Protecting the Fuel Tank Vents

From Bondline

Introduction

The mud dauber is a type of wasp that builds its nest using mud. The reason this is so critical for airplanes is that they like to build their nests in pitot tubes and fuel tank vents.

For some aircraft, the pitot-static system is more critical than others, and the crash of Flight 603 is a recent example of this system operating incorrectly. But for Grummans, the real issue with mud daubers is the fuel tank vents. For AA-1s, the risk is that the engine will not be able to draw fuel from the spar. For AA-5s, this could happen, but the more usual case is that the inboard part of the wing will begin to collapse due to the decreasing pressure inside the fuel tank.

Before attempting to protect the vent tubes, you should verify the lack of an existing blockage. According to Larry Tatsch,

Mud daubers build their nests (and populate them with one paralyzed spider) within the first half inch or so of the opening. Use string-trimmer line and probe the first inch. If there's something there, you will break it up and it should fall out. To help, you could apply suction with a rubber bulb - or your mouth, if spiders and mud are your thing ;-) Then you can run the line the rest of the way until it encounters a sharp bend that stops it. I keep a foot of string-trimmer line in the plane for checking the vent and the scupper drain (important as well).

Rain Bird Filters

To prevent this from happening, Rain Bird sprinkler filters can be installed in the fuel tank vents. The filters are fairly cheap and may be available at home improvement stores, by getting on the Grumman Gang and shouting out to Roscoe, searching for part number #107323 for the 1800 Series sprinkler heads (Rain Bird now lists A21511 for the 1800 Series. Are they equivalent?), or by calling the company Rainbird Parts 877-727-8772.

However, Rain Bird filters can cause their own problems.

We started using those a couple of years ago, and although I never had any problems personally, ONE of our Tigers suffered from fuel starvation as the tanks neared empty MOST OF THE TIME on descent. They couldn't figure out what his problem was, until those vent filters (Rainbirds) were removed... problem solved. He had plenty of fuel in the tanks, it just wouldn't feed. The guess is that because the small end is sealed, if there isn't enough room for air to get in through the side holes (the only ones) in a PARTICULAR VENT, then it's possible to block vent air completely from getting into the tank.... and as the tank empties, there is no vent air left.

Jan Savage
Tiger 67B

Some note that the correct method involves cutting the large end off and inserting that end into the vent tube. This makes it an "outie" rather than an "innie" and avoids this type of problem. Inserting the small end still leaves a possibility that stuff will crawl in there and clog up the filter.

Rainbird lawn sprinklers have a filter screen shaped like a golf tee. Cut off the bulge and insert the cut off end into the Fuel vent , this will eliminate any problems with bugs blocking the vents. I have been using these screens for years with no problems. Give it a try.

Bob Dillon

Rain Bird filters are not the official position of the AYA Safety Director.

Other Methods

The official position of the AYA Safety Directory is

BTW, while the Rainbird filters are fine, the official AYA Safety Director-approved solution is a pipe cleaner (preferably red or other color that contrasts with your wing underside color) bent into a _/\_ shape and stuck pointy end first into the inlet. The pipe cleaners will not create a problem if forgotten (enough air can get through to replace the fuel going out), are easy to see on preflight, and are very cheap when purchased in quantity. I've been known to hand them out to any and all at conventions in areas of high mud dauber activity, like SSI four years ago.

Ron Levy

And there is a paper clip approach:

I've gone back to using the paperclip method, ie: just bend a standard paper clip 90 degs, insert the larger end into the vent and let the smaller on hang out in the breeze. You can pull the paperclip on preflight to clean out/check for bug(gers) easily and reinsert. They don't cause any drag at all and are just about idiotproof.

Jan Savage
Tiger 67B

And don't forget my long-standing choice - large, plastic coated paper clips. Bend the center loop upward and insert - it will stay in place. To check for nests, just pull out and the loop will pull out any bugs with it. Can be left in place while flying. In 9 years, though, I've never had anything even try to make a nest.

Larry Tatsch