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1/4" rocket limits.


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#1 tacticalnoodle

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Posted 01 March 2021 - 11:24 AM

So after watching some of my club members launch some of their own homemade rockets I decided to give it a try. I thought it would be best to start small so I got some 1/4"x2" tubes and tooling from cannonfuse.com.

I got them working and flying reliably using screen mixed 75-15-10 and granulated BP. I'm using commercial airfloat charcoal with pre milled potassium nitrate and sulfur for my BP. Its just screen mixed four times with a kitchen strainer,wet with water to a brown sugar consistency,and grated thru the strainer again.

While the rockets do fly by perfectly fine themselves I cannot get them to fly with a small header. I tried to use a crackle ball as a header and those little 1" plastic ball sets from cannonfuse as well. The rockets will dart up to tree top level and fall back to the ground before lighting the header.

I feel like it flys as long as the core is burning and once it hits the portion of the rocket with out a core it doesn't have enough thrust and comes back down.

Iv read that its hard to get this size of rocket to cato using fast BP so could I just try a faster BP to get these to lift small headers? I just got my first ball mill in and want to try milling my BP to see if it will help...maybe order a faster charcoal like pine or Eastern red cedar to try as well.

Do you think these ideas will help or just result in catos? What kind of lifting limits do you think rockets of this size have? Iv saw videos of people lifting headers on these little guys so I know I must be doing something wrong here.

#2 SharkWhisperer

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Posted 01 March 2021 - 10:55 PM

So after watching some of my club members launch some of their own homemade rockets I decided to give it a try. I thought it would be best to start small so I got some 1/4"x2" tubes and tooling from cannonfuse.com.

I got them working and flying reliably using screen mixed 75-15-10 and granulated BP. I'm using commercial airfloat charcoal with pre milled potassium nitrate and sulfur for my BP. Its just screen mixed four times with a kitchen strainer,wet with water to a brown sugar consistency,and grated thru the strainer again.

While the rockets do fly by perfectly fine themselves I cannot get them to fly with a small header. I tried to use a crackle ball as a header and those little 1" plastic ball sets from cannonfuse as well. The rockets will dart up to tree top level and fall back to the ground before lighting the header.

I feel like it flys as long as the core is burning and once it hits the portion of the rocket with out a core it doesn't have enough thrust and comes back down.

Iv read that its hard to get this size of rocket to cato using fast BP so could I just try a faster BP to get these to lift small headers? I just got my first ball mill in and want to try milling my BP to see if it will help...maybe order a faster charcoal like pine or Eastern red cedar to try as well.

Do you think these ideas will help or just result in catos? What kind of lifting limits do you think rockets of this size have? Iv saw videos of people lifting headers on these little guys so I know I must be doing something wrong here.

Please post a video of 1) your BP burning in an unconfined pile so we can gauge quality/burn rate--it'll definitely speed up with milling and granulating, and 2) a pic of your tooling for 1/4" rockets--they won't do much as endburners, even with hot BP (which, no insult, I'm guessing you do not have right now but can easily develop), and 30 a video of a rocket with or without a header (both is better) launching. We can sort this out, but know that slightly larger-diameter rockets can be easier to troubleshoot. You're on the small end of small--approaching Chicom bottle rockets with pep.

 

What kind of charcoal? ERC is fast. Pine not so fast but sparky and pretty tails. Other charcoals have different characteristics. You'll definitely see a major difference after milling/wet granulating/drying/packing motors. How current charcoal made or sourced? If BBQ charcoal briquettes, you'll never get anywhere. If lump charcoal (Cowboy, for example), the less dense pieces can sometimes give decent fuel, though they are all made from woods sourced from different types and from different countries, depending on what's commercially optimal for the grill charcoal seller. Making your own is the best way if you don't have a source for high-quality hot charcoal, which can become expensive beyond minor hobbyist quantities (even then). How high do they fly without a header? How ambitiously? What's the weight of your headers (critical?). A lot of parameters that need to meet in the middle. All important. More details, please.


Edited by SharkWhisperer, 01 March 2021 - 10:58 PM.


#3 tacticalnoodle

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Posted 02 March 2021 - 10:43 AM

Thank you for your reply. I'm working on gathering all the information that you requested.

This is my tooling, tube, headers that I am trying to use. I do not have a built header on hand I can weigh. I'll get that as soon as I can.

https://app.photobuc...96-e1b15a81a3ca

Here is a burn test of my newly ball milled and granulated black powder. I used ball milled technical grade potassium nitrate, powdered sulfur (fine powder unsure of mesh), and commercial mixed hardwood airfloat charcoal from fireworks cookbook.I ball milled it for 9 hours and granulated it with denatured alcohol thru a kitchen strainer.

