3D Printing My "Cold Fuel" Rocket Engine

[n3tjm]

back when I was in jr high or high school one of my teachers gave me toy rocket that used vinegar and baking soda as rocket fuel. Well, I have been thinking about that and I decided to try and attempt to make my own version. Since my Jr high and high school career was 93-98, I don't remember much details about the rockets. lost to my knowledge was how the recovery system worked. I remembered they used some sort of burst disk pressure system that didnt work well. If anyone has any ideas, let me know what you think. In the mean time, I will share what I have drawn up so far:

 

[rocket_troy]

No idea. I'd be quite impressed if you could get that propellant combination off the ground.

TP

 

[n3tjm]

Yeah, Me to. But I think this would be an interesting little project

 

[Kelly]

Back when you were in High School they probably didn't have tiny, $15 altimeters that would pop a parachute at apogee. I would go with that solution now, rather than trying to design something into the motor.

 

[aerostadt]

I had one of these critic acid/baking soda Alpha rockets back in about 1960. It was a "bear" to launch. First, I poured in the critic acid solution while holding the rocket upside down. The hard part was putting in the baking soda. The baking soda was held in a small red thimble size container with slits in the side. This thimble/aft-end(nozzle) fit into the top part of the launch pad that had a restraining metal lever that that held the aft-end of the rocket to the rest of the launch pad until the owner released the rocket to fly. The user had to hold his finger tips over the thimble slits and quickly screw in the aft-end into the bottom of the rocket all the while holding the rocket upside down. Of course, as soon as the user started to do this operation some of the baking soda would start to fall down into the rocket and start fizzing. Acting quickly, once the aft-end was screwed in, the rocket was ready to launch. The rocket fell to earth without a parachute. The rocket was pretty tough plastic and had to be in order to hold the CO2 pressure.

https://richmond.com/discover-richm...cle_cc51ee7f-4952-5cad-9468-95746247ab88.html

 

[n3tjm]

That was exactly the set the teacher gave me. It's amazing the feeling I got when I looked at those pictures and the memories came rushing back.

 

[n3tjm]

I want to give an update on the project. I must say it is going surprisingly well. I am on version 4 of the design, with very minor changes between versions. Version 3 has had the first flight test using baking soda and vinegar. The motor produces enough thrust to lift its own weight and propels itself easily 100 ft accross the yard. Now version 3 of the tank had some leakage issues up at the upper bulkhead so I hope I fix that issue with version 4 of the tank with a thicker wall and thicker fillets at all the joints.. I also got some citric acid ordered for more thrust but the leakage issue must be addressed before I try that

 

[aerostadt]

OK, with the second drawing I can understand what you are doing, except I am a puzzled by the side walls near what I think are the baking soda thimble slots.

 

[n3tjm]

The baking soda thimble is made as thin as possible, however the windows don't last more than a couple firings.. so the ribs are there just for support. I was printing design number 4 but ran out of black filament. No problem. Whip out a new roll of blue Only to discover there is a clog in the filament tube. Could not get it out, so I ordered filament tube upgrade and it should arrive on Saturday. I told my Wife, the 3D printer is a machine, and machines do need periodic maintenance. I think I will take this short break to make some more adjustments thimble (I'm thinking the ribs are overkill), and I am thinking about extending the length of the tank a little.

 

[cerving]

I had one of these critic acid/baking soda Alpha rockets back in about 1960. It was a "bear" to launch. First, I poured in the critic acid solution while holding the rocket upside down. The hard part was putting in the baking soda. The baking soda was held in a small red thimble size container with slits in the side. This thimble/aft-end(nozzle) fit into the top part of the launch pad that had a restraining metal lever that that held the aft-end of the rocket to the rest of the launch pad until the owner released the rocket to fly. The user had to hold his finger tips over the thimble slits and quickly screw in the aft-end into the bottom of the rocket all the while holding the rocket upside down. Of course, as soon as the user started to do this operation some of the baking soda would start to fall down into the rocket and start fizzing. Acting quickly, once the aft-end was screwed in, the rocket was ready to launch. The rocket fell to earth without a parachute. The rocket was pretty tough plastic and had to be in order to hold the CO2 pressure.

https://richmond.com/discover-richm...cle_cc51ee7f-4952-5cad-9468-95746247ab88.html

Ah, memories... it had a big rubber nose, and when it hit the street after launching from our lawn it would bounce about 10' high. The fins were kinda flimsy, they would break after 5 or 6 launches. At an early age I discovered the utility of duct tape...

 

[prfesser]

FWIW an exit cone for the nozzle isn't necessary when the exhaust is liquid. The exit cone provides additional thrust from expanding gases (and it looks rocket-y). Liquids are virtually incompressible.

 

[n3tjm]

I know. I just did that because it looks cool

 

[aerostadt]

Looks like there might be some more out there.

https://www.ebay.com/itm/Vintage-19...er-Set-Complete-in-Original-Box-/383710544581
https://www.ebay.com/itm/1334570941...v=DefaultOrganic&_trksid=p2047675.c101224.m-1

 

[aerostadt]

There actually was a two-stage version of the Alpha-1 called the Lunar-1. I had one of these. I remember that the first stage only went up a short distance, maybe just 10 feet and then the small second stage took off really fast and went up very high. I remember the water air-pumped rockets did the same thing. The first stage went only a short distance and then right away the second stage would go up very fast.

https://www.worthpoint.com/worthopedia/lunar-stage-moon-rocket-scientific-1721387633

 

[n3tjm]

I had the two stage one too! Looking at these pictures brings back so many memories.

