How do you stage clusters?

[ScrapDaddy]

This has Been sitting in my head for quite some time now (I really don't know why) but is it possible to stage a clustered rocket? Like with 3 D12's on the bottom and a 3 b6's or somthing like that on the top stage?

 

[Luv2launch]

You would stage them the same way you do a normal staged rocket with all the engines in line with each other.

 

[ScrapDaddy]

Really? I thought there was a special Way to do that

 

[ScrapDaddy]

What if I wanted to use 4 engines in the bottem and 3 on the top

 

[Luv2launch]

Not with black powder motors it's pretty straight forward should even be able to gap stage them up to a few inches apart.AP motors on the other hand is a different story.

 

[Luv2launch]

What if I wanted to use 4 engines in the bottem and 3 on the top

As long as you can figure out a way to get the hot particals from the lower engines into the nozzles of the upper engines there no reason that shouldn't work also.Would just be a matter of how to line up the tubes I would think.

 

[ScrapDaddy]

This is kinda off topic but why don't you se more than a 3 stage rocket on the market?

 

[Luv2launch]

Dunno can't answer that one.The only one on the market is the Comanche 3 from estes which on a nice straight flight will put it up almost a half mile which can be tough on recovery if it doesn't fly straight up.

 

[JAL3]

This is kinda off topic but why don't you se more than a 3 stage rocket on the market?

Because they get lost.

The sustainer likes to disappear and the 2nd stage too can be hard to find because all eyes are on the other 2.

 

[NjCo]

Because they get lost.

The sustainer likes to disappear and the 2nd stage too can be hard to find because all eyes are on the other 2.

Yup, pretty much a one shot deal for at least some of the rocket. Buy as many Comanche kits as you want and add stages to your hearts content. The stages will likely keep working. But when the sustainer gets that high you will never find it. And say goodbye to all the stages except maybe the first one or two. Someone must have tried this by now and can confirm this but then again, maybe it's just too obvious that most of the rocket will disappear.

 

[NjCo]

What if I wanted to use 4 engines in the bottem and 3 on the top

Ducting the ejection charge from a 1st stage engine to the sustainer engine is usually how this is handled. I've seen some people use aluminum tubing or just body tubing angled from the 1st stage to the 2nd. Directing the ejection charge from one stage to the other is the way to go if they are not directly on top of each other.

 

[ScrapDaddy]

Oh boy that sounds complexatated

 

[Pat_B]

I read somewhere about staging more than 3 stages. The main idea what that the CG shift is too great when you go more than 3 stages. Too much weight eventually gets shifted forward and the sustainer would no longer be stable.

 

[JAL3]

I read somewhere about staging more than 3 stages. The main idea what that the CG shift is too great when you go more than 3 stages. Too much weight eventually gets shifted forward and the sustainer would no longer be stable.

Actually, I believe it is the bottom booster that has the stability problem. With all that weight aft, its hard to get the CP further aft. That's why the multi stagers tend to have ridiculously large rear fins.

 

[dave carver]

I've seen 5 stage D-motored rockets go up. The real limiting factor is how much a D engine can lift. I seem to remember the rocket not getting more than 25 feet up before it staged, the 4 stage carried it to about 100 ft. where it staged again. Amazing thing was he got all the stages back.

 

[ScrapDaddy]

Cluster staging is not for the faint of hearted

 

[plano-doug]

This has Been sitting in my head for quite some time now (I really don't know why) but is it possible to stage a clustered rocket? Like with 3 D12's on the bottom and a 3 b6's or somthing like that on the top stage?

There are several ways to do this, but I prefer to focus on two configurations. The first uses a clustered booster with the center motor lighting the next stage. Here's a shot of my Uber Tuber flying on a combo of a D12-0 and 3xC6-0 staged a D12-0 to an E9-6.


A burn string is employed to hold the rocket on the pad if the center (D12-0) motor doesn't light. Without it lit, the upper stages won't light. The center motor, when lit, burns the string allowing the rocket to leave the pad. I've flown this setup on 4 or 5 different rockets with good success.

