End Burner Formulas / Home made motors

[nordicwolf]

Hello...For a variety of reasons I want to try making some end burner motors and would like to ask about formulas people have used here successfully.

 

I used to launch Estes rockets years ago and now think it might be fun to try to make some motors that might fly a rocket similar to Estes models.

 

I have 4 ounce end burner tooling and a bunch of 1/2" ID tubes. The tubes are 5" long but I figure I can cut them shorter as needed.

 

Questions

1. what is a good BP formula for a 4oz end burner motor?

2. What is a good formula for the delay?

3. what is a good formula for the ejection charge?

4. What is a good model rocket to try with home made motors?

 

I need to look at the various pyro suppliers, but I am just looking for something simple into which to try home made motors. A basic tube for a body, basic fins (plastic even) and nosecone. Mounting the motor might be a bit tricky, but with a 3/4" body, maybe the 4oz motors can friction fit inside the tube if I wrap some masking tape on the motors to fatten them up a bit.

 

I think it might be fun (and less suspicious) to try a home made end burner in an actual rocket instead of taping it to a stick.

 

Thank you for any suggestions.

[MadMat]

Answers: 1. 75/15/10 BP will work fine for an end burner. 2. Add sodium bicarbonate to your BP for delay. Start by adding a couple % and experiment until you have slowed the burn speed to what you want. 3. The fastest burning 75/15/10 BP you can make granulated properly will work for the ejection charge. You want the ejection charge contained, but not packed tight like your grain. 4. I have no idea. You should probably experiment with your motors until you have everything dialed in and then think about a model.

Edited January 14, 2022 by MadMat

[Squatty]

To answer question 4. If you have a Hobby Lobby nearby, they sell kits that are relatively inexpensive. I bought my kids a set for Christmas that had 2 rockets, the stand, and the launch controller, for 20 bucks. I'm actually going down a similar road as well. I took out the engine blocks and modified them slightly to hold any size engine you'd like to stuff into them. The actually rocket body is pretty wide on one of them so it makes it relatively easy.

[Mumbles]

I think a member here was doing similar things. Looking for some of his posts might give some ideas or help with this project. I believe his name was "Bourbon".

 

One piece of advice I'd give is to try the motors out on their own first. They can be secured upside down. You'd probably at least want to confirm they're not going to blow up regularly before using even a cheap model rocket kit. It'll help to give you an idea of the burn time and delay time to get something in the ballpark of what you want. They're not too conspicuous on the ground. It basically will just look like a fountain or something.

[Bourbon]

Sorry Mumbles, not me. I've never built an end burner. I do know that "Shark" said he has spent years flying rocket kits with different types of BP, and sugar motors with great success. I could be mistaken, but I think he said everything from end burner, nozzled and nozzleless. I think "Justvisiting" was also pressing motors with the intent of making an equal to Estas.

[Arthur]

The convenience of an Estes motor is that (because of history) things just fit. Motor tubes fit motors, motors fit rocket bodies etc. Manufacturers tend to make kits for rockets to fit Estes motors.

[Mumbles]

I'll see if I can find who I'm thinking of. Sorry I was mistaken.

[nordicwolf]

Thanks everyone for the responses.

 

Someone told me to use commercial airfloat in the 75:15:10 if I run into CATOs with nozzled core burners.

That is part of the reason I want to try end burners, hopefully reducing likelihood of catos anyway.

 

I have ERC charcoal and no airfloat, so that is what I will be trying.

 

I know Estes products just fit. I am not so much interested in making Estes-compatible motors but rather make end burners to put into home made tubes / rockets and see if I can get those to fly. So I will need propulsion, delay and ejection. I read that core-burners have too much impulse power that could knock the fins off a model, and end burners (like Estes) have a slower lift off. So maybe core-burners are for fireworks whereas end burners are more for model rockets (but also used for fireworks I guess.)

[Bourbon]

Hey, nothing wrong with that. If 75/15/10 is too hot, just keep stepping it down. I'd make small batches of BP first for different combinations, before you make sizable amount for you perfected motors. I bet you find everything you need, in two of the four below.

 

75/15/10

70/20/10

65/25/10

60/30/10

 

Other folks change up the ratios more then I do when dialing in. Or, they keep good track of ratios and math by adding C to the mix to tone it down. I keep it pretty simple with the four above, and, I keep all four around at all times. I even have a couple 100 grams of 55/35/10 laying around for L..O..N..G delay. That's pushing though, in my opinion.

