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.