Prime, Fill, File – The Order Of The Day

The weather cooperated today, so was able to mix up a batch of Akzo primer and get the outside of the RV-12’s fuel tank sprayed along with the sender plate and a couple of miscellaneous small items. I used the HVLP spray gun for the task since a fuel tank is a large item for an airbrush. It hardly seemed worthwhile using the gun for less than five minutes considering all the time it takes for setup and cleanup. The bottom of the fuel tank was sprayed first then the tank was turned over and placed onto four wooden blocks that had a rivet mandrel pounded into the center of each block of wood to prop up the tank. This was done so it would not be necessary to wait for the primer on the bottom to dry before turning the tank over ... by doing it this way the tank was only sitting on four tiny points.

The RV-12's fuel tank and a few miscellaneous parts were sprayed in less than five minutes … hardly seems worth it because the cleanup takes about an hour.

After the spray gun was cleaned up and the tip changed for spraying the JetFlex top coat tomorrow, decided it was still warm enough to mix up a small batch of microsphere filler and slather it onto the canopy lay-up to fill a few of the remaining low spots.

While the fuel tank dried and the epoxy filler applied to the canopy lay-up cured, decided to break into the powerplant kit and begin deburring all the aluminum firewall forward parts with a file. Once the big stuff is smoothed down, will use a Scotch-Brite wheel to finish off the edges.

Beginning the process of using a file to deburr the shear marks on the aluminum parts that came with the powerplant kit.

Did not finish deburring the pie of parts today, so will continue on after the fuel tank and a few other parts are top coated with the Jet Flex interior paint. The forcast is for rain tomorrow in the early morning and clearing in the afternoon ...  hopefully I can get the spray session in at some point in the afternoon.

Preparing The RV-12's Fuel Tank For Paint

Today, preparations for priming and painting the RV-12 fuel tank began. Probably a little soon to be priming over the fairly fresh tank sealant (has only cured for two days) then painting, but the weather here  warmed up somewhat so it is going to be around 70 for the next two days … after that, it appears like a steady downward trend will begin. The task for the day was to carefully remove excess tank sealant from around the rivets on the outside of the tank. Decided if the blob of tank sealant around the rivets on the outside of the tank is the only thing preventing a fuel leak, than I have bigger issues. The edge of a wooden tongue depressor that was spit in half was used to scrape off the excess fuel tank sealant from all the rivets that will be visible from inside the cockpit.

Once the heads of the rivets were cleaned up, the tank was scuffed up with a maroon Scotch-Brite pad.  Will hold off on cleaning the metal with Acetone until just prior to priming.

After removing the excess fuel tank sealant from around the external rivet heads, the fuel tank was scuffed up using a maroon Scotch-Brite pad to prep the tank for primer.

RV-12 Fuel Tank Completed – Almost

In spite of the cold temperatures, with the help of Mike K. the remaining T-1204A-1 top tank skin was riveted onto the RV-12’s fuel tank. Because of the desire to coat every rivet on the inside of the fuel tank with sealant, a deviation from the plans was made and the mechanical fuel gauge was not installed at this time to allow for easier access to the inside rivets.

After mixing the tank sealant, a small dollop of tank sealant was placed on the threads of the fuel return line being careful not to place any sealant on the tapered portion of the fitting.  The fuel return line was placed in position and the fitting was made finger tight. The top tank skin was temporarily placed in position with a few Clecos to hold it ... then the two T-1216 clips were placed over the fuel return line and secured with Clecos. This was done so the fuel return line fitting could be tightened without moving the aluminum fuel return line out of position ... this was accomplished by reaching through the hole for the sender plate and using a crows foot wrench to tighten the fuel return fitting . After the fitting was tightened, the clips were removed and the top skin removed. Tank sealant was applied to the T-1204A-1 top skin and the associated mating surfaces ... then the parts were Clecoed together for riveting. Once the tank's top was riveted in place, the area around the rivet holes for the T-1216 clips was slathered with fuel tank sealant and the clips were placed over the fuel return line and riveted onto the inside of the tank. Next the tank was placed upside down on blocks of wood and by reaching in through the sender plate hole, a syringe filled with tank sealant was used to coat the shop heads of all of the 82 newly installed rivets with tank sealant ... along with filling the corners and gaps.

