Ok...back to finish the first 5 steps in Ch 8. Note it's been 9 mths since part 1 of this post. Mostly because I wasn't working on the Cozy for about 6 months while involved in some other projects, retiring from the USAF, securing a new job, honey-dos, etc.
Since I'm not using the plans version of headrests, I can skip part of step 1 and all of step 4 but of course that work will be replaced with other work to install custom headrests. At the beginning of Ch 8, I already cut the shoulder support. I also ordered and received my Saab headrests and the adjustable headrest guides from a Saab dealer. Now it's time to get it all together.
First I located where the birch hard points for the shoulder harness attachments would go. The plans call for 8.5" apart. This was a change made in Newsletter #50 which reduced the spacing from 11.5" based on a European safety study that gave 8.5" as the max safest distance for shoulder harnesses. I ended up adding 1/2" and making them 9" apart. At 8.5" they were just a hair too close to my neck...and I don't have a big neck. Researching the archives, I found that many builders questioned the change since there was no accident evidence to really drive it. Some chose to leave them at 11.5" and use an "H" cross piece to ensure the harness stays on the shoulders in an accident.
Shoulder Brace, inverted,
w/ birch hard points curing with 1 ply BID
At this point I had to start doing things a tad different. I couldn't install the shoulder brace onto the seat back until I designed the support structure for the headrests.
After some thought, I decided to install aluminum tubing for the headrest guides to slide into. This will provide more support than just gluing the headrest guides in place. My fear is that someone will grab the headrest and lean on it while getting into the plane so I want to make sure there's enough support in case that happens.
After ordering tubing with the wrong wall thickness twice, I finally got the right size to fit the headrest guides...3/4" OD w/ .049" wall. I located the holes for the tubes in the shoulder brace and drilled and glassed receiving holes for the tubes into the seat back w/ 1 BID to provide a more solid hold at the bottom. The holes aligned with the front inside edge of the shoulder brace. Later in the build, I'll adjust the length of the tubes if needed based on where I want the center of the adjustment travel to be...then they will be floxed in place.
|Pilot side holes for |
headrest support tubes
|Tubes used to form glass|
down into the holes
|Birch supports for top of headrest|
|Checking everything before glassing|
in the birch supports in place w/1 BID
|Inside of the shoulder brace. Headrest supports glassed|
in place, ready to secure the 4 nutplates with
flox & #4 screws before installing in the plane
The shoulder brace was then installed per plans and taped at the adjoining sides. Next I sanded a the sharp back corner of the seat back round to allow the 3 ply UNI reinforcements to take the corner properly. They were installed longer than plans at 17" instead of the plans 13". Since these are "reinforcements", I felt I wanted a little more than a couple of inches overlapping the seat back and behind the seat.
Another chapter down...on to chapter 9 and the main landing gear.