Center Seat Belt Attach Point

[Don_P]

View C-C on Onex drawing F03 shows the center seat belt anchor being bolted to the aft side of the main inboard spar, but installing the belt at that location would require cutting a hole in the seat to allow the belt to come through, something that is not addressed in the plans. I'm curious to know how other builders are handling this situation. One option would be to attach the belt to the forward side of the spar, but, in my humble opinion, this would put the belt too far forward to do any good in a crash.

[Sonerai13]

I am going to guess that you are referring to view E-E, which shows the crotch strap mounted on the lower main spar carry through. Everything is correct on the drawing EXCEPT the arrow pointing "Forward". It's pointing the wrong way, as you surmised. I'll make note of the error. The belt goes on the front side of the spar.

[Don_P]

Joe, thanks for the response. Your view E-E is perhaps on a Sonex drawing. On the Onex, it appears as View C-C. In any case, we are referring to the same thing. I guess I'm confused as to the point of having a center belt at all if it does not pull straight down. The purpose of the center belt is to prevent slipping under the lap and shoulder belts. Here's an illustration of a Simpson 5-point belt arrangement. Note the specified anchor point for the center belt: Slightly behind the chest line.

5-Point Restraint

[Sonerai13]

Joe, thanks for the response. Your view E-E is perhaps on a Sonex drawing. On the Onex, it appears as View C-C.

Ok, I've got Onex drawing F03 right here in front of me. Revision C, which is the current revision. The center seat belt (aka "crotch strap") mounted on the center of the main spar, is detail E-E, at the very top of the sheet. Detail C-C is the lap belt. That detail is located at the upper right, just below the revision history block.

In any case, we are referring to the same thing. I guess I'm confused as to the point of having a center belt at all if it does not pull straight down. The purpose of the center belt is to prevent slipping under the lap and shoulder belts. Here's an illustration of a Simpson 5-point belt arrangement. Note the specified anchor point for the center belt: Slightly behind the chest line.

You're welcome to mount it in an alternate location if that's what suits you. If you can find a better, stronger location for mounting that belt then go for it. That's the beauty of homebuilt airplanes. You can build it the way you want.

Suit yourself.

[Don_P]

Thanks again, Joe. You are absolutely correct. Although I posted all the changes associated with rev. C, I failed to note the change in the view designation.

Regarding other possible attach points, here's a photo I found of Merle Reppert's Onex (#0049) center belt configuration. I'm guessing that the anchor is simply attached to the aft side of the spar, as there is really no other suitable anchor point unless structure is added below the seat.

Onex 0049 Center Belt

[Klimek]

On my ONEX 090 I ran upon the same question with the center belt located on the front of the spar. Two things:
The belt adjustment could get caught between the stick and spar, not likely but could. Secondly I wanted the belt to be more vertically mounted so I could strap in tighter and be less likely to slide forward
during an unlikely bad event.
I mounted mine behind the spar, same hole, and cut an elongated hole in the seat pan and lined it so as to not chafe the webbing.
My seat upholstery has a notch in the center to clear the belt and this works well for me.
Frank
ONEX090
N1970T
YeeeeHa.

[Don_P]

Frank,
I ended up doing essentially the same thing. I think this is a more secure arrangement, plus it keeps the center belt well out of the way of the stick and the piano hinge. The slot in the seat has a doubler plate on the under side that sandwitches in a 1/16-inch thick Nylon "rub" plate with a slightly smaller slot.

Modified location for Onex center belt

[13brv3]

Hi Don,

That's really a first class mod. Did you buy those parts somewhere or make them?

Thanks,
Rusty

[Don_P]

Rusty,

No kits available that I know of. I just drew up something that I thought would work. The backer plate is 0.032 6061-T6. The 1/16-inch Nylon rub plate is a piece of an old cutting board, the scrap from which I've used for all sorts of things. I believe they can be purchased at The Dollar Store.

[SvingenB]

I think I have to copy that one :-) Installing belts etc right now.