SECTION 18: FUEL TANK

Build Instruction Updates

• 4/17/2025 18_10.pdf
  Reflects design changes made by the manufacturer of the fuel float on the F-385B and F-385C Fuel Senders.
  See also this FB thread.

Check for more recent updates here

Note: Seems, the T-1004 ribs have changed in 2024 to a -1 revision with a heptagon hole. See this FB thread.

Videos (Definitely watch the Vans Video!)

• Vans
• Plane Lady

Hints

• Deburr the ribs before fluting
• Check threads on leak testing
  • VAF 4/2022...
  • FB 3/2024
  • Consider doing a preliminary leak test with gasoline prior to installing the rear baffle. After installing the ribs, you can install the fittings and the fuel sender and let the proseal dry for a few days. Then you can put the tank in the cradle and fill with gasoline almost up to the rivet holes in the skin for the rear baffle. Consider putting dye in the fuel and using a UV light to check for leaks.
  • Final leak testing can be tricky. You need to use high-quality packing tape or something else to seal the fuel cap otherwise you'll leak air from there. If you use a balloon, it will also leak. If you connect a manometer, the connection to it can leak, or it can leak internally.
• Countersink 3-x skin rivet holes in T-1005
  • VAF 4/2020
• Priming tank parts
  • If you are otherwise priming your aircraft you need to make sure you don't prime anything that will make contact with fuel
  • You can choose to prime the parts on the exterior of the tank ahead of time or after the build is done, but be very aware of which parts need to not be primed. For example, the Tank Attach Zees shouldn't be primed where they are flush against the rear baffle, nor around where the pop rivets attach them to the rear baffle.
  • Some people choose to Alodine all of their fuel tank parts, inside and out. This is safe to do. You can also consider Alodining only the interior parts or only the parts that will be attached with sealant.
  • If you don't use Alodine then you definitely want to scuff the parts that will touch the sealant (again, see the Van's video).

Before You Start

Special/New Tools/Supplies

• You need a lot of Fuel Tank Sealant. There are probably builders who can build two fuel tanks with one quart but most builders will need one quart for each tank. If you are doing Skydesigns Extended Tanks you probably need a total of three quarts. Make sure it is less than six months old and store in a refrigerator if possible.
• You need a bunch of thick popsicle sticks and mixing surfaces. The Van's video shows a piece of aluminum, but consider small mixing cups like these.
• Some people use a pneumatic caulking gun like in the Van's video but you can also use a bag like one does for decorating a cake.
• You will need 100-200 disposable gloves and plenty of clothes that you are OK ruining
• You can choose to plug the holes in the end ribs with large rivets (see the Van's video)
• You may need a flaring and/or pipe-bending tool for the vent line (see below)

Possible Leak Areas

Here are areas to spend extra time on in order to avoid leaks.

• Red: The inboard bracket junctions -- put a lot of effort into this area, and especially handle the forward section of the outboard rib before installing the aft portion of the outboard rib. Many builders get leaks here. Consider ignoring the precautions about the drain hole and cleaning sealant out of that area after you have finished riveting the inboard rib.
• Blue: another common leak area due to the breaks around the flanges at the leading edge. Lots of sealant inside the tank is warranted.
• Green: these single flanges with only one rivet hole can be hard to access since they are down by the nose. By the time you surround the flange with sealant and also the tail of the rivet, consider just encasing the whole tab in sealant. Some builders get leaks here.
• Orange: when you are back-riveting the individual stiffeners you need to make sure to clean the sealant out from where the ribs will be installed later. But this may leave the edges of the stiffener vulnerable to leaks. After installing the ribs, consider a little extra sealant in the area between the rib and the stiffener.
• Brown: you can't easily see the area under the J-stiffener in order to cleanly apply sealant along this full-length stiffener. Consider using extra sealant and/or an inspection mirror for this process. Consider a preliminary leak test up to and past these rivets before installing the rear baffle.

Fuel Tank Leak Points

Page 18-2

• Step 3, the Tank Attach Zees need to be narrow enough to fit between the spar. They will be tight especially towards the wing root. Consider trimming them now before they are attached.

Page 18-5

• Figure 1, the picture may trick you into doing the riveting in any order, but per the instructions make sure you rivet the K100-08D nutplates first.
• Figure 3, the rivet diagram, has a hole with no rivet callout. It's near the bottom of the diagram, roughly in the middle. This hole is only on the bottom side to get the rear baffle oriented correctly. The flange angles are not the same for upper and lower side. Use the same rivet as for the neighbor ones (AN426AD3-3.5). See this FB post for details. See also this VAF post for details. See also this VAF thread for details.

Page 18-6

• The aluminum vent line needs to be flared. Otherwise, it may leak later or come apart. Consider buying one of these tools:
  • at Spruce Read the comments section, there are some great hints for the tool posted.
  • at Amazon
  • at Spruce

Page 18-7

• Step 1: The fuel sender wire is not supposed to rotate/twist around its own axis. A bend of the wire at the fuel sender end prevents that. Check the instructions that come with the sender. See also this post at the "Van's Aircraft Builders" Facebook group.

Capacitive Fuel Senders

A photo gallery of RV-10 tanks being built with capacitive fuel senders. Has a list of components needed and schematics with dimensions used for the plates.

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