Last Piece Of The Puzzle Prior To Engine Start – Ducati Voltage Regulator Installed

One item that has been on my mind is the voltage regulator instillation … which was discussed in depth last fall. A different voltage regulator has been procured and will be installed at a different location. However, in the meanwhile, have decided to install the Ducati voltage regulator that came in the Rotax engine box to keep the forward progress going so an engine start can be attempted. When everything else is finished, will begin working out the details for the new voltage regulator and mounting location.


Normally, the wires going to the voltage regulator would be inserted into a connector plug that slides into the voltage regulator. However, because this will be a semi-temporary instillation of sorts, have opted not to insert the female spade connectors on the ends of the five voltage regulator wires into the connector … instead, will use heat shrink over the bare metal spade connectors on the ends of the wires and just slide the spade connectors onto the terminals in the voltage regulator.

Placing heat shrink tubing onto the wires to cover the bare female spade connectors. The Ducati voltage regulator that will be temporarily installed is sitting on the coolant radiator in the foreground.

The female spade connectors for all five of the wires that connect to the voltage regulator were covered in heat shrink tubing in this manner. These are the two yellow wires from Rotax engine's dynamo.


The heavy gauge yellow wires from the Rotax engine with the braided ground shield covering them were routed under the wire run from the firewall, fan folded and wire tied along with the wires from the instrument panel. These two yellow wires are the output from the Rotax engine’s dynamo and connect to the terminals marked “G” on the Ducati regulator … the voltage on these wires is a sine wave, so it makes no difference which order the two yellow wires go onto the “G” terminals (input) on the Ducati’s regulator. The two white wires (P-156) that supply power to the switch and fuse module are connected to the R and B+ terminals. Here again, it makes no difference which of the two white wires are connected to the R & B+ terminals because the two white wires are connected together. The last wire that needs to be connected to the voltage regulator is the small yellow wire (P-761) which is connected to the “C” terminal on the Ducati regulator. The “L” terminal on the regulator is not used in this application … (believe this is for an indicator light).

The five wires connected to the Ducati regulator. Fellow RV-12 builders take note, the connector body shipped with the Ducati regulator is not being used so the spade connectors are slipped directly onto the male spades on the regulator. The use of the Ducati regulator is only temporary until the mounting is finalized for the much higher current capacity Silent Hektik regulator that will be used on the DOG Aviation RV-12.


Of note: The Silent Hektik regulator has the same mounting hole spacing and could be mounted on the firewall shelf where the Ducati regulator is mounted. However, the mounting location on the firewall shelf is directly in line with the outflow of warm air from the coolant radiator and very close to the #4 cylinder’s exhaust pipe. Blowing hot air onto a high current semiconductor device is not the winning formula for long term viability.

Finished mounting of the Ducati voltage regulator on the RV-12’s firewall shelf.


At this point the DOG Aviation RV-12 is ready for the first engine start which will happen really soon. The wings have been pulled off again to improve the fit and finalize the routing of the AOA tubing which will be covered in another post.

Just Fueling Around

Now that the fuel tank has been installed in the DOG Aviation RV-12, thought it fitting to fuel around so to speak and pour some petro in the tank and run a few tests. First test is to pour 4 gallons of fuel into the fuel tank, disconnect the fuel line leaving the gascolator to the carburetors and connect a hose to collect fuel in a vessel that is marked for one gallon. Before starting the test, figured may as well verify the mechanical fuel gauge in the fuel tank is at or in the red no takeoff zone defined by the transparent sticker on the on the gauge … it was. Moving on, when the setup is ready, the master switch is turned on (which normally turns on the fuel pump but I added a separate switch for the fuel pump) and the fuel pump switch was turned on. Next the fuel on/off valve is placed in the on position and the fuel flow is timed. The requirement is to pump a gallon of fuel in less than 180 seconds into a vessel approximately at waist height. The fuel pump and fuel system had no problem meeting this requirement. I ran three passes and found the time changes slightly depending on if the hose is down in the fuel capturing vessel or not … although, either way, the times were still under the allotted 180 seconds.

A one gallon milk jug was used to capture and measure the fuel during the fuel flow test.

