Chapter 23 Engine Installation - prop, extension, Step 3 cowl

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Catto 68" diameter 78" pitch prop with nickel leading edges and erosion tape.  

Freeflight Composites cowl.   Did multiple test fits and the line that was marked looked like it was going to be pretty close so I trimmed outside of that line.   To match the plans, the cowl needs a lip along the front edge, so I trimmed off where the CF meets the lip at the turtle back and similarly, trimmed the bottom cowl.    Then used hot glue and pop sickle sticks to hold the trimmed section on as a form for the inside lip.  In hindsight, I think a 2 to 3 inch wide 5 BID layup on this line before trimming might have resulted in less work.

The blocks had to be moved in order to apply the BID that lays up in front of the cosmetic piece.  This particular area of the cowl lips were a little proud and met the wrath of the belt sander.

Pop sickle sticks and hot glue worked pretty well and was easier to remove than Bondo.

To install the Camlocs, drill 1/2" hole where the cleco holes are.   Then drill 1/8" holes for the rivets to hold the receptacle.   The bottom hole here has a Camloc receptacle riveted in.   I used a small drill bit to bevel the holes for the rivets so the heads are flush.  I made a simple jig to locate and drill the holes for the receptacles.

3 BID curing while the trailing edge is shimmed up to help correct a tendency to sag.

A layer of duct tape is on the bottom of the turtle back/spar lip.  Flox was applied and peel ply over that.  Nut plates were installed on the cowl and screws are holding the cowl in place for the flox to harden.   While the flox is still green, it's sliced with a box cutter along the seam.  Then after the flox cures a little more, the screws are removed and light pops with my hand broke the flox loose along the cut seam.

Article comparing NACA duct vs scoop

The plans construction method for the cowl lip is to attach foam blocks to the inlet and carve the foam to this shape.   I opted to use a 1x2 piece of PVC foam and a belt sander.   

The cowl wasn't made to accomodate the scoop for the NACA inlet.  The lip has to come down and inch.   I cut the cowl back 7" to help make a ramp for the scoop that won't be to draggy.  

Prepping the foam lip to be glassed in.

Small fairing blocks on the bottom cowl ramp.

Two identically shaped blocks will help keep the boat tail cowl in position while the 5 BID inside layup cures.

I saw this method on another builder's web site. Make a "site window" that stays in place when the cowl is removed.

Remove the cowl and test access.

Carefully cut the 4.5" x 5" opening and confirm the position is good.  Using the  round shaped blade on a Fein tool.  Rotated the blade so that the heel of the blade made the cuts in the corners.

The plans 3" hinge is adequate, but appears would leak a little air.

The "J" hinge is a nice solution to hide the hinge.  The first one I made was to small.  It took about a day and a half to make this (including the spring).  ACS does sell this similar springed hinge for about $36.

Foam/glass will reinforce the inside of the door to keep its shape under pressure.  A oil bottle spout fits in there easily.   Latches are ordered. 

While the engine was off for the firewall installation, the engine with accessories, prop extension and mount are weighed.  Not included are the baffling and air cleaner.