Hybrid GSE Safety Procedures

[sparksrockets]

Hi, I have posted a couple times before about various hybrid topics and am somewhat close to finally launching a contrail hybrid rocket. However, I have been reading up on various NASA oxygen (I know they are not the same thing, but I thought that oxidizer safety would be fairly similar and there is alot more documentation on oxygen) safety manuals and ways to design fill systems and I have some concerns. I would like to get some opinions on the following questions from someone who has done it before:

1. How far do you go in order to clean your system? Do you use IPA and such and then blowdown the system with dry GN2, or just visually clean it with soap or something?

2. I have bought and looked through the pratt hobbies ground system, but from my reading it seems to be missing various safety mechanisms such as relief valves and/or burst caps in case of over pressurization. Would this just be overkill, or should I be worried?

3. Do any of you try to temperature control your nitrous for optimal settings in hot/cold environments? If so, I would love to see an example set up.

4. Do any of you have a place that I can get saturated liquid N2O tables for property calculations? I have a small chart from aspire space that has some values, but I would prefer a chart with a large amount of data.

5. Is there any obvious must read material for N2O that would lead me to more solid safety procedures?

6. Am I just greatly overthinking this and should just trust in the commercial GSE?

Thanks in advance!

 

[jderimig]

1. N2O isn't LOX. Whipped Cream (a highly fatty hydrocarbon) is shipped with pressurized N2O. Soap, water, rinse is good enough.
2. Your DOT tank will have an 1800psi burst disk that provides the overpressurization protection for the system.
3. I use water buckets and blankets depending on field conditions. For me keeping the tank cool and Nitrous density up in the summer is the challenge.

 

[H_Rocket]

The single biggest thing I can think of is your o-ring grease - you need to use something like Krytox (PTFE based) any petroleum based lubricant is an explosion hazard.

1. How far do you go in order to clean your system? Do you use IPA and such and then blowdown the system with dry GN2, or just visually clean it with soap or something?

If you are talking about the motors, I just wipe them out with a dry paper towel. I've never seen motors as clean as a hybrid is post burn.

2. I have bought and looked through the pratt hobbies ground system, but from my reading it seems to be missing various safety mechanisms such as relief valves and/or burst caps in case of over pressurization. Would this just be overkill, or should I be worried?

Works fine. For small hybrids I personally think a dump valve is slightly over the top. I just wait a few moments then have a long handles cuter that I sever the fill hose with.

3. Do any of you try to temperature control your nitrous for optimal settings in hot/cold environments? If so, I would love to see an example set up.

I've been known to sit my tank in a bucket of ice water on a really hot day. When it gets too cold, hybrids are too intricate to work with in gloves. So I have no thoughts on warming a tank up.

4. Do any of you have a place that I can get saturated liquid N2O tables for property calculations? I have a small chart from aspire space that has some values, but I would prefer a chart with a large amount of data.

Never needed one. See #6

5. Is there any obvious must read material for N2O that would lead me to more solid safety procedures?

I just read the instructions that came with it. However I did have the advantage of an experienced gas jockey like Kevin O'Classen around.

6. Am I just greatly overthinking this and should just trust in the commercial GSE?

From someone who over engineers things as a hobby, take my word for this - you are making it harder than it is...

 

[jderimig]

The single biggest thing I can think of is your o-ring grease - you need to use something like Krytox (PTFE based) any petroleum based lubricant is an explosion hazard.

Al, I think this hazard is overrated for N20. How come whippit cartridges with whipped cream are not exploding all over the country?

But Al is correct, Krytox is the recommended grease for orings. Expensive but a little goes a long way.

 

[H_Rocket]

To be honest, I always accepted that Krytox was necessary in the N20 environment. Damn expensive stuff. IIRC I paid on the order of $60 for an itty bitty tube.

Wouldn't flaming whipped cream shooting out of a dispenser make a great you tube video?

 

[jderimig]

To be honest, I always accepted that Krytox was necessary in the N20 environment. Damn expensive stuff. IIRC I paid on the order of $60 for an itty bitty tube.

Wouldn't flaming whipped cream shooting out of a dispenser make a great you tube video?

Don't tell anyone but I once cheated and used pure silicone grease on a hybrid motor o-ring and survived to tell about it!

 

[Len B]

Krytox is a no go for Hypertek hybrids. Just an FYI.

 

[kramer714]

1. How far do you go in order to clean your system? Do you use IPA and such and then blowdown the system with dry GN2, or just visually clean it with soap or something?

Most of the systems stay pretty clean. Not sure if you have a monotube Contrail or one with a separate tank. The ones with a separate tank you clean just like a regular motor case (NOT THE TANK, JUST DOWN WIND OF THE INJECTOR). For the monotubes I clean them with alcohol and a shop rag.

2. I have bought and looked through the Pratt hobbies ground system, but from my reading it seems to be missing various safety mechanisms such as relief valves and/or burst caps in case of over pressurization. Would this just be overkill, or should I be worried?

