Home > Filtered Air Box, Firewall Forward > Molded FAB Intake – 6 hrs

Molded FAB Intake – 6 hrs

Sunday May 5, 2013

The filtered air box connects to the air intake scoop with a fiberglass tunnel that is custom molded. I started by installing the FAB to the fuel servo and making sure that the front opening was pointed directly at the air scoop by looking in from the front. Then I removed the lower cowling and filed a slight taper to the scoop opening where the fiberglass will overlap. This is to give the fiberglass a surface to bond to without reducing the inside diameter of the scoop.

Then I fit the foam block into and against the opening from the inside of the cowl. This required me to carve away the corners of the block and taper the front edges a bit to get it flush with the inside surface of the cowl. After confirming it was flush I bonded it in with four big globs of bondo which cures up in only 30 minutes.


Then I put the lower cowl back onto the fuselage and began cutting out the tunnel. I started by drilling a 1-inch hole with a hole saw. Then I used a hack saw blade and a file with a curved face to carve out the foam back to the inlet of the air box.


It was pretty easy to carve the foam and get the shape to blend from the oval opening at the front to the more rectangular shape at the rear. The file was better for the finish work.


This is how the carved out tunnel looks from the inside. There is a slight taper as the opening gets larger as it goes aft.


I mixed up some epoxy and laid three layers of 8 oz glass around the inside of the tunnel. I wet the fiberglass between two sheets of plastic drop-cloth film and rolled it out to remove excess epoxy and that allowed me to put the layers down smoothly on the foam which was first wet with a thin layer of epoxy to help the glass stick. Then I put down peel ply to smooth it out and help minimize sanding later. I did not use a balloon as described in the plans.


Late in the day I pulled off the peel ply and sanded the inlet area a little. It looks pretty good. I still need to paint on a layer of epoxy to fill the weave but it looks very promising so far.


I chipped away the foam block and the bondo globs and sanded the outside of the tunnel to get the last of the foam off. This looks like some kind of weird fish orifice. Its not shown here but I also applied two more layers of fiberglass around the outside of the tunnel at the fillet with the cowl as recommended in the instructions to strengthen that joint.


I also worked on  installing the alternate air door on the bottom of the FAB. First I sanded the fiberglass shell because I found lots of cracks in the surface of the primer. I don’t know why that happened but I sure didn’t want to paint over that so now the box looks kind of ugly. Regardless, I drilled a 2-11/16 hole in the bottom of the box for the alternate air door bezel. The blue tape is the direction I plan to run the cable which is what I used to orient the bezel. You can also see the two 1/8 inch holes I drilled for drainage; one inside the filter and one outside the filter.


After match drilling the holes I put in machine countersinks for the rivets. I bent the little tab on the bezel which acts as a catch and a stop for the door. I mixed up some ProSeal and riveted the bezel to the box with ProSeal in the joint. THe I temporarily installed the door with the supplied hardware. Now the ProSeal needs 3-5 days to cure before I paint this thing.


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