Edited January 20, 2022 by Bourbon

[justvisiting]

Estes motors achieve the performance and storage ability they do because the propellant grain is very dense. They use high pressing force and the propellant is dampened. When I made end burners for testing, I could only get a density of 1.4g/cc. with dry powder, but with dampened powder I could get 1.8g/cc. That's the density Estes gets. Of course, you'll need a tube support and a press to approach the impulse Estes motors have. The water allows for the use of less pressing force, and a cheap tube support can be made from a strip of mylar .005" thick, snugly wrapped on the tube.

[SharkWhisperer]

Sorry Mumbles, not me. I've never built an end burner. I do know that "Shark" said he has spent years flying rocket kits with different types of BP, and sugar motors with great success. I could be mistaken, but I think he said everything from end burner, nozzled and nozzleless. I think "Justvisiting" was also pressing motors with the intent of making an equal to Estas.

OP Wolf hey there,

 

Have launched a bunch of hybrid Estes-like rockets driven by homemade BP motors. There's a lot of info in prior threads. One amigo, member "HCB" put some videos on Youtube. His first launch of an Estes Patriot Missile used a homemade 1/2" ID motor that outperformed the C-impulse motors that Estes recommends. That video is at:

. It's pretty cool. I had to pay him a whopping $1 for losing a bet that his first rocket would be doing cartwheels or CATO. It didn't--actually it was close to a textbook flight with perfect parachute ejection and recovery. He was getting a 3+ second burn on a long C-sized endburner that took his (likely overweight) rocket to 740 feet at around 140 mph, with G-forces over 15, I believe. He used homemade tooling for 1/2" x 5" motors. You could get it moving faster on a coreburner motor configuration, but you'd want to reinforce your fins (through-the-wall construction, aircraft plywood or balsa/basswood layered, thick filets) and strengthen your motor mount to take the higher G-forces. Personally, I like the long slow burn of an endburner or semi-coreburner in finned rockets.

 

The initial exchanges with HCB and several APC members here on the forum can be found in the following thread and other threads from around that time: https://www.amateurpyro.com/forums/topic/13482-final-steps-in-making-bp-motors-seeking-advice/?hl=estes&do=findComment&comment=185018 . Most exchanges were around Feb-March 2020. There are other threads related to delay/ejection charges from around the same time that might be useful. Some discussions (delays, ejection...) might have been taken offline.

 

You can also do a forum search for "Estes" etc., that should give you some ideas and expectations.

 

All of my BP motors have been hand-rammed to date. Many prefer to press and you will get higher densities with a press, but my motors work pretty well with standard tooling and a 3-pound deadblow hammer. Nozzled end- and coreburners; sometimes short cores (similar to Estes D motors). Usually 1-pounders (3/4" ID), and occasionally 3-pounders, but large BP motors have heavy tubes and a ton of BP in them--at a certain point it just makes sense to switch to lighter AP-based composite propellants. I haven't done any nozzleless motors, though others here do so routinely. Just search "nozzleless".

 

As Bourbon mentioned, Justvisiting is another member with a long history of experimentation on similar subjects. And several other individuals here at APC, too. Ned Gorski wrote a piece about re-creating Estes BP motors that you can find on the Skylighter website: https://www.skylighter.com/blogs/how-to-make-fireworks/how-to-make-estes-model-rocket-engines . However, please do not waste your time using the crappy hardwood airfloat charcoal that he did (and that Skylighter sells in their overpriced low-quality "BP" kits).

 

Flying hybrid finned rockets on homemade motors is a blast! Very rewarding. And way cheaper than motors from Estes or Aerotech, especially the larger ones (not counting labor). Commercial BP motors just went up in price at the New Year by about 15-20%, so there's that.

 

Good luck!

[nordicwolf]

Thanks all for the advice and inspiration!

 

Seems trite, but I am totally grateful for the research done and shared here. Thanks again!

Edited January 24, 2022 by nordicwolf

[Mumbles]

HCB was the member I was thinking of. Thanks for posting the right person SharkWhisperer.

[SharkWhisperer]

HCB was the member I was thinking of. Thanks for posting the right person SharkWhisperer.

My pleasure. The hybrid sport is a super fun specialty. The more the merrier.

 

OP, get your motors working consistently before you risk blowing up many hours of rocket construction :=}

[nordicwolf]

OP, get your motors working consistently before you risk blowing up many hours of rocket construction :=}

Most definitely! I have two pressed to try on sticks first - been reading old threads about how to balance.

After that, I plan to try making some motors with less BP but adding delay comp and ejection charge, and testing on the ground so I can time it.

Fun stuff. That HCB thread and video are awesome! Thanks for all the info!

[Richtee]

I just bought 3 Estes “Hi Flyer” kits. “C” class motors. Damn they think alot of them. Like $16. Anyway, they’ll never get my motor money Gonna build one for each of the three Grandsons.

