Composite cluster questions

I have several E,F,&G rockets already, but I have never tried a composite cluster. Now I have a 3" scratch build that I am outfitting with dual 29mm motor tubes. Allowing space between for the thrust rings, the tubes are pretty close to the airframe on their respective sides.

So the question is, what happens if one motor doesn't light? I don't mean weight-wise. I will make sure the total weight could be lifted by one motor. I mean with the off center thrust. Certainly this has happened to a good number of people here.

I could envision it both ways, spinning wildly around with off center thrust, or just arcing slightly because it's not THAT far from center. It's not like two motors positioned in strap-on boosters or something.

The other question is what igniters do you trust for this kind of job? Do any of you just use plain old Firstfires?

10fttall said:

The other question is what igniters do you trust for this kind of job? Do any of you just use plain old Firstfires?

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I cant tell you much about the other stuff you mentioned but I CAN make a recommendation on motor choice. Use cesaroni motors. They light SO much quicker then any single use AT G motor ever will. Yes, you have to buy different motor cases and yes, the reloads arnt cheap but It would be a great investment.

Alex

10fttall said:

I have several E,F,&G rockets already, but I have never tried a composite cluster. Now I have a 3" scratch build that I am outfitting with dual 29mm motor tubes. Allowing space between for the thrust rings, the tubes are pretty close to the airframe on their respective sides.

So the question is, what happens if one motor doesn't light? I don't mean weight-wise. I will make sure the total weight could be lifted by one motor. I mean with the off center thrust. Certainly this has happened to a good number of people here.

I could envision it both ways, spinning wildly around with off center thrust, or just arcing slightly because it's not THAT far from center. It's not like two motors positioned in strap-on boosters or something.

The other question is what igniters do you trust for this kind of job? Do any of you just use plain old Firstfires?

Click to expand...

Less lighting means underpowered. If using motor ejection, this can be bad for your delay timing.

Lots of other variables depend on the overall stability of a rocket. Some can fly on 3 different motors and do ok because they are a long, stable rocket with motors close together. A LOC viper 3 with a payload section added would be very stable. A old LOC mini viper was not stable and even if all lit, they had to be simultaneous.

Others will have to answer the ignitor questions. I did most of my clustering in the thermalite days. You need a low enough current for all to fire fast and reliable. If you have slow ignitor with single motor rockets, you need a different ignitor / propellant combo.

I'm a big fan of clusters, both BP and composite.
And yes, it's VERY important to get everything to ignite.

If one (or worse, two) of say three motors fail to ignite, you've got all kinds of problems - not enough speed off the pad, flights that arc over, failures due to ejection timing, etc.

So, what to do?

First off, make sure you've got enough juice to fire ALL your igniters - a big, FRESH 12V high amp source is crucial.
Second, use good igniters that your are SURE you can count on. I make my own for these, using QuickBurst pyrogen.
Third, make sure you've got good connections to your igniters whether you twist (and tape) them all together (in parallel) or you use a clip whip. I do both methods, depending on the rocket in question. My clip whip is also home made, and I KNOW I can count on it.
Fourth, especially if you use a clip whip, make SURE you've got no wires touching that shouldn't be. Pay attention to wind and other possible movement that could short connections after you walk from the pad to your launch control.
Fifth, test test test. Test all your igniters and connections for continuity - individually AND as a system.
Sixth, make sure your igniters are ALL the way inserted and that they are secure so that they don't shift or fall out after you've walked away from the pad.
And seventh, for all that......cross your fingers. Just make sure you enjoy that extra nervous anticipation before you press the launch button - it's actually kind of exciting in a weird way.

Another thing to try:
My favorite cluster rocket is a scratch built where I canted the three motors. When you do this (properly), if one motors fails to ignite you can still get a relatively straight flight. This assumes that you have enough thrust with just two, but that's another matter. But if you do some research on how to design canted motors and you don't mind the added build complexity, it's a great way to go.

I love to build and fly cluster rockets, and I highly encourage you to experiment with it. Just keep these things in mind, pay attention to the details, and have fun.

s6

You could also make the rocket spin, so it wont just ark over and crash, but rather corkscrew upward... If an engine fails to light.

