Rear Window Frame

On a recent trip to Fincastle, VA. I was talking with Bob Barrows and he gave me an idea for an alternate way to make the rear window frame out of aluminum instead of the steel channel as show in the plans.  Here is how I made my rear "D" shaped windows:

I had a roller tool that I bought cheap from Harbor Freight to roll stiffening beads into the fuel tank skins.  The rolling tool came with a couple of different attachments. I started with some .030" 5052 -32 soft aluminum sheet which is soft enough to shape easily.  The window shape was drawn out onto the sheet and then with some help from my friends, a 1/8" deep flange was rolled as shown below:

Here is the before and after picture of the flange:

Here is what the window channel looks like when pressed flat on a table.

During fuselage construction, I welded in a piece of .032 angle as shown above.  The base of the window is some .032 aluminum (2024-T3) and will be riveted to the angle and to the inside of the door flange as shown here:

A 1/2" stiffening flange was formed along the top and bottom of this base.

Here is a picture of the outside from the back looking forward:

Here is the window channel:

I found that it was still a bit flimsy at this point and was afraid that shrinking the fabric covering on the inside of the cabin would distort the window frame. To reinforce and stiffen it up some, a brace was fabricated as shown here:

The aluminum brace has a "Z" channel riveted at the bottom which rests against the fuselage tube running under the window channel.  The top part of the brace is attached with the window channel as shown.

What I like about this set up is that I can remove the rear window by removing the channel from the inside.  After covering the interior and exterior of the airplane, the plexiglass will be installed with a bead of RTV to seal it. Then I will use aluminum pop rivets to secure the window channel to the window frame.  These type rivets are easy to drill out if ever want to change the window out.

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