Installing a “Bender Baffle” Piggybacked With Regulator Relocation Mod - Part Three

This post will cover mounting a terminal barrier block which will be used as an interface between the existing RV-12 wiring harness and the wiring harness that will run to the Silent Hektik F-4118 regulator mounted inside the lower cowl on the baffle plate.


RV-12 builders planning to relocate the voltage regulator inside the lower cowl's air duct please take note of the following regarding the use of quick disconnect connectors for the wiring:


The wiring connector dilemma: Mounting the regulator on the baffle plate inside the air duct creates a wiring challenge because the wiring will need to be disconnected every time the lower cowl is removed. On a new aircraft like mine, removing the lower cowl will occur more frequently during the initial flight testing and then taper off to a few times a year for oil changes and condition inspections.  This, in and of itself, creates some issues. What’s the big deal you may be asking yourself? Just use a connector that has pins rated for the maximum current the Rotax 912 can produce (approximately 18 amps). Well, that’s easier said than done and here’s why ....


Because the regulator is a high current device, ANY connector utilized needs to have pins rated for high currents. Sticky wicket #1: … sure there are plenty of connector styles available on the market but ones with pins rated 15 – 20 amps are quite limited. Sticky wicket #2 and the main reason I suggest builders DO NOT use any quick disconnects for the regulator wiring is: ... if one looks deeper into the application data sheets for the connectors, unfortunately, you will quickly discover all the connectors that have pins rated for high current have a VERY LIMITED INSERTION LIFE CYCLE, with the majority of connectors being under 10 insertions. This means that after removing the cowling just 10 times (some were as low as 6) the pins in the connector would need to be replaced in order to remain within the max current specification the connector’s pins are rated at. The best connector I could find is a very popular expensive military connector rated at 20 amps per pin and that only has a life span of 25 insertions. Because of the limited insertion ratings of the connectors, I decided it best to forget about using a quick disconnect connector altogether and would suggest others do so as well …  at the currents we are talking about, a little increase in resistance at the connector pin can begin to create a considerable amount of heat at the connection leading to oxidation which increases the resistance generating more heat etc.,  to the point of melting insulation. This application requires a continuous low resistance connection … period.


My solution will be to use a very high quality screw-down terminal block rated for high temperature environments. Suggest others doing this not use the lesser quality plastic terminal blocks … you want the good stuff for this application. I chose a Cinch 6-142 phenolic terminal barrier block which is a 6 circuit barrier block rated at 30 amps per circuit and able to withstand temperatures to 300 degrees. Astute RV-12 builders may be asking themselves why use a 6 circuit barrier block when only 5 wires are run to the Ducati regulator? The answer is both the Ducati and Silent Hektik F-4118 regulators obtain their ground from the case being bolted to the aircraft airframe ... so this necessitates running a sixth wire that will be bolted to the regulator's case to supply the necessary ground for the regulator. So a ground wire will be run from the ground block on the DOG Aviation RV-12's firewall to the sixth terminal in the Cinch terminal block to provide the necessary ground.

The Cinch 6-142 phenolic terminal barrier block.

Decided a good and easy location to mount the Cinch terminal barrier block would be on the two rudder pedal studs that protrude the nutplates on the RV-12’s firewall shelf. Two 3/4" coupler nuts were screwed onto the protruding studs and blue Loctite was placed on the threads to prevent the nuts from coming loose.

Plenty of threads to protruding the nutplates to install coupler nuts to use as a mounting point for the Cinch 6-142 terminal barrier block.

3/4" long stainless coupler nuts with 10-32 threads were screwed onto the portion of the rudder pedal mounting bolts that protrude the nutplates. Loctite 242 (blue) was placed onto the threads prior to installing the coupler nuts.


Next a small mounting plate was fabricated with an offset to mount the Cinch terminal block. The small offset was used so there would be easy access for a screwdriver to remove the wires, The offset is not really necessary …. however, without the offset the coolant hose blocks easy access to some of the screws and would require the use of a stubby screwdriver. The Cinch 6-142 terminal block has an exposed bottom … meaning if one were to look up from the bottom one can see the metal inside. Although not necessary, I decided to cut a thin strip of Neoprene and use it as a sealing gasket under the connector block.


