Ejection delay composition?

[hcb]

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

[SharkWhisperer]

You can up the fuel and/or decrease the oxidizer, as this formula represents.

 

Or you can add a variable amount of an inert (at burn temps) substance like sodium bicarbonate (baking soda; dirt cheap). Start at 10% and watch your BP become tamed...

 

Adjust fuel/oxy or add burn inhibitor: Same effect.

 

You want a known burn rate, and the only way to discern this is to test it. Whether packed into a tube (rocket motor or spolette), it is a simple thing to measure the burn time of any given formulation to get a seconds/inch or seconds/cm value. Then just stick with it. Simples.

Edited March 15, 2020 by SharkWhisperer

[Arthur]

http://www.thegreenman.me.uk/pfp/other.html#Fuse

 

Includes some fuse formulations, shows how similar they are, and a few differences. AVOID the formula with realgar -it's too toxic for modern use.

 

 

Formulae close to the stoichimetric tend to burn faster, adding inerts makes compounds slower. Hard packing forces the unit to burn from the end rather than through between the grains. Ultimately a curl of visco will burn along it's length and fit more delay than a straight visco into a short length of rocket body

[hcb]

You can up the fuel and/or decrease the oxidizer, as this formula represents.

 

Or you can add a variable amount of an inert (at burn temps) substance like sodium bicarbonate (baking soda; dirt cheap). Start at 10% and watch your BP become tamed...

 

Adjust fuel/oxy or add burn inhibitor: Same effect.

 

You want a known burn rate, and the only way to discern this is to test it. Whether packed into a tube (rocket motor or spolette), it is a simple thing to measure the burn time of any given formulation to get a seconds/inch or seconds/cm value. Then just stick with it. Simples.

 

Okay, so I tried some BS (baking soda, not calling B.S.). I measured out 5 grams of 50/50 KNO3/charcoal which I had milled at 60/40 but was too fast for delay. I added 10% (0.5g) which *clearly* looked to be too little (I trusted my eye <snicker>) and then kept adding until I hit 40% (2g) of BS. Still not believing it would do all that much, I pressed about 3/16" (compacted) into a piece of an old motor casing (1/2" ID) and put some loose BP after that and then a bit of paper towel to keep it there. I taped a fuse to the bare end of the compressed 50/50 KNO3/charcoal now plus 40% BS and lit it. I thought nothing was happening and my 8 Y.O. son and I were kind of chatting about it not working when, long seconds later, it popped! SCORE! This is the kind of delay I was looking for!

 

Thanks for the tip, that is awesome! I tried a couple times to get one to work for my wife when we got home and it failed to light off the fuse. I had to ignite it with a torch briefly and then it did its thing. But I'm sure that, if it was pressed up against the fuel grain, it would ignite with no problems.

 

My only hope on the delay time was that maybe someone would have a pet recipe of (x%/y% and it burns at z-rate). I think this will be slow enough to do anything I want to do. I will have to do some testing but, on the second one which I did at home, when I remembered to start counting, I still counted 4 seconds before it popped. So, maybe 6 seconds from about 3/16" thick packed material. I'm talking out of my butt a bit because I didn't really study it closely. I need to do more careful tests and observations. But the result is definitely in the ballpark of what I am looking for.

 

Thank you again!

 

--HC

[hcb]

http://www.thegreenman.me.uk/pfp/other.html#Fuse

 

Includes some fuse formulations, shows how similar they are, and a few differences. AVOID the formula with realgar -it's too toxic for modern use.

 

 

Formulae close to the stoichimetric tend to burn faster, adding inerts makes compounds slower. Hard packing forces the unit to burn from the end rather than through between the grains. Ultimately a curl of visco will burn along it's length and fit more delay than a straight visco into a short length of rocket body

 

That's some cool information on the formulae. Understood re realgar.

 

I think I found what I was looking for with the suggestion above re baking soda. Preliminary testing looks great. I will, however, still tinker with some of those forumulas (which I guess is "formulae" to be correct). The Dark Fuse II looks interesting.

 

Thank you.

 

--HC

[SharkWhisperer]

QUOTE:
"My only hope on the delay time was that maybe someone would have a pet recipe of (x%/y% and it burns at z-rate). I think this will be slow enough to do anything I want to do. I will have to do some testing but, on the second one which I did at home, when I remembered to start counting, I still counted 4 seconds before it popped. So, maybe 6 seconds from about 3/16" thick packed material. I'm talking out of my butt a bit because I didn't really study it closely. I need to do more careful tests and observations. But the result is definitely in the ballpark of what I am looking for.

 

Response:

It's difficult to provide an X%/Y% standard recipe because everybody makes their own BP and they are by no means identical. This highlights the importance of BP and technique consistency--if you're milling small BP batches, you might want to combine them to get a large pool of BP with known burn characteristics.

