OVER PRESSURIZED BY STARTER

I have a Rocketflite Cluster Fire kit that I will use for my next AP cluster. I have used quickburst igniters with mixed results for clusters and while they work I am trying to duplicate the fast and reliable ignition that you get with CTI reloads. I was hoping the pyrodex pellets could be used with the much cheaper aerotech reloads to give similar results to the compressed BP pellets used in CTI motors.

terryg said:

I have a Rocketflite Cluster Fire kit that I will use for my next AP cluster. I have used quickburst igniters with mixed results for clusters and while they work I am trying to duplicate the fast and reliable ignition that you get with CTI reloads. I was hoping the pyrodex pellets could be used with the much cheaper aerotech reloads to give similar results to the compressed BP pellets used in CTI motors.

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Any time you are using nichrome for an element to ignite a pryogen there will be a "variance" in when each igniter begins to deflagrate. Basicly, they may be different lengths and have different resistances due to soldering or winding. plus they may be in series or parallel, which adds to the issue of supply voltage, and different lead lengths.The standard ematch uses a 50ga bridge wire, and is really consistent, about the best you will get. Another method is to use a resister as an initiator. https://www.aeroconsystems.com/tips/dahlquist_resistor_igniter/dahlquist_igniter1.htm

or if you felt like you might get all fancy dancy... heres a good way to light a motor.
https://davidree.se/content/2.talks...Thermites-for-Solid-Rocket-Motor-Ignition.pdf

with resistors being smaller than ematches, its possible to make ignitors teeeeny. just need a primer from the chip to the charge.


Then you need to come up with a model for how much juice(thermite or bp) you need for instant on. the only way is to know the burn characteristics of the proplellant, the volume and surface area. Then the combustion rate, gas production, and heat transfer rates of the bp or thermite being used. then lots of testing, with accurate measurements of startup.

But, be carefull something might go pop.

Probably cheaper to buy a motor with a pre-designed startup system.

If you have 2 of the same starters. As near identical as possible. Wired in parallel , clips attached at the same point on the wires for both pair leads.*** Is it only by chance that both starters will fire at the same instant??? With my testing , I cant find the set up that lights both at the same instant(very close though) every time.
Some flights this is not so critical but always desirable. Clusters are dang cool when they go right so Im gonna keep on flying them and really enjoy it when they go straight up doing my best each time.

Yes, it would be by chance. Try using a higher current and voltage power source.

Gerald

CzTeacherMan said:

I stand corrected... It was stuff on rolls, so must have been thermalite. I wonder what someone would do with small bits of it that have been stored for several years.

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Hi Erik,

Sorry, late getting to this thread. Several of us old school Midwesterners still have rolls of thermalite for use. I personally love the stuff. It is the bomb-diggity for simple airstarted clusters. So long as the small bits have been stored in a dry environment and they're not crumbly beyond use, they're totally fine to use. The art of wrapping wire around short lengths of thermalite is a lost art however...I don't know anyone who does it anymore (though I might on occasion just 'cause!).

My suggestion if you're planning to use it, is simply test burn one of the strands. If it lights easily, it is fine. If you're interested in the burn rates, measure the length before you burn it, then record the time it takes to burn in order to equate the burn rate. There was fast, medium, and slow thermalite. Red was "slow", burns about .6" per second. White was fast, and I think Yellow was "medium". Burn rates change as the product ages. Sheathed thermalite burns at least twice as fast as the open air equivalent lengths. Again, if burn rate matters, test before use.

Loc Heavy Duty Beauty and/or Loc Stovi + thermalite = really fun clustered flights!

Me personally: I don't trust thermite, but I have a soft spot in my heart for thermalite!

-Eric-

In comparison, What advantage would there be using a home made thermalite starter for example over the supplied manufacturers starter? Understandably you would have control over the burn time- rate but aren't the supplied starters satisfactory.? After thinking about the last question - no they are at times not . So give em a little dip or a sliver of thermalite or what ever it is these days and continuity check everytime. As for clusters- another question--"would 3 or 4 motor clusters tend to provide a more vertical flight because of the configuration"? Or does it matter?
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DRAGON64 said:

Define augmented for us...

