Tuesday, March 28, 2017

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.

Friday, March 3, 2017

Kicking Around Various Paint Schemes

It has been quite some time since there has been an update to the DOG Aviation Blog … mainly because no real work has been accomplished at the hangar on the RV-12 since the last work session. The lack of activity has, in large part, been due to sheer laziness mixed in with the cold weather. Another contributing factor has been Mike needed to have his kerosene heater back for a project he was working on … so I lost the heater the latter part of December to early February. Granted, I could have toughed it out and worked anyway. But the RV-12 is built and it does fly nicely, so there is no real sense of urgency …. plus, admittedly, there has also been some project burnout. Truth be told, not many good flying days have been missed … probably around 10 at the most since late December … and most of them were days in February. Overall, although the winter here has been mild temperature wise and there have not been any massive snows, it has not been good flying weather. By in large it has either been rainy, foggy, snowing, socked in with low clouds or just way too windy for test flights. So in the interim have been working on other RV-12 related items from the house such as making new checklists for a knee board, modifying an Excel weight and balance calculator to better suit my needs and kicking around ideas for the paint design.

I was lucky enough to find a photo on the Internet of a side view for a completed Canadian RV-12 that was mostly white to use as the canvas for my paint scheme. It already had a couple of paint lines that were similar to what I had in mind … so I just added and modified the photo a bunch to come up with what I feel will be the overall design for the paint scheme to be used on the DOG Aviation RV-12. The design consists of sweeping lines along the side of the fuselage and wheel pants. Behind the rear window there will be two trim lines of paint around the turtle deck. The wing tips and tips of the horizontal stabilator will have identical outer edge trim markings. The trim on the vertical stabilizer will be similar to that on the wing tips with the addition of an additional trim line. The only thing up in the air is the lower trim line on the fuselage just above the wing … may eliminate that line altogether … but will need to edit the design to see how it looks that way.

Choosing colors for the paint scheme is a whole other issue to be sure. Seemingly, the vast majority of builders gravitate towards paint schemes consisting of red, white and blue … and/or combinations thereof. Early on, while building the DOG Aviation RV-12, the decision was made to choose a color pallet a little less mainstream just to be different. Frequent readers of the DOG Aviation Blog know the flap handle, instrument panel and steps have been powder coated with a vibrant deep purple color and the stitching for the seats and baggage bulkhead cover was done using green thread.

I have always envisioned the base color of the RV-12 to be a light off white cream color that leans towards a brown and not a yellow …. think of a 50’s hot rod cream. Originally, the thought was to have green as the major trim color with deep purple as the accent color … but now I’m not so sure of that. While playing around on the computer, I reversed the colors making deep purple the trim color and green as the accent color and think I like that better. Then to really confuse the issue I played around with orange as an accent color to the purple.

Below are the three color schemes that are the likely choices for the paint job. Bear in mind the white that is on the airplane in the photo IS NOT the off white I’m thinking about for the final color. Of course, all this is just the rough doodling … the final paint scheme will have all the curves and trim lines evened out and the final colors will likely be tweaked somewhat as well.
This is how I first envisioned the paint scheme … the predominant trim color of a vibrant green with deep purple accent.
Playing around with the colors decided to try reversing the colors making the predominant trim color deep purple with green as the accent color. I think I find this more appealing than the previous paint scheme and at this point in time, will likely use this as the color scheme for the DOG Aviation RV-12.
On a lark while playing around with the paint scheme colors, decided to try using a purple and orange combination. Doubt that I will paint the RV-12 using orange as the accent color because the "RV-12" stitching on the seats and "EXPERIMENTAL" stitched onto the baggage bulkhead cover was done using a green thread.  The stitching would need to be changed to orange for a cohesive look both inside and out.  I do find this paint scheme quite alluring … have to admit, I really do like it a lot.

At the hangar, the RV-12 is still awaiting the instillation of the “Bender baffle” modification. There are also wheel pants need to be installed as well … so need to get on that project soon so it is completed prior to paint. As that work progresses, will also be working on an alternative mounting location for the voltage regulator … so there is still lots of work to do in the coming weeks.