Fuel Drains

As with any aircraft, there are drains in the bottom of the fuel wing tanks that allow the pilot to drain water that may have collected inside the fuel tank. An assembly for this drain is included with the kit.

I have begun cutting the holes needed to install the fuel tank drains. I will be posting information and pictures soon.

Optional Flush Fuel/Water Separator Assembly

The picture below shows the optional Flush Fuel Water Separator Assembly that Lancair offers, after it has been mounted on the lower wing skin. The picture shows what the assembly looks like from inside the fuel tank.

The picture below is a close up of what the drain looks like from the outside of the wing on a completed Lancair ES. The standard drain assembly that comes with the kit has a similar fuel drain valve as pictured, but it extends below the surface of the bottom wing skin by the height of the valve head. The construction manual instructs the builder to build a fairing out of micro around the drain valve.

I did not purchased the Flush Fuel/Water Separator Assembly. I am using the drain assembly that came with the kit. Although I do like the idea of the flush port, I do suspect that it would be more susceptible to clogging if debris were to get into the fuel tank. I think it would be essential to have an access panel into the fuel tank. Since I am not sure how to put an access panel in the fuel tank that won’t leak, I am not planning on putting one in. I have noticed that the Columbia has fuel tank access panels on the bottom side of each wing.

Installing the fuel drains is a very easy process. The steps involved for this installation are:

Drill a 1/2" hole that the drain valve through the bottom outer wing skin. Placement of this hole is scribed in the outer surface of the wing skin, so it is very easy to put this hole in the correct place. The hole is depicted in the photo included to the right.
Cut out a larger hole through the bottom inner wing skin and remove the Nomex core. The square hole below represents this in the photo to the right. I cut a square hole. At first I cut this hole using a 1/8" bit in a Dremel tool. This gave the corners a 1/16" radius. Then I read in an Advisory Circular (AC 43.13-1B) that rectangular holes should have rounded corners, I then used a diamond grinding bit in my Dremel to increase the corner radius to 1/4". If I ever do this again, I will use a hole saw to cut the inner hole. It is faster and easier to make a hole with a hole saw than to manually cut a rectangle.
Remove the Nomex core from the inside of the outer skin as depicted in the photo to the right.
Bond a square brass fitting which is fuel drain mount. This mount has a pipe threaded hole in the middle. . That threaded hole will be centered over the hole drilled in the outer skin.
Build an epoxy/micro fillet around the brass fitting.
Glass over the whole thing plus 1" of the surrounding prepreg with 3 BID. Make sure you don't get epoxy in the threads of the hole.

The photo below shows the 1/2" hole from the outside after the brass mount has been bonded into place with Hysol. Day-Glo pink modeling clay was used to protect the threaded hole in the brass fitting (pictured below). You can see the edge of the brass fitting between the fiberglass skin the and the modeling clay. Once the brass fitting was positioned in place, and a small weight was placed on top of it to keep it there, I carefully wiped away the Hysol adhesive that squeezed out. The extra Hysol is far easier to remove before it is cured than after.

1/2" Hole w/ Brass Fuel Drain Mount Bonded In Place
Modeling Clay is Protecting Pipe Threads

I will wait until after I have closed the wing to build the fairing around this hole.

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