OVER PRESSURIZED BY STARTER

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crazyed

crazyed

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Is there any danger of over pressurizing the case causing a CATO with starters that have been augmented to insure a good motor start?
(The 40-120 case with G-76 reload)
 
You know... when a rocketeer says "I augmented my igniter", it can mean anything from a little dip in pyrogen to attaching 4 pounds of thermite to the igniter... :p Just saying.
 
It depends.

A starter should provide enough heat over a specified period of time to begin a sustained burn for the motor.

There are mathematical formulae out there to help calculate based on the internal volume of the motor.

That said, "yes", it is theoretically possible to do this since you didn't specify what augmented means. Obviously, if a starter supplies pressure (as well as heat) and the total amount of pressure goes beyond the limits of the case, then something will let go.

A well designed starter will mitigate this risk.

Greg
 
ALWAYS check to make sure the 'starter head' (in the real world that's the igniter chip) will pass thru the nozzle unimpeded. Smaller gage wires (shooter's wire) with nichrome wraps are usually okay to go as the pyrogen deconflagrates only leaving the wire gage behind. Chip based starters can jam in smaller nozzles.
 
While you could have a problem if you did something totally crazy like packing the slot with thermite, the required amount of a good hot pyrogen won't be an issue. I have had 100% success on the loads for that case using 30ga twisted wire, conductive primer, and Magnelite pyrogen. The small Magnelite bridge wires works well also. Just make sure your wire isn't tight in the nozzle/slot. I have dipped too thick and had to build the igniter in as the motor was assembled.
 
If the augmentation produces a significant pressure wave (as in explodes) then it could damage the propellant resulting in an effective Kn much higher than originally intended. That can cause a CATO via overpressurization. Essentially, if you are hearing a report coming from the motor upon ignition, then chances are too much or the wrong type of augmentation is in use!

Gerald
 
crazyed said:
Is there any danger of over pressurizing the case causing a CATO with starters that have been augmented to insure a good motor start?
(The 40-120 case with G-76 reload)
Click to expand...

If the nozzle throat is small, the "starter" large then yeah, it could get stuck in the throat and cause overpressurization/CATO. I highly suspect one is talking about
staging here if using an "augmented" igniter or for drag racing?? Depends on how thick the pyrogen head it and how fast it burns. Kurt
 
I'm curious about this because 16 years ago... Thermite ignitors were standard fare where I launched. The table used to give out small clips of thermite and small gauge write to create our own starters or to include with copperheads... Since I've been back, I've seen no one using these. I'm not saying I still have some thermite clips, but....
Also, the First Fire starters seem to work fine for me so far. Wildman sells starters that are stupendous as well...
 
CzTeacherMan said:
I'm curious about this because 16 years ago... Thermite ignitors were standard fare where I launched. The table used to give out small clips of thermite and small gauge write to create our own starters or to include with copperheads... Since I've been back, I've seen no one using these. I'm not saying I still have some thermite clips, but....
Also, the First Fire starters seem to work fine for me so far. Wildman sells starters that are stupendous as well...
Click to expand...

Was it thermite or Thermalite?

https://en.wikipedia.org/wiki/Thermalite

Greg
 
thermite is generally speaking , a powder. I am not aware of anywere it can be purchased, only self-made. Lots of us use this form of thermite, but is not a good starter for smaller motors, very confinement sensitive, and mostly cause damage used in lower than a k sized motor. Thermalite, the stuff you ustacould buy in rolls, are out of production. you just cant source the stuff, but i have"heard" it makes great staging timers... thermite, is extreamly easy to initiate, thermalite, not so much.

A lot of research has been put into thermite, and how much to use per core volume. I have found it mostly to be voodo.
 
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.
 
crazyed said:
Is there any danger of over pressurizing the case causing a CATO with starters that have been augmented to insure a good motor start?
(The 40-120 case with G-76 reload)
Click to expand...
Absolutely possible, and quite likely if you have do not understand how igniters work.

Igniters need to supply a certain amount of energy per unit surface area in a certain amount of time to promptly ignite the motor. If you use significantly less than optimum, the motor will not ignite, and if you use significantly more than optimum the motor will explode from overpressurization.

The igniter supplied with a model rocket motor is sufficient to ignite the motor.

Bob
 
Copper thermite is not generally "easy" to initiate. It has a high heat of activation. BP is more dangerous relatively speaking.
There are ways to "doctor" thermite otherwise. It is not recommended unless one is willing to accept the risk.
 
Clustering G76G's I highly recommend going the cluster fire or magnelite direction.
 
ksaves2 said:
Copper thermite is not generally "easy" to initiate. It has a high heat of activation. BP is more dangerous relatively speaking.
There are ways to "doctor" thermite otherwise. It is not recommended unless one is willing to accept the risk.
Click to expand...
well, i guess that would mean that "easy" is a term of perception. my statement was in comparison between thermalite and thermite, remember copper thermite is 1 of many types of thermite, and different compositions of thermite are all different in the auto ignition temperature. (which is not required to cause initiation), some are static sensitive, and most of all thermites are again Powdered metals, which can "spontaneously combust" some are static sensitive, so I would always consider that to mean,... easy to initiate.
Any standard ignition bridge wire with 12volts is fine for initiating the common types of thermites.
 
