Ejection delay composition?

[hcb]

Determination is very good, hah ha. Your CP/CG issue is a true issue that needs correction or you're going to have an eventful launch, guaranteed. Model rockets are light--the heaviest thing in the is the motor/mount. So nearly doubling the length of your motor/mount is going to add a lot of weight and drag the CG backwards, as you've seen. CP/CG approximation is worrisome; reversal is a guaranteed rodeo! Overlap is a problem. Reversal by 6 mm is a bigger problem. Since you're successfully lifting 4 foot sticks high with your motor (very cool--congrats!), and those sticks probably probably weigh as much as your empty rocket, then you can probably afford to add some weight up front and fix your stability conundrum. Or glue on 4 additional thin mini-fins between the existing ones (crude, but slightly effective; similar effect as having bigger fins, but again you're adding a little weight in back).

 

In terms of assessing thrust, a cheap digital kitchen scale and a digital camera watching the scale readout is as complex of equipment as you need. You know how many frames/second your camera records in, so you can calculate and graph thrust/time frame-by-frame to get max and average impulse and total burn time (and delay time). Easy. Just put camera behind a piece of plexi if it's an expensive one to protect it in case of CATO, just in case. Cheapo action cams work well, too, and can be considered disposable.

 

When I switch from endburners to coreburners, I use the same tubes and BP components, just different spindles/rammers and BP component ratios. Dial those in and you're golden. And at a good place from which to experiment with alternative fuels. Beware full coreburners in model rockets--they tend to rip the fins off at takeoff, but that too is always fun to watch, hah ha!. I use 75/15/10 for endburners (even with a "small" core) and slower 60-65/25-30/10 K/C/S for coreburners. This is pretty typical for most folks using decent charcoal and a mill.

 

You're clearly a bright dude and making great progress, and really thinking through your modifications. But your first Patriot launch will be a hell of a lot more rewarding if you adapt your construction to accommodate the immutable laws of physics, instead of ignoring them. But it's always a blast to watch a missile do a spiral parabola into the dirt, just before it ejects its body tube skywards from its buried nosecone, kak kak!!! But generally, speaking, you don't plan those occurrences in advance :+} Hell, you might even get away with a clean flight--but I accept your $1 wager, hah ha!! Actually, I'd pay a buck to watch the video, so I'm guessing you're gonna break even!

 

Have fun. Can't wait to see the video!!! Consider wearing a motorcycle helmet in case your Patriot decides to intercept your melon!

 

I'm tenacious. And hard-headed. And sometimes I don't mind failure. And sometimes I take chances, but I consider the costs of failure. And I *will* be addressing the CG/CP problem before that first flight. I hate rodeos. Recovery deployment...well...that package is wrapped and I'm flying it, as is. Yes, that stick is *heavy* (for rocket stuff). I don't have an appropriate scale here at home or I'd have weighed it. I'm trying to get OpenRocket to run on my laptop. I'm having to install the JRE (java runtime environment). Always hoops... I'll try to make up a model in OR.

 

Yeah, I suppose I could do the really easy thing of videoing the motor on a scale. Why can't I think of simple stuff like that? I have a $45 GoPro knock off right here. :-| I tend to think in the box sometimes. Understood re frame rate/thrust curve/impulse. Wish I'd have thought of that days ago.

 

Understood re mix ratio for the core-burners. I take that as a "no" on retarding the full-strength BP. The core-burners will be for fireworks rockets only. I've always wanted end-burners to replace the Estes motors in model rockets (if they can do it, so can I type thing). I always thought of core-burners as a band-aid for poor rocket fuel. I realize now that they have a place for fireworks rockets where lower height and greater lifting power are desirable.

