Clustered staging/parallel staging

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ghostfather

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I have an idea for a 7 motor cluster using a large central motor surrounded by 6 smaller motors. Launch occurs with the central motor, 6 seconds later three of the smaller engines air start, and 4 seconds after that, the other three.

Not sure what to call it - clustered staging or parallel staging, but all motors remain in the rocket, there is no staging that falls away.

upload_2019-11-18_21-19-22.png

This is a 6" rocket with a central 54mm "booster", and 6x 29mm "staging rockets". The booster motor is 50% of the total impulse, followed by 2 groups of 25%. All together just short of an M.

I realize this is a complex project, and it might be a couple of years before I can build and fly it.
I would welcome any advice, especially in the following areas:
  • Is there a reliable manner of air starting 3 HPR motors simultaneously? Are there ways of increasing the reliability using dipped igniters or other pyrogens?
  • Is there a good way to keep the igniters in their place, and not be sucked out of the motor, as they are open at the bottom of the rocket during ascent?
  • Redundant electronics, any thoughts? I was hoping to use two Altus Metrum TeleMega's because it has a tilt sensor, which I can use to prevent 2nd or 3rd stage ignition in case the rocket isn't reasonably vertical. Pretty standard practice for multi-stage rockets, especially large heavy projects like this.
  • What kind of circuitry can I use to ignite 3 motors simultaneously. I realize most altimeters aren't designed to fire more than a single igniter, but it could trigger a simple circuit that is designed to fire multiple igniters.
  • Any other thoughts?
Here's the rocksim file. Fairly simple, it's a first iteration to give me some idea whether it's feasible.
 

Attachments

  • Senorita y Seis Hombres.rkt
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This would be an ideal application for an Eggtimer Proton plus one or two additional altimeters for deployment. The Proton has 6 channels, so you can wire up each airstarted motor to its own channel (add 2 altimeters for deployment) or do one channel for each group of airstarts (add 1 altimeter for deployment redundancy). It also has tilt/altitude/velocity lockouts.

If it was me, I'd go with CTI motors for the fast ignition with the BP pellet. A skewer cut to length holds the e-match in place nicely.
 
Looks like none of the motors is very far off the central axis. So I think even if your sets of three air started motors at six and ten seconds are not EXACTLY simultaneous it would not be a big deal. nor would it be a big deal if one or more of the outboards doesn’t light at all. As long as one of them doesn’t light AFTER DEPLOYMENT (which I think would be unlikely) I expect it would be a good flight.

Sounds like a cool project.

I like your name, although I was thinking more along the lines of

gran mama y siete muchachos

From Apogee Rockets, parallel staging is as follows

*******************

What is Parallel Staging?

Most modelers are familiar with “series staging” where multiple rocket motors are fired in succession. “Parallel Staging” is where you add extra rocket motors to the side of the rocket and they are all fired at the same time instead of one-after-another. The advantage is higher lift-off thrust so you can get those heavier rockets safely into the sky.

**************************

So I don’t think what you are doing technically is a form of staging. I don’t know if there IS a technical term for what you are doing, I would guess it is a Cluster with multiple phase Air Starts.

Hope you get seven straight trails and a soft landing!
 
I like your name, although I was thinking more along the lines of

gran mama y siete muchachos

I'm still going with "Senorita" for the large central motor.
"Fat Bottomed Girls make my rockin' world go 'round...."

but I like the idea of Muchachos instead of Hombres for the smaller motors
 
Airstarted clusters are really cool, one of my buddies did something very similar to your project at LDRS last year. The hard part (besides getting them all to light...) is getting it to be stable... there's a lot of hardware behind the CG.
 
