Lap belt attach points

[Tralika]

They make rubber and plastic nut caps that should work. Here's one example from McMaster https://www.mcmaster.com/#bolt-caps/=193ydi0 If you do a google search for rubber hex nut caps you'll see a bunch more. Plastic might be better than rubber, less friction against the fabric. A little dab of of adhesive on the end of the bolt should keep it from rubbing off.

[SuperFly]

Great thinking John! Thanks for the tip. Ill order, and report back with my findings.

[AV8R Paul]

Ahh someone that understands the Engineering load capacity behind the cable design. I doubt the aluminum tube that has been compromised with multiple holes drilled in would be anywhere close to adequate. I like your non-gender specific 200# person. Your analysis proves it will hold a 210# old guy that looks like Santa Claus.

Thanks, I thought it may have been crow.

As for the cable sizes, if you think about it, a 200# non-gender specific person at 9g is 1800lbs of force. Each half of the seatbelt carries half of that, or 900lbs. A cable loop has two ends, dividing the force at each end in half, 450lbs per eye, but the middle of the loop will bear closer to the 900lb because it is a single piece, not two separate cables at a given attach point. A 7x19 SS cable has 1760lb rating, galv is 2000lb. 3/32 7x7 is 920 lbs, so even it would be adequate. 1/8" cable is WELL suited and easy to work with. I am pretty sure the control cables are 3/32 as well, at least on my standard highlander.

[SheepdogRD]

In a discussion of Fuel Line Routing (http://www.wingsforum.com/viewtopic.php?f=218&t=24212), these two pictures showed the seat belts:

(viewed from the left side)

(looking down from the right side)

That brought this response:

My biggest takeaway here is your seatbelts are attached to the rails.

Now that you mention it, Dane, they appear to be bolted through holes drilled in the square-tube seat rails.

[kenryan]

Thanks, I thought it may have been crow.

As for the cable sizes, if you think about it, a 200# non-gender specific person at 9g is 1800lbs of force. Each half of the seatbelt carries half of that, or 900lbs. A cable loop has two ends, dividing the force at each end in half, 450lbs per eye, but the middle of the loop will bear closer to the 900lb because it is a single piece, not two separate cables at a given attach point. A 7x19 SS cable has 1760lb rating, galv is 2000lb. 3/32 7x7 is 920 lbs, so even it would be adequate. 1/8" cable is WELL suited and easy to work with. I am pretty sure the control cables are 3/32 as well, at least on my standard highlander.

Seems like the majority of the load would be carried by the bolt where the shoulder straps attach (under the turtledeck) leaving a much smaller load on the lap belt attachments. I bent some .032 4130 steel and used it instead of the cables. The advantage is that they are fixed and don't move around. Weight is about the same.

[SheepdogRD]

I think straps or cables seem like the best approach on our already-covered airplane, at least on the inboard attachments. Those are crowded by the flap pulleys and the elevator control rod.

At the outboard attach points, we have far more space, so we have another option. I talked to Crow (http://www.crowenterprizes.com/Pages/Aircraft.html), and their suggestion is to simply loop the seat belt around that 1" fuselage tube and back through the tightening buckle. Here's the concept from the Crow website:

Crow noted that this is the lightest mounting option. Crow also says they're used that way in many homebuilts. And that's the way they were when I was into stock car racing way back when...

If the plane wasn't covered, we'd add triangular pieces of .064" 4130 steel. They'd be welded to the inner sides of the seat rails and across that lower fuselage tube. Here's a mockup on the inboard side of the left seat, seen from the front:

(the two "extra" tubes are fuel lines)

The plates would be flush with the bottom of the seat rail at the back, and flush with the top of the seat rail in the front. That angle would aim the attach brackets up toward the seats.

These are 3" x 4", but they could probably be smaller. I spec'd .064" material because that's what the factory used on the shoulder belt attach brackets.

I think if I had a kit on order right now, I'd request that they weld in those triangular plates. For continuity, I think I'd order them for both inboard and outboard points.

[AV8R Paul]

Here are my attach points for 357TX. They are made out of a piece of cable about 6 inches long with loops swedged on each end, and some wear tubing slid onto the cable to prevent wearing on the structural frame tube.

I like kenryan’s bent strap much better. However, I would recommend putting some Teflon wear tape around the fuselage structural tube before installing them to prevent potential wear of the powder coat, or even the tubing.

I also recently added a piece of fabric (Oratex) to the same structural tube on both sides, to stop things that have fallen between the seats from sliding back under the floor boards and back into the tail. I’ve recovered my sun glasses, a lot of change, my iPhone. On my old Kitfox I recovered a LED Flaslight out of the tail feather area.

[kenryan]

I like kenryan’s bent strap much better. However, I would recommend putting some Teflon wear tape around the fuselage structural tube before installing them to prevent potential wear of the powder coat, or even the tubing.

If you look carefully at the picture you will see the strap is lined with 1/16 neoprene to protect the fuselage tubing.

[AV8R Paul]

I like kenryan’s bent strap much better. However, I would recommend putting some Teflon wear tape around the fuselage structural tube before installing them to prevent potential wear of the powder coat, or even the tubing.

If you look carefully at the picture you will see the strap is lined with 1/16 neoprene to protect the fuselage tubing.

I didn’t notice that, excellent!

[danerazz]

I am considering a couple of .063 4130 steel triangles bolted on both sides of and through the square seat tracks, just behind where the seat stops at aft travel. They will stick up enough to put a .25” bolt in double shear with a spacer; one set per track.

So far my math has that FAR exceeding any load requirements of such an attach point.