Completed fuel tank assembly (minus mechanical fuel gauge, sender plate and sender) placed in the warm  light box so the tank sealant can cure properly during the cold evenings.

During the next work session, plan to install the mechanical fuel gauge and screw the sender plate in position.

Bending Fuel Level Sending Unit’s Float Arm

In addition to the mechanical Moeller fuel gauge, the RV-12 fuel tank is also equipped with a sending unit that is connected to the SkyView … this allows the Dynon unit to receive fuel level information so it can be shown on the primary flight display. When the sending unit’s float arm is removed from the box, there is already a hooked end to capture the float …. However, the rest of the arm is straight and requires the builder to make two bends per the plans. The plans would suggest the drawing is 1:1 but on the plans there are measurements for 6 1/4" that do not match the drawing … my drawing appeared to be a little shorter. Decided to bend the float arm as shown in the drawing but used the measurements shown in the drawing. Below is a photo of the drawing and the sender unit arm after the first bend was completed.

Completed first bend of the sending unit’s float arm.

A vice was used to secure the float arm and the bends were made by using a piece of wood to bend the arm … doing this leaves the metal rod as straight as possible. Once the bends are completed and the excess rod cut off, the float rod slips onto clips on the sending unit’s arm. Ohm readings were made and were almost spot on to the published 30 to 240 ohms as the float arm is moved through its full range of motion.

Completed float arm attached to the fuel level sending unit.

At this point the plans have the builder temporarily install the sender unit onto the tank to check for clearances and to adjust the float position. At the bottom of travel, the top of the float is to be 1 5/8" off the bottom of the tank … and at the top of travel, the float is to be 10 1/4" off the surface of the bottom of the tank.  I used a ruler with two pieces of tape to identify the low level and high level and used that to make the adjustments. Also, the float arm is not to rest on the T-1208 baffle.

Top of the float in the low position is approximately 1 5/8" off the bottom of the tank.

Top of the float in the high position is approximately 10 1/4" off the of the bottom of the tank.

After completing the adjustments to the float arm, there should be clearance between the T-1208 baffle and the float arm. Looks good, I can get my finger between the two.

Today the plan is to install the top skin of the fuel tank … more fuel tank sealant fun, can’t wait ... not.

Fuel Tank Trial Fit – T-1211 Flange Bending

Did not get much accomplished yesterday because the two tasks for the day took longer than expected to accomplish. The inside of the fuel tank was cleaned up a little using wooden cotton swab sticks wetted with Acetone. The objective was to remove finger prints and miscellaneous smears and the occasional small string of sealant. The joints were left alone. After the tank cleaning, the top was temporarily secured onto the tank with Clecos and per the plans, the tank was placed in the baggage area and bolted in position. I used a bunch of washers under the bolts so as to not have to screw them in all the way.

Carefully slipping the fuel tank assembly into the baggage area to adjust the shape of the flange on the T-1211 fuel neck.

Once the tank is bolted in position, the flange on the T-1211 fuel neck is to be fitted to the curve of the turtle deck as best as possible by bending the flange of the fuel neck. The plans say small gaps can be filled with fuel tank sealant. I initially marked the areas where the flange could be bent to have an immediate impact. Then tweaked the flange with many cycles of removing, bending and reinstalling.

Placing masking tape to mark one of the two locations that will have the biggest initial effect on closing the gap between the flange and the turtle deck. The gap at the start of the process is significant as can be seen in the photo.

Due to the way the turtle deck curves and the surface area of the flange, I think it would be very difficult to get the flange to sit perfectly flush on the turtle deck. I found when attempts were made to fine tune the bends, larger gaps would appear in other areas. I suppose, if one had a shot bag and fender forming tools the flange could be made to be a near perfect fit … unfortunately, DOG Aviation does not have access to those types of body work tools. I got it fairly close, but admittedly, it is not perfect. However, later the area will be slathered with mold release or oil and a thick application of tank sealant will be applied to form a removable custom gasket so any small imperfections between the turtle deck skin and the flange on the T-1211 filler neck will be taken up by the tank sealant gasket.

After the fit was close enough to move on, I deviated from the plans a little and installed the fuel cap in the T-1211 filler neck. The outer edge of the fuel cap was used to visually center the filler neck in the hole on the turtle deck skin, the flange was then clamped to the turtle deck and match drilled to the holes in the turtle deck. … Clecos were installed to hold positioning after each hole was drilled.

