Are bulkheads necessary for 1lb nozzless core burners?

[jl88]

Hey guys. I'm making 1lb nozzleless core burners at the moment on Universal tooling. I have made mid speed BP rockets and fairly low power sali whistle rockets. First things first. The whistle rockets have no clay bulkhead, just a whistle delay. But if I press whistle mix until the end I get about a 7 second delay. Which was fine when I just had a 3" ball shell on it. As it coasted for a while and blew a couple of seconds after apogee.

 

I then tried A whistle rocket that weighed 950g and it lifted it to what I feel was a safe height for 2 x 3" shells and 1 2" shell... That was until it turned around and turned into a surface to surface missile :-S. I needed only about a 3 second delay. Now what I am worried about is that if I half the delay, the time delay wont be strong enough to act as a bulkhead as well. Also the bulkhead will be over an inch or two from the end of the motor... Seems like a waste.

 

Also, black powder motors, I am loving them. So consistent unlike my previous sugar rockets! But does a nozzless motor need a bulkhead? Or can the delay charge be used? If so, how short can you go? It would be nice not to need to use kitty litter.

 

The rockets are all being made on a 10 metric ton press in a Ben smith tube support (Which is a great investment if anyone is thinking about it!) so if extra pressure is needed, I can apply it.

Edited June 16, 2014 by jl88

[mabuse00]

I think your concerns are justified, but it depends on your setup.

 

I had lot's of CATOs with my little BP nozzled coreburners. There was no remedy, because my tubes where to short for a longer delay section or even a betonite plug

 

Going nozzleless solved (or rather evaded) the problem.

 

In my experience you can get away with much thinner delays/upper bulkheads when your rocket is nozzleless. With whistle and BP nozzleless my latest rockets had only 1,5 - 2x ID of delay without any additional plug, the tubes where filled to the brim.

 

 

IMHO you should just try it and gather experience with your own individual setup. Just do tests with a small flash charge and a ballast of sand/flour/ect.

 

 

If encounter problems you can still add a betonite bulkhead on top.

 

 

 

I'm making 1lb end burners at the moment on Universal tooling.

They're called coreburners by the way.

[jl88]

Thanks for that. All edited now. God only knows why I called them end burners... Yeah I can do plenty of testing on the BP rockets as I have similar sized spiral wound tubes are strong enough to use for them. For whistle though I only have a few more tubes until my next order comes. Would be great to get a few other accounts.

 

Thanks again.

[ddewees]

Bulkheads are a nice, cheap insurance/assurance policy...

 

If you're attempting precise timing, using shallow delays... I would recommend adding a bulkhead.

 

If you're just making rocket motors to watch them fly, bulkheads are not necessary, provided you have enough composition above the spindle.

[Bobosan]

Bulkheads do add some weight on the tube.

[dagabu]

Lots of ways to skin this cat:

 

1.) Use a clay bulkhead with a hole drilled or pressed into the bulkhead to pass the fire to the shell.

2.) Use a clay bulkhead with no hole and use a time fuse initiated by black match (lit from the visco) on the shell for timing.

2.) Use a pressed delay and use a time fuse initiated by black match on the shell for timing.

3.) Use a pressed delay with a hole drilled along the tube wall (parallel) to pass the fire to the shell, fill the hole with fine BP for passfire.

4.) Use a pressed delay long enough to act as a bulkhead.

5.) Develop a fast burning comp for the delay, use a pressed delay long enough to act as a bulkhead.

 

I am sure there are others as well but these are the common ones I have seen discussed here.

[nater]

Spiral wound tubes may not be your best choice. Some times they work, other times the flame will follow the spiral up and cause a CATO.

[Mumbles]

Do you think this is another case where waxed tubes might help? I'd imagine it'd help the fuel adhere to the wall, and prevent any jumps. Maybe even lightly oiled fuel would work instead to help it flow into the cavities left by the spiral.

[dagabu]

Do you think this is another case where waxed tubes might help? I'd imagine it'd help the fuel adhere to the wall, and prevent any jumps. Maybe even lightly oiled fuel would work instead to help it flow into the cavities left by the spiral.

 

NOW you're cooking with gas (how old is that anyway?)! Great idea since I have a bunch of spiral wound tubes that I have only used for inserts, that may be a way to cheat the "death spiral".

Edited June 16, 2014 by dagabu

[nater]

I was just thinking about trying a waxed spiral tube. My only worries, is for me spiral tubes are inconsistient, which makes it harder to pinpoint the problem. If Lloyd's theory of the wax inhibiting the flame front is correct, it should prevent the fire from working up through the spiral seams.