 

Just to be sure your delay isn't too slow (hard to ignite), it might be smart to press some straight BP against your delay to ensure fire transfer to the delay 100% of the time. I'm sure you're probably ok, but fuse should really have lit that mix up repeatedly. In the Skylighter article on building Estes-like motors, the ejection charge on a commercial E9-6 motor (6 seconds delay) was approx 1/2" long. He used a standard Tiger Tail star formulation for the delay in the new builds, which is 47% KNO₃, 47% charcoal, and 6% sulfur, screen mixed through a 40-mesh screen, dampened slightly and dried. His burn rate was 1 second per 3/16", and the delays (not propellant) was simply hand tamped (not rammed or pressed) and covered with a paper disk and masking tape (cardboard end tube and glue would work best he figured). Meaning clay probably not necessary as an endcap, though might be better for long-term storage.

 

The sulfur lowers the compound ignition temperature and facilitates ignition (just like in regular BP). Might be useful if your bicarb cools off the delay a bit too much (or you could just drop to 30% and measure burn rate. 40% seems like a lot to me. For endburners, I use regular hot BP (with 10% sulfur) and dumb it down with 20% bicarb, and get appropriate delay (I test each batch, and adjust volume instead of bicarb % to get desired delay--batches are usually pretty close to one another, thus results). For E/F-sized motors, I use around a half gram of hot BP granules (20-40 mesh) for the ejection charge, with good results. Maybe a little more for longer or fatter rockets. No compaction required (or desired) and two paper endcaps fit without glue, so pressure build-up is sufficient to blow endcaps but not rear nozzle, though I doubt that would happen anyways with a half gram or gram vented BP deflagration. Just want most of that smoke and gas blowing forward. You can add a round cardboard baffle with holes drilled throughout in your body tube if worried about minimizing the likelihood of excessive hot particles frying your retrieval gear (chute/lines...), but I usually only do that in long (e.g., 3-foot) rockets where my ejection charge is larger to accommodate the larger deadspace to the nosecone (or you can break your rocket in half and have it blow in half, controlled, instead of the distant nosecone--easy to do with an inner adapter tube to connect top/bottom body tube sections.

Edited March 16, 2020 by SharkWhisperer

[hcb]

QUOTE:

"My only hope on the delay time was that maybe someone would have a pet recipe of (x%/y% and it burns at z-rate). I think this will be slow enough to do anything I want to do. I will have to do some testing but, on the second one which I did at home, when I remembered to start counting, I still counted 4 seconds before it popped. So, maybe 6 seconds from about 3/16" thick packed material. I'm talking out of my butt a bit because I didn't really study it closely. I need to do more careful tests and observations. But the result is definitely in the ballpark of what I am looking for.

 

Response:

It's difficult to provide an X%/Y% standard recipe because everybody makes their own BP and they are by no means identical. This highlights the importance of BP and technique consistency--if you're milling small BP batches, you might want to combine them to get a large pool of BP with known burn characteristics.

 

Just to be sure your delay isn't too slow (hard to ignite), it might be smart to press some straight BP against your delay to ensure fire transfer to the delay 100% of the time. I'm sure you're probably ok, but fuse should really have lit that mix up repeatedly. In the Skylighter article on building Estes-like motors, the ejection charge on a commercial E9-6 motor (6 seconds delay) was approx 1/2" long. He used a standard Tiger Tail star formulation for the delay in the new builds, which is 47% KNO₃, 47% charcoal, and 6% sulfur, screen mixed through a 40-mesh screen, dampened slightly and dried. His burn rate was 1 second per 3/16", and the delays (not propellant) was simply hand tamped (not rammed or pressed) and covered with a paper disk and masking tape (cardboard end tube and glue would work best he figured). Meaning clay probably not necessary as an endcap, though might be better for long-term storage.

 

The sulfur lowers the compound ignition temperature and facilitates ignition (just like in regular BP). Might be useful if your bicarb cools off the delay a bit too much (or you could just drop to 30% and measure burn rate. 40% seems like a lot to me. For endburners, I use regular hot BP (with 10% sulfur) and dumb it down with 20% bicarb, and get appropriate delay (I test each batch, and adjust volume instead of bicarb % to get desired delay--batches are usually pretty close to one another, thus results). For E/F-sized motors, I use around a half gram of hot BP granules (20-40 mesh) for the ejection charge, with good results. Maybe a little more for longer or fatter rockets. No compaction required (or desired) and two paper endcaps fit without glue, so pressure build-up is sufficient to blow endcaps but not rear nozzle, though I doubt that would happen anyways with a half gram or gram vented BP deflagration. Just want most of that smoke and gas blowing forward. You can add a round cardboard baffle with holes drilled throughout in your body tube if worried about minimizing the likelihood of excessive hot particles frying your retrieval gear (chute/lines...), but I usually only do that in long (e.g., 3-foot) rockets where my ejection charge is larger to accommodate the larger deadspace to the nosecone (or you can break your rocket in half and have it blow in half, controlled, instead of the distant nosecone--easy to do with an inner adapter tube to connect top/bottom body tube sections.

 

Yes, well, I tend to dream sometimes. I'd like a pony, too.

