Passfire holes in rocket motors

[dangerousamateur]

I often see videos and pictures where people only drill a hole in the clay plug and put the shell with the primed timefuse or bag header on top.

 

Is this reliable?

 

Will the fire or sparks that blow through this little hole ignite what's on top of the motor?

 

 

How do you handle this, do you just use the hole or do you put some blackmatch or visco in there?

 

 

 

I allways put a tapematch from the nozzle to the header, with a delay element inside the header. But somehow this is not very elegant

 

[nater]

If I use a bulkhead, I drill the hole and fill it with a stick of blackmatch and / or loose BP. I fuse the header with black match and ensure it is long enough to coil on top of the bulkhead. This essentially turns the top of the rocket motor into a bucket and is very reliable. The timing depends on your delay grain, and can be very reluable if you drill it back to a known depth and have your delay comp dialed in with consistient timing.

 

When I do not use a bulkhead, I press a thin layer of whistle or hybrid fuel on as the last increment, as taught to me by Steve LaDuke. This will burn with a strong flame and easily pass fire to your heading. I also sprinkle a little loose BP on top of the fuel grain before attaching the heading as extra insurance.

 

Some masters do use a time fuse to their headings and passfire by quickmatch with the ignition of the motor. This is precise, but I feel part of the challenge of a good rocket is using the delay as the timing element.

[dangerousamateur]

i always fail at making reliable quickmatch. Loose powder must do the trick for me.

 

I like nozzleless and whistle motors and the problem with them is that they have no pressure when the core is gone. So the blow is not to strong.

[dagabu]

​Leave the clay bulkhead out and just use whistle for the delay, the fire from the delay will light the fuse. Anybody can made good black match, what is your process?

[nater]

Seems a post never went through. A whistle delay will not have much thrust, but will have a plenty large enough flame to light a heading. If you don't believe me, press a motor and mount it so you can see the flame from both ends of the motor. Once the core and delay burns through, you'll see a flame about 18" long come out the top of the motor. (Assuming a 1# motor)

[dangerousamateur]

I understand, i overead that you meant this for not using a bulkhead.

 

One more question:

Sometimes my rockets blow out the bulkheads or delays. What kind of delay composition does make the strongest grains but burns not to fast?

 

I have a large bunch of 1lb tubes here that are a little short. I cannot use blackpowder over the spindle, it would be to fast for delay. On the other hand it must compact very good to make shure i get no blowouts.

 

I wanted to use granulated Winokur39j, but after it already pumps so bad i dont think i will use it.

 

 

Anybody can made good black match, what is your process?

To be honest, I tried it one time and i was so pissed by the mess i never really bothered to do it again. I allways try not to use blackmatch.

I know there is a lot material on the forum, I will try this again sometime, it's hard to do pyro without blackmatch

[dagabu]

Honestly, I would cut the spindle down to fit the tubed and have another spindle made in the future once you get the right tubes. There is no best delay, BP and whistle (NEVER ram whistle) press to equally hard grains.

[schroedinger]

Get propper tubes and cut down the short ones for making stinger rockets

[dagabu]

Get propper tubes and cut down the short ones for making stinger rockets

 

That may be a LOT of stingers...

[MrB]

Thats quite all right, stingers are good fun anyway. Honestly, i love these things.I've been forced to find a way to stabilize them during spinup, due to putting a touch to heavy headings on them. But if you intentionally make them slightly off balance, and get them spinning good before they take of, you can get a good spiral action going. Looks awesome. Wouldn't dare to shoot them anywhere around people yet, i need to try a couple more (like 100 or so) to see if they are actually reliable. Don't want them to come back chasing the general public.

B!

Edited July 14, 2014 by MrB

[schroedinger]

 

That may be a LOT of stingers...

Sounds like a lot of fun, don't you think so?

[dagabu]

I agree, stingers are a blast! I bent a #3 Universal spindle a few years back and decided to make my own stinger set from the spindle and so I cut a bunch of 4" long tubes, pressed "nozzles" that were all clay up past the tip of the spindle and drilled two tangential holes 180° apart facing down 45°.

 

Fast paper fuse in both holes, 4" visco taped right where the fast fuse met, set them in a 10 penny nail pounded through a board and lit the fuse. Just the two tangential holes firing, no thrust from behind. A small report on top and they would go off at about 150'. Just gorgeous.