My pleasure. The hybrid sport is a super fun specialty. The more the merrier.

 

OP, get your motors working consistently before you risk blowing up many hours of rocket construction :=}

[SharkWhisperer]

I just bought 3 Estes “Hi Flyer” kits. “C” class motors. Damn they think alot of them. Like $16. Anyway, they’ll never get my motor money Gonna build one for each of the three Grandsons.

Hah! Those Hi-Flyers actually go really high on a C motor--I've lost several, a few on their first flight on a wimpy motor. You want a big field if you plan to get them back on a C-equivalent motor. They're pretty small--12" long and only about an ounce w/o the motor. Specs say 1500 feet on a C-motor. That's over a quarter mile. No way you're going to see a skinny foot-long rocket from a quarter mile away. That's why I like big fat slow rockets. They also make the larger Hi-Flyer XL, which D/E motors push even higher. I have an unopened kit someplace... Anyways, your grandsons are going to really dig them!

 

With respect, I would probably never try to convert those smaller-diameter Hi-Flyers to homemade motors, but that's just me. If you're determined then go for it! For me, it's easier to fashion a motor mount to a fat rocket than trying to finesse a motor into a small-diameter weak-walled body tube. The Hi-Flyer body tube is only 19mm diameter, and A-C motors are 18mm outer diameter. Check your tubing size for the motors you're considering building. Almost always you're going to find that your homemade motors are fatter and heavier than what Estes kits are designed for. This becomes problematic if you end up with an ass-heavy rocket (CG slides behind Center of Pressure) because stability goes out the window and your pointy rocket will do cartwheels off the launch rod. It looks cool, but those plastic nose cones can hurt at velocity. Balsa would, too, at the speeds you can expect. Paperboard, as well.

 

A longer rocket moves the CG forward. So does weight added to the nosecone. It gets a little more tricky than just attaching a longer/fatter stick (or two) for balance to a motor that for fireworking usually has a shell as a forward payload and no CG issues besides it needing to be moved back a ways with a stick.

 

Almost all of my conversions use 1-lb (3/4" ID) tubes, which replicate F/G impulse power ranges (going by rocket mass/altitude--haven't tested on a static stand). And fat long body tubes. I make most of my rockets from scratch, but if I'm modding a kit, you'll pretty much always need to make a custom-sized (and reinforced) motor mount for your homemade motors. Not hard at all, but necessary.

 

Never buy from Estes directly; as you know their prices are through the roof, even with free shipping over $50 if they're still offering that. All of my Estes-related stuff comes from AC Supply out of Missouri. It's always a straight 40% off of any price you find on the Estes website. Doug's a good dude and took over the biz from his Pops, and he sells about 80% of the products that are on the Estes website. For example, he sells the Hi-Flyer for $8.70 vs the $16 you mentioned above. https://www.acsupplyco.com/estes-model-rockets/estes-by-skill-level/beta-skill-level-1-intermediate/estes-hi-flyer-model-rocket All Estes prices went up by 15-20% in 2022, probably because everything besides motors comes from China... AC Supply offers free shipping (slowish retail parcel post) on orders over $100. I've never paid for shipping yet from them. I also buy rocket parts from Balsa Machining Service out in Nevada--good dude with decent prices and parts selection (not for rocket kits or motors, though). https://www.balsamachining.com/

 

The bulk motor boxes (24 per box) are expensive but a lot cheaper than buying 3-packs. I've bought some large lots on Ebay before, too. They're BP, so they will last forever if you don't do extreme temp cycling (below zero to 100F in an unheated garage/shed is bad; avoid temp shifts over 75F overall). Have fired off motors from the 80s that work like new. Homemade motors are both fun and cheap once you've dialed them in, but for me the smaller ones lost their luster quickly for the effort; substituting the "big" ones is a no-brainer--2-packs of F15s now cost $20 at AC and $30 from Estes (and F-motors require Hazmat shipping!).

 

Estes "starters" aka igniters are shit and overpriced. As a pyrotechnician you should have no problem making your own in bulk that are better and cheaper. I use 34 and 40g nichrome and a homemade pyrogen (various...BP, perc/metal, boron/viton) w binder; NC works but actually slows the burn of most pyrogens. A cycle or scooter battery and long fat firing leads are easy and waayyyy better than the measly Estes firing units. You'll want a little more stand-off distance for testing homemade motors than the puny 15-foot standard leads they have (30 feet in their units for "big" E+ motors).