The Cinch terminal blocks can use various mounting accessories. The DOG Aviation R & D department decided on using fast on connectors the side of the connector block that interfaces with the existing wiring which normally connects to the Ducati regulator. The beauty of this is ... if I decide to leave the Ducati regulator mounted on the firewall shelf as a spare, should the Silent Hektik regulator fail, the wires can easily be unplugged from the Cinch terminal block and moved back to the Ducati regulator. The wiring harness going to the regulator inside the lower cowl will have #8 ring terminals terminating at the Cinch terminal barrier block. This will allow the wires to be easily disconnected whenever the lower cowl needs to be removed. Sure it will be a bit of a hassle removing six screws every time the lower cowl needs to be removed, but the screw down terminal block will provide a very solid and low resistance interface connection between the existing wiring and the extension wiring to the regulator inside the lower cowl's air duct.

Fabricated mounting plate and the Cinch 6-142 terminal barrier block attached to the rudder petal bolt studs via two stainless 3/4" 10-32 coupler nuts. The Ducati regulator can be seen in the background and there is more than enough wire to easily reach the Cinch terminal barrier block.


Looking at the above photo, one can see that there are two 3/8" coupler nuts on the terminal block these will support a cover plate made from high temperature plastic that will cover the wires and connections when the final wiring is completed.

Installing a “Bender Baffle” Piggybacked With Regulator Relocation Mod - Part Two

Have finally gotten around to continuing work on the modified “Bender baffle” and during a few small work sessions, worked out the final positioning for the bushings ... this was after changing my mind a few times in an effort to maximize the full open position for the baffle. In the previous post, there is a photo of a box representing the size of the voltage regulator tapped onto to the cardboard baffle. This was used to see if there is enough clearance to mount the regulator on the baffle and clear the cowl throughout the baffle’s range of motion.

As can be seen, the bushing location has changed several times … this is the final location.

When playing around with the baffle’s position decided to move the baffle as far forward as practical so made another cardboard template because the curve on the cowl was just a little different at the new location.

New cardboard baffle made with a slightly different curve to match the new mounting location.

A dowel rod was wrapped with painters tape and slipped into the upside-down lower bushing ... the masking tape was used on the dowel rod to make a very tight fit with the bushing. Next the cardboard baffle was taped onto the dowel rod to verify the clearances ...  the cardboard baffle was swung open and closed with the cardboard regulator mockup in place and seemingly, the regulator mockup clears the side of the cowl nicely.

Baffle in closed position.

Baffle in open position.

Now that the lower pivot point has been determined, it is time to punch a hole for the bushing. The position for the bushing was traced onto the blue masking tape. To find the center of the hole for drilling, a 1/2" pilot point drill bit was slipped into the bushing and spun a little to create a center point mark that was used to begin the drilling process. A tiny lead hole was drilled followed by progressively larger bits until a step drill could be used. Because of the limited room under the air duct due to the curve of the cowl, the step drill could not be used to go directly to the final size so I stopped at 1/2". Next a Dremel tool with a sanding drum was used to take the hole close to the final size followed by a little hand sanding so a nice tight bushing fit could be achieved.

A 1/2" pilot point drill bit was used to find the center point for drilling the mounting hole for the bushing.

After drilling the 1/2"  hole for the bushing, a scrap piece of 1/2" rod was placed in the bushing to hold position so the bushing’s diameter could be traced so the final 5/8" hole could be made.

Using a Dremel tool outfitted with a small sanding drum to get close to final hole size of 5/8" for the bushing.

Tweaking the hole by hand to achieve a nice tight bushing fit.

Because the air duct’s fiberglass is fairly thin, decided it would be best to add a doubler plate to help support the added mass of the voltage regulator … so cut a piece of .032 aluminum and drilled a 5/8" hole in it for the bushing to seat into. I came to this conclusion while trying to mark the upper bushing location and discovered I could not get the exact same location twice. This was caused, as I later discovered, by pushing down on the bushing to prevent it from moving  while attempting to mark the upper bushing location. By pressing down on the lower bushing, it caused the fiberglass air duct to flex a little .... a little flex at the lower bushing end was creating a lot of movement 14" away at the other end of the dowel rod.

