Rear ejection and payload bay

[billdz]

Hello,

Last week I acquired a 5.5" crayon rocket with rear ejection. I've never had a rear ejection rocket, so I started by reading Tim Van Milligan's article at https://www.apogeerockets.com/education/downloads/Newsletter439.pdf. It seems to cover everything I need to know, but please advise if there is anything else to take into consideration.

This rocket appears to have a bulkhead about halfway up the airframe, but the nose cone is glued on. Is there some reason why it had to be glued, why can't the top of the airframe be used for a payload? As is, there does not seem to be any place for a tracking device. Any thoughts on how to mount a tracker?

Thanks,
Bill

 

[BABAR]

Nose cone (or payload bay) is going to have to stay on despite
1. Full burnt of ejection force (unless there is a solid bulkhead)
2. Sudden deceleration from shock cord at deployment (elastic and length are your friends) regardless of bulkhead or not.

Is there room cut the tube and put in a coupler between bulkhead and nose cone? You could "lock" it with some small screws after putting you tracker in.

 

[billdz]

a
Is there room cut the tube and put in a coupler between bulkhead and nose cone? You could "lock" it with some small screws after putting you tracker in.

I think you are right, I can't think of any way to mount a tracker without cutting the tube and adding a coupler.

Is there any reason why a JL Chute Release can't be used with rear deployment?

 

[BABAR]

I think you are right, I can't think of any way to mount a tracker without cutting the tube and adding a coupler.

Is there any reason why a JL Chute Release can't be used with rear deployment?

Only issue might be space. What is the diameter between the outside wall of the inside chimney tube and the inside wall of the outer body Tube?

 

[billdz]

Only issue might be space. What is the diameter between the outside wall of the inside chimney tube and the inside wall of the outer body Tube?

1.75" and 3.75"

 

[billdz]

Do we need to use wadding and/or nomex blanket with rear deploy? It looks like the top plywood ring separates the chute from the hot gas.

 

[billdz]

I launched the rear ejection crayon rocket today. The motor mount ejected properly but the chute got tangled on the chimney tube, which caused a rather hard landing. I wound the shock cord and chute around the tube, in accordance with Tim Van Milligan's article linked above and shown below. In hindsight, I'm not sure this is the best method, seems too easy for something to tangle, as mine did.

Anyone have any tips for a better way to mount the chute, or is Tim's method the gold standard? I was thinking about not winding anything around the tube, just place the shock cord and chute parallel to each other next to the tube.

Thanks,
Bill

 

[billdz]

Attached below is Tim Van Milligan's method for loading the chute on a rear-deploy rocket, any other suggestions? Tim's method did not work for me.

 

[mbeels]

I've only done rear eject a few times, with a streamer, and had issues each time, so I'm no expert. With the streamer, I wrapped everything around the motor tube and it came undone alright. What happened was that the force of ejection was strong enough that it almost pulled the shock cord out of the rocket mount. It seems that rear eject really puts a strain on the recovery system.

What about wrapping the shock cord around the motor tube, but leaving the parachute neatly bundled on on side of the motor tube so it can catch air and pull off? Is there enough room? I don't think that there is any gold standard here.

 

[Knuckledragger]

My Big Daddy is a rear eject but I fold the chute long ways, lay the lines on top of the folded chute, then fold the chute in half from top to bottom so the chute hits the air and pulls the lines. Shock cord is a 4x length of Kevlar.

 

[billdz]

What about wrapping the shock cord around the motor tube, but leaving the parachute neatly bundled on on side of the motor tube so it can catch air and pull off? Is there enough room? I don't think that there is any gold standard here.

Yes, there is enough room and I think I'll try this method next time. I may not even wrap the shock cord around the tube.

 

[billdz]

My Big Daddy is a rear eject but I fold the chute long ways, lay the lines on top of the folded chute, then fold the chute in half from top to bottom so the chute hits the air and pulls the lines. Shock cord is a 4x length of Kevlar.

What do you do with the shock cord? Wrap it around the tube?

 

[neil_w]

I would think that wrapping everything around the tube would reduce the chance that anything would possibly get wedged between the centering ring and the body tube as the mount is ejecting. Is that something to be concerned about?

Disclaimer: never flown a rear-eject model