I jumped the gun a little and decided since I had the fuel at the hangar, I would jump ahead and do the Dynon fuel gauge calibration. Typically, one would wait until after the empty weight and balance measurements have been made before filling the fuel tank. So yes, I will have to drain the tank ... but that is not that big of a deal except for using the stupid gas cans the asses at the EPA have shoved down our throats. Seriously, I have spilled more fuel in the last few years using the new “environmentally friendly” fuel cans than I have my entire life using the old style cans.


Speaking of gas cans, the ones I purchased for the 2 gallon fuel fills necessary to calibrate the Dynon SkyView are very hard to use. If used as designed, they spill fuel like crazy. The can does not have a traditional spout for the fuel to flow out of. Instead, the spout has a flat surface with an O ring on it that when not in use, seals the end of the spout. The spout is spring loaded and retracts when a tab on the spout is pushed against a fuel tank. The problem is … when the spout is retracted to allow fuel to pour out from the nozzle, the fuel hits the flat surface with the O ring and comes out of the spout sideways. This may be OK for a lawnmower but the RV-12’s filler neck has a taper before the straight pipe so the fuel coming out of the nozzle sideways hits the taper and flows right out of the filler neck and down the side of the airplane. I ended up using a wire tie to hold the nozzle open so the whole neck of the fuel nozzle could be placed deep into the RV-12’s fuel filler neck.

Wire ties were used to depress the filler neck on the fuel can’s mandated “environmentally friendly” nozzle so fuel would not pour out of the RV-12’s filler neck and onto the floor. Looking closely at the photo, one can see the flat surface I’m talking about with the O ring at the end of the nozzle that causes the fuel to come out sideways.


Prior to performing the fuel calibration test, Van’s wants the main wheels to be rolled up onto 2” blocks … (I guess to simulate level flight). To perform the Dynon SkyView fuel calibration test, the fuel calibration menu is selected for tank 1 and the calibration begins with establishing it is a 20 gallon tank and then an empty fuel point is established. Pushing the Add button on the Dynon SkyView will result in asking the user to pour fuel into the fuel tank in 2 gallon increments. Van’s instructions say it is only necessary to pour in 16 gallons for the calibration so that is what was done. I also cheated a little and poured one gallon into the tank and told the Dynon to start the test ...  zeroing with one gallon in the tank. So, in theory, when the Dynon thinks the fuel tank is totally empty, there will be approximately 15 minutes of fuel left.

The main wheels are to be put on 2” blocks prior to beginning the Dynon fuel level calibration.

The Dynon fuel level calibration wants fuel placed into the fuel tank in 2 gallon increments.

After the 16 gallons (plus the 1 gallon that was in the tank to start with) was poured into the tank the calibration procedure was terminated and the Dynon display showed an almost full fuel tank on the display.

Seat Belts & Wings Installed For EAA Tech Councilor Inspection

Prior to installing the wings for Saturday’s tech councilor inspection, decided it was time to install the seat belts in the RV-12 while it could be still be done standing adjacent to the fuselage. The seat restraints consist of a lap belt, two shoulder harnesses and a crotch strap. Instillation is a snap using AN4 hardware and bushings for the harnesses to move on without scoring the bolts. The crotch straps are a little tricky to get positioned but not really anything worth commenting about.

Completed instillation of the RV-12’s seat restraints.

Friday, after installing the seat restraints, the whole ground crew was available to help mate the wings on the RV-12’s fuselage again. The wing’s spar pins are tighter than I would prefer, so will sort that out later. Think the F-1204R retainer blocks need to have a little material removed because it appears they are touching the top of the spars and preventing the spar from sliding in the last 1/32" or so which is making getting the spar pins installed a really tight fight.

With the help of the ground crew, the wings were once again mated to the fuselage and now the eagle is ready for the EAA (Experimental Aircraft Association) inspection. Ground crew from left to right Mike T., Bernie, Mike K. and yours truly.


While in the process of installing the wings decided to install the previously mentioned gap seal that is a nicer looking option than the foam seal Van’s provided with the kit. An automotive edge trim was installed which is 1/8" thick between the inside of the slot and the outer edge which is exactly what the gap is to be between the fuselage and the wing skins.