 

I went back to the Skylighter article on the Estes motors and read it again regarding the delay and ejection charge.

 

I agree that 40% seems like a lot but I'm kind of hooked on the slow burn. That's not to say that I won't dial it back to 30% and test it (I probably will just because I'd like to know). I tried adding some sulfur to it today but that was a mistake (ending at a mix very close to the Tiger Tail comp). Two different tests ignited fine with a fuse but the kind of bubbled like a volcano. They also didn't leave the casing blocked like the plain KNO3/charcoal mix. When the "test charge" blew on the other end of the delay, it blew out the end I'd lit (with no blockage/nozzle) instead of the paper towel stuffed loosely in the casing to hold the test charge. When it was just KNO3/charcoal, the stuff burned in place, it seemed, and blew the paper towel out the other end. I think, when the delay is actually in a rocket motor, the intimate contact with the thrust fuel will guarantee ignition of the delay comp. I can then press about 1/8 tsp of fuel (75/15/10) dust on top of the delay and let that ignite the loose ejection charge. It'll all take some testing.

 

I like the idea of breaking a longer rocket in two for the recovery. Should be easily done as connector pieces for the tubes are available. So, too, a good idea about the baffle.

 

I have a lot tinkering to do before I'll have it all settled down. I'll get a mix/delay I like then make some test casings (no nozzle, just a touch of the thrust fuel then the delay and finally the test charge) and see how it goes. I'll try the 0.5g of ejection charge with these little ones, too, I guess. Better to hit it too hard and burn the 'chute and crash than too soft and crash with the nose cone in place. I've thought of using the paperboard cap like the Skylighter article mentions. I've got some Tidy Cats scoopable little ball litter which compresses pretty easily and I think I'll try both.

 

Thank you.

 

--HC

[davidh]

Try milling the delay charge. I've seen delay comps that will go out when rough mixed, but perform well when milled. That said, you want a delay comp that also smokes for model rocket type motors.

[SharkWhisperer]

 

Yes, well, I tend to dream sometimes. I'd like a pony, too.

 

--HC

I hope your pony is in your not-too-distant future. Ponies are nice.

[SharkWhisperer]

Try milling the delay charge. I've seen delay comps that will go out when rough mixed, but perform well when milled. That said, you want a delay comp that also smokes for model rocket type motors.

True dat, unless they're not meant to be retrieved, oh my!! In that event, the explosion will typically give you a pretty good idea where they ended up.

 

Just yesterday, my pal lost an Estes Big Daddy (fat, stubby, riding on a D motor). Commercial motor failure. Ejection charge never blew. That thing did a parabola and lawn-darted (atop a metal shed) at perhaps 100 mph. Sad to watch. A bitch to retrieve. Of course, Estes will make things whole, but a shame & moderately dangerous, just the same. I have never had a homemade motor ejection charge fail completely...

 

Usually, the extra charcoal in delays puts out some smoke, but you can add other chems to guarantee this (e.g. sugar/lactose, though watch the slag production...).

[davidh]

You might want to try a sulfur-based smoke mix. The nozzle should be about the right size.

Degn shows a white smoke formula KNO3 - 12, S - 16, Air float charcoal - 1 (Source: Westech, Novelty Fireworks, L-107)

[SharkWhisperer]

You might want to try a sulfur-based smoke mix. The nozzle should be about the right size.

 

Degn shows a white smoke formula KNO3 - 12, S - 16, Air float charcoal - 1 (Source: Westech, Novelty Fireworks, L-107)

Worth a try. Easy enough to whip together. Seems like a lotta sulfur there; curious what the burn rate would be...?

[davidh]

The sulfur _is_ the smoke. It sublimates and solidifies to form the smoke. That's why there is an excess. The burn rate is fairly slow. Just ram a motor tube with a nozzle (like an end burner) and then ram full of the smoke mix. Prime, fuse, burn, and time to test and determine the needed grain length.

[hcb]

Try milling the delay charge. I've seen delay comps that will go out when rough mixed, but perform well when milled. That said, you want a delay comp that also smokes for model rocket type motors.

 

Interesting that I'm back reading this thread at this moment and you've posted this. I mixed up some 30% BS added to 50/50 KNO3/charcoal, but I thought it was too fast. I took the balance left, calculated the minute amount more BS to add to it, and packed a tube with 7 increments of 1/2tsp. I did the "rocket fuel compressed then the delay fuel compressed to that" to test ignition of the delay comp. It didn't work. It's worked before. I'm pretty sure my calcs were right, but the stuff refused to light. I hit it with a MAPP torch 'cause I'm that kind of guy, and it kind of burned a moment and then fizzled out. I will need to make a fresh batch where I'm sure I'm not screwing something up, but I wonder if your suggestion would help. I'm sure going to try it.

 

Thank you.

 

--HC

[hcb]

True dat, unless they're not meant to be retrieved, oh my!! In that event, the explosion will typically give you a pretty good idea where they ended up.

