Archive for May, 2011

Tail Spring Fairing & Breather Tube Mod

Friends have been bugging me forever to fabricate a fairing for my tailwheel attach bracket. It’s a big, draggy bracket that attaches to where the original leaf spring tailwheel attached. The first step in the process is covering everything with either shelf paper (the white stuff) or vinyl tape to protect it from my sloppy application of cloth and epoxy resin.

With the area protected, I used modeling clay to form the shape of the fairing. The flash from my digital camera really emphasizes the surface irregularities. It really did look a lot smoother than that to the naked eye. Not a huge concern for a part like this, I guess. And the fiberglass cloth itself kind of smooths out smaller surface lumps and bumps.

I covered the clay and the surrounding area with PVA mold release and then applied 3-4 layers of 6 oz. fiberglass cloth and epoxy resin. This is the part after the resin is cured and the part has been separated from the aircraft.

This is the part after I’ve finished removing the clay and pealing the PVA mold release. I’ve also done some preliminary trimming with a Dremel tool equipped with a cut-off wheel. It was still a little cool in my hangar so the part hadn’t really cured enough to start sanding on it. I’ll probably take time to sand, fill and prime it before I put it on the airframe for a test flight. I tend to get some oil back there and I don’t want an unprotected, raw fiberglass part to get oil soaked. It’d be nearly impossible to get the paint to stick if that were to happen.

Another little nagging project I’ve been meaning to complete is the installation of a modified breather fitting. The original O-200 breather tube fitting is simply the threaded fitting you see in this picture. When screwed into the case, the fitting is flush with the inside wall of the case which allows oil to easily run down the inside of the case and get sucked out via the breather tube. If you look closely at the fitting in this picture, you’ll see that it’s been machined slightly to allow a bigger inside diameter on the treaded end of the fitting.

The larger inside diameter allows a 1/2″ copper tube to slide in and be silver soldered into place. Once the tube is soldered, it is cut down to 2-3/4″ from the end of the threads. This extended breather vent still provides the “breather” function, but it makes it more difficult for oil to actually escape the engine. (Or so the theory goes…) Big thanks to Dave Biesemeier–friend and machinist extraordinaire for his efforts in modifying the fitting.

This is the original fitting as it was installed on the engine at overhaul time. It was powdercoated with the rest of the engine at that time.

I lost the red powdercoating, but I still think the gold looks cool against the red. You can also see the bead of Permatex thread sealant that oozed out of the threads as I installed the fitting. On the advice of Dave B., I’ve started using the sealant on pretty much all my pipe threads. Never had a leak on a fitting with the sealant. Forgot to apply to one fitting on my oil filter housing and had a leak. Definitely worth the time and effort to use.