Anyone use a Kevlar loop in bulkhead for recovery harness attachment?

[tfish]

This is very similar to what manyy OSHA fall protection leaders use. A length of the leader is shrink-wrapped (with what looks like heat shrink, but I am sure its not) together in a folded bundle. When a load hits, the shock pulls the leader out of its fold to absorb some (much of?) of the shock.

I have been thinking about doing this exact thing as I recently had a kevlar cord break on an H flight, where it passed out of the MMT centering ring. I got the entire rocket back with only a cracked fillet on a fin and the payload section, still under chute landed another ~6k feet away, so I got lucky but everything now gets built with welded eyes and in a manner that the Leader is more easily replaceable.

It did come from my..being a retired Firefighter..high angle rescue..training.

Tony

 

[Back_at_it]

I've done it once but on a smaller scale. On my Estes Fat Boy I added a plywood upper ring and did a Kevlar loop through as an attachment point just to try something different. I drilled two holes in the upper plate then threaded the Kevlar through both holes and tied knots on the end. A little dab of glue to keep the knots from coming apart and it was good to go.

I can't recall exactly what I used but I want to say it was either 700# or 1000# Kevlar as those are what I typically have on hand. Works great and the last time I flew that rocket I saw no signs of damage.

 

[DigBaddy]

I don't have any photos of what I've done on a few recent builds to keep weight down over using a steel eye bolt. Some testing with good 1/8" ply shows a small piece of it with a hole in it can function just fine and take a crapload of force without breaking (put in vice and reef on it as hard as I can).

What I do is cut a notch in the edge of the CR. Then make a rounded rectangle of ply and cut an equal size notch in it so it's got surface area above and below the ring, and then surface area to epoxy up against the side of the BT as well. I attached a crude drawing of a CR and the wood eye piece. With creative tooling, the kevlar can be replaced (or just use a loop of kevlar).