The .032 aluminum doubler plate cut and ready for final instillation this should eliminate the flex and provide good support for the bushing.

Was planning on just riveting the doubler plate onto the air duct, but finally decided it would be best to bond it onto the air duct with a mixture of resin and flox so it would be really solid without any flex. The bottom of the doubler was sanded to scuff it up a bit along with the fiberglass it will mate onto ...then rivet holes were drilled. To prevent the fiberglass from being stressed while riveting, some #4 brass washers were procured to slip onto the rivet so the shop head could form on the washer as opposed to crushing the fiberglass.

Drilled doubler plate ready for a little resin/flox mixture and riveting.

Completed lower bushing instillation. A thin coating of flox is bonding the doubler to the air duct. Not in the photo ... small #4 brass washers were slipped onto the shafts of the rivets on the underside of the air duct so the shop heads would form on the washers as opposed to crushing the thin fiberglass.


Now need to complete the same operation for the upper bushing.  After the flox mixture cures, the upper bearing location will be marked and drilled.

Installing a “Bender Baffle” Piggybacked With Regulator Relocation Mod - Part One

OK, the time has changed and Spring thaw has finally hit NE Ohio in earnest …. Time to get to work at the hangar and finish up installing the “Bender baffle” I’ve put off finishing for far too long. The lower cowling has been off the RV-12 for the entire winter in the hopes of installing the “Bender baffle” and doing some flying during the winter. But for some reason, just couldn’t muster up the gumption to commit myself to working in the cold hangar … after spending 35 years in warm southern California, just have a hard time dealing with winter.


First a few paragraphs to establish a little background regarding the two modifications: You may be asking, what is a “Bender baffle”? The “Bender baffle” was first introduced to the RV-12 community by a gentleman whose last name is Bender. Bender is an early builder of the RV-12 and a frequent contributor to the Van’s Air Force RV-12 forums. Early on, Bender discovered flying the RV-12 during cold winter days was just plain uncomfortable, in that, there is not enough warm air coming into the cockpit of the RV-12 to keep the pilot warm and make winter flying enjoyable.


Traditionally, on most general aviation aircraft affordable to the average Joe, cabin heat is derived from the heat of the engine’s exhaust. This is accomplished by wrapping the very hot exhaust pipe with a heat muff which creates a chamber that air can be directed through and passed into the cockpit … thus providing an unlimited supply of warm air to heat the cockpit. There are potential risks involved, should the exhaust pipe become cracked, carbon monoxide can enter the cockpit which is why most savvy pilots incorporate a carbon monoxide detector in the cockpit.


In the case of the RV-12, Van’s chose to take a safer route to obtain cockpit heat by utilizing the coolant radiator’s outflow as the source for heat. The RV-12 is outfitted with a door on the firewall that can be opened to divert the warm air outflow from the radiator into the cockpit. This works well from a safety aspect, in that, carbon monoxide in the heated air is not an issue. However, there is a downside … unfortunately, when outside temperatures are below 35-40 degrees, the air is so cold that it does not get warmed up that much as it passes through the radiator because the overall coolant temperature is also low from the excess cooling … this is because there is no coolant thermostat on the Rotax 912ULS engine as there is on a car, so the only way to increase coolant temperature is to reduce the amount of cold air passing through the coolant radiator so the coolant can get hotter.


It is often said “necessity is the mother of invention” and that is certainly true in this case … Bender pioneered the idea of placing an adjustable baffle in front of the coolant radiator so the airflow through the radiator could be adjusted via a Bowden cable, allowing the coolant to get to an ideal 190 – 200 degrees or so … thus creating plenty of warm air available to heat the cockpit. The design was well received by the RV-12 community and has affectionately been dubbed the “Bender baffle”. The “Bender baffle” design uses hinge points made from 1/2" aluminum rod and washers are used as bushings for the hinges. One of Bender’s design criteria was to have the baffle flop open on its own should the control cable break … this is accomplished by offsetting the hinge points so the baffle wants to flop to the open position on its own. The use of washers as bushings offers a lot of angular slop allowing the hinge points to be installed offset from one another …. perfect for making the baffle want to flop open on its own should the control cable ever become broken.

