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Hermetically Sealed Ejection Cap

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saadzmirza

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Hi,
I've been perusing methods to successfully achieve black powder ejection at high altitudes. Talking near-absolute vacuum... ~130,000-200,000 feet... less than 0.0001 atm.

I saw one taking some kapton and electrical tape to pressure-seal a normal ejection charge. Another was the surgical latex tubing.
This all has to fit in a 29mm airframe. Preferably 24mm.

Crazy? Yes.
Any help/suggestions?
 

tfish

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I played around this past spring with a new take on Jim Jarvis's method. http://www.rocketryfiles.com/files/Technicalarticles/Jim_Jarvis_Highaltitude_deployment_2013.pdf Jim's device is VERY ENERGETIC. I agreed with his method but wanted to soften it reaction and still consume 100% of the BP. Below is what I came up with. I was only able to get my vacuum chamber down to 27.5 during the 5 min vacuum soak phase. I did not find it necessary to seal them. The black tape at the top of the charge is just to hold "things" in place.

final.jpg
Tony
 

NateLowrie

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I played around this past spring with a new take on Jim Jarvis's method. http://www.rocketryfiles.com/files/Technicalarticles/Jim_Jarvis_Highaltitude_deployment_2013.pdf Jim's device is VERY ENERGETIC. I agreed with his method but wanted to soften it reaction and still consume 100% of the BP. Below is what I came up with. I was only able to get my vacuum chamber down to 27.5 during the 5 min vacuum soak phase. I did not find it necessary to seal them. The black tape at the top of the charge is just to hold "things" in place.

View attachment 303867
Tony
I agree with Tony. You don't need to seal it airtight. The BP contains it's own oxidizer so it will burn without you needing to keep in Atmosphere. The research Jim Jarvis was doing pointed to a longer metallic tube to contain the pressure long enough for the all of the particles to burn. If you don't want to go Tony's route I would take a 4-6" piece of 1/2" copper pipe with an end cap. Powder and ematch go in the bottom and you stuff with cellulose wadding and painters tape over the top. I've done my own testing on this in a vacuum chamber and recorded 100% of powder burned in the 10 test cases I've done.
 

saadzmirza

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4-6"?! Why not like 1", that way it's more compressed. A >1 pound 29mm rocket shouldn't need too much BP anyway.
(also, our whole payload bay is 12")

Thank you for being so helpful!
 

OverTheTop

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The idea of the long charge canister is to ensure all the BP is burned at altitude. High aspect ratio tubes seem to offer more complete burning of the powder.
 

NateLowrie

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4-6"?! Why not like 1", that way it's more compressed. A >1 pound 29mm rocket shouldn't need too much BP anyway.
(also, our whole payload bay is 12")

Thank you for being so helpful!
The length is to allow complete combustion. If you start shortening it you will end up with some of the powder scattering out the tube before burn. You can probably make the ID smaller. 1/4" brass should work for a small charge. I normally mount mine right against the wall of the airframe and pack the chute next to it.

In your case Tony's method may be a better choice due to space. Make sure you are using vinyl tubing as indicated by tony.
 

saadzmirza

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How about using a MICROMAXX motor installed backwards in the upper bulkhead for ejection? It's compressed.
 

Incongruent

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I think the burn could be too long, you might end up with frayed or burned-through shock cords and stuff.
 

rharshberger

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I think the burn could be too long, you might end up with frayed or burned-through shock cords and stuff.
+1, its the granular nature of FFFFg BP that allows it to burn so rapidly, in a motor grain it can only burn from one end so it does not create enough gas rapidly enough to be good for ejection purposes.
 

rms

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I played around this past spring with a new take on Jim Jarvis's method. http://www.rocketryfiles.com/files/Technicalarticles/Jim_Jarvis_Highaltitude_deployment_2013.pdf Jim's device is VERY ENERGETIC. I agreed with his method but wanted to soften it reaction and still consume 100% of the BP. Below is what I came up with. I was only able to get my vacuum chamber down to 27.5 during the 5 min vacuum soak phase. I did not find it necessary to seal them. The black tape at the top of the charge is just to hold "things" in place.



View attachment 303867
Tony
What size charge do you have in that 3" piece of tubing Tony?
 

tfish

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0.5g for my 3" rocket.