Ummm, "nuff said? :jaw:

I really miss thermalite!!!

Just wondering, what motors are you using? Blue thunder light easier than White lightning or Black Max motors. Just take that into consideration.

Stealth6 has some great advice. I have a 29mm 2x cluster I fly with hobbyline motors. I use homemade igniters mostly but firstfire work good too. The important thing is that you match the motors and the igniters. My motor are canter 15 deg. like the Duces Wild and the thrust line goes through the CG, so I don't have to worry much about not having straight flights even if only one motor lights.

I had one flight with one motor & it was straight. A second flight one motor didn't light til 50ft up, it was still straight.

Thank you everyone for sharing all the knowledge. As much as I'd like to use reloads, I'm planning (for now) to use SU motors, since I would have to buy 2 cases. I don't get the opportunity to launch very often, especially above LPR, so reloads would be slow to return the money. It will be some type of easy-lighting propellant, like Blue Thunder.

I am going to model the max liftoff weight and CP/CG, once the rocket is done, adjusting the nose weight if needed. The problem is that I don't know for sure how much the whole thing will weigh, since I'm fabricating the nose cone, and other components. So it is nearly impossible to calculate an angle to cant the motors toward the CG.

So I'll check the continuity and resistance of each igniter and be careful to get them all the way in, and bend the tip to touch the propellant. I've got a couple 12 volt systems for launch too.

10fttall said:

Thank you everyone for sharing all the knowledge. As much as I'd like to use reloads, I'm planning (for now) to use SU motors, since I would have to buy 2 cases. I don't get the opportunity to launch very often, especially above LPR, so reloads would be slow to return the money. It will be some type of easy-lighting propellant, like Blue Thunder.

I am going to model the max liftoff weight and CP/CG, once the rocket is done, adjusting the nose weight if needed. The problem is that I don't know for sure how much the whole thing will weigh, since I'm fabricating the nose cone, and other components. So it is nearly impossible to calculate an angle to cant the motors toward the CG.

So I'll check the continuity and resistance of each igniter and be careful to get them all the way in, and bend the tip to touch the propellant. I've got a couple 12 volt systems for launch too.

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Dip the igniters in extra pyrogen, if you have some. It will help with ignition.

Or a small sliver of blue thunder.

Very useful info that will come in handy when I finally fly my PML AMRAAM 3 that I made to fly on 3 x 29mm cluster.The rocket was finished and put aside for over 6 years and never was flown for who knows why....perhaps afraid to fly composite clusters ?

Well it will happen on our next HP event for sure !

I have a Magnelite ignitor kit I bought in the US ,so I guess I best get busy and start dipping.

Cheers

Paul T

jimzcatz said:

Ummm, "nuff said? :jaw:

I really miss thermalite!!!

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I hear you Jim.

JoeG said:

I hear you Jim.

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Hmmmmm....I recently bought a roll of Thermalite igniter cord from a club member.It was made in Canada by the Canadian Safety Fuse Co.

The box says 33.3 feet of "SLOW"

Would this be good ?

Paul T

sodmeister said:

Hmmmmm....I recently bought a roll of Thermalite igniter cord from a club member.It was made in Canada by the Canadian Safety Fuse Co.

The box says 33.3 feet of "SLOW"

Would this be good ?

Paul T

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I think it is still made it Canada. I tried ordering some when I first got back into rockets several years ago. It can no longer be imported into the USA. So most likely it is the right stuff. Since you are in Canada, I don't think there is an issue.

i used quickburst twiggy's in my vintage VAUGHN BRO WILDTHING 7x29mm with a core 38mm paired with the clusterbuster. one thing i learned the hard way was motor propellent choice is key. some light easier than others. i used to try to mix cti 38mm with AT G80's very tough to get it to light all of them when the core comes up to preasure that fast. now i run a all CTI load.

View attachment 91173


Now off axis thrust can be a problem in the next series i only got the core and 3 of 7 29mm's to light



IT was rebuilt shortly after this and still flys to this day

I'm blaming this thread for my parts order this afternoon. 4" LOC tube, payload bay, NC, and a sunward 29 mm cluster.

I mean, I had two Estes retainers sitting around doing nothing. Can't just let that go to waste