Sunday, June 19, 2016

Fuel Tank Installed With Fuel Sump Modification & Bushing Placed In S-1201 Spinner

Saturday was a mixed event day as work bounced between a handful of small tasks, two of which notable … the spinner and fuel tank.

At the tip of the S-1201 spinner there is an epoxy plug that was predrilled at the factory for a bushing to be installed. The “point” on the tip of the spinner needs to be sanded or filed down evenly until a flat spot is created which is the same diameter as the S-1207 bushing. By filing the flat spot to the same diameter as the S-1207 bushing, when inserted into the spinner, it will match the curve of the spinner. The edges of the hole were tapered so the bearing fits snug and the inside of the hole was sanded a little with a fine piece of rolled up sandpaper until the bearing slid into the hole in the spinner. Once a good snug fit was accomplished, the portion of the bushing that is inserted into the spinner needs to be scuffed up with a coarse sandpaper a little so it can be glued onto the spinner with Loctite 241 (blue).
Filing the tip of the S-1201 spinner while rotating the spinner to insure the flat spot being created is even.
Test fitting the S-1207 bushing in the tip of the S-1201 spinner.
S-1207 bushing glued into the S-1201 spinner using blue Loctite 241.

While the Loctite 241 on the spinner and bushing was left to cure, attention was directed to installing the RV-12’s fuel tank. The fuel tank is installed with three bolts … one bolt at the aft end of the fuel tank at the baggage bulkhead and two special bolts used to attach the fuel tank to the center channel. The center channel bolts have evolved over the years the latest version being Rev2 with holes drilled into the center of the bolts to .370. The reason for the head of the bolts being drilled is to protect the fuel tank should there be such a hard landing or event that causes the center channel to buckle or distort. The theory being the bolts will shear off so the fuel tank won’t become distorted during the event and possibly breached. Care needs to be taken when installing these bolts so they are not over torqued … a torque wrench is your friend as the tightening is critical so the bolts do not become over torqued and shear while being tightened  … the standard torque of 20-25 inch pounds for AN3 hardware is used.
Installing the rear attach bolt that secures the aft end of the fuel tank onto the baggage bulkhead.
The two Bolt-00002 Rev 2 - .370 shear bolts that bolt through the center channel and into nutplates on the fuel tank.
Torqueing one of the two shear bolts Bolt-00002 Rev 2 .370 that secure the forward portion of the fuel tank to the center channel.

Prior to installing the fuel tank's outboard shear bolt, a ground wire modification was added. It has been reported by a few RV-12 builders that the pro seal on the fuel tank’s sending unit prevented the sender from getting a good electrical ground … so when the screws for the sender plate were installed last fall, a separate ground wire was added as a preemptive strike. The ground wire connects directly to the fuel sending unit on the fuel tank and runs to the fuel tank’s outboard mounting bolt at the center channel.
My fingers are pointing to the two Bolt-00002 Rev 2 - .370 shear bolts used to attach the fuel tank to the center channel. Note the outboard bolt has the black ground wire modification.

With the RV-12’s fuel tank secured in position, it was time to get underneath the fuselage to attach the fuel supply and return line to the fuel tank. Another modification is being installed here originally developed by Jerry Parr a builder (from England I believe) that adds a fuel sump under the fuel tank along with a CAV-110 aircraft fuel drain valve. Having a fuel sump and drain directly under the fuel tank makes good sense to me and is a modification I wanted to install on the DOG Aviation RV-12. Normally, the supply line sweeps up and connects directly onto a flair fitting on the bottom of the fuel tank. With this modification a short pipe with flared fittings on both ends is made as short as the flaring tool will permit. This short fuel line will connect directly onto the bottom of the fuel tank the other end will attach to an AN826-6D T fitting. The bottom of the T fitting is threaded and connects to an AN910-2D coupler. An AN912-1D reducer fitting screws into the coupler and finally the CAV-110 fuel drain valve screws into the 1/8” threaded hole in the reducer.
Fuel line modification to add a fuel sump and fuel valve directly under the fuel tank. From right to left the parts are a short piece of aluminum fuel line with flared ends, an AN826-6D T fitting, an AN910-2D coupler, an AN912-1D reducer fitting and finally the CAV-110 fuel drain valve.

Frequent readers may recall me posting a photo of this modification about a year or so ago. At that time the parts were ordered from a popular aircraft parts supplier and it was noticed the AN912-1D reducer would only screw onto the AN910-2D coupler 1/8 of a turn or so before binding. I knew the threads on the coupler were OK because other fittings screwed into it just fine … so the issue was with the AN912-1D reducer. I waited until last week and ordered another fitting hoping it would be from a different batch being a whole year later. Much to my dismay, it screwed on a little further … a whopping 1/4 turn before binding. These fittings are not the kind of fittings one can pick up at a local hardware store so the search was on to find some locally and quickly. Fortunately, I remembered race cars also use AN fittings for fuel and nitrous systems … so the DOG Aviation procurement department contacted Summit Racing and as luck would have it, was able to will call the fittings for a same day pick-up. Since this fitting is fairly inexpensive, I ordered two from different manufactures and they both fit just fine. The one from Aeroquip screwed on at least 2 ½ turns by hand so that is the one I went with.
The fuel line sump and fuel drain modification installed onto the bottom of the fuel tank. The main fuel line to the fuel pump attaches onto the horizontal leg of the T.

Unfortunately, a flashlight was not handy to illuminate the fitting at the tank but based on the photo showing all the parts for the modification, the viewer should be able to visualize how the modification connects to the tank. The brass CAV-110 fitting sits entirely below the fuselage skin.
The brass CAV-110 fitting sits entirely below the fuselage skin so a hole needs to be cut into an inspection plate so the fuel valve can protrude.

Return from the future: Creating the hole in the F-1276B cover plate has been completed and thought it would be appropriate to amend this post to show a photo of the completed cover plate thus keeping all the information for the instillation together in one spot. To read the post covering the drilling of the cover plate and information about the chosen grommet click on the following link:

Drilling F-1276B cover plate and grommet instillation.

A photo of the completed DOG Aviation RV-12 fuel line modification using a silicone outdoor rated grommet in the F-1276B cover pate for the CAV-110 fuel valve to pass through.