Automotive rubber edge trim gives the wing to fuselage mating on the DOG Aviation RV-12 a classy finished look.

After the wing instillation was completed on Friday, the EAA inspection took place on Saturday morning. Jim Strock is an A&P mechanic that volunteers his time as part of an ongoing safety program that the EAA has available for members building experimental aircraft. The idea is to have a knowledgeable and experienced person inspect the aircraft being constructed during various phases of construction to insure standard assembly practices and techniques are being followed and there are no builder created safety issues are being created by the manner in which the aircraft is being assembled. This is strictly a volunteer program which I feel is beneficial to the experimental aviation community and wanted to participate in.

EAA tech councilor Jim Strock is a FAA certificated A&P aircraft mechanic with many years of aircraft maintenance under his belt. Jim currently teaches hands on aircraft maintenance at a training facility.


Jim praised the quality of workmanship going into the DOG Aviation RV-12 and was amazed at the amount progress since his last visit towards the end of last year. Fortunately, there were no issues that caught Jim’s probing eyes other than the lose wires for the yet to be installed voltage regulator.

Coolant Added To Engine – Split Hose Issue Noticed & Resolved

The Rotax 912ULS engine has water cooled heads which require a coolant. Various coolants are approved by Rotax for the 912 ULS engine so opted to use an ethylene glycol Dex-Cool mixed 50/50 with distilled water. A concentrate was chosen as opposed to a 50/50 pre-mix so I could be sure it was diluted 50/50 with nothing but distilled water. I would suggest other builders consider the use of distilled water as well.


The top of a drinking water bottle was cut off to use as a small funnel to fit into a second water bottle that had its neck removed to be used as the measuring vessel for the 50/50 coolant dilution.

Pouring an equal amount of distilled water into the measuring vessel to mix with the Dex-Cool in the PowerAde bottle. The Dex-Cool looks good enough to drink … especially as a concentrate in a Powerade bottle. Not seen in this photo, but the bottle was marked as Dex-Cool and the Powerade label removed for safety.


After each batch of Dex-Cool was mixed 50/50 with distilled water, it was poured into the expansion tank for the radiator until it was topped off with the coolant.

Pouring the Dex-Cool and distilled water 50/50 mixture into the expansion tank on the Rotax 912 ULS engine.

When the expansion tank was full, the 18 psi pressure cap was placed on the expansion tank and as I was about to pour the remaining coolant mixture into the overflow bottle mounted on the firewall, noticed that the rubber fuel /vapor hose that connects the bottle to the expansion tank was beginning to split already. REALLY? It has only been on the bottle a few months and is already beginning to split! What gives?  When cutting the hose, a hose cutter was used … so I know it was a clean cut with smooth edges to begin with.

Photo of the Gates 3/16" ID fuel/vapor hose on the overflow bottle already beginning to split … and it has not had any service time yet. Not a good sign.


Admittedly, this hose was tough to get onto the bottle and expansion tank in the first place … and the fit is so tight, there are no hose clamps used at either end (there is no pressure here to speak of, just however many inches of water are in the overflow bottle). This got me thinking that the rubber is being stretched far too much for this application … so it got me  doing “a little FBI, 007 type investigating” to coin a phrase from a Dr. John’s song. The hose supplied is an American sized Gates 3/16" fuel/vapor hose that is being slid over 8 mm pipes that have 9 mm nipples on the end of them. The Gates 3/16" hose is actually 4.8 mm … so it is being stretched to twice its normal size. Other builders have reported this hose splitting at either the overflow bottle or the expansion tank. The DOG Aviation procurement department located some 7 mm fuel hose at a local foreign car parts supplier that is an unreinforced rubber fuel hose that has a cloth outer coating (think VW fuel line). I would prefer a reinforced rubber line, but feel this will be OK for this application for the time being. There were no specs available for the hose purchased, so I will likely switch it out later for some reinforced hose that is a known entity since the hose is relatively easily accessible. But for now, it is good enough for an engine start. Because the 7 mm hose used is only being stretched 1mm on the tubes on either end (not counting the nipple), thought it would be prudent to add band clamps to the hose as can be seen in the following photos.