Straight copper thermite, 12V nichrome bridgewire works. Must not use "real fine" powders or it can go off like a high order explosion. Must be course enough to
prevent that from ocurring. I know as that is exactly what happened to me many moons ago with some Ebay powders of questionable mesh. I was glad I was using launch electronics at a distance for the test. Those reagents went unused for rocketry purposes. Kurt
 
There are many forms of thermite. The copper one that seems popular is one of the more dangerous ones to use. It is more static and shock sensitive than many others, and burns explosively rather than progressively. It should not be stored but either used on the spot - or used on the spot. IMHO it is NOT an appropriate choice. If something goes wrong with preparation, handling, or use, you won't even have time to know it until it is over. There are far better choices.

There are also various pyrogen choices, commercial or EX, and of course pyrodex which works well and avoids lots of issues, where the motor is big enough to use it (75mm and larger, for instance).

Gerald
 
crazyed said:
Is there any danger of over pressurizing the case causing a CATO with starters that have been augmented to insure a good motor start?
(The 40-120 case with G-76 reload)
Click to expand...

Yeah, it is. Learned that one the boom way. The igniter passed the nozzle easy, and fit the grain easy. No thermite, just a standard igniter. BOOM!!


Christopher Short
Chris' Rocket Supplies
www.csrocketry.com
850-554-6531
 
A standard igniter giving a CATO on startup is not likely the igniter. It is likely something else that went wrong.

Gerald
 
marcusSRG said:
Based on my knowledge of twiggy's, that's a pretty fat pyrogen head to fit in an 18mm.
Click to expand...

Sandpaper.......You know, this was at least 6 years ago. Maybe it was a first fire from Aerotech. I honestly dont't remember what brand it was, just that it was a standard made igniter, that fit into the D21. Blew up instantly. The propellant grain never lit.
 
ksaves2 said:
Straight copper thermite, 12V nichrome bridgewire works. Must not use "real fine" powders or it can go off like a high order explosion. Must be course enough to
prevent that from ocurring. I know as that is exactly what happened to me many moons ago with some Ebay powders of questionable mesh. I was glad I was using launch electronics at a distance for the test. Those reagents went unused for rocketry purposes. Kurt
Click to expand...

G_T said:
There are many forms of thermite. The copper one that seems popular is one of the more dangerous ones to use. It is more static and shock sensitive than many others, and burns explosively rather than progressively. It should not be stored but either used on the spot - or used on the spot. IMHO it is NOT an appropriate choice. If something goes wrong with preparation, handling, or use, you won't even have time to know it until it is over. There are far better choices.

There are also various pyrogen choices, commercial or EX, and of course pyrodex which works well and avoids lots of issues, where the motor is big enough to use it (75mm and larger, for instance).

Gerald
Click to expand...

LOL, any other than "Real fine" powder isnt rocketry...
thermite slag hitting the pad....
attachment.php



whups.
attachment.php
 
G_T said:
There are many forms of thermite. The copper one that seems popular is one of the more dangerous ones to use. It is more static and shock sensitive than many others, and burns explosively rather than progressively. It should not be stored but either used on the spot - or used on the spot. IMHO it is NOT an appropriate choice. If something goes wrong with preparation, handling, or use, you won't even have time to know it until it is over. There are far better choices.

There are also various pyrogen choices, commercial or EX, and of course pyrodex which works well and avoids lots of issues, where the motor is big enough to use it (75mm and larger, for instance).

Gerald
Click to expand...

heres my last research flight , 76mm x 36.4" of propellant. this was lit with 4 muzzle loading bp/pyrodex pellets.
0.jpg
they slide right onto the ignition wire via the hole in the center. But, its also not an instant on....
[video=youtube_share;AO0QAvm5mbc]https://youtu.be/AO0QAvm5mbc[/video]
 
Can you get pyrodex pellets that are small enough to be used 54 mm or 38 mm reloads?
 
terryg said:
Can you get pyrodex pellets that are small enough to be used 54 mm or 38 mm reloads?
Click to expand...

you could use loose bp/pyrodex in a dooby ignitor. My thermite initiated j motor (38mm x 24" of propellant) had 1/2" cores, so an initiator and thermite dooby was used. Needed to use about 1/3 the amount of thermite i did. the only reason for doing this would be to pressurize the start-up, which may be a bad idea altogether.

But, the best way is to go with a slim gem from quickburst, or other diy ignitor of similar.

https://quickburst.net/slim_gem_igniter.htm for the cost of pyrodex pellets, and kits, these really cant be beat in my opinion. I have used these to light L motors with 3/4" cores.
 

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