 

Just yesterday, my pal lost an Estes Big Daddy (fat, stubby, riding on a D motor). Commercial motor failure. Ejection charge never blew. That thing did a parabola and lawn-darted (atop a metal shed) at perhaps 100 mph. Sad to watch. A bitch to retrieve. Of course, Estes will make things whole, but a shame & moderately dangerous, just the same. I have never had a homemade motor ejection charge fail completely...

 

Usually, the extra charcoal in delays puts out some smoke, but you can add other chems to guarantee this (e.g. sugar/lactose, though watch the slag production...).

 

Hmmm, I seem to recall that there's a recipe for making smoke bombs using powdered sugar and KNO3. I'd be interested to try some. And interested to see how much slag is produced. But, especially with more than one person suggesting/supporting it, I'll try milling what I've been trying.

 

--HC

[hcb]

You might want to try a sulfur-based smoke mix. The nozzle should be about the right size.

 

Degn shows a white smoke formula KNO3 - 12, S - 16, Air float charcoal - 1 (Source: Westech, Novelty Fireworks, L-107)

 

I'm not saying "no" but...I tried adding some sulfur to my 50/50 KNO3/charcoal delay test batch and it bubbled like lava. It seems to have eroded the inside of the motor casing quite a bit, too. This mix may burn differently because of the reduced amount of charcoal, therefore allowing a more complete reaction of the sulfur. Probably a good idea to test it.

 

Thank you.

 

--HC

[SharkWhisperer]

Might want to check out https://cannonfuse.com/pyro-projects-smoke-bombs.html

 

 

They're making sugar rocket fuel, in essence, but makes nice white smoke. You can use confectioner's finely powdered sugar and milled or screened KNO₃. This recipe says better smoke with cooking together, but simply well mixing through a screen is not an issue, and has worked fine for me. Milling wouldn't hurt, but use the same precautions as with milling BP. Some confectioner's sugars might have free-flowing/anti-caking agents in them, but it's never been a problem for my purposes.

 

There's a bunch videos available on formulations for KNO3/sugar smoke bomb fuel, and videos, obviously some better than others. But I personally would not take all the time and attention to make a heated batch solely for a delay composition. You can granulate the hot mix before drying and press like BP, though, but might burn your fingeys if in a hurry.

 

Slag production is a consideration if 1) you possibly will reuse tubes, even for gerbs, and don't want to build a new nozzle (often easy to just clean out with a little brush and/or awl), and 2) if hot slag balls get shot out alongside your ejection charge, it might overload your recovery system heat/flame protection, but this seems unlikely and I've never really considered it to be an issue.

 

Alternatively, you can make a passfire through a bulkhead and use a piece of whatever speed visco you wish (primed on both sides with NC/BP slurry), or even a BP-packed spolette like if you were lifting a shell, but you won't get much tracking smoke...

 

You might also enjoy Nakka's rocketry site for some ideas, though he makes sugar rockets loaded in PVC... https://www.nakka-rocketry.net/pvcmot12.html

Edited March 19, 2020 by SharkWhisperer

[SharkWhisperer]

 

Interesting that I'm back reading this thread at this moment and you've posted this. I mixed up some 30% BS added to 50/50 KNO3/charcoal, but I thought it was too fast. I took the balance left, calculated the minute amount more BS to add to it, and packed a tube with 7 increments of 1/2tsp. I did the "rocket fuel compressed then the delay fuel compressed to that" to test ignition of the delay comp. It didn't work. It's worked before. I'm pretty sure my calcs were right, but the stuff refused to light. I hit it with a MAPP torch 'cause I'm that kind of guy, and it kind of burned a moment and then fizzled out. I will need to make a fresh batch where I'm sure I'm not screwing something up, but I wonder if your suggestion would help. I'm sure going to try it.

 

Thank you.

 

--HC

Good ol' "BS", hah ha. Since it's not really a widely used abbreviation outside this thread, although it does add a little flavor, might want to call it bicarb, bicarbonate or sodium bicarbonate so those who jump in don't get confused. Just a suggestion.

[SharkWhisperer]

 

Interesting that I'm back reading this thread at this moment and you've posted this. I mixed up some 30% BS added to 50/50 KNO3/charcoal, but I thought it was too fast. I took the balance left, calculated the minute amount more BS to add to it, and packed a tube with 7 increments of 1/2tsp. I did the "rocket fuel compressed then the delay fuel compressed to that" to test ignition of the delay comp. It didn't work. It's worked before. I'm pretty sure my calcs were right, but the stuff refused to light. I hit it with a MAPP torch 'cause I'm that kind of guy, and it kind of burned a moment and then fizzled out. I will need to make a fresh batch where I'm sure I'm not screwing something up, but I wonder if your suggestion would help. I'm sure going to try it.

 

Thank you.

 

--HC

Hey weren't you using regular hot fuel BP and dumbing it down with bicarb, with mixed but promising results? Now you're trying a 50/50 KNO₃/charcoal mix and adding 40% bicarb? That's super fuel rich to start with, and then slowed further with the bicarb; I would have predicted it would be pretty inert.