 

I have my moments on my "brightness". I offset them with some really dim moments, too. No law of physics will beat me! Kidding, I will be handling that CG/CP thing before flying the rocket and apologize if I came across in an earlier post as if I didn't fear CP/CG order issues. Recovery deployment? I'll gamble on that a time or two. CP forward of the CG? No, that's gonna tumble, virtually guaranteed to not go in a straight line. But the launch will be smart and crisp. Pretty sure. I did notice that my test motor on a stick did fracture out a bit of the bottom end of the nozzle. I wonder if the graphite in the mix was a bad idea. That's the only question I have in the first part of the trip, the going up.

 

I'm looking forward to shooting the rocket and the video. Maybe tomorrow but I don't like to make commitments, my schedule is fluid and it's been raining here off and on for days.

 

--HC

[hcb]

Sorry, missed this before.

 

If it's been tried before, nobody's ever told me about it. Perhaps it's possible, but I'd stick with what's proven to work. Here, and again it's an interesting idea, it's a little like reinventing the wheel, and spending valuable time that you could use to perfect your Dragon Eggs (you'll become addicted quickly to DEs and crackle!).

 

Plus, it's likely a different story between screen bicarb to your dry BP for a delay (where 110% complete mixing isn't life-or-death) and versus incorporating bicarb into your BP in the mill--if wet granulating it, I'd be worried about the equilibrium point of a potential exchange reaction between KNO₃ and your bicarb, both water soluble. Inorganic chemists out there, advise, please. Because, if so, although potassium bicarbonate is used as a fire suppressant (Purple K) by thermal decomposition at pretty moderate temperatures to potassium carbonate while releasing CO₂ and water (hence fire suppression), similar to sodium bicarbonate thermal decomposition, they likely occur at different temperatures and kinetics. Regardless if it's potassium carbonate or sodium carbonate that is a burn product, I'm pretty sure either would slag the hell outta your nozzle if included in the entire fuel grain instead of only the much shorter delay composition where it doesn't really matter. Also, if this exchange reaction does occur, sodium nitrate, though a good oxidizer, is much more hygroscopic than KNO₃. Also, if an ion exchange occurs during BP wetting, at least in my hands it would likely be impossible to predict how much from batch-to-batch. For BP granulation, my wetting volume, time of kneading, and time/temperature/speed of drying are all empirical, so who knows what the final comp would precisely consist of. BP Soup.

 

I could find no reason to unnecessarily abuse my beautiful 3-component rocket fuel BP, made with lovingly selected and processed willow charcoal of the finest pedigree, by adding a barbaric adulterant like sodium bicarbonate (except for delay comps). Apart from being a recipe for extreme slagular/CATO frustration, the idea is simply sacrilegious! You'd be effectively re-inventing the BP wheel, but starting with an unpredictably oval design!

 

In short, go with what has worked for an eternity. Just manufacture your beautiful BP as you already do for your endburners, with the only adjustment for making core-burners being the oxy/charcoal ratio modification.

 

Phew.

 

If there is a firework that I want to create it's whatever is the in the commercial shows (and some stand fireworks) that crackles. Launch, rise, break, maybe tails from dozens of stars, then a raucous, simultaneous crackling from all of the stars. Sometimes it seems the stars may wiggle or spin as this noise is emitted. I like those. Kind of paints the whole area of the sky at that moment.

 

Okay, so, I got As in Chemistry...but that's been a hot minute. I get that the baking soda isn't a cure-all answer to retarding BP. I can follow along with the chemical discussion enough to understand some of the complexities. Okay, I'll go back in the garden and eat worms and not put baking soda in my fuel mix. You make a good point about the slag, too, by the way. I'll try some of the 60-65/10 KNO3/Sulfur (balance charcoal) mixes, thank you. I don't want to reinvent the wheel, and you're saying oval designs are bad, so no Fords. That's harsh.

 

I'm having better luck with my ERC charcoal from bedding chips than from my willow charcoal which I harvested myself. There are several variables, this is not holy writ. Just sayin'. FWIW.

 

"Slagular"

 

Thanks for the time and info (always).

 

--HC

[Mumbles]

No worried on the exchange reaction between potassium nitrate and sodium bicarbonate. It wants to stay that way. If it was a problem, there'd be a whole lot of glitter formulas in trouble.

