I read in VAF that the tank can remain in position but you need to be careful when drilling out rivets for the new skin doubler so that the drill doesn?t protrude and damage the tank. I can use a drill stop and even slid a piece of steel sheet metal between the side skin and the tank for precaution. Can someone confirm that this is doable?
 
My opinion - -

Have the tank out for landing gear mod. If you have not worked with tank sealant, it may be hard to convince you it is not that hard to do. If you can find a builder near you for help, I'd suggest doing tank yourself. Messy, but you will have a better understanding of the tank. My opinion again, but just take the top off. Much easier to do the 2 mods to the tank, and close the window if it is there. Good time to do vent kit, and mechanical gauge.
 
I think we all dreaded the tank, then when we did it we felt silly for the worry. Just do it, it is one of the simpler jobs of building the plane!
 
And another opinion...

To answer your original question, yes you can use the methods you describe to safely remove the rivets without removing the tank. We have done it that way here twice on 2 different RV-12s. The only down-side is that it is difficult to clean out the removed rivets from behind the tank.

That said, since you also have the tank mods to do, I would take out the tank and do those mods or plan to install your new Van's built tank at that time. Since you have the LG SB to do, then you will have the tools necessary to do the tank SB's. To do this part, for instance, you need the countersink tool and the right bits for the different flat head rivets:
i-SQtFTBh-M.jpg


The tank SB is fairly difficult for an in-experienced non-builder owner in my opinion. So is the MLG mod.

You may be better off with a new tank but realize that for that much money you can buy some tools and get experience about the tank, as J. B. has said. And like he says, get help and take the top off and work from the top as opposed to trying to work through the front cover. Getting the top off is not a big deal:
i-5TFB2Fj-M.jpg


Also, if you are going to work on the tank, do install the little anti-rotate device on the bottom fuel return fitting:
i-HkSTxwx-M.jpg

A new factory built tank will no doubt have this already installed.

Regarding the vent install, if I were doing it again, I would skip that. It doesn't help all that much and creates it's own minor issues. Like dripping gas on the hangar floor if you fill the tank and are using a non-vent cap.

Regarding the window, there was a window SB a long time ago that addressed problems with the original window. If that has been done, and your window does not leak, then keeping the window is an option.

Some will argue that the window will leak eventually. There are loads of opinions about the window on this forum.
 
Echo most of the responses. Follow the service bulletin and remove the tank prior to implementing the landing gear repairs. You will be doing a lot of drilling in the tank area.

Working on the tank is not that hard. After you have tank tank removed, REMOVE the top of the tank and implement the tank service bulletin and all of the improvements. Here is my short list....

Remove the window if still present.
Add the Moeller gauge.
Add the fitting for the fuel vent (even if you do not install the vent line).
Add the anti-rotation device to the bottom of the tank.

Working on the tank top is quite simple. Use a thin putty knife and drive it with a hammer around the perimeter to break the seal, per Tony's photos. Scrape the old sealant with the putty knife. I then used a wire brush in an electric drill to brush and clean the mating surfaces. Implement the changes, vacuum and wipe down the inside of the tank. Re-rivet the top of the tank using the correct rivets. Let it cure. As a final step, I added about a gallon of gas to the tank, sloshed it around, drained the gas thru coffee filters and repeated till the coffee filters were clean.
 
Thank you all for very detailed answers. I really appreciate everyone sharing their time and knowledge.

I have another question... If I buy a new tank from Van's, and I don't want to install the vent, can I continue using the vented cap and then plug the vent fitting? I think this is my preferred option at present.

Seeing as it's winter in northern Ohio perhaps I will buy and install tank now and wait until warmer weather to do the gear SB. Gear SB doesn't bother me - I have previous aircraft sheetmetal experience and also a friend who is A&P.

Then the real question is - does installing the tank, removing the tank at a later date, and re-installing again after gear SB propose a risk for developing leaks or other unforeseen problems?
 
Piper J3 said:
Then the real question is - does installing the tank, removing the tank at a later date, and re-installing again after gear SB propose a risk for developing leaks or other unforeseen problems?
Click to expand...

Not really, Only risk is twisting the fittings on the bottom of the tank and breaking the sealant between the fitting and the tank bottom. Use a backup wrench and you will be fine.
 
Anybody have the part number for the anti rotation device? I am doing all the revisions now sooooo, might as well do that also.
 
Save yourself $800 or whatever a new tank costs and repair the original tank. While the top of the tank is off, install the vent fitting whether you intend to use it or not. At least you will have the option at a later date. Follow John Bender's example using 1/2 inch tube.
 
Mich48041 said:
Save yourself $800 or whatever a new tank costs and repair the original tank. While the top of the tank is off, install the vent fitting whether you intend to use it or not. At least you will have the option at a later date.
Click to expand...

AGREE! Save the $$$$. Tank work sounds intimidating but is NOT! If you have not worked with tank sealant, find ANY RV builder to help!! They ARE, no matter the rumors, are quite friendly.
 
Or just do what I did when I realized I'd forgotten to order the schnazzy bracket and didn't want to wait another week for it. I used a short chunk of .125 stock sliced from some scrap bin AL angle. Butt it up against one flat of the fitting, drill and rivet.
 
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I had no problem doing the Main Gear SB without removing the tank.

Consider this: Do the side skin doubler portion of the Main Gear SB while the tank is out, and do the rest later. That portion of the SB is very simple.

