Recovery System Design Help

I am at the last part of my build and I need some help to make sure I'm doing this right. The rocket was a Estes Star Orbiter that I have bashed into an IQSY Tomahawk.

The instructions just have the builder using the trifold shock cord mount with a 48" piece of elastic going to the nose cone and then the parachute attaches to the nose cone as well.

One of the modifications I decided to build in was a ejection baffle that will be glued in the body tube. It has a screw eye for the attachment of the recovery system. I intended to attach Kevlar string to eye hook and then transition to the shock cord. After doing some reading it seems I should make that transition inside the body tube to prevent the Kevlar from zippering the body tube so I was thinking of a 6" loop of Kevlar with the 48" elastic attached to it. This is what I have come up with:



Here's the actual parts:


Does that all seem correct for what I have? I also have ball bearing swivel with interlock that I believe I need also but I'm not sure how many to put in or where they should go.

Need some advice please.

Thanks,
-Bob

That'll work. Several folks will say ditch the elastic and put in 20' of Kevlar, but I'm not in that camp.

The swivel.....if you have the opportunity, put it on Kevlar/elastic transition. That way the booster should be able to spin with the wind and not twist the chute (happens more on larger models, but now's as good a time to start as any.

+1 to everything Nytrunner said, plus I would add one more thing: instead of attaching the parachute to the nose cone, I would attach it further down on the shock cord, with optional swivel. This distances the nose cone from the shroud lines and minimizes shroud tangling with the nose cone. After trying to hopelessly untangle a parachute where the nose cone weaved in and out of the shroud lines, you'll know what I mean. Learned this tip from Chris Michielssen"s blog.

Thanks for the replies. So kuririn, that seems a valid concern. The lines for the parachute don't seem very long and I can picture the 8.5 nose cone getting caught up. Sounds like a plan

Thanks again,
-Bob

Found it! Post on Chris' blog from nearly 8 years ago:

https://modelrocketbuilding.blogspot.com/search?q=parachute+attachment

I'll check that out tonight. This computer won't go there...

In searching for answers about the knots to use another thing came up... Maybe I should change out the rubber band shock cord for some actual elastic.

Thanks again,
Bob

kuririn said:

instead of attaching the parachute to the nose cone, I would attach it further down on the shock cord,

Click to expand...

Remember to make the lengths so the airframe and the NC don't bang together

Thank you all for the tips. I went to WalMart for some real elastic because the rubber shock cord just didn't seem reliable to me. I never knew there would be so many types of 1/4 inch flat elastic. There was one kind that doesn't get skinny when stretched and I thought that would be great but they were out of 1/4 inch I'm not sure about how to tie elastic so I thought I would fold it over a few times at the ends and sew it. I also plan on sewing a loop 1/3rd of the length, so at about 16 inches. Now I'm gonna have to go to Hobby Lobby again

-Bob

The real shock cord that is used in yachting is good, much better than undies elastic. There should be some guidance on the interweb about knotting it.

all looks good!

So I went to Hobby Lobby and bought some 1/4" knitted elastic and some split rings. Also picked up a Protostar kit on clearance for $7.49 but I digress. Got the elastic home and sewed in a loop at each end and a third loop far enough from the nosecone to keep it away from the parachute but not so far that it would beat up the body tube. The elastic is quite stretchy but I think it will be good. I'm going to attach the parachute via a swivel to the split ring. It's all ready for the baffle to be glued in the tube.


I guess I need to decide if the D12-5 will work for the first flight or not. The sim said 300 feet and I wonder if that will give enough time for the chute to deploy...

Thanks,
-Bob

Nice work, Bob. Let us know how it comes out on your flight.

Use split rings with caution, they seem to have an uncanny ability to un-do themselves at the most inconvenient times...

I tugged on everything until it was uncomfortable on my hands so hopefully it'll hold together. I figure the lines will pull thru the stock parachute before anything else fails

The recovery system is full install now. I thought that was it but it turns out I still need to epoxy the motor retainer to the tube.

I need to decide on the initial flight engine and find someone with a launch pad (etc) that can help me get it in the air.

Thanks again for everyone's help,
-Bob