Fuel vent lines

We ran into several issues with the original plan for a vent line to the wing tanks.  The engine (Rotax 912is) installation manual states that a 1/2 inch vent line should run from the header tank to the wing tanks.  We reviewed the plans of other builders who have installed a vent line, but it looks like the few other builders who used this engine installed 3/8 inch lines and not 1/2".  The larger diameter is a much larger challenge because the vent holes, fittings, and hoses all have to be larger, and the area we are working in is already tight.  But we now have a plan (well, actually we had multiple plans, but had to scrap them and rework our plan until we had something that will work).

We drilled a hole in the side of the fiberglass tank for the vent hole.  Originally we planned on using a fitting from Sonex, but had to scrap that because it required access from inside the tank, so instead settled on a more common alumninum fitting. We wanted to minimize any dust or debris that ended up in the tank during drilling, so prior to drilling, we attached a blower (actually a vacuum hooked up in reverse) to the fuel door on top of the wing to put positive pressure in the tank so most of the debris would blow out of the tank.  This worked great.  We started with a small 1/8 inch drill bit, then used a step drill to increase the size of the hole until it was slightly undersized for the fitting.  Next we actually used a large (3/4" NPT) tap to thread the fiberglass hole.  We don't expect it to seal well at the threads because there are so few threads, but it will help hold the fitting in place.  We will be using West Systems epoxy and flox for final installation to assure a leak-proof seal.

Hole drilled in fiberglass tank.  Blue fitting temporarily installed

A finger-strainer will be installed inside this fitting, and then a 1/2 inch elbow (on order) will be installed.  1/2 inch fuel hose (also on order) will attach to this elbow.  The fuel hose will run to the cockpit above the door, and will have enough slack to allow the wings to be folded (same as the fuel outlet hose).

Hours: 10