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How I can passfire from rocket engine to rocket header (noob alert)

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#1 fieldworker

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Posted 22 November 2021 - 12:12 PM

I have made shells(canister+ball) as there are so many good tutorials in yt regarding shells, but for rockets there are no good ones. I know how to make a rocket engine and have all the knowledge about the rocket tools and since I have made shells I can make the nozzles spherical or canister header for a rocket but I want to know how the header and the engine should be connected specially how I can passfire from engine to header. Is it like the top clay filling of the rocket should be hand drilled and the spollette should be inserted into the rocket engine and the header should be hot glued at the top. Can anyone clear my doubt, I know I am pretty much noob.



#2 justvisiting

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Posted 22 November 2021 - 01:32 PM

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Edited by justvisiting, 22 November 2021 - 01:36 PM.


#3 justvisiting

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Posted 22 November 2021 - 01:36 PM

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#4 justvisiting

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Posted 22 November 2021 - 01:38 PM

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#5 justvisiting

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Posted 22 November 2021 - 01:50 PM

The method shown above is one way to do it. I use a passfire tube glued into the shell with black match inside, which touches the top of the delay portion in the motor. Sorry for the multiple posts, but figuring out how to post a picture is a new adventure for me each time ;)

 

If you are using a clay bulkhead, there's a better way than hand drilling. Woodys sells a bulkhead forming tool. That tool is based on an adaptation of a method shown in David Sleeter's second book. To make a poor man's version, simply take a piece of drill stock, and drill a hole in a piece of larger rod that fits the tube ID, so that the first rod is a sliding fit. Then you can hand tamp some BP into the top of the motor, hand tamp your clay on top, and push the small rod down into the BP. The larger piece can then be used to press the clay into place. Slide the larger piece off the small rod, and then twist out the small rod with pliers. You'll now have a bulkhead with a hole in it, and BP at the base of it. Stick some black match in the hole and this will convey fire for you. Sorry for the poor explanation, but hopefully I got across what I meant.

P.S. Sleeter uses a small disc of cardboard with a hole in it to center the small rod. Also the small rod needs to be short enough not to bind when pressing the bulkhead in place, of course.



#6 fieldworker

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Posted 22 November 2021 - 02:44 PM

Thanks a lot for explaining me the passfire technique @justvisiting, I will definitely give it a try :)



#7 Arthur

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Posted 22 November 2021 - 04:13 PM

Somewhere between rocket and shell you need a delay, probably between 1/4 and 1 second, to let the rocket coast as high as possible. This is usually better done by ramming delay increments rather than time fusing the shell. Some shells benefit from firing from the centre so black match up a tube is a plan. If the rocket is still rising at burst it could be a bit short a delay if the rocket has turned over then the delay is too long.

 

I'm really not sure about the stability of big shells in rocket flight. 3" shell rockets have been commercial here but need a good stick after that it's a dark art for you to perfect in a safe place.



#8 fieldworker

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Posted 23 November 2021 - 12:24 AM

Somewhere between rocket and shell you need a delay, probably between 1/4 and 1 second, to let the rocket coast as high as possible. This is usually better done by ramming delay increments rather than time fusing the shell. Some shells benefit from firing from the centre so black match up a tube is a plan. If the rocket is still rising at burst it could be a bit short a delay if the rocket has turned over then the delay is too long.

 

I'm really not sure about the stability of big shells in rocket flight. 3" shell rockets have been commercial here but need a good stick after that it's a dark art for you to perfect in a safe place.

Thanks Arthur for the reply



#9 fieldworker

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Posted 23 November 2021 - 12:32 AM

Btw can anyone explain me that where should be the passfire holes in this construction cuz he didn't mention it clearly https://www.amateurp...nister-heading/


Edited by fieldworker, 23 November 2021 - 06:22 AM.


#10 Arthur

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Posted 23 November 2021 - 01:51 AM

Possibly the top of the rocket delay fires the shell burst directly.

 

Consider whether the ball shell interferes with the aerodynamics of the rocket, and more so as the shell get's bigger. Consider whether this is a reason why the bigger shell headed rockets tend to have cylindrical headers. Is it reason or fashion? 

 

In my opinion, the stick is a vital part of flight stability but after the burst it is a hazard. 



#11 justvisiting

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Posted 24 November 2021 - 01:53 AM

I make mostly nozzleless rockets, and the delay is the same as the propellant, with Ti or FeTi for sparks. I mostly lift 4" shells on 1lb rockets, and 5 or 6" ball shells on 3lb rockets. I've got an extra long BP spindle for the 3lbers, so the motor is 12" long when finished. Rockets with this much power and a large heading can tend to want to go squirrely. To make them fly true every time, I use 2 slender sticks, taped together at the bottom to form a shape like a crutch. I launch them from a piece of cardboard or ABS tube attached to a long stake in the ground. 

This is one of the 3lbers with the 2 sticks:



#12 fieldworker

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Posted Yesterday, 02:39 AM

I make mostly nozzleless rockets, and the delay is the same as the propellant, with Ti or FeTi for sparks. I mostly lift 4" shells on 1lb rockets, and 5 or 6" ball shells on 3lb rockets. I've got an extra long BP spindle for the 3lbers, so the motor is 12" long when finished. Rockets with this much power and a large heading can tend to want to go squirrely. To make them fly true every time, I use 2 slender sticks, taped together at the bottom to form a shape like a crutch. I launch them from a piece of cardboard or ABS tube attached to a long stake in the ground. 

This is one of the 3lbers with the 2 sticks:

wow what a break man hands down :o






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