  • 1 Is there a reliable manner of air starting 3 HPR motors simultaneously? Are there ways of increasing the reliability using dipped igniters or other pyrogens?
  • 2 Is there a good way to keep the igniters in their place, and not be sucked out of the motor, as they are open at the bottom of the rocket during ascent?
  • 3 Redundant electronics, any thoughts? I was hoping to use two Altus Metrum TeleMega's because it has a tilt sensor, which I can use to prevent 2nd or 3rd stage ignition in case the rocket isn't reasonably vertical. Pretty standard practice for multi-stage rockets, especially large heavy projects like this.
  • 4 What kind of circuitry can I use to ignite 3 motors simultaneously. I realize most altimeters aren't designed to fire more than a single igniter, but it could trigger a simple circuit that is designed to fire multiple igniters.
  • 5 Any other thoughts?
1 one of most reliable methods to light clusters is using e-match which are low current and easily fired by electronics. It can by dipped or paired with pellet of some type... BP..BKNO3.. Pyrodex. I have lit 7 with standard altimeters/staging electronics.

2. Yes buy a bag of bamboo sticks at grocery store used for shish-la-bob's for smaller motors [12inchlong] and 1/8 in dowels for longer motors. Tape match to top of stick to hold in place , cut flush with nozzle and hold in place with nozzle cap.
3. I use a Telemaga or RRC3+ for staging/clusters [just 1] and a standard altimeter for back up deployment. Using 2 staging/cluster altimeters just adds unneeded complexity into the mix. would love to use all the features on some Eggtimer units...but alas I don't solder stuff and they are all kits.

4. Any, as long as using matches which are easily lit. You can add 11.7 Volt lipos to current dumping side of most altimeters then use standard igniters, but this gets really complex for a beginner. I do not recommend. Just saying it can be done. I know a flier who does this with central 54 and 6 38's regularly as I made him custom igniters for the purpose. Extensive ground testing needed.

5. I find a 6in rocket with 54 central and 3 38's much simpler to learn on,you can use reduce to 29's if ya wish.
This project will weigh around 25-30 lbs when ready to fly, more if fiberglass. 6 29's just don't do it for me at these weights' Do NOT try delay more than 1-2 seconds in rocket of this size as you may experience gravity turn before ignition and risk turning into a cruise missile.
What ever you do, starting with getting all motor lit on the ground first. Mastering ignition of all is paramount. [ or just central and 3 outboards]
Remember this when choosing motors: smaller diameter motors come up to pressure faster than larger.
Most electronics use a comparator of some sort for choosing how the sequence of events will happen. This means if using several events, such as altitude, velocity, tilt...the order in which the chain must happen to fire.
Example. I want 1800ft minimum altitude...velocity no less than 400ft/sec..and no more than 10 degree tilt. sounds simple, but doing those setting
can be complex depending on what you are using. Start simple, master the game before proceeding with complex delays.

If not using all holes, plug empty ones or risk base drag sucking fire into motor mounts and scorching them. Also the unused hole need to be plugged so ejection pressure is not lost out the back...[or chute won't come out].
I negated this issue by using a centering ring that only had hole in it for the central 54 on top. The outboards were essentially plugged by being below it. Easily done in your case just move top ring up inch or so.

Good luck and have fun.Remember this clusters/staging are not 2wice as hard...they are 10x harder/more complex!;)
 
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1 .Remember this clusters/staging are not 2wice as hard...they are 10x harder/more complex!;)

I hadn't thought about the safety issues of air starts. Off axis/tilted position at time of air started motor ignition I guess has similar risk to off axis/tilt at staging.

Saw a high power launch at NSL this year that did a complete loop about 100 feet above pad. Fortunately ended up a bit more vertical than horizontal. Was scary enough as it was. REALLY would have been scary had there been air started motors mid loop.
 
blackjack2564, thanks for the tips and bits of wisdom. I'm pretty aware of the complexity, that's why I'm taking my time and asking questions.

I've done 3 motor clusters and a 5 motor cluster, but those were lit from the ground. I've never air started a cluster, which were probably the source most of my questions.

I've also done simple staging, and learned lots about the importance of tilt sensors, though I only have experience with the TeleMega. I don't need a rocket become a cruise missile. The TeleMega is a fantastic altimeter/tracker, but a bit expensive. It just works, I've used it, and I trust it.