Tony
 

tfish

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That is kind of large for that size charge, but if it works that is what matter.
With other charge containment methods, I would use 1.25g or more for my 3" rockets. I've found this current method to us very little compared to other methods. This method is more efficient (consumes a larger % of the BP) and is more direction then other methods.

That's why ground testing is very important. Just because Joe Blow uses 2.5 grams in his 4" Mega Raptor, does not mean it will also work for you with your containment methods. You could either break your shock cord or barely get it to separate.

simple things like igniting it from the bottom or on top make a difference.

Tony
 

markkoelsch

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With other charge containment methods, I would use 1.25g or more for my 3" rockets. I've found this current method to us very little compared to other methods. This method is more efficient (consumes a larger % of the BP) and is more direction then other methods.

That's why ground testing is very important. Just because Joe Blow uses 2.5 grams in his 4" Mega Raptor, does not mean it will also work for you with your containment methods. You could either break your shock cord or barely get it to separate.

simple things like igniting it from the bottom or on top make a difference.

Tony
Tony, I am not arguing with the results. I was just surprised at the length needed for that size charge.

Where do you place the ematch within the charge? Is it in the middle?
 

Steve Shannon

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Tony, I am not arguing with the results. I was just surprised at the length needed for that size charge.

Where do you place the ematch within the charge? Is it in the middle?
Ahh, I took your original statement to mean that the rocket was kind of large for that size charge, not the charge container.


Steve Shannon
 

tfish

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Mark, Sorry for the confusion on your question. I place my ematch on top of the pile of BP. I'll give some history, then I'll state what I think is really happening (albeit non-scientific terms) I'm the guy that came up with the surgical tubing charges, Up to that point getting consistent deployment at high altitudes was iffy. The guys that seem to go well, at recovering from high altitudes seemed to a lot of BP. High altitudes (back 20) ago seemed to be flights of 20K or better. Yes, some colleges, Mark Clark, Frank and others had some really high flights. I did my L3 about 18 (?) years ago and went to 19,696 which at that time was a pretty high L3 cert flight. By the way I'm fortunate in that Black Rock is my "home field" For the longest time I just used charges in the tips of fingers from Latex gloves. I can't really recall what happened to make me look into a different confinement methods. I'm guessing the loss of a rocket or two! So my buddy Steve and I made up and 6" PVC vacuum chamber. I was testing things that I had seen on some of the college high altitudes shots. They were a lot like those big fire cracker things 80M (misspelled on purpose) As a professional Firefighter, I did not feel good about making or putting those sorts of things in my rockets. We did test some of them. They tended to scatter the BP all over the place along with all the parts of the charge "holder" too. We even tested an Estes B engine at a simulated 70K altitude. It lit fairly quickly but had way to much fire inside and outside the test chamber. Yep it ended up outside the test chamber on one test! I managed to extinguish the fire (yep we caught stuff not involved in the testing o fire. I guess now would be a good time for ...Kids, if you've read to this point please do not be like me! Don't play with fire!...So, at this point all of our test sucked. We had always heard that the reason for BP not working was that there was no 'air' for the BP to burn. Or it was to cold for the heat to transfer etc. I got to thinking. BP has it's own "air" and it's not 'up in the cold long enough to matter. It had to be a container issue. I used to race control line airplanes and we used to use surgical tubing for fuel bladders. We would use a syringe to fill the bladder with fuel and it was like the motors were on crack..sorry kids, just say no to drugs...So, I made up some BP charges using latex tubing. They worked really well. At the time I figured we had found a way to burn 100% of the BP at high altitudes. The highest altitude that I know of where the latex tubing charges were used was the 104K
Over the years I would hear of a project or two where the latex charges did not work. Jim Jarvis had written up a paper on some of the tests he had done on BP at high altitudes. Jim found that they were not consuming 100% of the BP and that the % at times, was really not good at all. Jim came up with his copper pipe containment system that is pretty slick. So, a year or so ago I made up one of his systems and did some ground testing. In Jim write up http://www.rocketryfiles.com/files/Technicalarticles/Jim_Jarvis_Highaltitude_deployment_2013.pdf Around page 9 Jim makes a statement that his confinement system is VERY ENERGETIC. After my first ground test, which luckily was not in a rocket but out on the ground, there was no way one of my crappy rockets could withstand that! I put the stuff aside while I figured out what was going on and why.