Replacement 7mm rubber hose with additional band clamp on the pipe protruding from the overflow bottle.

At the expansion tank end of the hose, the hose clamp needs to be positioned so it does not go under the flange on the tank for the pressure cap … if it does, the cap will snag on the clamp because clearances here are VERY tight. The clamp in this photo needed to be moved a tiny bit to the left so the coolant pressure cap would fit on the expansion tank without snagging the clamp.


Suppose ¼" ID fuel/vapor line would be a step in the right direction if one wanted a tighter fit than the 7mm hose can offer. The ¼" hose equates to 6.3 mm which will require far less stretching than the 3/16" hose supplied, so it may resolve the issue nicely as well. Plan on contacting Van’s to see if there is a specific reason 3/16" hose was chosen for this application.

Small Time Consuming Issues

The majority of the week has been taken up by working through a few issues … some known, some discovered. Although not big deals, in and of themselves, collectively they have taken quite a bit of time to resolve.


The first issue arose when Bernie swung by to assist installing the canopy assembly … it was discovered the nut and washer would not fit between the canopy strut and the faring. When doing the canopy layup, foam blocks were placed in this area knowing there was a possibility for issues here. Apparently the foam blocks could have been made just a bit thicker because the first layer of the glass cloth sagged just enough from stippling the epoxy resin into the cloth that the nut and washer would not fit … it was close but just not quite enough clearance. Had to use the Dremel tool to remove just a little bit of fiberglass to gain clearance for the nut. Of course, the screw also needed to be ground a little shorter as well so it did not push onto the fiberglass … this took a few on/off cycles on each side to resolve. Fortunately, Bernie was available to give me a hand holding the canopy while the adjustments were made. The left side had the issue with the fiberglass and the right side had enough clearance but the screw needed a few threads removed for a correct fit … the end result, one thread was left protruding the nuts on both sides.

Bernie giving me a hand … finally, after fussing with the fiberglass on the left side and cutting a little off the length of the screws, the canopy struts were able to be installed.


One item that has been known about since the initial wing fitting is the inboard edges of both wing skins needed to be cut back a little so there is 1/8” of clearance between the inboard edges of the wing skins and the fuselage … this is for a foam rubber gap seal Van’s has the builder place between the wing and fuselage. Not liking the look of the stick-on foam strips, the DOG Aviation procurement department found automotive trim rubber which will provide a clean finished look. The last time the wings were on measurements were taken and marks were placed on the wings. Using a Dremel outfitted with a sanding drum, the small amount of excess material was removed. More material needed to be removed from the lower skins because of the double plates on the fuselage. Unfortunately, the Dremel has a tendency of creating small scallops in the metal so it was necessary to stop short of the line and hand file to the line. The material sands away slowly and to complete both wings took many more hours and sanding drums than one would have thought.

Using a Dremel outfitted with a sanding drum to remove excess material from the wing skins.

Another issue was discovered when adding coolant to the Rotax 912 engine but will cover that in the next posting.

Yes! – We Have Brakes!

Now that the eagle’s propulsion has been squared away, it’s time to work on the claws when returning to terra firma. The brake lines have been installed for quite some time, but the system has not had brake fluid installed yet. In general, aircraft do not use the typical DOT 3 or 4 brake fluids common in automobiles, instead, they use various forms of specialized hydraulic fluid. At DOG Aviation the decision has been made to use Amsoil’s full synthetic ATF fluid for the brakes … it has a very high flash point of 453 degrees F, which is a good thing and actually higher than a few of the recommended aviation hydraulic brake fluids. In a pinch, when on a trip, Moble 1 ATF can be added and it is available at any automotive store on a Sunday afternoon … aviation brake fluid, not so easy to procure on a Sunday afternoon. By no means is this a recommendation to use a non-aviation brake fluid … it is just a decision made for the DOG Aviation RV-12 based on a little research. If the decision turns out to a bad one, I’ll return from the future and edit this post accordingly … but that is not very likely to happen.


