Passing fire to header

[Swede]

It's time to cease making simply rockets for me. I've got a good, consistent 4 ounce BP rocket that has power. Now I need to work on a header or two. There are plenty of resources describing how to make various headers, but I've seen inconsistencies regarding capping the fuel and firing the header, and I'd like to know what works for you guys.

 

There seem to be several options.

 

1) Tamp a section of delay comp on top of the BP fuel, which in turn fires a stub of QM leading to the header burst.

 

2) Add a clay plug. Drill the plug, and insert QM or similar into the hole

2a) Use a paper plug rather than clay, then drill

 

3) Or simply place your header crossmatch in contact with the end of the BP fuel.

 

Does the motor require a strong plug for best performance?

 

I am going to start with charcoal streamers initially, then hopefully move on to some reds, greens, and blues. Thank you all.

[oskarchem]

Add some delay comp on top of your motor, plug the top, drill a passfire (not in the middle but on the side of the plug) and blackmatch it.

[FREAKYDUTCHMEN]

Almost like option 2,

 

Ram or press some bentonite 10 to 15 milimeter on top of the fuel, drill a 3mm hole through the bentonite, press some fuel in the 3mm hole untill it is on top, then add a little bit of fuel (BP) and ram it one more time.

Never had any failures. And there will be a delay of one seccond untill the payload goes off.

 

The last one of this video is a good example of how they look like:

http://nl.youtube.com/watch?v=m8qqCs_9chc

[cojonesm]

If you make very fast core burning rockets u'd better put in some slow meal. Yesterday i've had a cato with a 16mm core burner with a burn rate of 0.5 seconds without compressed meal in the passfire hole...

 

 

http://www.youtube.com/watch?v=y4-zjk7vnlw

 

My shell didn't work well too, I hope i can find some pieces back.

 

 

 

First post.

[psyco_1322]

Im not sure if a core burner needs the clay plug at teh top or not, that may be determined by how hot of a motor you are making. When I make mine I usually put on in anyways since I have the clay out. None of my nozzle less bp or whistle motors have a clay plug. If you do want to add a clay plug I would suggest drill the hole off center, to insure complete fuel consumtion, drill a bit into the fuel and not just to it. Then just put a pinch of fine granulated bp and maybe some Ti in on top. Making sure the bp if fine enough to go into the hole. Seat your header on top of that and glue. Packing the hoel will just make a longer delay, possible causing failure to pass fire.

[Mumbles]

In the few rockets I've built with others I've never used a clay bulkhead. However once I get my tooling and press setup, I will be using one. Clay is cheap, and it certainly can't hurt. Might prevent a CATO or blowthrough at some point, so thats all that counts.

[psymon]

I used to drill the clay end plug for a passfire. However I have had far more success with adding a delay and then get a thin piece of visco and place this in the top of the rocket, holding on to the end of the visco add clay and ram it. You may have a little problem with the fusebeing down the side of the rammer but if its thin visco its not usually that difficult. Ram the clay end plug as usual. You will then have a passfire fuse going to the header, cut off the extra visco and there you go...

[MilkyJoe]

I had an idea similar to yours psymon.

 

I was thinking of turning up a rammer with a small hole drilled off center the diameter of visco. You simply put a bit of fuse in the rammer and then ram your clay and you should have a visco passfire encased in clay.

 

The only problem I can see with this is the visco getting pinched to tight and not burning through.

 

~Milky~

[Mumbles]

I'd think it might be a bit more reliable to tamp in the fuse with a little bit of delay mix/BP/whatever. It'd hold it in place and ensure good contact with the fuel grain. Then the clay rammed/pressed on top of it. This would provide the bulkhead, as well as locking in the fuse to the fuel. When reading Psymon's description, it sounded like rammer was shaved off a bit on one side, and the visco ran up next to the wall.

[MilkyJoe]

ah, if the rammer had keyway on the side for the fuse... brilliant

 

I was thinking psymon was just squashing the fuse against the rammer hehe

 

I might give it a shot then, I'll tell you all how it goes.

 

~Milky~

[psymon]

I'd think it might be a bit more reliable to tamp in the fuse with a little bit of delay mix/BP/whatever. It'd hold it in place and ensure good contact with the fuel grain. Then the clay rammed/pressed on top of it. This would provide the bulkhead, as well as locking in the fuse to the fuel. When reading Psymon's description, it sounded like rammer was shaved off a bit on one side, and the visco ran up next to the wall.

 

 

Quite right mumbles. I have never had any problems with the passfire. Worked every time so far.

 

When I used to drill a passfire hole I had several headers fail to go off. One rocket had an excellent header, packed with stars and burst charge. Took about an hour to construct it. The rocket went up perfectly, deep whoosh, excellent height, perfect vertical flight... Delay... Nothing... Arrrggghhhh!!!

 

Since then I used the fuse at top of engine touching delay, fuse beside clay plug and out into header method using a thin fuse or shaved rammer (flat edged). Passfire works every time and I am sure the method will work for other things like stingers etc.

[Swede]

These tubes are exceptionally strong and thick. How about marking the interior of the tube where the passfire fuse would ultimately lay, then taking a dremel and a 1/8" burr, and cutting a little channel in the tube? The tube at this location will not see high pressure. The fuse could snake down the channel and ultimately poke out a bit at the end towards the bottom, taking fire easily, yet being firmly captured by the clay bulkhead. Then, it can be linked to the header in final construction.

