Clustering Options

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kswing

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I'm working on a LOC Precision Ultimate that I'm hoping to launch in the fall at BattlePark. So far I'm thinking I'll use 5 or 6 - F42T (Blue Thunder) motors with QuickBurst Twiggy starters. Another option I'm looking at would be 4 - F67W (White) motors also with Twiggy starters. I'm wondering if these seem like reasonable plans and how much harder it is to get the white motors to light. I'm not new to HP rocketry, but, I am new to clustering so any advice is greatly appreciated.
 
Here is what I have been doing for clusters and I have not had any failures:

For all black powder motors, MJG BP starters always work (I have used them in clusters of up to 12 BP motors without a failure): https://electricmatch.com/rocketry/see/23/6/bp-rocket-starters

For composite motors up to 29mm, I use Rocketflite Clusterfire with the low resistance pre-wrapped wires they sell: https://www.rocketflite.com/store/index.php?route=product/category&path=61

For 38mm motors, the core of the grains are usually 0.5", so I put half a .50 CAL Pyrodex pellet in the upper grain and start with two igniters in each motor - one with a common Nichrome wrap and Magnelite Pyrogen and the other starter is a an ematch with Quickburst Procast.
https://www.rocketflite.com/store/index.php?route=product/category&path=59http://quickburst.net/qb/procast-order-page/
For 54mm motors and above, I use the same dual starters, but glue the pyrodex pellets to the bottom of the delay grain.

These procedures also work very well for airstarts.
 
I'm working on a LOC Precision Ultimate that I'm hoping to launch in the fall at BattlePark. So far I'm thinking I'll use 5 or 6 - F42T (Blue Thunder) motors with QuickBurst Twiggy starters. Another option I'm looking at would be 4 - F67W (White) motors also with Twiggy starters. I'm wondering if these seem like reasonable plans and how much harder it is to get the white motors to light. I'm not new to HP rocketry, but, I am new to clustering so any advice is greatly appreciated.
https://www.rocketryforum.com/threads/clustering-information-data-archive.151367

Dave F.
 
As a follow-up to this thread, today I launched the Ultimate with 3 - G125T (Blue Thunder) motors using Quick Burst twiggy starters with the local club's launch system and all three lit successfully. My electronics and tracker also worked as expected, so, it was recovered successfully after an apogee of about 1900'.
 
I plan on flying a 6" x 9.5' rocket on three K535 DMS motors this weekend. I'm starting to worry about how much black powder to use as the ejection charge. The 14 second delays are only about a second short from ideal, but I plan on using a chute release and can also fly it with electronics if needed. I opened one of the motors and it comes with just under 1.5g of black powder. If all three ejection charges go off simultaneously, that would be almost 4.5g of BP.

It seems best to use the motors as primary ejection and the electronics as a backup. Then the question comes back to, how much BP to use? The calculators I've found tell me to use between 3 and 7g, quite a large range. I could use 4.5g and approximate what could happen with the included charges.

I always see "ground test, ground test, ground test"!!! But how can I block the three 54mm motor mounts without using the DMS motors themselves? Doesn't seem very safe, with the chance to ignite the ejections charges, or worse, the grains themselves. I guess I could cover the forward closure with aluminum tape and hope for the best? I could use random 54mm cases, but then how do you plug the aft closures?

Questions, questions...
 
I always see "ground test, ground test, ground test"!!! But how can I block the three 54mm motor mounts without using the DMS motors themselves? Doesn't seem very safe, with the chance to ignite the ejections charges, or worse, the grains themselves. I guess I could cover the forward closure with aluminum tape and hope for the best? I could use random 54mm cases, but then how do you plug the aft closures?

I wouldn't test with the motors in place. You can probably plug the motor mounts with old rags or if you have spent casings use them with a piece of electrical tape over the top. I've used cotton rags that are a snug fit for similar tests in the past and didn't have any trouble with the black powder lighting the rags as the explosion is very brief and the charge was coming from the coupler bulkhead.

Also, for my recent flight I used electronics for the apogee separation since the proper delay would vary greatly if all three motors didn't light.
 
It seems best to use the motors as primary ejection and the electronics as a backup.
I disagree. If you have electronics already installed in the rocket that can do the job I would always opt for that. You mentioned the delay on the motors is already less than optimal. Also, in my experience, delays can vary by a couple seconds from what is specified so the odds of them firing all at once to effectively mimic a large single charge are slim in my estimation. At the very least I would beef up the supplied charges with the motors with some additional BP.

If you have access to a 3D printer you could print out some plugs to plug the motor tubes, or even just some circles cut out of plywood or fiberboard would do the trick (that is what I have done in the past). I agree that using the motors themselves is not a good idea.
 
I could use random 54mm cases, but then how do you plug the aft closures?

Questions, questions...

I agree with the sentiment that electronic deployment is your best bet on a 6" diameter rocket. Trusting the motor eject on a rocket that large is not reliable.

For plugging the motor mount tubes, it sounds like you have some 54mm reloadable cases? Just put the empty cases in the tubes with the forward closures installed, that will plug up the tube. If the forward closures are the kind with a well for an ejection charge, just put some tape over the hole. I wouldn't worry if the cases are different sizes. I would try to use the smallest cases you have to better simulate the "worst case" of volume inside the airframe you will have to deal with.

If you really want to simulate worst case, don't put anything in the motor tubes at all, just tape the aft ends of the motor tubes. This would simulate the absolute maximum volume you would have to pressurize. It would probably lead you to an overcharge, but, if you aren't using a backup charge, better to be on the large side of an ejection charge than not have enough. Essentially, if you can eject the laundry with all the motor tubes empty, you should have no problem ejecting the laundry when they are full.
 
But how can I block the three 54mm motor mounts without using the DMS motors themselves?
You can make removeable plugs with 54mm tube couplers with lite ply discs glued to one end. Also drill two small holes in the discs and add paracord or Kevlar loop so you can easily remove them. they're safe and very light.
 
Is there a way to get ThrustCurve.com to "run motors" for a cluster? I have scratch built a rocket that uses modular motor mounts. It is 2.56" in diameter and about 44" tall with an AV-Bay. It is 9" shorter without the AV-Bay. RockSim says it can accommodate:
a 4x18mm config., a 24mm config., a 3x24mm config., a 29mm config., and a 38mm config. I want to compare RockSim and OpenRocket simulations as well as ThrustCurve, but I don't see that capability in ThrustCurve.

Carlos McCauley
 
I have a whole family of Ultimates, from BT-60 13 mm to 5.5" 38 mm.
For up to 3 motors, I use the starters that come with the motors. Larger BP clusters, the MJG BP starters work well. Composites I use dipped in ProCast or my tiny starters. This is my tiny starter in a Q-Jet B4-4.

Ultimates.jpg

18mm igniter in B4-4 4.jpg
 
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