As a side note anytime I do a test like this again I'll use a fuse to light it. Looking back at it lighting it directly with a lighter was pretty stupid.


https://app.photobuc...e7-03395577725a

Once I get a bit more time I'll press a rocket and make a header...ill post a video of a rocket with and without a header and the weight of the header.

#4 tacticalnoodle

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Posted 02 March 2021 - 04:22 PM

I was thinking about this at work and i think I might of figured out what my problem was.

So when I made my first couple rockets that flew I was pressing in a 1/8" thick nozzle, the BP, then the last 1/8" of the rocket was another 1/8" clay plug. This made it so the rocket had about half the rocket with a core and the other half being a solid plug of BP like a end burner.

I figured this "end burner" section would continue to provide thrust and keep pushing the rocket higher in the sky. I don't believe this is true anymore after watching this video of my original rocket over again.

https://app.photobuc...00-bd39c4268c40

As you can see it quickly darts up into the sky then it peaks and begins to fall back down right before it burns out. I think this solid "end burner" portion isn't providing much thrust at all and is more so acting as a delay. The rocket is just coasting after the cored portion is finished...I think it just happened to have enough energy to fly the weight of the rocket alone for how long it burned for.

That would explain why once I added the extra weight of a header it just flew up to tree top hight before falling back down to the ground and blowing up.

With my new slightly stronger BP and a shorter "delay" section it might actually fly right...what do you think? Something to try out tonight.

#5 SharkWhisperer

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Posted 02 March 2021 - 04:35 PM

Thank you for your reply. I'm working on gathering all the information that you requested.

This is my tooling, tube, headers that I am trying to use. I do not have a built header on hand I can weigh. I'll get that as soon as I can.

https://app.photobuc...96-e1b15a81a3ca

Here is a burn test of my newly ball milled and granulated black powder. I used ball milled technical grade potassium nitrate, powdered sulfur (fine powder unsure of mesh), and commercial mixed hardwood airfloat charcoal from fireworks cookbook.I ball milled it for 9 hours and granulated it with denatured alcohol thru a kitchen strainer.

As a side note anytime I do a test like this again I'll use a fuse to light it. Looking back at it lighting it directly with a lighter was pretty stupid.


https://app.photobuc...e7-03395577725a

Once I get a bit more time I'll press a rocket and make a header...ill post a video of a rocket with and without a header and the weight of the header.

Your tooling looks pretty reasonable for a 2/3 core bottle rocket. Can't tell exactly, but with most larger coreburners the nozzle opening's approx 1/3 tube ID. You didn't mention CATO issues that you could expect if your nozzle was too small. What is your spindle diameter? Is yours perhaps a little larger than 1/3 ID? This could restrict thrust generation, for sure. Especially for using generic airfloat charcoal, that's really not a bad burn rate at all. What's your total weight of fuel that you can load into each motor? Have you tried wetting with 1-2% water sprayed on just before pounding? Some swear by it. They're not all that much bigger than small Chicom motors, but your tubes are probably going to be thicker (and heavier overall). I'm guessing your header, though small, might nearly double the total weight of your rockets, which might be asking quite a lot for such a small motor. Especially if you aren't for some reason extracting maximal realistic thrust.

 

So...Spindle base/tube ID ratio? Propellant weight? Total rocket motor weight. Header weight? Total rocket + header weight?



#6 SharkWhisperer

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Posted 02 March 2021 - 04:41 PM

I was thinking about this at work and i think I might of figured out what my problem was.

So when I made my first couple rockets that flew I was pressing in a 1/8" thick nozzle, the BP, then the last 1/8" of the rocket was another 1/8" clay plug. This made it so the rocket had about half the rocket with a core and the other half being a solid plug of BP like a end burner.

I figured this "end burner" section would continue to provide thrust and keep pushing the rocket higher in the sky. I don't believe this is true anymore after watching this video of my original rocket over again.

https://app.photobuc...00-bd39c4268c40

As you can see it quickly darts up into the sky then it peaks and begins to fall back down right before it burns out. I think this solid "end burner" portion isn't providing much thrust at all and is more so acting as a delay. The rocket is just coasting after the cored portion is finished...I think it just happened to have enough energy to fly the weight of the rocket alone for how long it burned for.

That would explain why once I added the extra weight of a header it just flew up to tree top hight before falling back down to the ground and blowing up.

With my new slightly stronger BP and a shorter "delay" section it might actually fly right...what do you think? Something to try out tonight.