 

Careful not to change too many variables at once or you can end up with soup that is hard to pick apart and troubleshoot.

[hcb]

Good ol' "BS", hah ha. Since it's not really a widely used abbreviation outside this thread, although it does add a little flavor, might want to call it bicarb, bicarbonate or sodium bicarbonate so those who jump in don't get confused. Just a suggestion.

 

Yes, good point.

 

--HC

[hcb]

Hey weren't you using regular hot fuel BP and dumbing it down with bicarb, with mixed but promising results? Now you're trying a 50/50 KNO₃/charcoal mix and adding 40% bicarb? That's super fuel rich to start with, and then slowed further with the bicarb; I would have predicted it would be pretty inert.

 

Careful not to change too many variables at once or you can end up with soup that is hard to pick apart and troubleshoot.

 

No, I had not tried the hot BP with the baking soda. Your prediction would be correct. I tried the same mix, from the same container of test material, a couple more times with crappy results. Fickle finger of fate or whatever: the first test was *perfect*...then I couldn't reproduce the results, even from the same test batch. Perhaps the mix is sensitive to compression levels and my first test was very briefly compressed to the target pressure with no dwell time. Whatever I did, I failed to recreate the success of the first test.

 

I went through several tests. Day before yesterday, I spent about 4 hours testing different comps. I had hell recreating results. I pressed all samples dry into motor tubes at 3k PSI. I had started initiating the samples by putting 1/8 tsp of fuel BP (75/15/10) into the tube first, compressing it to 3k PSI, then putting the delay mix on top of that. That simulates how it will be used in the actual motors anyway. I packed 1/8 tsp of the fuel BP on the other end to "pick up the fire" from the delay mix in case it was anemic in its burn, and put a little loose BP (pucked/cracked screen sorted) on top of that I finally settled on 50/50 KNO3/charcoal plus 30% of that weight of baking soda, ball milled. I press it dry to around 3k PSI. It may very well be the compression of the mix that affects its performance because, as I was being more consistent and allowing more compression dwell time and allowing the compression to hover around the target pressure instead of just peaking, the +30% was working fine.

 

So, to try to put that into something more usable for others: My current mix is half and half KNO3 and charcoal plus 30% of that weight in retardant (baking soda). Any amount, by weight, of KNO3 added to the same amount, by weight, of charcoal, which is ball milled (equal amounts, by weight: 50/50). To the weight of that combination, no matter what amount of that mix I make, I add 30% of that combined weight in baking soda and ball mill that in. E.g. 75g KNO3 + 75g charcoal = 150g batch of delay fuel. 30% of 150g = 45g. I add 45g of baking soda to the 150g delay fuel as retardant. Final amount = 195g retarded delay fuel.

 

Testing this mix has given me about 5 seconds of burn time per 1/2 tsp compressed to 3k PSI in a 1/2" diameter tube. The depth of that is a touch over 1/8", approaching 3/16". I inserted a stick and marked it on top of each increment for 6 increments to get an idea of the depth of each increment. I chose to dispense this powder by volume because it was faster than weighing. If this works well, I can come up with a weight of material to achieve the same depth so that future batches can be fairly closely matched to this depth.

 

I have my first complete rocket motor loaded, including this mix for the delay. Sooner than later, next day or two, I should get to fly the rocket and we'll see if it works. I would like to try some of the other mixes suggested here but I needed to see this one mix through. And I'm too excited to try out a home made motor in a rocket, so I want to get one in the air "right now". I'll test some other mixes when that step is complete.

 

Thank you.

 

--HC

[SharkWhisperer]

 

No, I had not tried the hot BP with the baking soda. Your prediction would be correct. I tried the same mix, from the same container of test material, a couple more times with crappy results. Fickle finger of fate or whatever: the first test was *perfect*...then I couldn't reproduce the results, even from the same test batch. Perhaps the mix is sensitive to compression levels and my first test was very briefly compressed to the target pressure with no dwell time. Whatever I did, I failed to recreate the success of the first test.

 

I went through several tests. Day before yesterday, I spent about 4 hours testing different comps. I had hell recreating results. I pressed all samples dry into motor tubes at 3k PSI. I had started initiating the samples by putting 1/8 tsp of fuel BP (75/15/10) into the tube first, compressing it to 3k PSI, then putting the delay mix on top of that. That simulates how it will be used in the actual motors anyway. I packed 1/8 tsp of the fuel BP on the other end to "pick up the fire" from the delay mix in case it was anemic in its burn, and put a little loose BP (pucked/cracked screen sorted) on top of that I finally settled on 50/50 KNO3/charcoal plus 30% of that weight of baking soda, ball milled. I press it dry to around 3k PSI. It may very well be the compression of the mix that affects its performance because, as I was being more consistent and allowing more compression dwell time and allowing the compression to hover around the target pressure instead of just peaking, the +30% was working fine.