[Pyrohawk]

Sounds like an accident to happen if I understand what your planning to do... I always say you should keep things as simple as possible, don't get me wrong that is the only way new things are ever created...but it seems like whenever I try to modify things and creat new tricky things something goes wrong and I learn why in a thousand years of experimentation noone else did it.

 

Plus, making a weak spot in your tube, even in a spot without a lot of pressure sounds dangerous... You might get away with it. Might be worth an experiment if your curious, but I wouldn't recomend trying it for the first time with a device you care about in case it does blow thorough.

[superdank]

Both drilled clay and drilled cardboard work great

[Swede]

Pyrohawk, I'm talking about notching the tube before there's anything placed in it. The top of the tube sees very little pressure; you're not going to weaken it there.

[Aquarius]

Old post, but I'll give it a bump:

@ Swede; are you still using Red Gum/acetone to bind your fuel?

 

The way I make passfires/delays is to ram a delay of BP with no clay bulkhead. Just use the same mix as your fuel, it takes fewer operations and save a bit of weight as well.

If I really want to out-do myself, a bit or TI or MgAl give a nice silvery effect before the header goes off.

And using the "wet-approach" gives a hard and solid grain, especially since I press my rockets. The downside is drying time.

 

If you do a static test on a solid packed spoulette with your fuel, you'll find the burning rate by dividing time by length.

Say, if you make a delay of an inch, and this burns for four seconds, you know the max delay on your driver. Now, for timing the delay to say three secs, drill a small hole into the delay my 1/4 of the delays length. This shortens the distance and therefore time before the flame reaches the hole from the thrust burnout. A bit like making a crossette, if you know them.

 

By altering the depth of the hole, and all other parametres beeing equal, you will be able to time the delay quite exact. Never fails for me, I used clay bulkheads before, but this saves time and effort, mixes, different rammers etc. Sprinkle some BP on top for a positive ignition. Not too much, if you don't want the header/shell separate .

 

Just my 2 C.

[Swede]

Thanks Aquarius! That's some excellent info. I especially like the idea of spiking the delay with some sort of color comp to enhance the effect.

[tentacles]

You don't want to omit the clay plug at the top of the fuel grain; it's there to keep it inside the tube! I have seen fuel grains literally go up and leave the tube behind, it looks like a CATO until you see the rocket still sitting in the tube! It's more work to put the plug in but it absolutely makes your rockets more reliable.

 

Also, you should always put a piece of blackmatch down the passfire hole from the rocket to the header. The reason being that loose material (flash, BP, whatever) will get thrown to the top of the rocket after the thrust cuts out - you'd think it would fall back down and all would be fine, but it doesn't always, in fact it doesn't *often*. Those bits of blackmatch are cheap insurance, well worth the price!

 

FrankRizzo and I threw together some quick rockets a couple months ago and I forgot to drop in BM... out of 4 rockets, two headers went off - the two MnO2 rockets that didn't leave the tube! In fact, one of them we stuck in the ground. I figured molten Mn dripped down into the header to light that one.

Edited December 17, 2008 by tentacles

[FrankRizzo]

Yep, blackmatch makes the fire transfer *much* more reliable. The best way to think about it this: As you're accelerating down the road in a car, the seat is pressing against you and bringing you up to speed. When you put he brakes on, the car slows down before you do, and you strain forward against the seat belt until you've reached an equilibrium. The same thing happens to the loose comp in a header. As the rocket is burning it's fuel, it's accelerating and the comp is forced against the bulkhead. As soon as the fuel is exhausted, air resistance immediately "puts the breaks on", and the comp ends up packed against the other end just like you straining against that seat belt. The blackmatch provides a "ladder" for the fire from the delay grain to travel the whole length of the header tube and get to the comp no matter where it is. A little dab of glue to keep the blackmatch from separating from the passfire hole and/or a length of black match long enough to end all the way through the header is also a good idea.

[Aquarius]

Well, not including the clay plug is a matter of choice. If you ram your fuel dry, I agree fully.

 

But as stated, I press my grains, bound with RG and acetone. Some of you may think is is a bit over the top for a rocket driver, but I find it to work perfectly. As this is for my 1/2 inch ID/ 4 oz rocket driver it is not too powerfull, but it might be scaled up to a certain extent, I have a 8 oz driver ready for firing.

And I would rather make a "safe", working driver, spending three more minutes on it than a fast and unreliable one.

 

If there is one thing I really hate, it is a device that I have spent time buliding that goes boom when not supposed to.

And worse, if I know that it is because I took too many shortcuts, I'm the only one to blame!

 

And I concur on the blackmatch...

[psyco_1322]

Are you guys saying that straight clay is going to hold onto the walls of a tube better than black powder? I think a well bound bp would hold up just as good as clay. I could be wrong though.

[FrankRizzo]

Absolutely. The abrasive nature of clay will give a much better bond to the inner surface of the tube.

[tentacles]

And your best bet is to grind it from kitty litter only a bit - you only want about half of it to be dust.. the chunks really bite into the tube nicely. I have NEVER seen one of Frank's nozzles fail.. even those MnO2 rockets. Or were those nozzleless? I seem to remember a nozzle.

[FrankRizzo]

Yep, they had nozzles.

[NightHawkInLight]

You don't want to omit the clay plug at the top of the fuel grain; it's there to keep it inside the tube! I have seen fuel grains literally go up and leave the tube behind, it looks like a CATO until you see the rocket still sitting in the tube! It's more work to put the plug in but it absolutely makes your rockets more reliable.

Agreed, I have also seen that...In one of my own rockets I had a good laugh when I realized what had happened when watching it later on camera.

It's worth the 'work', though really it's so simple of a step I hardly consider it more work.