Questions about Rocketry

Aerospace / RC
#1

I’m looking to build a small experimental, liquid rocket motor (Not a rocket, just a bench model). I plan to use liquid propane and carbonated salt water as propellants. The reaction is room temperature, and there is no flame or combustion. Pressure is generated solely by the liquid propane changing to gas. As the temperatures involved should be between -50 and room temperature, all the custom parts can be printed without worry of melting them (even the nozzle).

My questions are:

  1. Are we allowed to do experiments like this?
  2. If so, who would I talk to about doing it?
  3. Is there a committee for this? (Aerospace or science?)
  4. Is there anyone interested in doing it with me?
2 Likes
#2

Pressure creates heat, and so does the friction at the nozzle. I’d be very surprised if ABS could handle anything high pressure enough to achieve the kinds of velocities normally associated with rockets. Has this been done before?

#3

I doubt there would be heat generated unless there was an ignition source. The pressure would likely be too high for plastic. You might get away with aluminum.

#4

I’ll state again, this is a bench model. It is not going to be producing a usable amount of thrust. It will never be installed in a rocket, nor will it ever attempt to fly. It will be mounted to a board. It is merely a platform to learn about the plumbing of liquid rocket motors. Making models like this is very common practice. Many variants of these models can be found documented on You Tube and various other sources. A simple google search will lead to many others. Heres a link to one of my favorite You Tubers and his model using nitric acid and bicarbonate solution
Cody’s Lab liquid rocket motor model

2 Likes
#5

Please note the materials used in his model :slight_smile:

#6

  1. Is it allowed? Now that you have asked, I’m sure someone can complain ore make up an excuse to try and stop you. But, yes until someone officially tries to stop you this is allowed. But, your working with propane so take appropriate precautions, aka be outside.

  2. Who do I talk to? No one, be safe. Fund your own project and don’t store the propane at Dms.

  3. Is there a committee? Nope, the closest I know of is @Bill makes solid fuel rockets from time to time and @Lampy and I build rockets with a pyrotechnics group locally.

  4. Is anyone interested in doing this with me? Probably not, but if your excited to build it and learn go for it. But, please be safe. If you wouldn’t do it in your house/garage don’t do it at the Makerspace.

4 Likes
#7

This could fall under either committee, if either wanted to get into it… :slight_smile:

On that note, I know that the current Chairperson over Aerospace / Remote Control hobbies committee has been swamped at work, and has mentioned that he doesn’t really have the time to devote to being chair at this time. We will be having chair elections soon. There may very well be an opening for the Chairperson role for that committee… (hint hint). Who knows what direction, and which types of projects, the committee will focus on going forward. :wink: :slight_smile:

#8

liquid propane

If you aren’t igniting it, why not use something nonflammable instead? Large volumes of propane gas created by this process seem like they’d be a fire hazard.

A motor which is actually firing (burning) would be safer, as it would be consuming fuel and creating nonflammable exhaust products.

4 Likes
#9

Using a true combustion would mean that I could not print ABS parts capable of the task. Also, yes, many gasses work, but LPG is of the proper temperature range (low enough that it will rapidly expand when introduced to a room temp liquid but not so cold that it will make the plastic brittle enough to fail). There may be other gases that are suitable, but I’m unaware of how to source them in large quantities.

#10

Gas cools when expanded such as in a nozzle.
Now as far as pressure is concerned, FDM is apparently capable of quite a bit as demonstrated by our friends at Defense Distributed

What about using a 3D print for an aluminum (or copper) casting? It wouldn’t survive for long as the throat gets eroded through quickly but it would be interesting nonetheless.

#11

Again, ABS plastic should work fine and can be printed right on the Polys at DMS

#12

I’m not against changing materials if needed, but I wouldn’t want to needlessly complicate the project at this stage.

#13

I doubt you’re gonna be able to get any type of sealed chamber through 3d printing. I had a hard time trying to get one my designs to hold water without any pressure. Not sure the types of structures your planning on printing, but I don’t think they will be able to contain pressurized gas.

#14

Instead of LPG, you could use the same stuff as in air duster cans.

1 Like
#15

Was going to ask the same about CO2 assuming the carbonated salt water wouldn’t freeze and clog the nozzle.

#16

Not exactly the same as the OP, but air pressure rockets, made of plastic, have been around for quite a while.

https://www.walmart.com/ip/Estes-Sonic-Boom-Air-Rocket-Launch-Set/49156027?wmlspartner=wlpa&selectedSellerId=0&adid=22222222227037675540&wl0=&wl1=g&wl2=c&wl3=80417829169&wl4=aud-273067695102:pla-177634929889&wl5=9026804&wl6=&wl7=&wl8=&wl9=pla&wl10=8175035&wl11=online&wl12=49156027&wl13=&veh=sem

With some proper precautions (shielding), it seems worth experimenting with.

1 Like
#17

If r-134a is used the boiling point of it is about -15f at atmospheric pressure. Also r-134a has a high GWP. If you believe in the greenhouse gas. Coincidentally it is used in some dusters & inhalers.

I can not legally open a bottle though, last check was a 25,000$ fine.

#18

It is an interesting idea, I wonder if there is a way to reduce the localized cooling the expanding gas will cause on region surrounding the nozzle and the nozzle itself (not sure that makes a difference). Not sure ABS would get cold enough to affect the outgas, but as the system temperature decreases I am assuming the expansion you’d get would decrease. Maybe hot water to counteract the cooling and cause the gas to expand more rapidly. The other worry is what happens to ABS’s properties when it is cooled a bunch. Also wonder if the thrust would increase much more than the outflow pressure… but that is what experiments are for.

#19

Yep, experimentation is the best way to find out. With some plexiglass shielding, should be perfectly safe to experiment with, at least at reasonable sizes.

#20

Yup. Crazy big fine for venting a cooling system using R-134a into the atmosphere, but you can buy a case of air dusters or freeze spray and vent those all day. Same chemical. Go figure.