Purging the brakes on any RV airplane can be problematic because of the crossover brake lines that connect the four master cylinders (two pilot and two co-pilot) together for each of the wheel brakes. The crossover lines tend to be high spots and are prone to capturing air which can be difficult to remove by just pressing on the brake pedals to bleed them.


The ultimate method is to use a hand vacuum pump connected to the fluid reservoir on the firewall and pull fluid in from the wheel cylinders or a pressure pump to push fluid… but they are pricey. The second best way is to push fluid up from the wheel cylinders using a hand pump. I elected to try using the hand oiler approach and had acceptable results once I got the hose attached to the oiler to stop leaking. (Suppose a small pump-up garden sprayer would work even better). I was thinking of making a small pressure vessel out of a quart Mason jar if the oiler did not work. When using the hand oiler, care must be taken to not pump more than about half the fluid out of the container …. this allows for the top to be unscrewed and the pump moved aside so the tank can be topped off again without lifting the pump out of the fluid which will induce air into the pump.

Pumping fluid into the brake bleeder valve using a large hand pump oiler. It would have been nice if the oiler squirted a larger volume of fluid per pump, but it did work OK and got the job done.


At the brake fluid reservoir on the firewall a ¼" threaded fitting was connected to a vinyl hose to collect the excess fluid. I would have preferred using a barbed fitting but my local big box store did not have any with ¼" pipe threads so a hose was slipped over the threads, which of course leaked … but that is not a big deal at the reservoir end because the hose is only for collecting the fluid.

At the brake fluid reservoir on the firewall a ¼" fitting was screwed into the reservoir and connected to a vinyl hose to collect the excess fluid. The use of a ¼" NPT to barbed fitting would be preferable here as opposed to the ¼" NPT to ¼" NPT fitting that was used.


While performing the purge, the bleed valve on the caliper can be left open while vigorously pumping the oiler ... however, a hand should be kept on the vinyl tubing to keep it  from popping off the fitting while pumping and making a big mess (ask me how I know).

Carburetor Choke Controls Installed – Ready for Engine Start

Yesterday, did make it to the hangar for a short work session to finish up installing the remaining control cables on the carburetors which consisted of the two choke cables. Installing the choke cables is a snap … the control cables are routed to the carburetors and inserted into a curved cable mount tube attached to the carburetors. As with the throttle cables, the longer of the two choke cables is installed on the right carburetor. The attachment of the choke cables to the carburetor is much simpler than the throttle cables, in that, the cable slips through a CT-00100 wire swivel with set screw.

As can be seen in the photo of the drawings, the choke cable is attached to the carburetors using a CT-00100 wire swivel with set screw.


The choke cable instillation is simplistic … with the choke control lever on the instrument panel positioned all the way in (choke off), route the choke cable through the curved cable mount tube, insert the CT-00100 wire swivel into the choke lever on the carburetor, slip the cable through the tiny hole in the wire swivel and lock down the cable with an Allan set screw.

Routing the left carburetor's choke cable through the curved cable mount tube attached to the Rotax 912's carburetor.

After inserting the choke cable in the wire swivel, the slack was pulled out of the cable while the Allan set screw was snugged up. Final tightening of the set screw was done while holding the wire swivel with a wrench to prevent the cable from twisting.

Holding the wire swivel with a wrench while using an Allan wrench to tighten the set screw onto the choke cable.

Completed throttle and choke cable instillation on the right carburetor ... the excess ends of the control cables still need to be cut shorter.


Basically, at this point the RV-12 is complete construction wise. There are a few items left to do but for the most part it is just attaching things that have already been fitted such as the rear window, bolting on the canopy, bolting on the steps, screwing the ELT antenna in place, etc.


There are a few items left to figure out such as mounting the new voltage regulator (may just install the original Ducati on the firewall shelf for the time being), installing the parking brake and placing foil at strategic locations on the inside of the lower cowl. Oh, can’t forget about putting coolant in the engine, bleeding the brakes, not to mention performing the fuel flow test and fuel level sender calibration on the SkyView. So I’ll still be busy the next few days.