The following was, and still is what I think is going on when we use BP for ejection charges. BP has it's own "air". Our (at least my rockets) rockets don't spend enough time in the cold to have much of an affect on the BP converting into gas. The issue has to do with confinement and length of time that the BP is confined. I'm not using the word confined as in sealed. I'm using confined as in keeping the BP in close proximity to itself, each grain close to another. I'll talk about guns for a bit now. I know that guns with longer barrels shoot better then those with short barrels because the gun powder has more of a chance to be used up. So, a long skinny tube is better then short fat tubes for more complete consumption of the BP. Less will be scattered and not burned? Now where to put the match. Placing it at the bottom of the pile will start the process and start the burning pile towards the end of the barrel. Maybe some will not be actually burning by the time it reaches the end of the barrel? Now take that same pile of BP and put the match on top of the pile? The top catches fire and that gas heads for the exit while the piles is consumed it all has to pass the fire to escape out the open end of the tube? So why vinyl tube and dog barf. That's my attempt to make this type of ejection charge system not so violent but still use the "gun barrel" confinement method. I feel that the vinyl tube will expand some during the burn. The dog barf at the plugged end (hot glue plug) should help cushion the shock that way. The dog barf at the open end mainly holds the ematch and BP in place. The electrical tape just keeps things from spilling out. I found that it does not need to actually seal the air inside the tube.

Also, this type of devise actually directs the gasses in a useful direction..and not just filling the body tube with gas.

Always ground test...

If I had to pick a number where to start thinking about high altitude issues it would be 23K MSL.

That's my story and I'm sticking to it...

Sorry for the gramer and spelling issues!

Tony
 
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rms

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0.5g for my 3" rocket.

Tony
Tony I tried your charge containment method today and used .5 grams which would be significantly less than other methods I have used for charge containment. I experimented in a ground test of my 4" HED nosecone deployment. I used rocket proxy instead of hot melt glue as I had some mixed up anyway, I think it worked great as well. I didn't bother attaching the recovery harness to either end as I figured .5 grams probably won't be that much. My thinking would have worked with normal methods but not with these. Boy I was wrong! It shot the nosecone 75'! That method of containment is certainly energetic! Like WOW energetic.
More tests to come for sure.
Thank you for sharing your method. I think they are certainly worth persueing further.

Greg
 

tfish

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Greg, Glad to hear you had similar results to my tests. My actual vacuum chamber tests were the same out of the vacuum chamber, using my simulated electronics bay rocket body "thing". I guess it really matters what your ejection charge containers "shape" is and ematch placement to get the most out of your BP.

Tony
 

Incongruent

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The more energetic ejection is caused by the containment on the BP. Since it's sealed up in a container that won't fail under low pressures, the black powder can build up pressure and temperature, which accelerates the reaction and when the container fails, provides a large amount of gas much quicker than conventional methods of charge holding. I can't quite remember but it might be because the flame travels between the particles as well as speeding up the the reaction. The same principle is used by firecrackers. (though most use flash powder nowadays since it provides a sharper bang and brighter flash) (as well as other things) If you pour a line of black powder and burn it, the flame travels comparatively sluggishly as the pressure and temperature can't build.
 

rms

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The more energetic ejection is caused by the containment on the BP. Since it's sealed up in a container that won't fail under low pressures, the black powder can build up pressure and temperature, which accelerates the reaction and when the container fails, provides a large amount of gas much quicker than conventional methods of charge holding. I can't quite remember but it might be because the flame travels between the particles as well as speeding up the the reaction. The same principle is used by firecrackers. (though most use flash powder nowadays since it provides a sharper bang and brighter flash) (as well as other things) If you pour a line of black powder and burn it, the flame travels comparatively sluggishly as the pressure and temperature can't build.
I am aware of the why they work but Tony has come up with a relatively easier way to accomplish this containment than Jim Jarvis's method. Although to be fair, I have not tried Jim's method. Both Tony and Jim have my respect for there experience in these matters.
I'm sure you are a very smart young fellow but unfortunately experience trumps all!
 

Incongruent

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I am aware of the why they work but Tony has come up with a relatively easier way to accomplish this containment than Jim Jarvis's method. Although to be fair, I have not tried Jim's method. Both Tony and Jim have my respect for there experience in these matters.
I'm sure you are a very smart young fellow but unfortunately experience trumps all!
Sorry, I interpreted the later parts of your comment as concerning the principle rather than the method.
 
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