The other configuration I've flown matches a sustainer motor with each booster motor. In this case, the risk is that the booster section will separate when the first booster burns out possibly resulting in multiple sustainers not lighting. The trick is to have each booster motor in its own, individual booster section. Yeah, it's more pieces to track to the ground, but offers a better chance of getting all the sustainers lit. Here's a shot of an upscale Midget staging 3xB6-0's to 3xB6-6's. Each of the booster fins descends independently of the others. HTH. Doug .


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[adrian]

This is kinda off topic but why don't you se more than a 3 stage rocket on the market?

Every stage above the first is deadweight until its motor ignites. The more stages you have, the more deadweight the first stage has to lift. This means the first stage had better have plenty of thrust!

If the rocket weathercocks, the next stage will end up starting off at an angle. If it continues to weathercock as each successive stage ignites, the sustainer may end up igniting near horizontal...

Having said all that, I have personally seen a Comanche-3 with two additional boosters fitted. It did go straight up and might even have come down again, but only the first two boosters were found.

My own contributions to clustered staging are Rheinbote and MIRV Gatling. See the above note about the first stage needing lots of thrust; Rheinbote has a total of nine C6's, six of them in the first stage, of which one is ducted to ignite the second stage. (Or rather, had - last time I flew it, I only found the first stage.) MIRV Gatling does the opposite of plano-doug's second configuration; a single, six-motor clustered booster stages six separate sustainers.

 

[bobkrech]

This is kinda off topic but why don't you se more than a 3 stage rocket on the market?

Actually that's quite simple to answer. The last thing you want is to have a stage fire downward towards the ground.

All simple multiple stage kits use BP motors and hot gas staging. Every stage adds weight, and at some point there simply is not enough thrust from a BP motor in the first stage to insure that by the time you would get to 4th stage ignition, the rocket is still heading up. A rocket staging horizontally or past vertical is a hazard and kit manufacturers know this and I believe at one time NAR prohibited them just for this reason.

Bob

 

[shreadvector]

Actually that's quite simple to answer. The last thing you want is to have a stage fire downward towards the ground.

All simple multiple stage kits use BP motors and hot gas staging. Every stage adds weight, and at some point there simply is not enough thrust from a BP motor in the first stage to insure that by the time you would get to 4th stage ignition, the rocket is still heading up. A rocket staging horizontally or past vertical is a hazard and kit manufacturers know this and I believe at one time NAR prohibited them just for this reason.

Bob

NAR never prohibited them for sport flying, but they were (or are - I'm too lazy to check) prohibited in competition via the Pink Book rule against more than 3 stages.

 

[JAL3]

There are several ways to do this, but I prefer to focus on two configurations. The first uses a clustered booster with the center motor lighting the next stage. Here's a shot of my Uber Tuber flying on a combo of a D12-0 and 3xC6-0 staged a D12-0 to an E9-6.


A burn string is employed to hold the rocket on the pad if the center (D12-0) motor doesn't light. Without it lit, the upper stages won't light. The center motor, when lit, burns the string allowing the rocket to leave the pad. I've flown this setup on 4 or 5 different rockets with good success.


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Doug, can you explain more about how the burn string is rigged? That sounds like a great idea.

 

[plano-doug]

Doug, can you explain more about how the burn string is rigged? That sounds like a great idea.

John,

Here's a good shot of the burn string attach points:

The string is tied to the two loops on either side of the center motor opening.

Here's a little write-up with additional info:
https://www.doug79.com/burn-string/

I want to emphasize that the string must cross under the nozzle, on top of the stick, in order to ensure that it burns thru when the motor lights

Doug

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[JAL3]

John,

Here's a good shot of the burn string attach points:

The string is tied to the two loops on either side of the center motor opening.

Here's a little write-up with additional info:
https://www.doug79.com/burn-string/

I want to emphasize that the string must cross under the nozzle, on top of the stick, in order to ensure that it burns thru when the motor lights

Doug

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That is most helpful. THanks.

What kind of string do you recommend to straddle the divide between "strong enough to hold the rocket down" and "light enough to burn through"?

 

[plano-doug]

What kind of string do you recommend to straddle the divide between "strong enough to hold the rocket down" and "light enough to burn through"?

