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Can you put more core-burners together for lifting heavier shells?


Ubehage

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I'm wondering if it would be possible to put 5 (or even more) core-burner rockets together, and attach a rather heavy shell on top of the middle one?

Does anyone have experience with this?

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I think I saw something like that on some video covering TRs rockets.

 

Clustering rocket motors is indeed interesting. If you get them next to 100% reliable and find a way to ensure absolutely simultaneous ignition... E-matches? QM + topfusing?

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I'm only guessing here, but you'd probably have to ignite them simultaneously, produce synchronized thrust, and have them 'em burn out together, or else the assembly might steer itself somewhere that you didn't intend.✴✴✴✴✴
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look on YouTube for the Christmas tree rocket, they did a clustering of I think 36 core burners. I have done a cluster of seven Rocket motors and I just made sure that the quick match lighting all of the Rockets was of equal length to get simultaneous ignition. Edited by dagabu
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For girandolas, I use a home run fusing system where I send the fire 180° apart to the other side of the hope when the lift Motors ignite and then they light the adjoining Motors from left to right.

 

The quick match really travels all the way around the frame in a complete circle so that if the fire goes out going One Direction it most certainly will make it the other direction.

Edited by dagabu
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U, Myth Busters did a piece on "ancient Chinese astronauts", something like that.☯ Dozens of rockets affixed to a chair's feet. They had to light 'em all at once.✴ It didn't end well for the dummy. (Not Adam. ) Worth watching for a laugh.
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I strapped 4 half inch nozzleless rockets onto a ¾" one with QM from two of the smaller ones lighting the larger (redundancy) and it went very well. Somewhere there is a big stick with a big head poking out of a cornfield.
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U, Myth Busters did a piece on "ancient Chinese astronauts", something like that.☯ Dozens of rockets affixed to a chair's feet. They had to light 'em all at once.✴ It didn't end well for the dummy. (Not Adam. ) Worth watching for a laugh.

 

Yeah, I remember that one. What they should have done was put buster and the chair on the end of a huge stick! it may have yielded better results :)

 

@Ubes.

You could always start off with a cluster of 3. Since ignition timing needs to be accurate as possible, I'd be inclined to light them using electronic ignitors. You'd also be relying on your motors having a similar thrust profile.

 

I suppose with more motors, any fluctuations in thrust would be less noticable.

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There was no guide rail so i could see the 'flip' a mile away!

 

Hey Dave - are you saying that you were lucky enough to see that test?

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Yupper...

 

Dave, that must have been great fun to see. The Mythbusters do there stuff around California?

 

Getting back to "clustering" motors. The benefits are that you can lift more weight. Generally though, this would be done in concert with a main central motor.

 

That is, a main booster with a smaller cluster or array of motors around the outside. Reason being that after the initial huge thrust, then the outer clusters, having done their job, can fall away, leaving a lighter and more streamlined central motor to go further in altitude.

 

I guess if your going to put a pyrotecnic shell on top of that, then I would expect/suggest something huge. I reckon around 2 meters diam.(6 ft) containing 6 inch stars or similar.

 

I'm quite partial to glitters, and even the good old tiger tail should suffice - 2 kilometers up!! What a show that would be!!! :)

Edited by stix
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Are you sure that 6" stars are big enough at 2 km? What would you use for a stick, stix? Perhaps a telephone pole?
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I need to make another up but with a salute or heading so I can tell where it ends up. I hope it doesn't break my ACME test stand.
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I was there for several of cplmac's 3" rockets. The sticks and tubes float down surprisingly gracefully. Still you wouldn't want one to land on your car.

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  • 4 months later...

I have done a lot of experiments on this matter. Had a few fails and many more successes :D

 

My conclusion to my own question is, that you can cluster together as many rockets as you wish, and use their combined lifting power.

It is also possible, and maybe an advantage, to cluster a few end-burners on a core-burner, for a continous lift after the initial lift-off.

 

It is important to attach all the extra rockets AROUND the middle one which will be holding the payload.

Balance out the rockets. Don't attach some on one side and none on the other.

You must also attach the stick to the middle rocket, and balance out the stick as usual.

 

This is a rough drawing on how to balance out the clusters around the middle rocket.

vawcn7M.jpg

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I've been working on this and talking to David Ferguson of BFR fame about it and am getting better at it. Here's a mock-up of my latest trial that I've actually flown since I took the pic. Had a problem passing fire t the center rocket (it is 2 stage) until it was suggested I make my 2 passfire rockets an increment shorter to pass fire to the central rocket before the smaller outer ones quit providing thrust. I'll have to post the text and add the pic from my phone...

 

post-20116-0-61503100-1512879530_thumb.jpg

Edited by OldMarine
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Be nice to hear and see some vids of these clusters rockets taking off. What sort of burn time and altitude?

Edited by stix
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Burn time is the same as always. You haven't changed the motor any.. Lift all depends on what you are lifting with it. :)

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Be nice to hear and see some vids of these clusters rockets taking off. What sort of burn time and altitude?

Burn time is the same. Altitude is higher - some times :)

 

Let's say you have a functional rocket with a 3" shell that rises to 200 feet.

If you cluster 2 more core-burners onto that, it will rise to 250-300+ feet.

 

On the other hand, if you have a rocket that can just lift itself to an acceptable height, you can cluster a few end-burners onto that and help it with a steady flight. The altitude won't change much in this case.

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It can and has been done (as others have noted). In fact, a couple guys in our club are playing with this right now. The trick is to get the motors to ignite at the same time. A jig or fixture for securing the motors in alignment is also a must. With core burners, the actual thrust is fairly violent and short term. As such, if one motor ignites even a fraction of a second before the others all sorts of problems arise. My personal preference (and again, ask 10 people their thoughts and you'll get 12 different answers), if you are wanting to cluster motors is to start with end burners. I feel they are easier to work with in this setup.

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Ben, I'm using nozzleless rockets and you are spot on about the ignition timing. I've settled on using the super fast white visco cut to identical lengths with the ends gathered in a paper bucket containing my ignition source (visco or Ematch) along with a bit of fine BP to make sure everything ignites at once. Until I figured that out I had rockets taking off and immediately going horizontal!

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Burn time is the same as always. You haven't changed the motor any.. Lift all depends on what you are lifting with it. :)

 

Yeah thanks guys, I kind of already knew all that. I was referring to the image in OM's post #19 as it looks like it has quite a large central motor.

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