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since the post I have done a bit of testing and flying. the addition was a brushing of pyrogen around the base of the igniter tip. first fires. worked great and lit the motors well. The starters left alone might have done the job but i wanted to be sure of the cluster start. After thinking a bit I remembered guys making igniters with 2" long pieces of thermalite back in the mid 90's. No over pressure there.:y: Some have mentioned though that they have had a cato due to a presumed "hot starter" and im sure it happens . With some single use casings a slight over pressurizing could result in cato as with the reload casings."
Looking forward to Tucson Nov.16- more cluster fun

crazyed said:

In comparison, What advantage would there be using a home made thermalite starter for example over the supplied manufacturers starter? Understandably you would have control over the burn time- rate but aren't the supplied starters satisfactory.? After thinking about the last question - no they are at times not . So give em a little dip or a sliver of thermalite or what ever it is these days and continuity check everytime. As for clusters- another question--"would 3 or 4 motor clusters tend to provide a more vertical flight because of the configuration"? Or does it matter?
View attachment 245194

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I would say that a rocket that has an UN-intended flight path due to motor ignition issues has a design flaw somewhere. This is why on large rockets there are more times than not a central motor that ignites that has the capablity to get the vehicle off the ground at required speeds, then the cluster air-starts. Usually triggered by liftoff detection. Another problem you see is that people use too short of a launch rod. They use the same length guidance for a complex cluster that takes more time to light as they do a single motor. Additionaly, canting your motors toward the CG will help with off axis thrust in the event there are variances in motor performance, off timming, or failure to ignite.

planning a complex flight properly is about much more than just packing in energetics and trying to bounce the rocket up off the go button.


BTW, your mixture of BP and composite motors is NOT a good idea, unless you plan to airstart the bp motors... i have seen these go up about 20' on the bp motors (under powered) then the composites light and shoot the rocket at the crowd.

i would always say a larger central motor, and airstart a cluster around it. GO ALL BP , OR ALL COMPOSITE, dont mix the two unless you can airstart the BP...they often burn out before the composite comes up to pressure.

Thanks ClayD Actually I did fly that pictured configuration and it was a great flight, straight up and they all lit , But after the education ive been getting here on the rocketry forum, I believe it was pure luck the flight went that well all 4 burning off the pad.*** I do not intend on doing it again***. Also I have regular success with the G53fj and G64 clusters. For my Quick trip to the field launches I will keep trying and testing the cluster itch I have and fly the reliable clusters at the club launches for safety. Thanks for the insight and knowledge,
Havin a blast

Time for another cluster test Sunday. Im going to burn 2 G53FJ motors in the 4-29SS. If it it goes as my previous flights (both lit and straight up flt.) I will continue to use the FJ and G64W motors for this rocket when flying twin G's. Next will be 4-F20 , F27, or F42 motors in the LOC 4-29SS. Im thinking each(cluster rocket) will have different flight characteristics with different motor types. The starters will work- over pressure from starters doesnt seem to be an issue. Getting the motors to pressure at the same exact moment a bit difficult. So how the vehicle reacts to a slight variation in thrust and positioning of the motors and the over all design of the rocket needs further consideration.

Yep.. Those G53FJ's fired right and had another perfect flight.(Sunday Nov 16 SARA launch) Of coarse Terry had the "cluster buster" for positive Juice to the cluster. So far I have to say for the 4-29SS the G64 and G53 reloads provide great reliability for cluster launches (equipment and conditions considered) Pics of launch on SARA website /Flicker

Sweet! Great job. Fast Jack is great to cluster with. I did a G80T w/two G53FJ and they beat out the G80 by a long shot. It didn't light until about 50-100' I'd say. Used Q2s dipped in ClusterFire. It was a good ways up.

marcusSRG said:

Sweet! Great job. Fast Jack is great to cluster with. I did a G80T w/two G53FJ and they beat out the G80 by a long shot. It didn't light until about 50-100' I'd say. Used Q2s dipped in ClusterFire. It was a good ways up.

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Yep ,, Its awesome when they fire right and the smoke- sound with a straight up flight. Nice alltitude - Then good deployment and a long healthy hike to recover topping it off with no damage and the casings still locked in,,, by golly time for more:y: