Chapter 23 - Section 3

Cowling Installation


I bought my cowling from Featherlite per Plans' recommendation. It arrived about 30 days later in a big box. It consists of three parts - the top, bottom and a stiffener for the top cowl. I measured the width of the lip at the forward edge of the cowl - it was not uniform. With a long sanding block, an electric hand sander and ~30 minutes, I have a uniform forward lip of 1 3/8" in width.








Cowling Attaching Flange

I scrounged several 2" foam blocks (scraps) and cut them to appropriate sizes. With 3 to 4 dabs of 5 min. epoxy, I glued them to the firewall per Plan. Then I sanded their edges flush against the firewall. 


I prepared 4 layer BID tapes with dimensions of 40" x 3.5" and 13.5" x 3.5" respectively. Since the foam will be cut out after the BID cures, I was debating whether to put packing tape on top of the foam prior to glassing OR micro the foam and glass on top of it. I tried the packing tape approach first and found that the plastic tends to bunch up at the aft end because the flange is tapered. I went ahead and microed the foam. The BID tape lay down directly onto the foam nicely.





After cure, removing the foam was not too troublesome either. I used a small wood strip and marked off 1.5" along the entire length of the lip. Then I trimmed and sanded to dimension.










Here's a picture of the lower lips.











Aft Cowling Template

There is supposed to be a 1 1/4" spacing between the cowling and the engine gear hub per Plan. I made a template (out of a wood board) and bolted it onto the gear hub. This template helps to support and align the upper cowling prior to mounting.


With the template in place, I pre-drilled five 1/8" holes on the upper cowling lip at 7" intervals per Plan. Then I aligned the cowling under the canopy lip and match-drilled the holes. Note the clecos at the upper cowl...


Once I got the cowlings in place, I re-mounted both wings back on. I took the opportunity to re-measure the level of my wings to the fuselage. My right wing level  (0.0o) and the left wing is 0.2o high to the fuselage. Since a thin washer adds 0.4o (per Plan), adding a thin washer will make the wing 0.2o low. Since the thin washer is 0.032" thick, I need to find one that is half the thickness. With the original thin washer between the wing and the spar (per Plan), I just need one that is 1.5 times the thickness of the thin washer. I found one in McMaster Carr. Will see how it turned out.


Supporting Lips

The supporting lips along the wing root and aft strake were pretty straight forward per Plan. Here's a picture for holding the cowling level with the wing root. The first set of plies (5 layers) were easily accomplished. The subsequent supporting (single) layer, however, was a bit more challenging because it has to wrap around a sharp corner. It turned out that peel-ply (Per Plan) and patience did the trick.








Installing the Lower Cowling

With the upper cowling mounted, I proceeded to install the lower cowling. It was a bit more challenging than expected because gravity is working against you. A bit of sag here, and bit of sag there...while you are stooping under the wings looking up. I tried many tricks (to hold up the lower cowling) which allowed me to keep the cowling in place for precise mounting. they included the laser cross-hair, a plum, masking tape on the plum line to establish the center and lower cowl lip position, and a cross-hair taped at the center of the engine.


I pretty much repeat the same as the top cowling except its a bit more shaping and preparation. The key was to pay close attention to the aft end of the cowling matching the gear plate and prop extension.




So far so good...I still have to add the lip to the aft end opening and the trailing edge. That's next!











I added the joining lips at the trailing edges per Plan. I did not separate the forward cowls by 8.5" per plan. Instead, I made my own separation measurement at the strakes. They turned out to be 8.3" - not much of a difference, especially since the cowlings flex quite a bit. Note all the dead weights I used to keep the cowl halves in place for glassing and peel- ply.    








Installing the Prop Extension

My prop extension arrived (from Saber Manufacturing) and it is a very nice machine part. I was alerted by Sam (the owner) that it has a very tight tolerance fit. I may have to rotate the prop extension, just to find the perfect fit. I tried all six possible positions with no avail. I finally slid all 6 bolts through the prop extension and allowed them to guide me along. It worked! I hand turned the bolts at 1-4-6-3-5-2 sequence (a slight turn at a time) until the forward face of the extension met the gear plate. 







Nut Plates 

Between the top and bottom cowl, I used a total of 49 nut plates to hold them to the fuselage, wing root and each other - that's a lot of nut plates. The Plan suggested camloc fasteners in some but not all locations. I figure if I have to remove a bunch of screws from those nut plates, I may as well get a powerful electric screwdriver and remove them all.


I picked up a nut plate installation preparation technique from the Cozy forum and decided to follow. Instead of mounting a nut plate on a flat washer, I made a flat base material (~8" X 10") out of 6 ply BID. Then I marked them to 1"x.5" rectangular tabs and its center locations. With my drill press, I drilled all center locations on the board at once. Using a nut plate as a template, I drilled all the rivet holes as well. Then I countersunk all rivet holes. Using the band saw, I cut out all the nut plate tabs for subsequent use. I spread wet flox on the underside of the nut plate assemblies and held it in place with the bolt through the cowling. Then I packed them with flox and laid 2 ply BID over it.



After the nut plates were installed, I floxed in the stiffener. My stiffener fit onto the upper cowl very nicely - maybe one small gap at the forward edge. I filled it with flox and glassed all edges with 1 layer BID per plan.


Here's a picture of the cowling after all the nut plates and stiffener are installed. I did not use any camlocs at this time.








Scoop Lip

The scoop lip was not too difficult. I made a couple wood templates to shape the scoop. The top template was used to round off the bottom edge of the scoop first. Then I used the second template to complete the rounded 5/8" lip at the forward edge. I followed the Plan for making the rest of the air scoop.








Here's a picture of the completed scoop lip. 











Oil Check Door

The next step is the oil check door. Though it is pre-marked with the Featherlite cowling, I like to make sure the door is at the appropriate location before cutting. I tied a laser pointer along side of the oil check tube and project a dot onto the under side of the top cowling. By rotating the laser pointer around the oil check tube, a partial circle is drawn.


According to Plan, the oil check door is to be cut from the top cowling and re-used. Since the cut will be on a curve surface (especially the lower right corner), a poor cut around the corners will end up with a wide seam. I decided to make a   backup door as insurance. I pre-marked the door location and covered it up with packing tape. Then I laid up 6 ply BID over the door area. Once cured, I popped it off for future use. The effort was pretty simple and straight forward.


I followed the Plans and completed the oil check door without much problem. I used a combination of my Fein Tool and Jig Saw to complete the cut. The seams are not perfect, however, the fill and sand stage will probably do the job. I did not have to use the backup door at this time.