Step 13.7 Baffling

Given a choice, air would rather not cool your expensive airplane engine.  Due to its stubborn nature air must be confined and directed to flow past the cooling fins on the engine's cylinders.  This is not such an easy thing to do, but fortunately Vans has thoughtfully included a baffling kit within their 'Firewall Forward' kit. So what exactly is a baffle?  It is simply a box inside the engine compartment that has inlets in the front to let the cool air in, and outlets beside each cylinder to let the air out through the cooling fins.  The box must fit tightly around the top half of the engine so that all of the air passing through does its cooling work.  Much of the work in assembling the baffles is the trimming and test fitting process that tailors the baffle kit to a specific engine.  Let's get started:

In this photo I've just begun building the back corner.  The baffling kit is actually pretty good and the instructions are clear if not entirely complete and we shall see.

This is a hole I put in the left rear to connect a 4" hose to the oil cooler.

These two holes will be connected to become a spark plug wire pass through.

Here is a view of the right side mostly complete.

Time out to play.

A well know defect of the cylinder cooling design has fins that are too short or blocked near the base of the cylinders 3 and 4.  A solution shown below, it to pop out the box a bit to allow a little more air to flow by in this region.

One of the really annoying things about the ECI cylinder is that it has tapered fins that reduce in height toward the base of the cylinder.  This was probably done to reduce weight, but the baffle kit is not setup for these tapered fins.  Consequently, some additional pieces had to be fabricated to seal the box along the cylinder base.  As you can see it is a complex shape that takes a bit of time to discover by trial and error.  In this case, error and trial, seems more accurate.

Its just about impossible to get a good photo on these things installed.  The black item behind the baffle is the base of a cylinder.  Using some imagination, one can see how the complex shape forms a cap to fit the inside edge of the straight baffle to the bottom of the tapered cylinder.

It was about this time when I realized that the baffle instructions did not include the "snorkel."
The snorkel is the pipe that directs air from the front of the baffle box to the engine's air intake. Because the intake is below the engine this pipe runs up to the baffle it kind of resembles a "snorkel." Anyway, to fit the snorkel to the baffle, a big hole had to be cut out of the front left side of the baffle and then a flange was fabricated to attach the snorkel.  I really hated to take the snips to the nearly completed baffle, but I also really hate not finishing the plane...

I didn't take time to photograph the snorkel before I found out that it doesn't fit at all.  I had to make multiple adjustments to alleviate interference from the starter and from the alternator.  When I finished glassing in those changes I realized that it was just too long to mate up with the baffle box so I cut a half inch out of the middle and glassed it back together.  The photo below shows some of my handy work. The hole is a second stab at clearing an unused mounting tab that is inconveniently sticking out of the bottom of the starter motor.

After getting the snorkel to fit. I began work on a sliding door to act as an alternate air source.  The theory is that were the input to become clogged with ice or some other debris, it would be nice if the engine didn't shut off for lack of air.  The alternate air door can be opened in this unusual case to allow air in from inside the cowling.  Although it is unfiltered air, it's better than nothing.  The Vans supplied door has been found lacking -- the ability of close it once opened, for example,  So I thought I would try to design my own sliding door.  

And so here is the snorkel with the alternate air door completed.

A view of the snorkel from below after painting.

Air filter installed.

And finally the last step on the baffle project is to apply the fabric seal to the top of the baffle box. The seals press against the inside top of the cowling to prevent the air from escaping out of the top of the baffle box.

Step 13.6 Oil cooler

Air cooled engines, like the one in my airplane, are actually cooled by more than just air blowing past the cylinder's cooling fins.  Internally, some of the heat is carried away by the engine oil.  This cooling is improved by the addition of  a radiator for the oil.  In this posting, I will illustrate the installation of my oil cooler.

The engine in my plane is a little larger that the standard engine for this aircraft and so I elected to go with a larger oil cooling radiator.  The trouble is that the larger radiator will not fit in the standard location which is hanging off of the baffles behind the rear left cylinder.  To overcome this problem, I will be relocating the cooler to the left side fire wall.

Whenever you veer off of the plans to make some sort of  modification to the stock aircraft you are skating on ever thinner ice as you go.  But this mod doesn't have any structural ramifications so I think I'm pretty safe here.

First up:  make some brackets to mount the cooler to the firewall.

The cooler's air source will be the higher pressure air above the engine on the left side and will be connected to the cooler by a flexible 4" hose.  An intake plenum is required to adapt the hose to the cooler and that will be constructed of fiberglass.  A male mold is fashioned using modeling clay and a roll of tape that is just the right size for the hose (after I peeled off about 5 ft of tape).

The mold is covered with about 4 - 6 layers of  9oz glass fabric and West Systems epoxy.

The plenum is then readied for painting 

And the brackets are installed.

And then the painted plenum is mated to the cooler and bracket.

Finally, with the addition of the hose, the cooler is complete.

Year 4 Retrospective

Well another year passes and I find that it's helpful to consider the progress made.  My lack of blog posts recently is indicative of this final stage of construction -- the 90% complete with 90% to go phase.  It seems that many of the tasks at this point are interdependent such that completing one requires completing all of them and I have been reluctant to post on half completed tasks.

It is tempting to feel that not much progress is being made and so to remind myself and the gentle reader, last year's progress is reviewed to dispel any doubt that I have visited the shop this year. Once or twice...

January:  The interior components are test fit and the wiring is wrapping up.

By February I was on to fitting the rear window.

In March I was cutting the slots for the canopy hinges in the top forward skin.  This is the last skin to be riveted on and it marks a major milestone -- fuselage structure complete.   Later that month I decided to add electrically activated cowl flaps. The cowl flaps allow more cooling air to be cycled through the engine compartment.  This is important to while climbing to keep engine temperatures down.  At the same time, closing the flaps allows for a modest speed increase in cruise because the cooling drag is reduced.

 

Around April I thinking seriously about hanging the engine.  The first step was to transition to the engine stand where I could more easily add the accessory components 

In May we were working on the canopy.  We added a targa strip over the top and two side lips to help center the canopy and stiffen the structure.

And by June we were painting.

The painting continued right through the summer and fall.  Somewhere along the line I applied the N number.

...And hung the engine.

By December I was connecting control cables to the throttle quadrant.

An oil cooler (right) was added and the engine baffling (left) was begun.

By the end of December the cowling was being prepared for paint.

Trina slept though most of it.

And on the last day of this year's work, I mopped the shop floor.  This was the first time the plane has been rolled outside.