 

So, to try to put that into something more usable for others: My current mix is half and half KNO3 and charcoal plus 30% of that weight in retardant (baking soda). Any amount, by weight, of KNO3 added to the same amount, by weight, of charcoal, which is ball milled (equal amounts, by weight: 50/50). To the weight of that combination, no matter what amount of that mix I make, I add 30% of that combined weight in baking soda and ball mill that in. E.g. 75g KNO3 + 75g charcoal = 150g batch of delay fuel. 30% of 150g = 45g. I add 45g of baking soda to the 150g delay fuel as retardant. Final amount = 195g retarded delay fuel.

 

Testing this mix has given me about 5 seconds of burn time per 1/2 tsp compressed to 3k PSI in a 1/2" diameter tube. The depth of that is a touch over 1/8", approaching 3/16". I inserted a stick and marked it on top of each increment for 6 increments to get an idea of the depth of each increment. I chose to dispense this powder by volume because it was faster than weighing. If this works well, I can come up with a weight of material to achieve the same depth so that future batches can be fairly closely matched to this depth.

 

I have my first complete rocket motor loaded, including this mix for the delay. Sooner than later, next day or two, I should get to fly the rocket and we'll see if it works. I would like to try some of the other mixes suggested here but I needed to see this one mix through. And I'm too excited to try out a home made motor in a rocket, so I want to get one in the air "right now". I'll test some other mixes when that step is complete.

 

Thank you.

 

--HC

30% is still a hell of a lot of bicarb, particularly with a slow BP mix to begin with. Always simpler to just dumb down your actual propellant than to invent a new comp for delays.

 

I know you want to see flight, pronto, and you can, but you might learn more by doing a static burn test on the ground to more easily measure your delay time and assure sufficient gas ejection, in the correct direction and estimated strength, when it goes off. Maybe press out several identical motors, test one or two on the ground to evaluate your ejection timing delay accuracy and reliabiity, and launch a few on sticks. N=1 is always anecdotal, and your results have not been completely consistent so far.

 

With the Patriot kit, I see two potential issues that you can predict ahead of time: 1) motor ain't got enough juice, so it never gains sufficient speed for stable rise=unpredictable & unstable flight, if power is even sufficient to lift it off the pad. If it only goes 100 feet up then maybe could become a lawndart under power and long before the ejection blows; and 2) improperly timed/inconsistent delay/ejection timing. You want it to blow at apogee, but don't know your motor's impulse/power, so can't reliably estimate how long it'll coast after burnout. A bigger problem if delay takes too long and doesn't blow in time--aerodynamic lawndart is worst case, and damaged rocket/recovery if it pops at downward speed or close to ground. Too short a delay and blowing ejection while rising before apogee can possibly damage chute/lines if speed still high, but at least with the cone separated and some chute possibly still attached, it's less aerodynamic and unlikely to poke holes into things on return, but might hurt your rocket.

 

Primary points are that you need to know your motor's power and how high it's expected to lift your rocket, and how fast, before you can select a delay time. And that delay time needs to be reasonably accurate and ejection be entirely predictable. That's ground testing and then stick launches, before it goes into a constructed rocket.

 

I think you said you bought 3 kits at some point. If they're all Patriots, it'd be a good idea to build one per kit instructions and see how it flies on a B6-4 and C6-5 commercial motor, so you know that specific rocket a little better. Then launch your custom build with your own (tested) motor. Strongly recommend not flying something that size on an A-motor ("*A8-3 for first flight" is ubiquitous Estes recommendation) because of insufficient power that'll struggle to get it off the pad, let alone to any altitude.

 

You're almost there, but you don't yet know your rocket well yet, and you definitely are in ground and stick testing phases with motor construction (which, almost certainly, will not equal commercial motor impulses on early builds).

 

But super cool progress!!!

[hcb]

30% is still a hell of a lot of bicarb, particularly with a slow BP mix to begin with. Always simpler to just dumb down your actual propellant than to invent a new comp for delays.

 

I know you want to see flight, pronto, and you can, but you might learn more by doing a static burn test on the ground to more easily measure your delay time and assure sufficient gas ejection, in the correct direction and estimated strength, when it goes off. Maybe press out several identical motors, test one or two on the ground to evaluate your ejection timing delay accuracy and reliabiity, and launch a few on sticks. N=1 is always anecdotal, and your results have not been completely consistent so far.

 

With the Patriot kit, I see two potential issues that you can predict ahead of time: 1) motor ain't got enough juice, so it never gains sufficient speed for stable rise=unpredictable & unstable flight, if power is even sufficient to lift it off the pad. If it only goes 100 feet up then maybe could become a lawndart under power and long before the ejection blows; and 2) improperly timed/inconsistent delay/ejection timing. You want it to blow at apogee, but don't know your motor's impulse/power, so can't reliably estimate how long it'll coast after burnout. A bigger problem if delay takes too long and doesn't blow in time--aerodynamic lawndart is worst case, and damaged rocket/recovery if it pops at downward speed or close to ground. Too short a delay and blowing ejection while rising before apogee can possibly damage chute/lines if speed still high, but at least with the cone separated and some chute possibly still attached, it's less aerodynamic and unlikely to poke holes into things on return, but might hurt your rocket.

