Sunday, September 13, 2015

Ch 9.4: Main Gear Cover (1 of 2)

While I'm waiting for the main gear mounting parts to arrive from the Cozy Girrls, I decided to keep moving and work on the main gear access cover.

I did not follow the plans method for this.  Instead I followed Wayne Hicks method which I highly recommend.  Earlier when prepping the bottom for glassing, I did not make the joggles with the foam at the front main gear bulkhead because I new I was going to use this method.  With this method, you don't need those joggles, you don't need the aluminum slugs installed into the edges of the bulkheads, it's much easier, and will be form fitting when your done.

The first step was to stuff the area between the bulkheads with foam.  I found enough urethane foam scraps around so I didn't have to buy any.

Once the foam is stuffed, I sanded it down to the shape of the fuselage bottom and NACA scoop.  The picture to the left is in the middle of this process.

Once sanded to shape, I glassed the NACA scoop with 2 ply BID and then the rest of the bottom of the cover with 2 ply BID as well.

After the glass cured, but BEFORE I removed it, I attached two straight supports with Bondo across the NACA scoop.  These served to keep the cover in the proper shape while I work on the underside.  The picture at the left is just after I removed the entire foam plug with the top completely glassed.

After sanding the forward/aft edges of the cover to fit, I removed all but approximately 1/4" to 1/2" of foam all over the other side of the cover and all the foam around the perimeter of the cover about 1" wide.

There needs to be room for the gear so, as recommended by Wayne, I sanded some indentations under the NACA portion to ensure the cover would fit over the gear without rubbing.  Then I glassed the underside with 2 ply BID and shaped.

After that, I installed 2 ply tape along the forward and aft edges to reinforce the bare edges for the fasteners.

The only thing left to finish this up is to install the ledge and fasteners along the bulkheads that will hold the cover in place.  That will have to wait until I get the gear mounted because it would be harder to work on the installation of the gear after the cover mounting flanges are in place.


Ch 9.3: Main Gear Installation (2 of 4 cont'd)

With the outside LG tab layups now complete and straight, I can now accomplish the inside layups to finish off the LG tabs and be ready to start mounting the gear between the bulkheads.

Once the outside tabs are built and shaped, the inside tab layups are pretty easy.  This pretty much went according to plans however I did add layers of glass (~10 as I recall) to try to get the total thickness of each tab to approx 1" like the drawings seem to indicate.  You'll find multiple comments about this in the Cozy Group archives.  According to the archive comments, what's important is that the min # and type of plys are used regardless of how thick (or thin) it comes out to be in the end.

Glass ready for inside layups
Outside Main LG Tabs before
starting the inside layups
The one problem that might be created by added the extra plys is that there may be a bit of a stack up of glass where the glass makes the turn from vertical to horizontal over the gear bow...particularly on the thicker leading edge.  There might not be enough clearance for the MKMGA cross tube to be mounted without having to sand out a little glass in the middle first.  Since I added ~10 plys, I don't consider this much of a problem as I'll just be removing some of what I added.

And here are the tabs after the inside layups had cured and were trimmed. You can see how the plys stack up on the leading edge (left side of the left hand pic below).  That's where I might have to trim a bit out of the middle to make room for the MKMGA mounting tubes.
 Next up...Alignment and mounting in the fuselage.