Designing the air intake for Milan GT

Now that I have the out-flow holes in the rear of the Milan for exhaust air, I started work on the Stagnation Point Air Intake (SPAI). I try different ideas along the way, trying to determine a reliable method of getting the contours of my plug to match well with the subject. Tried a new approach this time, and it seems to have worked very well.

I masked off the lower portion of the Milan’s nose, to protect against any errant resin drips, and then covered the rest of the nose with overlapping layers of release or “flash” tape. I then mixed up some resin and put 2 layers of carbon fiber (CF) over the release tape, and then taped some peel-ply fabric (that light blue colored cloth) over the CF. The peel ply helps to give you a smoother finish. After curing overnight but before removing the piece, I marked off the location of the headlight cut outs, and the vertical centerline of the Milan.

Peel ply fabric over 2 layers of carbon fiber, over blue flash tape.

Once the piece was removed I trimmed off the rough edges, and used a paint marker to indicated the shape for my air opening. I cut that area out, and then took a 12″ x 12″ piece of MDF board and a couple layers of foam, hot glue to hold them together, and used sanding blocks to shape the foam to match the CF piece, and then glued the CF piece onto the foam.

Starting the plug for the Milan GT air intake

The CF piece had an uneven surface layer, so I sanded down the high spots using a desk top belt sander. Then I used various tools to cut out the air opening segment of the plug. A coat of auto body filler to smooth things out, and provide a stronger surface than the foam. I use polyisocyanurate foam sheets, 2 pound grade. It is easy to shape with sanding blocks, I use Perma-Grit sanding blocks, that extruded aluminum shape you can see on my work surface to the left of the plug. They have titanium oxide coated panels, smooth and rough on opposite sides of the block. Sorta pricey, but very worth it to remove lots of material quickly.

I also really like the Foredom rotary tool that I purchased; hanging motor with 3′ long power shaft, and hand held tool end. Uses a very small drill chuck to hold the bits, and they have some very handy bits available. Great for stuff like this:

Rotary tool helps to speed along material removal

Rough coating of body filler, sand and shape, fill in low spots, sand again…. once I was satisfied with the shape, I brushed on 2 layers of molding gel coat. Air cures nice and hard, and can be sanded to a smooth finish before mold making. Spraying it would give a better finish with less sanding, but I don’t want to fuss with cleaning the gel coat gun!

2 coats of molding gel coat, then will get busy sanding!

Trying something else that is new to me: removing the mold from the plug is going to be difficult, because you have 2 very hard surfaces and neither wants to give or flex if there’s a problem. So, I drilled 2 holes through what is effectively the center of the SPAI, and through the MDF board. Then filled the holes with wax. When I’m ready to remove the mold, I will use a couple dowel rods through those holes to help push the mold off from the underside. The holes fall in the area of the mold that won’t be used for molding anything, so it won’t be an issue.

2 holes filled with wax, dowel rods will assist with removing the mold.

Before I started the mold, I made a test piece off the plug, to confirm the body contours match well with the Milan’s.

I masked off the outer edges of the plug to guard against resin spills and drips. I also taped off the center hole in the plug (I had just put some gray gel-coat on some areas where the body filler was showing). I then put a couple layers of CF onto the exterior surface of the plug. Once that was cured, pulled it off and checked it against the Milan. All looks good, and moving on to making the mold. If I wanted to change anything on the plug, this would be the easiest time to make changes.

Made this up quickly, as a last check of the contours.
Matches the Milan GT curves well, so on to making the mold!~

I put up the mold late this morning, and removed it this afternoon with only slight damage to my plug. Used the Foredom rotary tool with a cut-off wheel to clean off the edges of the mold, and added some orange gel coat to fix some cracks that occurred. Tomorrow I will be able to sand that down, and then wet sand and prepare the mold, hoping to put up a piece in the mold tomorrow!

Ready to de-mold. Plastic wedges and dowel rods to push through the plug.
Repaired a couple minor cracks, will wet-sand and polish the mold tomorrow