[Juiceh]

3.) Use a pressed delay with a hole drilled along the tube wall (parallel) to pass the fire to the shell, fill the hole with fine BP for passfire.

 

I think you meant press a clay plug and drill the hole through the clay along the tube wall down to the delay and fill that hole with fine BP for passfire? Right?

[nater]

Right, Dag just means that the hole through the clay bulkhead is off-center, close to the side wall of the tube. Since the flame burns with a conical shaped flame front, this helps ensure your delay does not burn through prematurely.

[Juiceh]

Right, I know this. My question about clarity wasn't the location of the hole but what was suggested to drill through for the passfire. I figured it was just miss worded.

[Mumbles]

Most of my spiral tubes I've recieved from pyro suppliers tend to be relatively consistent. They have good ID and OD consistency, as well as similar groove width usually. The ones I scrounge from the grocery store and other places do tend to be more inconsistent.

 

As an aside, is the flame jumping ahead more of a problem for core burners or end burners? Or is it equal opportunity?

 

I'm thinking about this more more from a shell insert point of view. I tend to use parallel wound tubes for basically everything now. If I could use spiral wound tubes for some low performance inserts, it'd be a little more economical.

[nater]

What I meant was the performance of spiral wound tubes is not consistent. When everything else is equal, sometimes they CATO and sometimes they don't. The ones that CATO, I found burn marks following the seam. I suspect, if Lloyd is correct, that wax would prevent that. It would take a number of tests from a few different builders to confirm it.

 

I was trying spiral tubes with core burners and ended up using them as headers instead. I still have a few tubes left that are uncut which I could use for core burning motors. I'm not willing to test them in my neighborhood until it gets closer to the 4th or the next club shoot I can attend in the middle of July. Even a 3/4" BP motor popping on a test stand will not keep the neighbors happy.

 

I have never tried making inserts with them either. For inserts I usually use the pulpy parallel wound tubes to save a little money over using NEPT. The only spiral tubes I have at the moment are 3/4" ID and a few that were once a section of a consumer mortar which I chopped up for bottom shot cores.

[ddewees]

Right, I know this. My question about clarity wasn't the location of the hole but what was suggested to drill through for the passfire. I figured it was just miss worded.

Some people do drill back their delay comp (not clay bulkhead) for precise timing... so he could have actually meant what he wrote.

[dagabu]

I think you meant press a clay plug and drill the hole through the clay along the tube wall down to the delay and fill that hole with fine BP for passfire? Right?

 

 

Right, Dag just means that the hole through the clay bulkhead is off-center, close to the side wall of the tube. Since the flame burns with a conical shaped flame front, this helps ensure your delay does not burn through prematurely.

 

 

Right, I know this. My question about clarity wasn't the location of the hole but what was suggested to drill through for the passfire. I figured it was just miss worded.

 

Nope, no clay bulkhead for that one, #3 is drilling back the delay comp just like DD said. This is used among some of the winners of the PGI rocket competition, it does in fact give precise timing without adding weight to the rocket going up nor to the inertia of the rocket coming down.

Edited June 16, 2014 by dagabu

[jl88]

Hey guys. This is all good info so thanks heaps. I will be trying the drill back through the delay comp as this seems like the easiest way for me. Will have a few rockets tried out this weekend. Can't wait.

 

The tubes I am using have been waxed NEPT standard 1lb tubes. But the spiral wound ones I have are also waxed, and very consistent. I'm sure they will get more trials when my NEPT ones run out (very soon)

 

Also using the drill back through the composition method, is a bulkhead necessary with a BP motor? Obviously I don't use a bulkhead for whistle and it works fine, but does BP have the same structural integrity? Or at least strong enough for its reduced thrust?

[dagabu]

Hey guys. This is all good info so thanks heaps. I will be trying the drill back through the delay comp as this seems like the easiest way for me. Will have a few rockets tried out this weekend. Can't wait.

 

The tubes I am using have been waxed NEPT standard 1lb tubes. But the spiral wound ones I have are also waxed, and very consistent. I'm sure they will get more trials when my NEPT ones run out (very soon)

 

Also using the drill back through the composition method, is a bulkhead necessary with a BP motor? Obviously I don't use a bulkhead for whistle and it works fine, but does BP have the same structural integrity? Or at least strong enough for its reduced thrust?

 

The drill back method is fine for timing of any rocket but you need to use caution, dont use an electric drill, hand drill only and a 1/8" bit in a pin vice (grind the end down to 3/32") works great.

 

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