The fill tank is DOT approved and has an over pressure relief in it. Make sure that ALL of your hardware between the tank and the solenoids is the real pressure rated stuff (Mcmaster has it all) don't use Home Depot fittings, once you are after the solenoids you shouldn't be that close to your rocket when you are filling it. Or if something isn't right when you are filling the tank and you need to take a look, send your kid up close to look at it, if somethings happens they heal much quicker than us old folks.

3. Do any of you try to temperature control your nitrous for optimal settings in hot/cold environments? If so, I would love to see an example set up.

You want to keep the motor in a reasonable range of pressures. Where I am (So Cal) too hot is usually the problem, I wrap the tank in a wet towel, evaporation cools it nicely.

4. Do any of you have a place that I can get saturated liquid N2O tables for property calculations? I have a small chart from aspire space that has some values, but I would prefer a chart with a large amount of data.

More info then you ever wanted.....
https://edge.rit.edu/content/P07106/public/Nox.pdf

5. Is there any obvious must read material for N2O that would lead me to more solid safety procedures?

Yup, read the directions, some call out for Krytox others call out for synthetic grease, follow what the guy who designed it said to use. Best way to do Hybrids is watch someone else do it and ask questions. BTW pay that forward. thanks Wayne Marzek, Ron McG, etc...

6. Am I just greatly overthinking this and should just trust in the commercial GSE?

Yup, Black Dog makes a good setup (Ron M helped me a lot when I was figuring this stuff out), Pratt knows his stuff too. Building your own isnt too hard either.

 

[Dave A]

To warm a tank you can use warm water in a bucket and try to maintain the tank pressure by having a gauge.
You want to get real hi-tech and get a bottle warming system from Nitrous Express.
It has a small electrical blanket. You can power it with a motorcycle or lawn tractor battery.
They even have an upgrade that does the temperature control via pressure switch.

 

[karlbaum]

Very good questions..

1) I clean my motors with dish soap just like I do solid motors. As for piping and parts exposed to nitrous IPA is a good cleaner. Never use any petroleum based products. Never oil regulators or pipe threads. Use teflon on pipe threads and pipe dope that is safe for use with oxygen only. Krytox is the go to lube for the o rings.

2) For your solenoid manifold you should be using a pressure gauge. I think it is a critical component. Ideal pressure is somewhere around 750 PSI give or take a hundred. As far as pressure relief the ground tank provides that for the closed side of the solenoid manifold. On the motor side it is less critical because of the open system. For the U/C valve motors like Rattworks and Contrail the nylon fill line acts as a pressure relief valve. If you are using Hypertek you can use nylon fill line as a pressure relief system.

3) Yes temperature control is critical. I place my tank in a bucket with a wet towel over it on days over room temperature. I have never had to warm a bottle but if I did I would use the bucket with warm water. The temperature is monitored with the pressure gauge. I also have a fish tank thermometer near the bottom of my tank.


I use a vent sensor to determine when the motor is full https://www.youtube.com/watch?v=TQFo-DyOEa8
If you are interested contact me at [email protected]

 

[karlbaum]

I also offer a hybrid launch control system that has a vent sensor. [video=youtube;vh3V2MvVK-w]https://www.youtube.com/watch?v=vh3V2MvVK-w[/video] The vent sensor circuitry is also available if you want to add it to your own GSE. If interested my email is [email protected]

 

[cwbullet]

Link did not work for me.

 

[jderimig]

Be careful with teflon tape upstream of your valves. A sloppy wrap with an overhang off the edge can cut off a fragment that can get stuck in your solenoid valve.

 

[karlbaum]

Link did not work for me.

Which link did not work?

 

[G_T]

N2O by itself is a monopropellant; therefore one should avoid potential inadvertent ignition sources.

As mentioned, petroleum products of various kinds are not compatible with N2O (+ probably lots of organics in general, powdered metals, etc). N2O can dissolve many of them somewhat, and the mixture becomes a "better" (easier to ignite and more energetic) monopropellant. N2O can have various other things dissolved into it (O2 comes to mind) which actually increase the energy required to get the N2O to dissociate, which render it no longer a monoprop. The gas mix (Nitrox) provided at the dental office is such a mix. It is not an explosive hazard because of the ~50% O2 content, but you wouldn't want to get it near a spark as it will vigorously burn most anything else.

That's why Whippit mixes are relatively safe. The N2O is not pre-mixed with a good fuel. In any event, N2O can mix with gasses and dissolve various other things. Letting N2O do either of these things can significantly change its properties. For the intended rocket motor use this is not likely to be a good thing.

N2O is an oxidizer once it dissociates 2(N2O) -> 2(N2) + O2 (triggered by the addition of sufficient energy) but before that it is a pressurized gas / liquid and a solvent of sorts. It is easier to handle than most other oxidizers because it is not a room temperature oxidizer. But nothing which works well in a rocket motor is ever going to be truly completely safe! Even if it is not a room temperature oxidizer, it is still a high pressure liquid/gas mix. If something goes seriously wrong, tank parts can become high speed projectiles even if there is no ignition. Any high pressure gas system can kill if mis-handled.