I've been using construction twine, which is synthetic and has a twist. But I imagine just about any burnable string would work. For example, kite string is quite strong. As long as it burns, and doesn't readily break when you pull on it, it will work.

Re: overall strength, keep in mind that the total force at any given time is still pretty low. For example, if all three C6's and the center D12 peaked at the same instant, the peak thrust would be ~72N, about 16 pounds. While I'm no Charles Atlas, I can readily impart 16 pounds of force to test a string So if you can't break it by stoutly pulling on it, it's surely strong enough - no fancy test equipment required

Doug

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[JAL3]

I've been using construction twine, which is synthetic and has a twist. But I imagine just about any burnable string would work. For example, kit string is quite strong. As long as it burns, and doesn't readily break when you pull on it, it will work.

Re: overall strength, keep in mind that the total force at any given time is still pretty low. For example, if all three C6's and the center D12 peaked at the same instant, the peak thrust would be ~72N, about 16 pounds. While I'm no Charles Atlas, I can readily impart 16 pounds of force to test a string So if you can't break it by stoutly pulling on it, it's surely strong enough - no fancy test equipment required

Doug

.

Thanks again and I'm going to go out on a limb and ask some more things.

I don't have my Tuber here with me. From what I recall, though, and looking at your photo, you seem to have modified yours (prototype?) so that the lower booster will couple to the upper booster. Assuming that is correct, can you give some info?

Also, do you have any plans for your lower booster? I would like to make one. Don ought to sell it as an accessory!

 

[plano-doug]

From what I recall, though, and looking at your photo, you seem to have modified yours (prototype?) so that the lower booster will couple to the upper booster. Assuming that is correct, can you give some info?

Also, do you have any plans for your lower booster? I would like to make one. Don ought to sell it as an accessory!

Ping me again in a couple weeks, and I may have some drawings. But the 2nd stage is indeed different as you surmised. It was (re-)designed with the intent of mating with the added first stage, so it lacks an after motor block and has the aft centering recessed to make room for the coupler from the first stage. There are a few other minor differences as well.

I'll pass your comment along to Don

Doug

.

 

[JAL3]

Ping me again in a couple weeks, and I may have some drawings. But the 2nd stage is indeed different as you surmised. It was (re-)designed with the intent of mating with the added first stage, so it lacks an after motor block and has the aft centering recessed to make room for the coupler from the first stage. There are a few other minor differences as well.

I'll pass your comment along to Don

Doug

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Thanks.

 

[MarkII]

Dunno can't answer that one.The only one on the market is the Comanche 3 from estes which on a nice straight flight will put it up almost a half mile which can be tough on recovery if it doesn't fly straight up.

The Estes Comanche 3 is a really cool classic design, one of Estes' best. But it isn't the only 3-stager kit on the market. The totally sweet FlisKits Nomad also boasts 3 stages.

Cluster to cluster staging was really frowned upon in the early days of model rocketry. It was said to be simply too unreliable. Some of that point of view probably still survives, which may be why you don't see it more often. That, and also because cluster to cluster staging tends to be unreliable.

In the early days, the principle rationale for clustering was to provide increased impulse to lift heavier payloads. That reason is now pretty much history. Very large, very heavy rocket projects still benefit greatly from clustering, but for most of us, if we need more impulse, we just select a larger motor. So why do we even build clustered-motor rockets at all now? It can't be for practical or utilitarian reasons anymore, unless you are building a true-scale version of a large missile or space launcher that uses clusters (nearly all do) and you want to include the multi-engine layout for realism. Otherwise, the reason is really for the aesthetics of it. There's nothing wrong with that; one of the principle reasons that most of us fly model rockets is because we enjoy the aesthetic experience.

Another, somewhat related question about kits. Why don't you see more multistage high power kits on the market? They are, relatively speaking, rather rare. I can think of a few reasons.

MarkII

 

[cjl]

I think primarily because multistage high power is quite complicated, and most of the people who are building complex enough rockets to do staged HPR are also primarily scratchbuilding their rockets.

 

[MarkII]

I think primarily because multistage high power is quite complicated, and most of the people who are building complex enough rockets to do staged HPR are also primarily scratchbuilding their rockets.

Exactly. Plus, they'll go freakin' high. :shock:

MarkII