 

You can also build composite AP-based motors (APCP) that have a higher specific impulse than BP, and fewer shipping restrictions. But the pre-made (think Aerotech) are even more expensive than commercial BP motors. Making composite motors from scratch is a whole new talent to learn though plenty of folks do it (I haven't yet).

 

Looking forward to seeing how your experiments work out!

 

 

Edit: Rereading your original message, you might've meant that the C motors you bought were $16. They come in 3-packs. That's through the roof pricey. At the Estes website they're $13 (plus shipping of course) which is stupid expensive. Almost $5/motor? Sheesh. Even at AC they're $9, which I'd have a hard time paying. It's a pretty good bet that you'll lose those birds on a C motor if there's even the slightest breeze, unless they're sacrificial and you fasten a packet of Vitamin F to the motor ejection charge (maybe scrape off the clay cap first) or fuse up the nosecone. You'll get some altitude out of a wimpy A8-3 for sure, with a much better likelihood of recovering it. It'll probably go invisible on a B motor. C motors will probably send them over to the next state. Bulk packs with 24 total A, B, and C motors are $53 at AC (friggin' $80 from Estes; what a rip...). They were $43 last month, but prices went up on Jan 1. https://www.acsupplyco.com/estes-model-rockets/model-rocket-engines/estes-standard-engines?page=2 If they keep jacking the price on already pricey motors then a lot more folks are going to be learning to make BP and pounding/pressing their own!

Edited February 7, 2022 by SharkWhisperer

[Richtee]

YEah that was not very clear..the KITS were $16 I’m not buying the motors. A good heavy craft paper, some good wood glue and a 5/8” dowel give me a direct sub. Don’t know how they are gonna handle ramming yet...but they fit like a glove...

 

Ya know I kinda forgot how much fun these were to build.

 

Yeah..looking at that thing... I don’t think I’ll bother painting it. Prolly never see it again

 

Oh hey! Cool website I miss 6th grade

Edited February 8, 2022 by Richtee

[SharkWhisperer]

YEah that was not very clear..the KITS were $16 I’m not buying the motors. A good heavy craft paper, some good wood glue and a 5/8” dowel give me a direct sub. Don’t know how they are gonna handle ramming yet...but they fit like a glove...

 

Ya know I kinda forgot how much fun these were to build.

 

Yeah..looking at that thing... I don’t think I’ll bother painting it. Prolly never see it again

 

Oh hey! Cool website I miss 6th grade

Well there ya go! Even with commercial tubes, if they're a little oversized you can probably just peel off a few layers to get a good fit. The rocket crowd has pretty much abandoned the old standby metal retaining clip that is still in half of Estes kits, and you can save some build time by omitting them yourself. Everything's friction fit now, even on very large motors. This would also make it much easier to adapt homemade motors because they won't need to be built or cut down to exactly 2.75" long to fit the retainer hook.

 

The builds are fun, for sure. Yeah, fireworking is always a blast. But a lot of people revisit finned model rocketry as adults after years/decades away from early tries as a kid. They're also a hell of a lot of fun. But hybridizing the hobbies gives the best of both worlds, to some extent. Anyways, it's a hoot. But even simple kits take hours unless they're the (still pricey) plastic-finned prebuilts, so you want to be selective about motor testing so you don't risk blowing up maybe hours of work/rocket.

 

HCB's selection of the Patriot was a good choice for a first kit bash. There are a couple of others that I've used and would recommend, mostly 3'-long simple kits with a prebuilt plastic fin can and screw-on motor retainers (can be omitted); these are big enough to accommodate typically larger-diameter homemade motors and large enough to see in the air. And decently priced (for commercial kits). Some you might want to consider are the Top Shot https://www.acsupplyco.com/estes-model-rockets/estes-by-skill-level/skill-level-0/estes-top-shot-model-rocket , and the Show Stopper https://www.acsupplyco.com/estes-model-rockets/estes-by-skill-level/skill-level-0/estes-show-stopper-model-rocket . I've bashed several of both and they work really well. Both have plastic fin cans, and cutting/sanding/attaching/(painting) fins is probably the most tedious task in building finned rockets. With these kits, most of your effort will be in modding the motor mount set-up. A lot faster to the field, and several fewer build hours that can be destroyed or lost in a mishap.

 

Most of my rockets get white or grey primer and don't see actual paint until they've proven themselves in a first launch (and I get 'em back).

 

If the bug catches on, you might find yourself with a similar variety of rocket body tubes and motor mount items as you have likely accumulated for pyro devices. This cuts costs waaaay down. But you can always make rockets from paper towel tubes and duct tape that'll fly fast and cheap, kak kak! Plenty of threads and Youtube videos elsewhere.