The baffles have been fitted to the cowl, but the cowl isn't finished yet. I still have to attach the intake ducts to the inside – these will help the air enter the cowling volume and slow down before flowing through the engine.
I put the cowl on the airplane, then reached in through the inlets and traced the position of the baffles onto the inside of the upper cowl:
The lines make it fairly straightforward to locate the ducts on the cowl. I also trimmed back the lips of the cowl inlets slightly in order to make them symmetrical.
I drilled and clecoed the ducts to the cowl to temporarily hold them in place:
Then I glued the ducts in place using epoxy and flox:
I used more flox and microballoons to fair the ducts into the cowl. Even though you can't see this area from outside the airplane, the oncoming air sure can, so I figured a smooth transition would help cut down on cooling drag.
This area was particularly interesting… the cowl is relieved here to clear the #1 cylinder on the bigger 200 hp engine, which prevents the intake duct from fitting properly. I used a heat gun to reshape the corner of the duct, and filler to bring it all together.
The space between the cowl surface and the intake duct forms a tunnel between the high and low pressure parts of the cowl, which is known to cause a loss of cooling air and resulting high cylinder head temperatures. Many folks end up closing off one end or the other in order to force the air to go through the cylinder fins and oil cooler, where it will do some actual work. I figured I might as well go ahead and make this modification now while it's easy.
I started by cutting some endplates out of balsa, and coated the soon to be hidden surfaces with epoxy to make them resistant to oil and water.
Then I glued them in place on the inner face of each intake duct "tunnel".
Once the wood was glued securely, I laid up some glass over the top to provide the real strength and close up the remaining gaps. Hmm, since wood is composed of fibers that are made of carbon, do you suppose I can get credit for this as a "custom carbon fiber part"?
As I went along, I wiped down the inside surface of the cowl with whatever unused epoxy I had left over in each batch. Eventually the entire surface will get an epoxy coat to seal it, so I figured why let perfectly good glue go to waste.
Finally, I squeegeed on a coat of filler to smooth the edges of the glass layup on the endplates, and sanded it all smooth. It looks like hell, but it's smooth to the touch, which is the point. This might be overkill, but when you stick your hand in and feel around for how I did the baffles (which is something all builders do) hopefully you'll say "hey, craftsmanship!" Not to mention, maybe all this effort will make the airplane 0.001 knots faster… every little bit helps.
Next: Trimming the baffles to fit the cowl, again!