Seat belt hard points

According to the plans, the seat belt hard points are installed in Chapter 8; however, many builders (like me) opted to install them in Chapter 7. This allows you to fill the countersunk bolt head and glass over it rather than having to patch it up later. Here is what we are trying to accomplish.

I should note that I decided NOT to install the external foot step - so I made ALL four attachment points the same. So wherever it says "six per airplane", I switched to 8.

I started out with 1"x1"x1/8" 2024-T3 angle (about 1 ft). I cut it into 4 pieces, 2" long each.

I then drew a line to round the corners..  

Using a disk sander, I rounded the corners down....

Using the drill press, I made the holes for the 1/4" bolts.

Seat belt brackets complete! Well... not really... still have to alodine them!

Using 1/4" ply (does it look familiar? This was the hole I cut out from the firewall bulkhead!) I cut a few bars to make the pucks which the aluminum brackets attach to (see page 8-3 in the plans).

Cut them to fit at a 45 degree angle of the fuselage corners.

 I then rounded the edges so that the 7 (yes, seven!) plies of BID that later go on top of the pucks would have a nice transition. (Note the two top pucks in the picture are right side up... two bottom pucks are up side down... just to show more detail).

All four pucks complete!

I forgot to mention - each puck is 3 inches long...

I then cut my 28 plies of BID (7 plies per puck); all at 45 degree. I used all my BID scraps.

Prepreg time!

After measuring out where the pucks needed to be installed, I sanded the area smooth. I then applied regular epoxy to prep the area for floxing/glassing.

Mixed up some wet flox and applied it (heavily) onto the puck.

Positioned the puck in place and let the access flox ooze out...

I then cleaned up the access flox, painted on some plain epoxy onto the top surface of the puck and installed my 7 plies of prepregged BID.

 Removed all air bubbles and peel plied all edges.

Also peel plied the surface for which the aluminum bracket will mate with.

 After letting cure overnight, I removed the peel ply.

Seat belt brackets ready for alodine! Same procedure as the main landing gear brackets.

Here is the hardware I used for the install:
     (8) MS21042-4 nuts
     (8) AN525-416R16 washer head screws
     (8) AN960-416 washers

The plans do not call for washers before the nut, but I thought it couldn't hurt. The outside doesn't need it since the AN525-416R16 screws are the washer head type so it acts like a washer.

Started out by marking the drill points with a sharpie...

 Using the 45 degree guide and the smallest drill bit I have, I made the initial holes.

This got me in the right ballpark. The plan here was to continue stepping up the diameter of the drill bit and bias it in the direction I needed to go.

 Closer...

 Closer... perfect!

 I then bored the head screws...

Test fitting the bored depth; I made sure I had at least 0.45" of bolt length sticking out on the other side...

 Sanding everything smooth and ready to bond the brackets in place!

Mixed up some wet flox and applied it to all the bolt shafts.

Inserted the bolts in place...

Applied flox to the bracket mating surface...

Installed bracket and added the washers...

 Applied loctite to bolt threads...

 Installed the nuts and torqued them down.

Cleaned up the access flox. Seat belt hard points complete!!

Pilot seat belt hard points..

Passenger seat belt hard points.

I then used leftover flox to fill the screw head cavities. I put a piece of tape to keep the wet flox from oozing out. Once cured, I removed the tape and sanded everything nice and smooth - the outside fuselage is getting closer to be glassed!