My last comment estimated your spindle as producing about a 2/3 core. Maybe a longer spindle could help. And check your nozzle/ID ratio. These are small rockets so you don't need much of a delay to effect time, and because they're not high-flyers you don't have a lot of leeway in timing them to guarantee they don't go off at an unsafe altitude. Once dialed in, they should be easily reproducible, though. How are you delaying propellant to header ignition?



#7 tacticalnoodle

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Posted 03 March 2021 - 11:06 AM

Okay so I finally got all the information you asked for.

Spindle is 0.125" diameter or 50% of the ID of the tube. A bit larger than the 33% you estimated. It is also 1" long so I get a 0.875" long core in the BP after I press in a 0.125" thick nozzle.

The tooling also has a 0.25" long base that slides into the bottom of the rocket to form the nozzle. This leaves 0.75" left in the rocket tube for the non cored section. I pressed in a 0.375" long section of solid BP leaving room for the header.

In total the motor and stick weigh about 4 grams. 1.5 of it being the BP.

The headers weigh 4 grams in total. 2 for the plastic shell, 1 gram of crackle stars, And 1 gram of BP for burst. I then taped it shut with paper packing tape. I put a pinch of loose BP in the tip of the rocket to help light the header and a folded piece of visco in the header as a passfire. Later I found out it wasn't needed as the loose BP will reliably light the header. At this point I wasn't trying to add a delay.

Anyways I got them to fly now. With a header they go above tree level and break at what appears to be an appropriate height for these small rockets. They now could use a slight delay to coast a half second or so though.

https://app.photobuc...65-2d5381f7f4b7

The video and the angle of it doesn't do it much justice but they still could fly higher or go a little faster. I think my original unmilled BP was the problem and ball milling it solved it. I will experiment with faster charcoal in the future to see if I can get even better performance or start getting catos.

Also I have not tried pressing in damp BP before...that practice is news to me. I thought it was supposed to be bone dry. I normally let mine dry overnight if using alcohol or a few days when I use water to granulate it.

#8 SharkWhisperer

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Posted 03 March 2021 - 12:36 PM

Okay so I finally got all the information you asked for.

Spindle is 0.125" diameter or 50% of the ID of the tube. A bit larger than the 33% you estimated. It is also 1" long so I get a 0.875" long core in the BP after I press in a 0.125" thick nozzle.

The tooling also has a 0.25" long base that slides into the bottom of the rocket to form the nozzle. This leaves 0.75" left in the rocket tube for the non cored section. I pressed in a 0.375" long section of solid BP leaving room for the header.

In total the motor and stick weigh about 4 grams. 1.5 of it being the BP.

The headers weigh 4 grams in total. 2 for the plastic shell, 1 gram of crackle stars, And 1 gram of BP for burst. I then taped it shut with paper packing tape. I put a pinch of loose BP in the tip of the rocket to help light the header and a folded piece of visco in the header as a passfire. Later I found out it wasn't needed as the loose BP will reliably light the header. At this point I wasn't trying to add a delay.

Anyways I got them to fly now. With a header they go above tree level and break at what appears to be an appropriate height for these small rockets. They now could use a slight delay to coast a half second or so though.

https://app.photobuc...65-2d5381f7f4b7

The video and the angle of it doesn't do it much justice but they still could fly higher or go a little faster. I think my original unmilled BP was the problem and ball milling it solved it. I will experiment with faster charcoal in the future to see if I can get even better performance or start getting catos.

Also I have not tried pressing in damp BP before...that practice is news to me. I thought it was supposed to be bone dry. I normally let mine dry overnight if using alcohol or a few days when I use water to granulate it.

Whoa, that nozzle is just too big and you're wasting energy with a low pressure burn. Without the header, you'd probably get twice the altitude by reducing nozzle size. I'd probably want a core to be a little longer, too--almost to the end so  the delay's effectively burning a split second after takeoff. If you don't have a lathe and stock to make different spindles (you  need a different spindle!) then you'd be surprised what you can get away with using a correctly sized nail hammered or epoxied through a piece of wood (old school homemade tooling). But a rammer that thin  would be delicate. There's bottle rocket tooling kits for about $30-40, but that seems a lot for bottle rockets if you plan on increasing size (you will if you stay with it). And your header weighs as  much as your rocket, which is not trivial and highlights the need to tap all available energy out of your motor. That spindle/tube ID 50% ratio is hugely inefficient--I'm actually surprised that your motors get off the ground! They will fly higher with some more nozzle restriction. And the video shows the need for a longer delay, but you already know that. Yes, after granulating and drying, some use it "as is" (there is often water remaining when it feels bone dry--storing it with color-changing silica bead packets overnight will tell you this. I store mine dry. But yes, the addition of perhaps 2% water before packing is used by many to increase final BP propellant density and some think the water itself, counterintuitively, actually increases burn rate. But for now---that spindle width, argh.  And the delay. Getting there--all the parts are in place and just need optimizing.



