Is there a difference in the ejection charge between Estes C11-3s and D12-5s?

[Bill S]

I've been having some problems using C11-3s in my Estes Vapor. Both times, there have been failures of the recovery system (18" nylon parachute). The first time, the shock cord made of an new kevlar material seemed to tangle up and snag the parachute, resulting in a crunched body tube (which was repairable). I replaced the shock cord with the kevlar I have been using for a while, and today the shock cord seemed to hang up on the parachute - the parachute itself wasn't tangled up and the lines weren't twisted/snarled up - resulting in a tail first dive which actually caused the motor mount to shove up into the body.

I simmed the C11-3 in Rocksim, and it looked like a suitable choice, but I am starting to wonder. It occurs to me that if the ejection charge in the C11-3 was weaker, and all that kevlar and elastic cord just wasn't being ejected out of the body tube forcefully enough, that could account for the crashes, especially in the long BT-60 tube of a Vapor. Does anyone know if there is a difference in the ejection charges in an C11-3 vs an D12-5 (which flew perfectly today)?

 

[crossfire]

Where are you tieing off the chute. Are you putting all or most of the shock cord below the chute? You need to get tha chute out and rest of cord will follow. Are you useing a chute protector? Dog barf might be better for this rocket.

 

[Bill S]

Crossfire,
I'm tying off the chute 1/3rd of the length of the elastic shockcord down from the nose cone. I'm using 2x the length of the rocket in kevlar, then 1.5x the length in 1/4 cotton elastic which is attached to the nosecone. Parachute is a nylon thin-mil chute from Top Flight (which I am very happy with, by the way).

I've only used a sheet of wadding as a covering for the front half of the parachute that goes into the body tube first. The Vapor directions suggest 8-9 squares of wadding, vs 7-8 squares for a rocket of the same diameter (BT-60) for some reason.

 

[mo2872]

I’m about done building a Vapor, and that long body worried me. I ended up putting a bulkhead in the coupler, and splitting it there instead of the nose cone. Sounds like that may have been a good mod.

 

[Ronz Rocketz]

I've been having issues with the Kevlar getting tangled so I limit the length from the BT. I've also been attaching the parachute swivel to the elastic cord a couple inches from the NC. I use about 2' of elastic for the 18mm rockets and 4' for the 24mm rockets. I believe all of my 13mm rockets use streamers.

My rockets did have several hard landings during my recent trip. The Bull Pup XL broke three fins. I'm still not sure why the parachute shredded on a C11-3. The Goblin clone is built like a tank and suffered no damage despite the tangled shroud lines.

 

[rocketman4h]

I have use this method to tame Kevlar shock cords and have used it on many high power rockets. From Apogee...

 

[rocketman4h]

Oh yea I just do it by hand... no crochet needle

 

[neil_w]

I tried a hand-crocheted shock cord (1/8" elastic) on one rocket. In my hands, it worked perfectly, pulled clean with almost no effort. In the rocket, it did *not* pull clean; it pulled partway but many of the stitches were still in place when I recovered the rocket. I don't know if it was the friction of the elastic (Kevlar would probably work better for this) or what, but I was pretty disappointed, especially after having spent several days practicing my finger-crocheting.* Not sure what I'll do next time I fly that one.


*OK, I admit it was fun.

 

[Bill S]

I emailed Estes about this, asking if there was a difference between the ejection charges between the C11 and D12 motors. They said that the D motor might be a little stronger, but not by much, and that it was possible the C11 was from a batch that had a slightly weaker charge (which apparently happens from time to time). After looking at Rocksim again, I decided to just skip using the C11s and stick to D12-5 motors from now on, and to shorten the Kevlar and elastic a bit. I'll also try to move the parachute closer to the nosecone and see if that helps.

I have new centering rings, etc, coming in the mail, so hopefully I can get the rocket repaired and try again at the next launch in early Sept.