 

Primary points are that you need to know your motor's power and how high it's expected to lift your rocket, and how fast, before you can select a delay time. And that delay time needs to be reasonably accurate and ejection be entirely predictable. That's ground testing and then stick launches, before it goes into a constructed rocket.

 

I think you said you bought 3 kits at some point. If they're all Patriots, it'd be a good idea to build one per kit instructions and see how it flies on a B6-4 and C6-5 commercial motor, so you know that specific rocket a little better. Then launch your custom build with your own (tested) motor. Strongly recommend not flying something that size on an A-motor ("*A8-3 for first flight" is ubiquitous Estes recommendation) because of insufficient power that'll struggle to get it off the pad, let alone to any altitude.

 

You're almost there, but you don't yet know your rocket well yet, and you definitely are in ground and stick testing phases with motor construction (which, almost certainly, will not equal commercial motor impulses on early builds).

 

But super cool progress!!!

 

Understood re the baking soda percentage. I agree with your take on modifying the existing BP. Now. Making a new mix made sense when I started but not so much now. I had hoped that the mix with no additives would have worked (50/50, no baking soda or other ingredients). Ironically, I'm back on the computer now to check the forums and ask another question and it will be about retarding my fuel BP. I'll post that here at the end and make a new thread if requested to do so.

 

In all of my testing I have been dialing details in. I'm confident that the motor will make the rocket fly. I accept it if it blows up my model. I bought 3...just in case. Not being rude or a jerk here, just feeling enough confidence that it will work and I will accept failure if it happens. I just flew a stick about 5 minutes ago with a similar motor to what I'll be using in the rocket model (just less fuel). I used a full-length 48" 3/16" dowel rod as a stabilizer. It took off *hard* and went high. The delay was a bit sketchy, it's hard to tell from the ground. That's where your static testing would help. I've not done a static test of a motor with a delay. I've done static testing of the delay mix and amount, but not in the full stack as it is in the motor. I'm gambling. I'm okay with that. And it's getting video'd either way, sink or swim, and going online.

 

I messed with the Patriot a bit earlier today. I balanced it with the recovery gear in the nose area and the full motor in the rear, found CG. I then traced out an outline of it on heavy paper and cut it out and balanced it for CP. CP is about 6cm closer to the nose than the CG. If I'm remembering things correctly, that's backwards of what it is supposed to be. I'll check that to be sure. I understand the delay and ejection of the chute. Timing is going to be a trick to figure out. I'm downloading OpenRocket right now. I'll figure out what I need to do to get the CG and CP positions right. I'm likely going to tank this first model on recovery. But watching this thing take off with my home made motor in it will be worth it. I bet you one dollar this thing gets off the ground under power and will be stable (Trading Places).

 

I agree with needing to know the motor's power. I've seen a video or two where some guy had a remote scale hooked up to a data logger and did a static test on the sensor. I'd love to have something like that but I've not found anything like that for sale. I've seen some sensors and data units that could be bought separately but they need to be hooked up and configured and some of the offerings involved Raspberry Pi or Arduino interaction and I'm not into the electronics. I've thought about doing it on a scale where I could watch it but I don't want to be that close to one of these things just in case it comes unglued. I'm open to suggestions.

 

Yes, all three are Patriots. I could stuff a spacer in the one I've built and use a factory motor in that. And I have B6 and C4 motors. I'll do that. CG will be only marginally different than factory as the only difference is the length of the motor holding tube. Yeah, I remember seeing the "start with this gutless motor first".

 

We've not painted the rocket fully yet, so it may still be Monday before it's ready to fly. Monday I should get the AltimiterTwo, so maybe fly it Tuesday. I know I'm not being as cautious as I could be, but the risks to the rocket are ones I'm willing to accept. The motors aren't blowing up and I'll be in the middle of 100 acres of private property so if it comes down intact and fast then it'll just plow a little hole in a big patch of dirt. I'm very confident that the motor will get it off the ground with plenty of oomph. Recovery deployment is questionable. A video is guaranteed.

 

Speaking of retarding the regular fuel....and maybe I should make a different post about this, advise if so: I built tooling to make a core-burner today. I'd like to make some fireworks rockets that will carry payload and where maximum height isn't the goal, so core-burners seemed like a good idea. I was thinking that I'd like to not make different fuels (funny, that's the theme of the beginning of this exchange). The question: can I use the regular BP and retard its burn rate with baking soda for the core-burners? Usually I see folks use different mixes of the standard BP components.

 

Thanks for your help, always. And I'm not trying to be rude or ignorantly dismissive. I know I'm taking a chance with the first model flight, but no one is going to get hurt (and if I do it's my fault). Besides, CATO videos are more fun.

