Seat Belt Shoulder Harness Attachment Options

[dougm]

Ok, my fuse is getting closer to being ready for finish welding and I have a question on the rear seatbelt shoulder harness attachment as it relates to the rear baggage compartment. The plans call for an attachment point to be welded at what would be roughly the middle of the baggage compartment (if you chose to install one). I don't feel like having a seatbelt in the way in the baggage compartment so I'm wondering about other forms of attachment. I suppose I could do something like the CB-1, but that involves more weight from the additional bracing behind the rear 'pit.

So, for you folks who have done something different than the std. Classic plans... what did you do? Thoughts? Options?

[M Lightsey]

Not sure if it's applicable to the Classic, but this is what we did on NX1279. We mounted the shoulder harnesses using the bolts that attach the top of seat. The harnesses were then routed over a structure that keeps them higher than shoulder height to prevent spinal compression. The tubing structure was easy to fabricate and install and didn't interfere with our side door baggage compartment.
Mark

[dougm]

Thanks Mark. That's kind of what crossed my mind... what dia/thickness tubing did you use?

I don't have the CB-1 plans, but don't they call for some additional bracing on that structure? I'm only saying that based on what few CB-1 construction photos I could find that showed that location. Yours doesn't look like it would be much different weight-wise form the extra tube & mounting point called for on the Classic.

[M Lightsey]

Doug,
I'm pretty sure that structure is not part of the CB-1 plans. The CB-1 plans show that area as access to the baggage compartment and shoulder harnesses aren't addressed.
I don't remember exactly what wall thickness we used, but I think it was .035 like most of the rest of the fuselage. I figured that if I hit something hard enough to start collapsing steel tubing, my shoulders would have yielded first.
Mark

[dougm]

Thanks Mark. I guess the photos I've seen then are just other folks' solutions. What is the height of the shoulder harness guide loops above the top longeron?

[M Lightsey]

The height will vary depending on your height, the thickness of your cushions, etc. Just sit in the airplane with something approximating the thickness of your cushions and then place the support about an inch or two lower than the tops of your shoulders. You want the shoulder straps to wrap over the top of the tubing under normal conditions. If the bar is too high, the straps will lift and try to rub the rear bulkhead. We added some 3/16 rod to keep the straps in place. Make these big enough to get the shoulder straps fittings through. You'll also need to add something to the bulkhead cut-outs to keep the straps from chafing. The fact that the bar is a little lower than your shoulders is OK. The seat foam tends to compress after you've been sitting in it a little while. It will also compress some more in the event of an impact.
A couple of inches of compressive force is one thing, you just don't want to compress your spine by 1 or 2 feet.
Mark