Your suggestion of testing a smaller air start configuration (1 central and 3 peripheral air starts) sounds good, but I'd try it with a smaller rocket and less total impulse - maybe a central 38mm and 3x 24mm - as test platform. Would give me some practice with the electronics as well.

When I did the 5 motor cluster (with a group), the more experienced rocketeers insisted on that the central booster be more than sum of the rest in the cluster to insure that it would fly more or less straight up if any of the peripheral motors didn't light. That principle has always stayed with me, and I've applied it to this cluster as well.

Perhaps another side question as far as air starts - I'm aware that some propellant types are harder to light than others. I'm thinking of using white or classic propellants for upper stages because of that they light easily and reliably, and because they are relatively slow burning (ideal for upper stages). I usually fly Cesaroni, but the famed Aerotech Blue Thunder propellant is known for ease of ignition.
Question: Are there propellants that I should stay away from on air starting motors? Any favorites?
 
I hadn't thought about the safety issues of air starts. Off axis/tilted position at time of air started motor ignition I guess has similar risk to off axis/tilt at staging.

Saw a high power launch at NSL this year that did a complete loop about 100 feet above pad. Fortunately ended up a bit more vertical than horizontal. Was scary enough as it was. REALLY would have been scary had there been air started motors mid loop.
I saw that NSL flight too, and one at ROCStock that went nearly horizontal. That's the problem with launch-actuated timers... they have no provision for detecting flight abnormalities. I recommend using something that can do altitude/velocity/tilt qualifications... there are a number of choices on the market right now at relatively reasonable prices, so there's not much excuse for not using one anymore.
 
blackjack2564, thanks for the tips and bits of wisdom. I'm pretty aware of the complexity, that's why I'm taking my time and asking questions.

I've done 3 motor clusters and a 5 motor cluster, but those were lit from the ground. I've never air started a cluster, which were probably the source most of my questions.

I've also done simple staging, and learned lots about the importance of tilt sensors, though I only have experience with the TeleMega. I don't need a rocket become a cruise missile. The TeleMega is a fantastic altimeter/tracker, but a bit expensive. It just works, I've used it, and I trust it.

Your suggestion of testing a smaller air start configuration (1 central and 3 peripheral air starts) sounds good, but I'd try it with a smaller rocket and less total impulse - maybe a central 38mm and 3x 24mm - as test platform. Would give me some practice with the electronics as well.

When I did the 5 motor cluster (with a group), the more experienced rocketeers insisted on that the central booster be more than sum of the rest in the cluster to insure that it would fly more or less straight up if any of the peripheral motors didn't light. That principle has always stayed with me, and I've applied it to this cluster as well.

Perhaps another side question as far as air starts - I'm aware that some propellant types are harder to light than others. I'm thinking of using white or classic propellants for upper stages because of that they light easily and reliably, and because they are relatively slow burning (ideal for upper stages). I usually fly Cesaroni, but the famed Aerotech Blue Thunder propellant is known for ease of ignition.
Question: Are there propellants that I should stay away from on air starting motors? Any favorites?

Mojave Green is difficult to start, Blue Thunder the easiest, from what I've read. I would stick with Whites or BT on the airstarts.
 
Mojave Green is difficult to start, Blue Thunder the easiest, from what I've read. I would stick with Whites or BT on the airstarts.

Yep, I usually go with White or Classic propellants any time I need to make sure it starts. I generally prefer CTI motors because of the start pellet in the top grain that makes them easier to light, but I've used a sliver of Blue Thunder taped to my igniter to get "hard to ignite" motors lit, like moonburners on upper stages.

I've also have access to some "secret sauce" to dip my igniters in to make them burn real hot, something used in professional firework shows. I'm not so worried about getting the motors lit.

I'm concentrating now on the electrical circuit, making sure it's safe and reliable for lighting a cluster in the air, mostly to handle the current, but also to operate if one of the igniters should short out and draw lots of current. A current limiting circuit seems to make sense.

Might be a year before I get around to building this staged cluster, but just doing the research for now.
 
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