bang-fai-yai

watching rocket festival videos, big ass rocket
i started wondering, is there any documentation/ pictures on there construction?
i mean how the hell do they do it?

How do i bet on it??!

I would imagine that is pretty slow burning BP in there, given the surface area for gas production. Probably little more than green mix with large granular charcoal.

now thats a rocket, you would know more than me but im geussing its a retarded fuel with extra charcoal or mineral oil some of them had different coloured tail's so maybe both[on different rockets] truly amazing how they get 4 minutes airtime
is this the same place they make 4 metre diameter girandola's?
dan

My linkslow fuel for sure, im wondering what they use to form the case, and how they make the fuel grain, rammed then a large drill?
id be chuffed if i could pull off a 6 lb'er

Edited by dr thrust, 30 May 2011 - 10:39 AM.

Impressive rockets! From the video, you can tell that the case is a long piece of plastic pipe about 6 inches (150mm) internal diameter. It's not stiff enough to support its own weight, so they carry it in a metal trough that's removed when the rocket is on the frame. It's an end burner, because they hold it tied down for five seconds after lighting and the sound doesn't change at all in that time, and it doesn't take off as smartly as a core burner would. It's choked to about half diameter, judging by the flame shape. I guess the length to be 20 to 25 diameters. It would be quite reasonable for an end burner of those proportions to burn for two or three minutes. If I guessed the size right, there must be between 100kg and 150kg of fuel. I have no idea how you would press or ram a case of this size - pile driver, perhaps?

Impressive rockets! From the video, you can tell that the case is a long piece of plastic pipe about 6 inches (150mm) internal diameter. It's not stiff enough to support its own weight, so they carry it in a metal trough that's removed when the rocket is on the frame. It's an end burner, because they hold it tied down for five seconds after lighting and the sound doesn't change at all in that time, and it doesn't take off as smartly as a core burner would. It's choked to about half diameter, judging by the flame shape. I guess the length to be 20 to 25 diameters. It would be quite reasonable for an end burner of those proportions to burn for two or three minutes. If I guessed the size right, there must be between 100kg and 150kg of fuel. I have no idea how you would press or ram a case of this size - pile driver, perhaps?

Looks like the casing could be an old carpet role tube. pile driver? = most probably, but I would not be surprised if they adapted a log splitter with hydraulic hand pump, or a fence post rammer.

Would love to see the ukps chaps make one of these some day with tail fins & logo to look like thunderbird one, but Im not sure the CAA, MOD or the HSE would be up for it!

The worrying thing is - these things have to come back down - I hope they're on a 'chute

Yes, these are impressive to watch. But would need better than plastic or cardboard tube to handle that sort of burn time especially being end burners!!

Yes, these are impressive to watch. But would need better than plastic or cardboard tube to handle that sort of burn time especially being end burners!!

plastic has no place in pyrotechnics, some pressure rated pipes can handle thousands of psi the bigger ones less and properly made paper ones the same. the internal pressure acting on the walls of the motor casing in an end burner decreases as the propellant burns away and the volume of the motor increases only the first few seconds produce enough thrust to get up, this leaves a very small surface are for the pressure to act on in the first seconds and would most likely blow the plug instead of the casing.
i dont know of plastics suriving high temps for sustained periods but the motors do look too flimsy to be anything else maybe the grain is inhibited in some way lining the walls of the pipe with a flexible fire resistant resin.
dan

plastic has no place in pyrotechnics, some pressure rated pipes can handle thousands of psi the bigger ones less and properly made paper ones the same. the internal pressure acting on the walls of the motor casing in an end burner decreases as the propellant burns away and the volume of the motor increases only the first few seconds produce enough thrust to get up, this leaves a very small surface are for the pressure to act on in the first seconds and would most likely blow the plug instead of the casing.
i dont know of plastics suriving high temps for sustained periods but the motors do look too flimsy to be anything else maybe the grain is inhibited in some way lining the walls of the pipe with a flexible fire resistant resin.
dan

Perhaps aluminium tube liners are used, but even they would give way soon enough if the burn time was 'minutes' imagine the constant heat and pressure around the nozzle end of the motor with those times!
As you say, maybe a really good inhibitor resin is used. Love to know what it is if that's the case.
Actually, it's very doubtful that any of these 'Thai' rockets burn for minutes, more like seconds (30-40) I havent seen any that do yet and we know if they did, we arent going to be able to see the proof let alone hear it!!

Edited by Markel, 21 April 2011 - 06:51 PM.

It doesn't say it burns for 4 minutes, it says it can take 4 minutes to come back down. It could very well burn for 30 seconds or less to achieve that. My little half-inch rockets burn for 2 seconds or so and take more than 10 times that long to come down.

it was you that said they could burn for 2 to 3 minutes and your capacity estimation has a 25kg tolerance, anyway this should get some chins wagging it appears a big drill is used,[i dont want his job] shame about the kids so close and the other dozen or so rockets


dan

great find, dan
its answered the question about the core design/construction, no expensive or fine-tuned tooling needed then!
the drill bit in the video looks very similar to the 1 meter long "sds" carbide tipped masonary drills electricians use for drilling through very thick walls at work.
yep certainly curtains for all concerned if there was an accidental ignition whilst performing said procedure

Edited by dr thrust, 22 May 2011 - 09:49 PM.

The cases are possibly charged with a big wooden drift and 2 or 3 men using sledgehammers. This is how the largest Congreve rockets were charged.