Photo of the original “Bender baffle”. One can see the hinge points are offset (the upper hinge is aft of the lower hinge) … the slop in the washers used as bushings allows this to occur so in case of a cable break, the baffle wants to swing to the open position on its own.


On to the voltage regulator: About a year ago, I posted my views about the shortcomings regarding the Ducati regulator supplied by Rotax for the 912ULS engine not to mention Van’s suggesting it should be moved from the firewall shelf to inside the cockpit under the instrument panel base. (For what it is worth, regulators have continued to fail after being relocated to the instrument panel base). That posting can be found at the following link for those inclined to read it:


The Ducati voltage regulator dilemma.


Last year when making the above post, I vowed to NOT install the voltage regulator inside the cockpit and decided to work out a better cooling method and/or location for the regulator. The original mounting location Van’s chose on the RV-12’s firewall shelf is NOT the ideal location for a semiconductor device that creates plenty of heat of its own … the mounting location on the firewall shelf not only subjects the regulator to hot air outflowing from the coolant radiator, but is also adjacent to the #4 cylinder’s exhaust pipe which generates a tremendous amount of heat in the vicinity of the regulator.


About two years ago I remember reading a posting on the forums by Jean-Pierre, a North Carolina RV-12 builder, who came up with the idea to move the regulator inside the air duct in the lower cowl and mounting it ahead of the coolant radiator. This location offers the most abundant amount of airflow available, shy of hanging the regulator outside the aircraft. At the time, I complimented Jean-Pierre on thinking outside the box and placing the regulator inside the box, so to speak. (The abundance of airflow inside the air duct makes this a wonderful place to install the regulator from a cooling standpoint). Jean-Pierre has since made the comment that unfortunately, he can’t install a Bender baffle because his regulator is now in the way. That comment has bothered me for a long time and I’ve been thinking about it a lot ever since … why not try? Below is a photo of Jean-Pierre’s voltage regulator relocated to the RV-12’s lower cowl air duct. Recently, Jean-Pierre told me the regulator has just shy of 90 trouble free hours at the new mounting location.

Photo posted by Jean-Pierre of his RV-12’s Ducati voltage regulator relocated to the lower cowl’s air duct. This location has worked out well for him for over two years thus far.


Now for the groundwork to blend two good modifications into one … the DOG Aviation way.


After giving the issue considerable thought during the winter, decided it just may be possible to blend the two modifications into one instillation. Priority will be given to the “Bender baffle” … but if it appears mounting the regulator onto the baffle is doable, will go that route. However, there are a few issues that need to be taken into consideration and resolved starting with the baffle’s pivot points. Placing the voltage regulator on the “Bender baffle” will add a significant amount of mass to the baffle assembly … which in turbulence, could lead to bad things happening if there is an abundance of movement. For that very reason, I feel strongly the hinge points need to have real bushings with no slop. The original “Bender baffle” design is simplistic and works great … but the use of washers as bushings for the hinge points is not suitable for my purposes because there is far too much slop when washers are used as bushings for the amount of mass that the regulator will add to the baffle assembly.


Prior to getting to the DOG Aviation changes to the “Bender baffle”, the general shape of the baffle needs to be established. The following steps used here will serve any builder in need of a “Bender baffle” quite well. First, the general curve of the fiberglass cowl needs to be established so a working cardboard template can be made. The easiest way to do this is by using a narrow strip of cardboard approximately 14” long placed along the cowl and using a pen laid against the fiberglass to trace the curve …. this process takes a few cycles, so be patient.

Using a pen to trace the curve of the fiberglass cowl onto the narrow strip of cardboard.

