Going to build a hybrid rocket from scratch, tips apreciated

[rock]

Hello

I am a student of mechanical engineering and my next project will be a hybrid power rocket. This is outside of the curriculum so i cannot really expect any help from the university more than locales to work in.

This will be a rocket from scratch, i'm thinking of a very simple design to start with, two paintball co2 tubes joined, with some kind of regulating valve in between. The oxidator will most likely be NO2. The choice of fuel has not been decided, but expect something simple.

So, lets get to the fun parts, how to make it. A couple of questions right from the top of my head:

1) When you buy the over the counter pressure containers designed for paintball use, i suppose you want to change the valve. To what type of valve? Is it a straightforward operation just unscrewing the things, or are there measurments to prevent you from doing that? What kind precautions must one take when assembling the new valve with the tank. Supposedly that tank has to hold 300 bars of pressure, so you dont want anything but a rock solid fit. Are the measurments standard, are there a specific brand of valves or tanks preferred?

2) Nozzle manufacturing. How do you know what type of nozzle to use, is it simply a figure it out as you go along type of deal? Should the back end of the combustion chamber tube be threaded for greater resistance to failure due to overpreasurization? Finally, material, what kind of material, and where can i get a hold of it, say a 5 times 5 cm piece of graphite?

3) How straight can you expect your rocket to travel? I can imagine that if you get the slightest missalignment when lathing the nozzle, you screw up the trajectory of the rocket big time. Any tips on how to make the flight as straight as possible?

4) Fuel, what type is recommended. I read somewhere that you can use plastics, like polyethylene, and alltough you can cast that relatively easy, i cant imagine it being near that easy to light it with a match, or whatever ignition technique you prefer. You have to cover it with some type of easy ignitable solution in order for it to catch, so that you will get some kind of combustion.

5) In order not to reinvent the wheel, and save a buck or two, i'd like to for our first project at least, to be inspired by a previous design. Is there a suitable project thread on this or on a similiar kind of internet forum that you could refer me to?

 

[tsai]

I can't answer most of your technical questions, as I am not a hybrid flyer, myself. What I can do is make sure you are aware of the regulations in place for what you propose to do.

I don't mean this to sound as a "don't do it" message, but more as an FYI of what lies ahead.

1) All hybrids are categorized as HPR (High Power Rocket) motors. For all practical purposes, this will mean an FAA waiver to fly it. The easiest way to fly under an FAA waiver is to fly with a club that already has the waiver.

2) Most clubs with FAA waivers will belong to NAR or Tripoli. Since you mention neither, I'm going to assume you are not a member. With few exceptions, you will need to join one of these organizations to fly HPR with these clubs.

3) Your particular spin is making your own rocket motor, not just rocket. This falls under the category of Experimental or Research rocketry. You mush be level 2 certified with Tripoli to engage in these activities. Further, you can only launch these at an event designated as a Research launch. NAR does not have provide a categorization for this activity.

As for your technical questions, I would strongly suggest you purchase an existing commercial motor system and reverse-engineer from a known working state. HyperTek and Sky Ripper Systems are two of the hybrid manufacturers I know off the top of my head.

Good Luck! Sounds like a fun endeavor.

Cheers,
- Ken

 

[eggplant]

https://www.skyrippersystems.com/

That is a manufacturer of commercial hybrids. You might be able to get some inspiration from them, or possibly use some of their parts. You will not have to worry about the regulations if you only build and burn the engine, not put it in a rocket.

 

[bobkrech]

Rock

Making rocket motors is not for beginners. In the US you must be high power certified by either NAR or TRA to launch any high power rocket which includes all hybrids. You are not going to get advice on making a hybrid rocket motor from scratch on TRF.

Bob Krech, TRF Moderator

 

[CarVac]

You can't use CO2-designed canisters, valves, and others, because NO2 is an oxidizer and thus could degrade the seals and corrode the metals, causing HUGE safety issues.

 

[edwinshap1]

CarVac brings up a good point. While a single run of NO2 may not cause any serious damage, over time the canisters would fail at one point or another, and if you're designing this rocket to actually fly, then you'll want to design it to be 100% reusable.

As to what the above posters are saying, they are missing one key fact. If you intend to launch within the regulations set forth by TRA's experimental regulations, you will need to be in Tripoli and level two certified (successfully fly a motor with over 640 N*s of impulse).

However, some clubs have the necessary waivers and permits to launch experimental vehicles without TRA or NAR requirements. I know of two within a two hour drive from my house, both of which have much more stringent safety requirements, but also allow for experimental solid, hybrid, and liquid fuel testing and flying.

Since you are with a university, I would expect that you will not have too difficult a time finding a location to launch, but you will need to ground test the motor before trying to send it up, or you'll be begging for disaster.

 

[G_T]

You can't use CO2-designed canisters, valves, and others, because NO2 is an oxidizer and thus could degrade the seals and corrode the metals, causing HUGE safety issues.

It is a good oxidizer once decomposed at around 600 degrees... It is not an oxidizer when stored as a gas or under pressure as a liquid. Thus the issues are a bit different than the case of LOX, H2O2, RFNA, etc.

Gerald

***** CORRECTION ***** I had assumed you made a typo specifying NO2 instead of N2O. The previous poster is likely quite correct about some of the dangers of using NO2.

 

[G_T]

I was presuming you mean N2O for the oxidizer rather than NO2. My previous comment DOES NOT apply to NO2. Moisture + NO2 is going to be corrosive, and I really wouldn't want to be breathing traces of the gas. I do not know its properties well enough to want to comment on it. I'd suggest using N2O instead.

If you really want to build your own hybrid motor, you probably could copy an existing design and make it work. If you want to design your own motor though, a bit more reading may be in order.

I'd suggest the following sources:

Hybrid Design Factors, by William H. Colburn

Fundamentals of Hybrid Rocket Combustion and Propulsion, by Martin J. Chiaverini and Kenneth K. Kuo, editors

Rocket Propulsion Elements, by George P. Sutton and Oscar Biblarz

Space Propulsion Analysis and Design, by Ronald W. Humble, Gary N. Henry, and Wiley J. Larson

Modern Engineering For Design Of Liquid-Propellant Rocket Engines, by Dieter K. Huzel and David H. Huang

I'd recommend the Colburn book for a start if you can get it. If the task still interests you, then dive into the others.

Hybrids are a direction I've been considering, and that was some of my reading list to become educated for the task.

0.02c

Gerald

 

[dave carver]

If I remember right he does not need to belong to one of the rocket orgs. If it's a college project then there an exclusion in the codes covering it.

...if it's a college project.