Match drilling the T-1211 filler neck to the F-1277R turtle deck skin using a #30 drill bit.

Final fit of the T-1211 fuel filler neck to the F-1277R turtle deck after the match drilling process. There is still a tiny gap but that will easily be taken up with fuel tank when the custom gasket is formed.

Canopy Removed & Fuel Tank Work Continues

With a little help from Mike K. the RV-12’s canopy was unbolted and easily removed from the fuselage by lifting straight up. (Frequent readers of the DOG Aviation blog may remember the canopy lay-up was broken free from the Vaseline covered tape a week or so ago). The reason for removing the canopy now is two fold in that the temperatures forecasted for the next few days are not ideal for properly curing the epoxy filler so figured the canopy can be trimmed to the final size so it needs to be removed for that … and the fuel tank needs to be temporarily bolted in place in the fuselage so the filler neck can be adjusted to the shape of the turtle deck and then match drilled.

Mike K. giving me a hand with removing the canopy from the fuselage.

Now that the canopy is removed, figured may as well also remove all the protective tape layers and masking. The duct tape and masking tape came off without any issues … HOWEVER the packaging tape was another story. For some reason there were spots where the adhesive pealed away from the tape and remained on the aluminum. Did not want to use solvents to remove the adhesive, so used the duct tape that was just removed to pull the adhesive off the metal. This was time consuming but eventually all the adhesive left behind was removed.

Removing the duct tape that was placed onto the upper forward fuselage skin for the canopy lay-up.

Using duct tape to remove the brown adhesive left behind from the removal of the packaging tape.

Tape collecting the brown adhesive that pealed off the packaging tape.

Back to looking like aluminum after removing the brown adhesive.

Moving on to the fuel tank, the rivets placed into the T-1203 aft bulkhead yesterday, were coated with tank sealant. Once again a syringe was loaded with the tank sealant and used to apply the sealant around all the rivets. The plans also call for plugging the tooling holes in the T-1207 & T-1208 baffles so the tank sealant was used to fill the four tooling holes in the baffles. Also installed the fuel tank vent fitting on the T-1204A-1 top skin and placed sealant around the nutplate rivets on the sender plate.

The rivets installed yesterday were covered with tank sealant along with the nut plates on the sender plate.

T-1204B flange and AN837-6D fitting for the new fuel tank venting system installed on the T-1204A-1 top tank skin.

The fuel tank is now ready for the T-1204A-1 top skin to be Clecoed in position and the fuel tank temporarily installed in the fuselage so the filler neck can be match drilled for the instillation of nutplates. Once the drilling is completed, the top skin will be removed and any debris that made its way into the tank can be cleaned out.

T-1203 Aft Tank Bulkhead & T-1214 Bracket Added To Fuel Tank

More messy, sticky, gooey, progress was made on the RV-12’s fuel tank with the addition of the T-1203 aft tank bulkhead. Bernie was available to lend assistance, so the two of us cleaned the mating surfaces for the T-1203 aft bulkhead and mixed up a batch of fuel tank sealant.  The fuel tank sealant was applied to the mating surfaces of the aft bulkhead and while Bernie flexed the fuel tank’s sides outward, the T-1203 aft bulkhead was set in place and the tank sides were carefully allowed to come in while making sure the T-1203 was placed under the flanges on the T-1201-1 main tank skin.  The aft bulkhead was then riveted to the T-1201-1 main tank skin. Next, the replacement for the incorrectly machined T-1214 bracket was riveted onto the T-1203 aft tank bulkhead. The upper seven rivets that secure the T-1214 bracket onto the aft tank bulkhead are AN470AD4-4 solid rivets, so they were squeezed with the pneumatic squeezer.

Fuel tank with T-1203 aft tank bulkhead and T-1214 bracket now riveted in place … Bernie caught in the act of cleaning up.

Also during the work session the five K-1000-08 nutplates that attach to the T-1209 sender plate were also riveted with AN426AD3-4 solid rivets.

The tank was placed back into the hot box to cure. Because the temperatures have dropped here, will not attempt to apply any more microsphere filler onto the canopy lay-up until the temperatures are a little warmer.