Mostly I'm just reinforcing what others have already said. Use as intended and it should be relatively safe.

If you get a non-ignition which vents the N2O through the combustion chamber, the rocket may still leave the rail. It depends on the area of the injectors. What you have essentially is a large water rocket but a bit more energetic (higher pressure and the liquid will expand to a gas in the combustion chamber unlike the case of a water rocket). In some instances N2O can contaminate and somewhat sensitize a fuel grain. To some extent this should make the fuel grain burn faster if re-used. IIRC, there was an O CATO due to re-use after a couple fill and dumps which contaminated the fuel grain. So if you end up inadvertently spraying liquid N2O over the fuel grain you might want to consider if you really want to use that grain...

Gerald

 

[kramer714]

G_T makes a couple of good points here,

If the fill lines let go, the rocket can / may / most likely will leave the rail, or at least jump up a bit. When I go to launch a larger hybrid, one of the things I do is to 'pump' the solenoid, hit fill for 1 second. Then check to see if there are any leaks (nitrous coming out of the motor = leaking fill), leaks near the vent, leaks at the fill tube connection, etc.

On this note, it is good form to cable tie the fill hose from the tank to the tower or something solid. This keeps them from whipping around and possibly damaging something at launch.

If the nitrous dumps through the grain, lots of bad stuff can happen, not just the grain absorbing nitrous, in some cases (Hypertech!) the grain can get cracks in it from the sudden cold temperature that can cause it to CATO. With Skyrippers, I have spit out fill lines, re-attached them, and then launched without any ill effects.

 

[jason-and-his-toys]

Lots of great answers / advise in this thread. My two cents will be in and about below!

Hi, I have posted a couple times before about various hybrid topics and am somewhat close to finally launching a contrail hybrid rocket. However, I have been reading up on various NASA oxygen (I know they are not the same thing, but I thought that oxidizer safety would be fairly similar and there is alot more documentation on oxygen) safety manuals and ways to design fill systems and I have some concerns. I would like to get some opinions on the following questions from someone who has done it before:

1. How far do you go in order to clean your system? Do you use IPA and such and then blowdown the system with dry GN2, or just visually clean it with soap or something?

I'll run a piece of paper towel on a dowel down a motortube if it looks dusty/dirty. No real worries. It's fairly common sense about pushing the reload out the nozzle end but there will be less grime and ease going this way and not the long way out the top. It will keep grease in the reload end not the NOS tank.

2. I have bought and looked through the pratt hobbies ground system, but from my reading it seems to be missing various safety mechanisms such as relief valves and/or burst caps in case of over pressurization. Would this just be overkill, or should I be worried?

All the motors you fly are vented. Hard to over pressure a vented tank while filling. The storage tanks have burst valves to protect them. Pratt GSE will load and launch with no issues. I elected to build my own system as a project. Was fun and I can fix it if there is issues.

3. Do any of you try to temperature control your nitrous for optimal settings in hot/cold environments? If so, I would love to see an example set up.

I try to keep my tanks at the temp I want them at all the time. I set up a piece of sonotube, I think it was 10 inch, and used two part foam to insulate up to the tank. Works good to keep heat out, or in depending on the day. I'll put a towel around the top to keep sun off the tank, add water or ice for real hot days. The towel also keeps it warm enough when flying in cold weather. Take the tank out of the truck just before you fly and it works great. The heat wraps that run on batteries suck a whole lot of power and don't seem to do a whole lot in my view.

4. Do any of you have a place that I can get saturated liquid N2O tables for property calculations? I have a small chart from aspire space that has some values, but I would prefer a chart with a large amount of data.

5. Is there any obvious must read material for N2O that would lead me to more solid safety procedures?

If you follow the manufactures directions regarding pressures and protect yourself from direct contact with liquid nitrous you should be fairly safe.

6. Am I just greatly overthinking this and should just trust in the commercial GSE?

You are getting too worried about this. Just get to know your GSE and figure out what works for you and fly as much as you can!
Couple of random add ons: Do not use krytox on HyperTEK grains. Like Len said not recommended. All I use is DOW 111 for grease on nitrous end orings on all motors. Nozzles and grains get standard grease. I recommend you do not use any grain that have had nitrous dump through them. I have had a K Contrail dump through the grain and when I took it apart it had froze and pulled the one side of the grain in so far it looked like a heart when looking end on the grain. Kinda cool. Need to find that picture. HyperTEK grains will micro fracture and pop when they do light the next time. Been there done that as well. The best thing I did for flying hybrids was set up a wireless camera system to monitor the vents on fill. At 300m it's very hard to see vents! I've had poor success with the indicator lights but I haven't tried anything lately. As others have said I'll usually do a short burst at the pad just to check for leaks or a line popping off. Sucks to have to go back out and hook something back up. Makes hybrids look finicky and I like smashing that myth!

Jason

Thanks in advance!