Chapter 8: Shoulder Brace and Seatbelts
Step 1-2, 4: Headrests
Back in 1998, my original thoughts were: “I'm not too particularly enamored with the triangle headrest design. While I recognize the need for rollover protection, I want something a little more classy. I might opt for something like Brian Deford has, or try a couple of chromed rollover bars like those in a Midget racer.” Then I finished with the statement, “I can always come back and make these headrests if my other ideas don’t pan out.” Well, fast forwarding to 2005, it was finally time to incorporate headrests. However, I still didn’t like the cosmetic non-appeal of the triangle headrests, even thought they are highly functional and easy to build. So I tried my hand at fashioning two composite roll bars integrated into the shoulder support. Like this:
The roll bars were constructed with shear webs and spars like we do on the wings and center section spar. I designed a pleasing shape that fit within the shoulder strap anchors, made some plywood templates, and hot-wired the hoops from left-over blue wing foam. I carved spar cap troughs on the outside and inside, then cut off the forward faces so I could lay up a 6-ply UNI shear web (45-degree bias). Once cured, I micro’d the forward face back on. I had some spar cap tape left over from the wing construction, but I wasn't sure I wanted to use it. The troughs on these roll bars are 2 inches wide as opposed to the 3-inch troughs used elsewhere. Plus, these spar cap troughs are obviously not flat and I could foresee the epoxy running off the spar cap tapes and onto the floor. Instead, I made the spar caps like we used to do before spar cap tape was invented. I wet out a whole 36"x38" rectangle of UNI on plastic, then folded in half on itself, folded it again, and folded it a third time. That left me with a 4.5-inch strip that was 8 plies thick. I cut two strips from that and applied them into the spar cap trough for a total of 16 plies. Believe it or not, it took only 20 minutes to lay up a spar cap. You can see the shear webs and spar caps in the pictures below. The foam between the "uprights" is there only to hold the uprights to the correct width until the spar cap cures. This spacer foam got cut away after cure.
After curing the spar caps under a heat tent, I rounded the forward and back sides of the roll bars into nice oval shapes. I applied 2-BID torsional wraps to the forward and back ovals, with the wraps overlapping each other over the spar caps. I then cut some oval-shaped holes into the top of the shoulder support so I can insert the roll bars through the shoulder support. I cut each leg at a 45-degree angle so they would fit flush onto the part of the seatback that's inside the shoulder support. Once I was happy with the fit, I started floxing and glassing the roll bars in place. I carefully removed the fronts on the shoulder support so I can reach in there and glass the roll bars with 2-BID to the front seat back, inside shoulder support areas, and to the large plies holding the anchors for the shoulder straps. As you can see in the pictures, the pilot's headrest is permanently mounted to the shoulder support. It is not attached to the canopy like in the plans. I didn't find the pilot headrest to be that much of a hindrance from getting in and out of the back seats.
How will they work? I don't have an engineering answer to that and I don't want to find out the hard way (in a crash). I'm confident my beefed-up roll bar I included in the turtleback is stronger than the plans-built TB1 bulkhead. I feel that the composite roll bars are stronger than the triangle headrests. So if "A" is greater than "B", and "B" is greater than "C", I'd think "A" is stronger than "C". My intuition tells me that if I ever go inverted on landing and the canopy gets squashed, the roll bars are likely to break away the shoulder brace and seatback. Thus, you'll "fall" and/or recline into the back seats. Your head will be below the upper longerons and hopefully won't suffer massive trauma. Yuck! Tough to think about. :-( If anything, I can store my headsets on the roll bars!!
Steps 3 and 5:
Before building the shoulder brace, I realized that one of the bolts for the aft canopy hinge would be held in place by a nut located permanently inside the shoulder brace. I wanted the option of being able to take off the aft hinge. So I took a hint from the archives and installed a nutplate under the upper longeron for the one hole that's within the shoulder brace.
Building the shoulder brace is straight forward. I did take another hint from the archives and installed nutplates on the inside of the brace before glassing the brace to the seatback. The method I used is straight out of the Chapter 8 FAQs. I riveted the nutplates to 1-inch aluminum squares, drilled holes in the aluminum for flox retention, floxed the nutplates to the wood inserts, and installed two small screws to secure the nutplates. (See the poor quality photos below.) In this manner, you don’t have to muss and fuss with cutting those hokey slots per Step 5.
Step 6: External Step and Outside Seatbelt Attachments
Making the hardpoints for the outboard seatbelt attachments was straight forward. However, the bolts specified by the plans were not the right length. I had to special order the bolts.
Back in 1998 when I was building on Chapter 8, I couldn’t decide whether to use the Brock step or go with a retractable step. So, I went ahead and installed the wood reinforcement and installed the Brock step. After 8+ years of using it, I've concluded that I don't care for the placement of the step. For me, the most natural way to climb into a Cozy is to place my left foot onto a step, then swing my right leg into the cockpit. I can't do that with the Brock step. My right leg hits the strake on the way up and on the way down. In my opinion, the step is in the wrong place -- it's too far aft. I think the step needs to be more forward., like at FS-41 along the bottom of the instrument panel. (Bob Bittner used this location.) There’s nothing wrong with the Brock step itself. It’s simple, lightweight, and insignificant aerodynamically. I just couldn’t live with the location. Period. (If you're thinking about installing extended strakes, I'd be willing to bet the extensions render the Brock step useless.)
So, I decided on Christmas Day '07 to install a retractable step similar to what Zeitlin and Bittner are using. My concept is shown here. The step slides out about 5 inches. The loads on the step are taken up by a sleeve, a wooden compression pad, and a ring of flox. A square tube has a guide slot in it that accepts an AN-3 bolt. The bolt is secured between the compartment bulkhead and a bracket under the front seat. The bulkhead is part of my front seat mod. The bolt provides the mechanical end stops and more importantly, keeps the step from turning under foot. The ends of the step and the sleeve are shaped to match the outside of the fuselage. I’ll probably install a push-pull cable like Zeitlin for moving the step in and out.
These pictures show some of the installation details. The first picture shows the sleeve and wooden compression pad. The one-inch hole through the fuselage side is drilled just above the lower longeron. I was going to put mine along the bottom of the instrument panel, but moved it back 5 inches to accommodate my front seat modifications. I dug out the fuselage foam in and around the sleeve and filled the void with flox. The second picture shows the set-up I used to hold the step level to the floor and parallel to the instrument panel while the flox cured. After the flox cured, I disassembled the step and applied 4 plies of BID to further secure the sleeve and compression pad to the fuselage. The third picture shows the step extended. You can see that the sleeve and the step has been shaped to match the fuselage. The last two pictures were taken from a position forward of the pilot's seat looking aft through the small door. You can sort of see the fiberglass bracket that's on the compartment bulkhead. Its job is to hold the AN-3 bolt going through the guide slot in the square tube. The step is retracted in the first picture and extended in the second picture.
Step 7: Rear Heat Duct and Center Seatbelt Attachment
Before cutting the side pieces for the rear heat duct, I cut a small two by four to size, marked it off in 1 inch increments, and temporarily jigged it into place between the seatback brace and the forward landing gear bulkhead. I then measured the distance from the top of the 2x4 to the bottom of the floor at each 1-inch increment. I then traced these dimensions onto the side pieces for the rear heat duct. According to the plans, the bottom edges of the rear heat duct are supposed to follow the lower longerons. Mine didn’t, so I’m glad I took the time (20 minutes, whoop-de-doo) to find the exact contour.
I found that electrical tape worked best for covering the transition piece prior to glassing it. Electrical tape conforms to oddly contoured surfaces and it makes for an excellent release tape.