 

[aerostadt]

So, what do your plastic parts look like?

 

[n3tjm]

I’ll post some pics once I get all the current revisions printed.

The new filament tube came and Igot it installed. I also decided to up the temp to 215 due to recommendations on forums about Inland brand pla+ on the ender pro. I extended the tank a little, and made some minor tweaks to the baking soda cup.

 

[n3tjm]

Finally got a working "firing pin" to print and be able to use without breaking (at least before a full pressure test). It is designed to use a spring from a common promotional clicky pen.

 

[n3tjm]

Version 4 of the Baking Soda Thimble is done printing and I must say I like how it came out . It does look like there is a glitch though. Looks like some of the ribs did not print. Looks like this is a problem in the Fusion 360 file. I must of accidently deleted 3 of the ribs. I will correct and reprint most likely tomorrow.

 

[Bruce]

This is very cool! I want to build one too! Might you be willing to post the .STL files so I could build one and help with debugging the project?

Thank you!

 

[n3tjm]

I am thinking about posting the stl files soon. I made a revision 4 version of the nozzle, making the rim thicker because the rim broke on the one I printed red and at 215C. I also made some adjustments to the launcher. Making the shaft thicker and adding the place to attach it to the launch pad. I also designed the fin can and fins for the first rocket. The fin can will slip over the motor and the fins will glue into slots on the fin can. That way they can be replaced easily if they break.

Here are the Version 4 Fuel Tank and Baking Soda Thimble. Version 3 Nozzle but the Rim failed. Version 4 will go on the printer soon once the current new launcher is printed (will be done soon).

 

[n3tjm]

Now I am beginning to brainstorm a safe rocket to fly with these. They won't go very far, so I am not sure if one of those $15 altimeters mentioned before would be ideal for this. One reason for this is they usually have a min altitude threshold, and I'd be surprised if this rocket will go above that. I am thinking that some sort of break wire timer will might be a better choice? Any thoughts?

Oh, another idea I had is maybe this will make a good sport rocketry article, but maybe I will need to be a little more scientific about it. Meaning... calculating what is the best amount of baking soda and vinegar is? Citric Acid and Water ratios? nozzle throat diameters? Do I need to go in that detail? Any one have a low power test stand I could borrow for such experimental research?

 

[Bruce]

Perhaps a small, light rocket with a blunt / soft foam nose like a stomp rocket? Fly over grass?

Maybe concentrate on the propulsion details before adding the weight of a relatively complicated recovery system?

 

[aerostadt]

Ordinarily, I don't think that these things will have a high altitude. I think the original Alpha-1 probably went less than a 100 feet. This is something that could be launched in someone's back yard. I like your baking soda cup design. The cup dome before the slots looks big enough that the soda won't fall into the acid during assembly. This is a problem that the original design had. I do love the overall original rocket design shape and contour.

 

[n3tjm]

Another frustrating thing I am running into... the tank leaks... upside down... with just gravity.... so I now I am doing a couple changes. Thicker bulkheads and walls, removed the anchor point for the shock cord mount, and I also set the z-zone setting to be random so it does not create a seam down the cylinder. This is where it seems to be leaking.

 

[n3tjm]

Good News and Bad News. Good news is setting the Z Seam Alignment to Random solved the case leakage problem. Bad News is now the path of least resistance is through the nozzle... not through the nozzle throat... through the plastic of the nozzle itself lol. I am goin try the Z Seam Alignment on the nozzle. Also, when I increased the temp of the PLA it changed the tolerances a little so there is some leakage around the o-rings. That can easily be fixed.

 

[n3tjm]

I just had a epiphany. I wondered if PLA+ is water proof. That might explain my leakage issues. So I google it. Sure enough, it is not. And I did a pressure test during lunch and this time all the seals held up fine but it was sweating everywhere. So, PLA is a bad choice. So looking at what else my Printer can do, ABS might be the best choice. next time I am in the area of a Microcenter to pic up some ABS will bein a couple weeks, so I was wondering if anyone can send me a parial roll to play with? I'd like to try ABS out before I invest in buying several rolls of various colors.

 

[Bruce]

I am thinking about posting the stl files soon.

Perhaps if you posted the .STL files, we could print and test it and get some feedback to you?

 

[n3tjm]

Hint Hint Hint.

How about this. If anyone wants to print and test it, PM me and I will send the current STL files. I really don't want to make them public until I am done the project.

 

[JoePfeiffer]

I just had a epiphany. I wondered if PLA+ is water proof. That might explain my leakage issues. So I google it. Sure enough, it is not. And I did a pressure test during lunch and this time all the seals held up fine but it was sweating everywhere. So, PLA is a bad choice. So looking at what else my Printer can do, ABS might be the best choice. next time I am in the area of a Microcenter to pic up some ABS will bein a couple weeks, so I was wondering if anyone can send me a parial roll to play with? I'd like to try ABS out before I invest in buying several rolls of various colors.

I had similar results experimenting with printing e-bays in PETG. Could not stop getting a nasty pressure spike when ejection charges went off, and finally discovered through a water test that the e-bays were leaking like sieves! I've gone back to only printing things like the sleds, and have utmost respect for those who've gotten printed bays to work.