When you do remove the tank, split the rear bulkhead cover and floor plate so you never have to remove the tank again. You can follow that mod as shown in the sticky mods thread, and it is one of the simplest mods you can ever do, or get replacement parts from Vans that are already split.
 
Baggage Bulkhead Mod

While the tank is out order the aft baggage bulkhead mod so you won,t have to take out the fuel at the next annual. p/n "12 Baggage upgrade kit" $36.15
While working on the gear mod you might want to do the
"12 spar switch kit" update p/n bag 2753 $45.45.
 
Some have installed TWO fittings, in case you ever want to carry extra fuel and transfer it to the tank in flight.
Mich48041 said:
Save yourself $800 or whatever a new tank costs and repair the original tank. While the top of the tank is off, install the vent fitting whether you intend to use it or not. At least you will have the option at a later date. Follow John Bender's example using 1/2 inch tube.
Click to expand...
 
Question about Fuel Tank Removal Procedure...

I?m beginning planning for fuel tank removal and replacement with new tank from Van?s to comply with SB. I have question on disconnecting fuel line and return lines. Access Via the inspection openings is very limited. It looks like I could use a a CrowsFoot wrench to hold the bulkhead fitting while turning the compression nut. This looks tricky and I?m afraid of causing a sealant leak if the bulkhead fitting is disturbed. Is there enough flex in the fuel lines to allow the tank to be lifted an inch or so to allow straight open-end wrenches to be used above baggage floor level?
 
If you are not going to use the old tank, then do not worry about it. Just pump the tank empty and then disconnect the fittings. If you sell the old tank or give it away, the new owner can lock the fittings in place when they take the old tank apart to do all of the service bulletins.
 
Piper J3 said:
I?m beginning planning for fuel tank removal and replacement with new tank from Van?s to comply with SB. I have question on disconnecting fuel line and return lines. Access Via the inspection openings is very limited. It looks like I could use a a CrowsFoot wrench to hold the bulkhead fitting while turning the compression nut. This looks tricky and I?m afraid of causing a sealant leak if the bulkhead fitting is disturbed. Is there enough flex in the fuel lines to allow the tank to be lifted an inch or so to allow straight open-end wrenches to be used above baggage floor level?
Click to expand...
There may be, I'm not sure. But more to the point... if you want my advice, which is worth every penny you pay for it, read on. I just did my tank SBs a month ago.

The fuel supply line is not an issue. That fitting is an NPT screwed into a riveted flange, so you won't break a seal there. The return line is just an AN fitting with tank sealant. I would suggest that you plan on removing it, cleaning up the sealant and re-installing with an anti-rotation bracket so you don't have to worry about it the next time. You can get them both loose from under the belly with open end wrenches -- I was able to get even my enormous hands in there. If you're going to have the tank apart anyway, it's really no big hassle to re-install the return line fitting in a manner that eliminates the chance of breaking the seal in the future. And if you're going to buy a new tank from Van's, why care about whether the old one leaks?

While a new tank from Van's is certainly an option, and maybe an attractive one, doing the SBs yourself is not a big deal if you have some prior building experience. It took me a couple of evenings to remove the top, clean up the sealant, apply all the SBs and get it back together.
 
I shortened and bent a couple of extra box wrenches I had laying around and at the same time converted them to "flare-nut" style box ends. They fit in the restricted area beneath the floorboards just fine. As noted by others, if you keep your original tank (which I likely would do), be sure to add the nut anti-rotation piece.
 
Fix it this way and you will never have another problem with it.
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Mich48041 said:
If you are not going to use the old tank, then do not worry about it. Just pump the tank empty and then disconnect the fittings. If you sell the old tank or give it away, the new owner can lock the fittings in place when they take the old tank apart to do all of the service bulletins.
Click to expand...

Speaking of old tanks Joe, what happened to that masterpiece you built a few years back?
 
Dave12, I realized that my homemade tank was vulnerable to rupturing in the event of an accident, just like Van's tank was before the service notices and mods. So I removed my tank. I then modified Van's tank per service notices and put that back in. I might redesign my homemade tank some day. I discovered that it takes much, much longer to design and fabricate parts (without CNC machines) and assemble them, then it takes to assemble Van's perfectly designed, cut, punched, and bent and formed parts. DonFromTX might vouch for that. :D Some RV-12 builders might not realize how easy they have it compared to scratch built E-AB planes.
 
Don,

Nice looking work! Do you think moving the weight of the fuel to the wing tips will affect roll stability/rate with "dumb bell" effect?

In my I'll spent youth on subs we used to pump our trim from amidship to fore and aft in heavy seas before going to periscope depth. The dumb bell effect made a big difference on resistance to pitching up and down.

Rich
 
The weight fore and aft is essentially the same of the original tank. The weight is evenly distributed from wingtip to wingtip.
 
Research polar moment of inertia.....

Having the exact same amount of weight, but placing it at different span wise positions on the wing can have a major influence on flight characteristics. In particular, spin recovery, but it also can have an influence on roll inertia (can effect roll rate and ability to capture bank angle precisely), and yaw stability and a few others to some degree depending on the amount of weight that is move outboard.

In simple terms....
Fuel in the wings of an RV-12 negates the results of all of the spin testing done by Van's (can be view on you-tube).
As far as spin recover goes, until the new configuration is tested, it should be considered as a total unknown....
 
I'm just getting ready to add the mechanical fuel gage and the fuel vent. If I install the T-1010 anti rotation device what size rivets do you use to attach it. Do plans come with the T-1010?
 
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