#9 tacticalnoodle

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Posted 03 March 2021 - 07:28 PM

Funny that you mention the $40 bottle rocket tooling being sold. The tool set being sold on pyrocreations, cannonfuse, and pyro direct is the one that I have been using.I think one of the members here makes them but I can't remember his name.

Oddly enough I am a machinist by trade who runs cnc lathes daily 🤔 maybe one day ill make my own set of tooling for these with a 3/32 spindle if my boss will let me...I might not monkey around to much with tooling since I'm eyeing a 4 OZ core burner set at the moment.

For now anyways I think I'm in the ballpark where I can fine tune this till I'm really happy with the performance.I think I have a few things to try and experiment with. Thank you for your help and setting me on the right path.

If I figure anything else out or do anything cool with them I'll post an update sometime for anyone else interested.

#10 tacticalnoodle

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Posted 12 March 2021 - 07:17 PM

So just to post my results here for anyone else wondering.

I am easily lifting 1" ball shells with these rockets and I'm sure you could go larger...But I don't really feel the need with these.

I'm sticking with 75/15/10 milled black powder using commercial hardwood air float charcoal. It works so I don't see a need to try anything hotter.

I like putting a quarter of a gram of flash inside the rocket tube as a report or attaching a 3/8" pumped star on top as a "secondary tail". Keeping them small and basic is a lot more satisfying than a tiny color shell to me.

I also found that adding +10% -30+80 mesh spherical titanium sponge to the delay is a pretty pleasing effect. Long silver tail with a soft crackle ish sound to it.

Using a 1/16 teaspoon as an increment I press three increments of straight BP to get to the top of the core. Then I press in three increments of the delay. This seems to be close for timing.

Here's a video of one of my rockets topped with a 3/8" crackle star. Reminds me of a shooting star.

Https://app.photobucket.com/u/pallystu/p/051247a2-60ab-4660-a933-118333a5fbe2

Edited by tacticalnoodle, 12 March 2021 - 07:21 PM.

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#11 SharkWhisperer

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Posted 12 March 2021 - 08:21 PM

So just to post my results here for anyone else wondering.

I am easily lifting 1" ball shells with these rockets and I'm sure you could go larger...But I don't really feel the need with these.

I'm sticking with 75/15/10 milled black powder using commercial hardwood air float charcoal. It works so I don't see a need to try anything hotter.

I like putting a quarter of a gram of flash inside the rocket tube as a report or attaching a 3/8" pumped star on top as a "secondary tail". Keeping them small and basic is a lot more satisfying than a tiny color shell to me.

I also found that adding +10% -30+80 mesh spherical titanium sponge to the delay is a pretty pleasing effect. Long silver tail with a soft crackle ish sound to it.

Using a 1/16 teaspoon as an increment I press three increments of straight BP to get to the top of the core. Then I press in three increments of the delay. This seems to be close for timing.

Here's a video of one of my rockets topped with a 3/8" crackle star. Reminds me of a shooting star.

Https://app.photobucket.com/u/pallystu/p/051247a2-60ab-4660-a933-118333a5fbe2

Nothing wrong with those, and that Ti tail is a really nice effect. Won't piss off the neighbors, either.

 

(but I gotta say Tac, "liking" your own posts is rather "tacky"...please don't do that :=)



#12 tacticalnoodle

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Posted 12 March 2021 - 08:31 PM

You know I keep doing that by mistake and can't figure out how to undo that. I'm on a cell phone and fat finger everything.

Longest time I clicked on it trying to get an options menu to reply or edit stuff :)

#13 SharkWhisperer

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Posted 12 March 2021 - 11:30 PM

You know I keep doing that by mistake and can't figure out how to undo that. I'm on a cell phone and fat finger everything.

Longest time I clicked on it trying to get an options menu to reply or edit stuff :)

No worries.

 

Continue your pyro adventures!!!



#14 Arthur

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Posted 13 March 2021 - 04:09 AM

I had some commercial rockets about that size, they fly nicely but only contain one small star. Be very careful not to overload the motor.

 

Most importantly make one change at a time, that way you can easily determine what each change has done to the performance.

 

Small fireworks usually work to short and close timing.






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