Once the complete curve is established on the strip of cardboard, it can then be used to cut the final piece of cardboard that will eventually become the template used to cut the metal for the baffle. Fortunately, the inboard edges of the tunnel are more or less square, so I started out with making the baffle template a 14” high x 5” wide rectangle {Return from the future .... ended up cutting off 1/8" from the width so starting with 4 7/8" will require less final trimming} and then trimmed it down to match the curve made on the thin strip of cardboard. The above measurements should work well as a starting point for any builders making a “Bender baffle”. More material will need to be removed in the final product after the hinge points are established because we are not striving for a total closure …. ideally there should be around 1/8" to 1/4" of a gap between the edges of the baffle and the fiberglass cowl when the baffle is fully closed … so even when the baffle is fully closed, there is still some airflow possible.

The template for the baffle begins with a rectangular piece of cardboard 14” high x 5” wide.

After the cardboard rectangle has been cut to the above dimensions, the curve established on the narrow strip of cardboard earlier can be transferred to the cardboard rectangle. Note that the bottom of the baffle is flat for 2 3/4" before the curve begins so I placed the curve template over the cardboard rectangle and began tracing from the 2 3/4" mark.

Tracing the curve onto the rectangular cardboard template beginning at the 2 3/4" point.

After cutting out the traced curve, the cardboard baffle template was test fit in the tunnel. Looking good so far.

This is the point where the DOG Aviation design parts company with the original “Bender baffle” design. Rather than using a washer with lots of slop as a bushing, real bushings with no slop will be used instead. This creates a minor complication because the original “Bender baffle” utilizes offset hinge points to make the baffle want to flop open on its own. Unfortunately, don’t think offset hinge points will work with bushings because there is no play between the aluminum shaft and the bushing to allow the shaft to move at an angle. As such, my thought is to drastically offset the baffle on the hinge points in such a way that the airflow itself will fully open the baffle should the control cable break or come lose from the control arm.

One can see the amount slop that there would be if using 1/2" washers as bushings for the hinges. This is OK  for the standard “Bender baffle” when offsetting the hinges to create a “it wants to flop open by itself” design. However, this is way too much slop to support the mass of a regulator bolted onto the baffle.

As one can see there is no side slop when using a bushing. the downside for using bushings for the pivot points is it will require extra care to make sure the upper and lower bushings are aligned as close as possible.


Prior to punching holes, needed to try finding a good way to test assembly movement and mark the upper and lower hinge points so they are in alignment and test for clearances. After some brainstorming, came up with the idea of taping a wooden dowel rod onto the cardboard template much the same as the instillation will be and then use a syringe slipped over the dowel rod that can be pushed up to mark the upper hinge point. The wooden dowel rod is slightly undersized compared to the aluminum rod so needed to place a couple or wraps of painters tape on the dowel rod so it fit tight in the lower bushing. The dowel rod was taped onto the cardboard 1 1/2" in from the edge … this may be tweaked a bit later, but proved to be a good starting point for phase two. Oh, looking closely at the photo below, one can see the holes in the washers are much larger than the hole in the bushing (which the 1/2" aluminum rod barely fits into).

Pivot point mockup … a 1/2" wooden dowel rod is taped 1 1/2" from the inside edge of the baffle template with a bushing attached to the lower portion of the dowel rod. When the desired pivot point is established, the syringe can be slid up to mark the center location for the upper bushing. The thought here is … “theoretically” by having the centerline of the hinge point offset to the right side of the baffle, the air pressure on the left side of the baffle SHOULD be greater thus naturally wanting to swing the baffle open if the control cable were to break.


After placing the above mockup inside the air duct and checking for free movement and general fit, all seemed well. The next step for the mockup process was to make a cardboard box the same size as the Silent Hektik regulator that is planned for the modification. The box was taped onto the forward side of the cardboard baffle mockup and the assembly was set back in place inside the air duct. The assembly was rotated and it appears as though there is enough room to allow the regulator to be mounted on the forward side of the baffle.

Regulator mockup tapped onto the front of the baffle ready for a trial fitting. The good news is there appears to be enough clearance to move forward with the project and begin punching some holes.


Thus far, blending the two modifications looks very encouraging. Still want to work through a few more minor issues prior to punching holes in the lower cowl’s air duct.