 

--HC

[SharkWhisperer]

 

Understood re the baking soda percentage. I agree with your take on modifying the existing BP. Now. Making a new mix made sense when I started but not so much now. I had hoped that the mix with no additives would have worked (50/50, no baking soda or other ingredients). Ironically, I'm back on the computer now to check the forums and ask another question and it will be about retarding my fuel BP. I'll post that here at the end and make a new thread if requested to do so.

 

In all of my testing I have been dialing details in. I'm confident that the motor will make the rocket fly. I accept it if it blows up my model. I bought 3...just in case. Not being rude or a jerk here, just feeling enough confidence that it will work and I will accept failure if it happens. I just flew a stick about 5 minutes ago with a similar motor to what I'll be using in the rocket model (just less fuel). I used a full-length 48" 3/16" dowel rod as a stabilizer. It took off *hard* and went high. The delay was a bit sketchy, it's hard to tell from the ground. That's where your static testing would help. I've not done a static test of a motor with a delay. I've done static testing of the delay mix and amount, but not in the full stack as it is in the motor. I'm gambling. I'm okay with that. And it's getting video'd either way, sink or swim, and going online.

 

I messed with the Patriot a bit earlier today. I balanced it with the recovery gear in the nose area and the full motor in the rear, found CG. I then traced out an outline of it on heavy paper and cut it out and balanced it for CP. CP is about 6cm closer to the nose than the CG. If I'm remembering things correctly, that's backwards of what it is supposed to be. I'll check that to be sure. I understand the delay and ejection of the chute. Timing is going to be a trick to figure out. I'm downloading OpenRocket right now. I'll figure out what I need to do to get the CG and CP positions right. I'm likely going to tank this first model on recovery. But watching this thing take off with my home made motor in it will be worth it. I bet you one dollar this thing gets off the ground under power and will be stable (Trading Places).

 

I agree with needing to know the motor's power. I've seen a video or two where some guy had a remote scale hooked up to a data logger and did a static test on the sensor. I'd love to have something like that but I've not found anything like that for sale. I've seen some sensors and data units that could be bought separately but they need to be hooked up and configured and some of the offerings involved Raspberry Pi or Arduino interaction and I'm not into the electronics. I've thought about doing it on a scale where I could watch it but I don't want to be that close to one of these things just in case it comes unglued. I'm open to suggestions.

 

Yes, all three are Patriots. I could stuff a spacer in the one I've built and use a factory motor in that. And I have B6 and C4 motors. I'll do that. CG will be only marginally different than factory as the only difference is the length of the motor holding tube. Yeah, I remember seeing the "start with this gutless motor first".

 

We've not painted the rocket fully yet, so it may still be Monday before it's ready to fly. Monday I should get the AltimiterTwo, so maybe fly it Tuesday. I know I'm not being as cautious as I could be, but the risks to the rocket are ones I'm willing to accept. The motors aren't blowing up and I'll be in the middle of 100 acres of private property so if it comes down intact and fast then it'll just plow a little hole in a big patch of dirt. I'm very confident that the motor will get it off the ground with plenty of oomph. Recovery deployment is questionable. A video is guaranteed.

 

Speaking of retarding the regular fuel....and maybe I should make a different post about this, advise if so: I built tooling to make a core-burner today. I'd like to make some fireworks rockets that will carry payload and where maximum height isn't the goal, so core-burners seemed like a good idea. I was thinking that I'd like to not make different fuels (funny, that's the theme of the beginning of this exchange). The question: can I use the regular BP and retard its burn rate with baking soda for the core-burners? Usually I see folks use different mixes of the standard BP components.

 

Thanks for your help, always. And I'm not trying to be rude or ignorantly dismissive. I know I'm taking a chance with the first model flight, but no one is going to get hurt (and if I do it's my fault). Besides, CATO videos are more fun.

 

--HC

Determination is very good, hah ha. Your CP/CG issue is a true issue that needs addressing or you're going to have an eventful launch, guaranteed. Model rockets are light--the heaviest thing in them is the motor & mount. So nearly doubling the length of your motor/mount is going to add a lot of weight to the tail and drag the CG backwards, as you've seen. CP/CG approximation is worrisome. Overlap is a problem. Reversal by 6 cm is a guaranteed rodeo! 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 at, 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. Cheapo action cams work well, and are more disposable than GoPros (bought one after my GP-6 sank to the bottom of the Atlantic, ack).

 

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 for initial launch oomph) and slower 60-65/25-30/10 K/C/S for true coreburners. This is pretty typical for most folks using decent charcoal and a mill. You can easily strap a coreburner into a finned rocket, but Estes etc kit rockets just aren't strong enough to handle the thrust but options are endless for original design.

 

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!

Edited March 22, 2020 by SharkWhisperer

[SharkWhisperer]

 

I built tooling to make a core-burner today. I'd like to make some fireworks rockets that will carry payload and where maximum height isn't the goal, so core-burners seemed like a good idea. I was thinking that I'd like to not make different fuels (funny, that's the theme of the beginning of this exchange). The question: can I use the regular BP and retard its burn rate with baking soda for the core-burners?

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.