Seat Belt Crotch Strap Install Questions

[Saville]

Hi all,

I need to install the crotch strap for my Hooker Harness and I have some very newbie questions:

The belt lug is already installed in the airplane:



I've looked at the plans and found this section of Drawing 18 (RV-8) "Misc Parts":



I cannot tell if this is for the lap belt attachment, the crotch strap attachment, or if it works for both. I am assuming the latter.

My harness is a Hooker Harness and I called the company to order the crotch straps (got them). The guy I spoke with said I need an "AN4" bolt for the attachment which is a 1/4" bolt.

I read - possibly here on VAF - (yes I did a search) that you need to install a bushing over the bolt. However the attachment lug on the crotch strap already has a bushing in it which brings the hole down to 1/4". So I'm confused and have a bunch of questions:


1) On the plans, the two pieces that make up the attachment lug are bent slightly to provide a 1/16" gap. The attachment piece on the harness is 1/8"
wide....

I take it that the harness piece does NOT go in between the two leaves of the attachment lug - correct?

What is to prevent the tightening of the bolt from removing that 1/16" spacing between the two leaves?


2) If it does not go in between then does it go in front of the two leaves, in back or does it not matter?


3) The plans show that the hole for the bolt is 1/4" in diameter. But the bolt I'm supposed to use is 1/4" in diameter. Furthermore as you can see the plans call out for a 5/16 "Seat Belt Lug Spacer"

...Am I supposed to ream out the 1/4" hole in the attachment lug so that I can fit a 5/16 "Seat Belt Lug Spacer" into the attachment lug?


Or do I simply run the bolt through the spacer that's already on the harness, through the 1/4" hole in the attachment lug, and finish off with washers and a nut?

Do the plans call out for that spacer because the Van's harnesses do not come with one (as the Hookers seem to do?)


4) Once the appropriate holes/spacer confusion is cleared up, I then have to finish off the bolt with a washer(s) and nut:

One flat washer and one lock washer?

What kind of lock washer?

Some AN4's that I look at have holes in the bolt for, I imagine, a cotter pin. Should the bolt be cotterpinned with a castle nut?

Or safety wired?

Or should a nylon nut be used?


5) Lastly, certainly the bolt should be long enough for sufficient threads to be grabbed and the cotter pin hole revealed - but can the bolt be too long, in this application?

Lots of newbie questions I know and I appreciate any help.

Thanks!

[Saville]

no one has any answers/insights tp my newbie questions?

[Ron RV8]

If the lugs are in place the spacers are already installed in the centre section of the spar.

On my -8 I just flexed the lugs to slip the seat belt tang between them. I bolted it in place with a 1/4" AN bolt, one washer on the nut side, and a nylon AN lock nut. The bolt should be long enough to stick out of the lock nut by 2 threads.

Some harness like Crowe have a larger hole so must be bushed to fit the 1/4" bolt. To do this on the Crowe I used a stack of 6mm washers. Hooker might be different...

If you find this confusing, you might consider asking someone who has constructed an aircraft to give you a hand...

Good luck...

[flyinga]

What Ron said. I have the Hookers and I just spread the tabs apart to insert the crotch strap. Do not just run the bolt through the tabs and then through the strap.

[SMRacer]

The tab on the sub belt goes between the two tabs on the spar attachment. Do not ream the holes. Use a 1/4" bolt. If the hole on the sub belt attach is 1/4 inch, just insert the bolt and use a nylock nut, or if you prefer (and the 1/4 inch bolt has a drilled end) use a castle nut and cotter pin. I prefer the nylock since tightening it will pinch the tab and hold the tab straight up. The castle nut option usually leaves a part free to rotate. If the hole in the sub belt tab is larger than 1/4 inch you will need a very thin bushing that is i/4 ID and with an OD to match the hole in the sub belt tab. The thickness of that bushing would be the same as the thickness of the sub belt tab.

Some plans don't make sense when viewed literally. Remember you are not sourcing all components from the same vendor. Van's plans cannot accommodate all possible options.

For example: It would be perfectly OK to ream the hole in the spar tab to match the hole in the sub belt tab. Let's say 5/16 and use a 5/16" bolt. It would also be OK to ream the hole in the spar tab to 5/16 and use a full length 5/16 bushing (long enough to be at least flush with the outsides of the spar tab and perhaps just stick out a bit on both sides) and then use the 1/4 bolt. Both OK, at least in my mind, as long as all edge distances were maintained.

The interior dimension of the spar tab shows 1/16. If the sub belt tab is 1/8 just open the gap to accommodate the sub belt tab.

Jim
RV4 444JT
RV8 37PK
Both purchased flying, so what do I know about building?

[Saville]

Thanks to all who replied.

To Jim:

Originally Posted by SMRacer

The tab on the sub belt goes between the two tabs on the spar attachment.

Got it.

Do not ream the holes. Use a 1/4" bolt. If the hole on the sub belt attach is 1/4 inch, just insert the bolt and use a nylock nut, or if you prefer (and the 1/4 inch bolt has a drilled end) use a castle nut and cotter pin. I prefer the nylock since tightening it will pinch the tab and hold the tab straight up. The castle nut option usually leaves a part free to rotate.

Sounds like Nylock is the way to go.

If the hole in the sub belt tab is larger than 1/4 inch you will need a very thin bushing that is i/4 ID and with an OD to match the hole in the sub belt tab. The thickness of that bushing would be the same as the thickness of the sub belt tab.

Ok well the hole in the spar tabs are 1/4". The hole in the belt tab is 1/4" but only because there's already a bushing in it. See the attached picture below:



As you can see, the bushing is pretty thick. It's held in place because it's flared. If I understand you correctly, I should file that bushing down so that it's flush with the tab, then insert the tab between the spar tabs and bolt it in with a 1/4" bolt.

Do I have that right?




The interior dimension of the spar tab shows 1/16. If the sub belt tab is 1/8 just open the gap to accommodate the sub belt tab.

Got it. Thanks!

[Saville]

What material should the bolt be?

Aircraft Spruce shows Stainless and CAD plated.

Thanks

[Raymo]

Cadmium plating is fine.

[brad walton]

I removed the lug in the seat belt which reduces the hole size to 1/4 inch because it spreads the seat belt attach point too much. Refer to the plans and cut a spacer from the tubing to reduce hole diameter to 1/4 inch. Use the AN bolt of specified length only. Too long will interfere with the seat cushion as the crotch strap passes through a slit in the cushion. Use a castle nut and cotter pin per the plans.