 

I don't mean to discourage you, but 5 seconds for ~1/8" seems like a really long time to me. It is however probably good for model rocketry. If you make more pyro based rockets, I doubt you'll ever need anything that long. Your base, the 50:50 nitrate to charcoal is almost the same as Shimizu's Chystanthemum of Mystery. It is popular as a delay for a few very prominent builders. It is a rather unique effect that is quite beautiful. It's just not something you tend to see with other compositions, or ones containing sulfur at least. Worth a try at night sometime if you get a chance. A little titanium makes it a little easier to track in the night sky and adds a different dimension to the effect.

[SharkWhisperer]

No worried on the exchange reaction between potassium nitrate and sodium bicarbonate. It wants to stay that way. If it was a problem, there'd be a whole lot of glitter formulas in trouble.

 

I don't mean to discourage you, but 5 seconds for ~1/8" seems like a really long time to me. It is however probably good for model rocketry. If you make more pyro based rockets, I doubt you'll ever need anything that long. Your base, the 50:50 nitrate to charcoal is almost the same as Shimizu's Chystanthemum of Mystery. It is popular as a delay for a few very prominent builders. It is a rather unique effect that is quite beautiful. It's just not something you tend to see with other compositions, or ones containing sulfur at least. Worth a try at night sometime if you get a chance. A little titanium makes it a little easier to track in the night sky and adds a different dimension to the effect.

HC, you just got word from a true master. Dude know chemistry and dude knows pyro. And Mumbles, you're right about that being a slow burn time even for model rocket motors. 1/8" in 5s is a smoulder. I'd want it a little perkier. Like around 4-5x that speed.

[PyroGround]

This ties in with my "finishing steps" on the BP motors but I thought it would be worth asking as a separate thread just to keep it clear and easy to find.

 

What composition should I use for the delay from the fuel grain to the ejection charge? This is on end-burners, so just stacking more fuel on top of the spindle/core isn't going to work.

 

I tried a quick test: milling some 60% KNO3 and 40% charcoal but it was still pretty quick. Only tested it once in a tube and that was on a motor I flew so I didn't get very good data. I'm going to tackle this in the shop on my next visit so I'd like to be prepared. I've read from the Skylighter article on Estes motors to use 47% charcoal, 47% KNO3, and 6% sulfur, so, unless directed otherwise here, I'll try that, too. I need to do some testing under more-controlled conditions.

 

Any suggestions of what other composition(s) I should consider? Any documented or rule-of-thumb burn rates for them?

 

Thank you.

 

--HC

Do you have tried using the 75/15/10 mix? I usually use this composition for my 15mm core burner motors, and I have obtained very good results. I normally ballmill the ingredients 1h/cm of delay.

I attach you a video of one of the first tests I did. I hope I've helped you

https://www.youtube.com/watch?v=jMUjFopAfbA

[shockie]

I think Estes uses 3F Black Powder for it's ejection charges:

 

F (1F) powder is the corses giain avaiable. good in large bulk items like artilery guns .

FF (2F) powder is good for canons and shot gun loads. It is ground smaller than F powder.

FFF (3F) powder is ground finer than 2F is and is used in rifles and pistols from .30 to .62 cal. It has a lower ignition point than 2F and will burn faster also.

FFFF (4F) powder is used in flint locks for priming the flash pan. It is ground finer than 3F and has even a lower ignition rate and will burn even faster than 3F.

Embedded in the top of the delay fuel was a 1/8-inch layer of granular black powder ejection charge. When scraped away from the rocket engine's delay fuel grain, this ejection charge weighed 0.5 grams.

https://www.skylighter.com/blogs/fireworks-information/black-powder-grades-sizes-mesh

[shockie]

https://pyrodata.com/composition/burst-charges

 

I think burst charges and ejection charges are more or less synonymous with one another.....one is a pyro term while the other is a model rocket term