Ejection charge difference in Estes motors?
 

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)?

There SHOULD be no difference in the ejection charge for a C11, D12, E9, or E12.

The C11-3 is only good for large models, I flew the C11-3 in the 2.6” Diameter Red Flare, which was fine. It sounds like the chute was out on both flights so I wound blame the charge. Make sure the chute is forward of as much cord as possible.

I believe was the method of parachute packing coupled with ejection while the model is still ascending that caused your entanglement. While you occasionally may get a random weak charge, as long as it is enough to get the chute even a couple inches out of the tube, it will recover if packed correctly.

Here's how I have been packing.

Wadding first, pushed 8-10" down into the tube. Normally a BT-60 tube requires 7-8 squares of wadding, but the directions for the Vapor specify 8-9. The kevlar is then pushed into the tube (about 8' of it as I recall), followed by most of the 1/4" shockcord.

The parachute is attached about 1/3rd of the length of the 1/4" shock cord down from the nose cone. The parachute is packed with the z-fold method (which has worked very well so far in about 20 launches), and inserted, then the last 1/3rd of the 1/4" shockcord is put in the tube.

I've prepped a fair number of rockets using this method and haven't had any issues until I was flying the Vapor.

Having run some Rocksims of the Vapor on C11-3s, I am starting to see where the chute is popping just before apogee. I was under the impression that this was a good thing, but maybe the rocket is still moving and runs into the chute, hanging it up?

Packing methods are like glue threads, everyone has an opinion and most chutes open anyway you pack them especially nylon. However having a lot of loose cord above the chute seems like trouble.

You want it to be as close to zero velocity as possible. If it is still ascending or already descending at a decent speed, it will sometimes shove the chute and shrouds back into the model, causing it to hang in or on the BT.

Your description sounded to me like the chute hung in the body tube or got wrapped up with the body tube enough to have a nose first ballistic return on the first one, and just enough laundry out on the second to come in tail first. It's hard to say without seeing it.

We all have occasionally gotten entanglement of the NC and/or cord with the shroud lines if we put the chute somewhere between the NC and body as compared to at or near the NC. However, it still ejects completely and even though you don't get a clean canopy, it slows the model enough that usually the worst case is a busted fin.

As far as the Z fold...I just sort of grab the center and pull the chute opposite of the shrouds, then loosely fold the chute around the shrouds to keep them from hanging anything. I then roll the chute up only as tight as I need to. I don't fold tight, never have pleats, etc. The uglier it looks, the better it seems to work. :chuckle: If the plastic wants to cling to anything at all, I add a little talc. On larger tubes, make sure you have enough wadding to get a piston action and push the chutes out. I've seen dual 24" chutes stay inside a BT-80 tube because the ejection gases just vented through/around the wadding and chutes. It is usually a perfect storm with a combo of large volume tube, some forward velocity (usually still going up), and not enough inertia from the nose cone to pull the chutes by itself.