Alternative Igniter

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Could it work?

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Lefield

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Hello All,

I was thinking of planning some testing for an igniter design but wanted some feedback about my idea first.

I was watching slow motion YouTube videos when I came across a couple slo-mo clips of a shotgun primer going off,

Watch starting at 1:58 m,

Watch starting at 5:00 m,

It got me thinking of mounting it in a bulkhead and pointing the business end down my fuel core, to use as an igniter for my APCP fuel. At a glance, the volume and rate of gas produced does not look significant enough to cause a CATO. Though, I'm not certain where it would fall within the bounds of reliability and effectiveness in terms of being too much or too little.

Thanks for your thoughts!
 

MClark

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How are you going to fire the primer, (firing pin assembly)?
A primer firing directly into grain is likely to damage the grain. Primers fire very fast, typically a motors light better with a more persistent igniter.
Some ejection seat motors are fired by small pistol primers but there is a lot of stuff between the primer and motor grain.

M
 

Steve Shannon

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What problem are you trying to solve? The igniters we have work very well and are compatible with the launch systems we have.

Like Mark, I doubt that enough heat would be transferred from a primer to ignite propellant, but it would work well for ignition of ejection charges.
The other day I received an “offer” (okay, spam) for a “survival fire starter” that uses “2000° plasma”. I confess I did wonder about using it to light motors.
 

rharshberger

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For those who are into ammo reloading, there is a story from many many years ago about an individual who worked in a primer factory moving primers from one area to another in a bucket, the dust from the primers inside the bucket detonated leaving very little of the individual to be found. While the story is most likely a wives tale, it does serve to demonstrate the power of priming compounds, they are very sensitive and detonate unlike our igniters which burn, they also create enough shock that damaging the grain is possible which can increase burn rate and pressure to the point of motor cato.
 

jqavins

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Igniters traditionally employ combustion.

Rocket motors employ combustion.

Ejection charges employ combustion.

Primers employ detonation.

Every time people talk about a rocket motor burn as a controlled explosion we are quick to correct that notion, and often point out the trouble that representatives of our hobby had convincing the BATF of that, an effort that had to go to court.

You are proposing to use a detonation device as a part rocket launch. My opinion is that you should absolutely not go there, for these reasons as well as the technical ones like maybe not reliably lighting the motor die to insufficient heat and/or has not reaching the top of the stack, and the possibility of cracking the grains.
 

Alan15578

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I think Aerotech knows how to do that, so ask them. In any event our rockets still need to be "started" electrically, or at least remotely.
 

Lefield

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Igniters traditionally employ combustion.

Rocket motors employ combustion.

Ejection charges employ combustion.

Primers employ detonation.

Every time people talk about a rocket motor burn as a controlled explosion we are quick to correct that notion, and often point out the trouble that representatives of our hobby had convincing the BATF of that, an effort that had to go to court.

You are proposing to use a detonation device as a part rocket launch. My opinion is that you should absolutely not go there, for these reasons as well as the technical ones like maybe not reliably lighting the motor die to insufficient heat and/or has not reaching the top of the stack, and the possibility of cracking the grains.
I see, the chemical rate of reaction is very important to you. Must stay within the speed limit. Hmm, well it's a good thing I'm not talking about rocket fuel then, but a legal and commercially available product (with a FOID card).
 

tomsteve

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I see, the chemical rate of reaction is very important to you.
no, the chemical rate of reaction is important in motor ignition and not only in the model rocket community.
im willing to bet that in the past 100 or so years there was more than one rocket scientist that tried primers for motor ignition.

anyone come up with a better wheel??? sure seems round one could be improved on.:)
 

ksaves2

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Ummmmmm, if really stressed, just buy a commercial igniter dip and/or go on the “dark side” on the internet and research igniter mixtures. You’ll find it’s more economical (and easier) to purchase an igniter mix online. I know ‘cause I’ve done both. If you have money to diddle with fine, if not go commercial, follow the instructions and you’ll be fine. Ematches? Stay away from the kits. I never had any luck until I rolled my own blanks and made my own dip. After I saw the cautions on the dip, I only made milligrams amounts and was extremely careful about wiping the lip of the jar of the container that held the dip so I could dip some more “next weekend”. Never hurt myself even though I threw a micro sized bottle of dried out ematch dip into a bonfire. It blew even through there was only a couple of milligrams of dried dip and the glass was contained by the logs on top of it. The bottle was about the size of on old Testors enamel bottle (showing my age). The bottom though blew out the side of the pile fortunately away from me. Can’t discuss recipes here but for ematches it’s the same thing used in the cap guns “us” kids from the 1960’s had. I never forgot that smell after they “popped”. Got to re-initiate myself after I took a sledge hammer to smash the end of a dried toothpick I used to stir the ematch dip with. I indeed had face protection on but there was a “pop” and the smell of childhood was liberated. The same recipe for “caps” for cap guns from the old days is the same for ematches folks.
Kurt
 

Lefield

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no, the chemical rate of reaction is important in motor ignition and not only in the model rocket community.
im willing to bet that in the past 100 or so years there was more than one rocket scientist that tried primers for motor ignition.

anyone come up with a better wheel??? sure seems round one could be improved on.:)
You are correct. I know it's important. However, it may be accounted for through various design specifications. I'm not trying to make a better design, just a different one.

I've noticed that igniter design is similar, in terms of shape and function.
 

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Oberon

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Combustion rate isn’t “important”, it’s essential. To light AP motors you need a hot, relatively long burn at relatively low pressure. The goal is to transfer a lot of heat in a short but nonzero time. The very biggest AP motors on the side of the Space Shuttle / SLS use basically a smaller rocket motor (roughly the size of a beer keg) to light them, not a bomb.

A shotgun primer is a supersonic blast wave - extremely fast, very high pressure, minimal heat transfer. There are some propellants that can light via detonation (smokeless powder in a confined area being one of them obviously) but AP based rocket fuel of the type used for our hobby is not one of them.

Lighting a hobby rocket motor with a primer is like trying to light a bonfire with a starter pistol... it could maybe be jimmied to work under the perfect circumstances, but it’s more dangerous and much much harder than just using the right tool for the job.

For another example, one of the more common igniter failures in HPR is when an igniter over-pressures and pops itself out of the motor before the fuel lights. A primer would be that times a hundred.
 

BABAR

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Combustion rate isn’t “important”, it’s essential. To light AP motors you need a hot, relatively long burn at relatively low pressure. The goal is to transfer a lot of heat in a short but nonzero time. The very biggest AP motors on the side of the Space Shuttle / SLS use basically a smaller rocket motor (roughly the size of a beer keg) to light them, not a bomb.

A shotgun primer is a supersonic blast wave - extremely fast, very high pressure, minimal heat transfer. There are some propellants that can light via detonation (smokeless powder in a confined area being one of them obviously) but AP based rocket fuel of the type used for our hobby is not one of them.

Lighting a hobby rocket motor with a primer is like trying to light a bonfire with a starter pistol... it could maybe be jimmied to work under the perfect circumstances, but it’s more dangerous and much much harder than just using the right tool for the job.

For another example, one of the more common igniter failures in HPR is when an igniter over-pressures and pops itself out of the motor before the fuel lights. A primer would be that times a hundred.
Agree.
For the most part, electrically activated igniters produce mainly heat, relatively little expansion/blast. Your proposing the opposite, I'd be considered it would blow the rocket off the pad without lighting it, and/or blast might damage the clay nozzle.

Nothing wrong with thinking outside the box. In this case, though, if it works well (electrical ignition), don't fix it.
 
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