Nitrous Deployment

[kramer714]

Just wanted to run this one past the 'collected masses'. I have been working on a concept for a 'motor topper' that can be used on Hybrid Systems. The basic concept is a small chamber at the top of the motor with a check valve in it. When the hybrid motor is filled, the chamber fills with nitrous. At a set altitude or time, a valve or burst disk releases the nitrous into the rocket as a deployment charge.

Has a few advantages over pyro systems, including;

No pyro
low cost, no consumable parts other than the nitrous
safe handling until the motor is charged (safe to walk around with)
not subject to altitude ignition problems.
low volume / good location location on the rocket.
Safe and arm can be tied to motor pressure.

Problems as I see them,
How to 'disarm', possible pin hole leak or small vent valve.
Temperature issues.
Electronic system to open a valve?
Doesn't help for dual deploy

Any thoughts?

 

[TheAviator]

The only really big problem I see with this is that nitrous is an oxidizer (otherwise we wouldn't use it in motors!) Paper is simply an alternative form of cellulose, which has been used as fuel. Basically what I'm saying is that this has the potential to turn your rocket into a Roman Candle.

I would suggest a CO2 system as an alternative. I know that Caleb Boe developed a reusable CO2 system last year, check out the NARAM-50 R&D reports.

 

[kramer714]

using CO2 would add another entire system. The goal is to use the nitrous that fills the motor to eject the chute too, one less system plus safe to handle.

I don't think that the nitrous would react with the body tube unless there was a good source of heat. If nitrous would react with combustibles that easily, whipped cream cans would be exploding on the shelf.

 

[jderimig]

I think it would work. N2O has about the same gas properties as CO2. 12g should be enough to pressurize up to 4" tubes easily, 16g if larger.

The hard part is the valve. There is probably nothing off the shelf you can use. You'll have to make one yourself that will hold 700-900psi but be able to be released with a small servo or motor. Pyro actuated valves are probably out.

 

[troj]

As a separate chamber, on top of the motor? I think it's very viable.

-Kevin

 

[Handeman]

I'm not sure about the NO2 vs. CO2 or if it makes that much difference. As it was stated before, the problem is the valve. It has to dump the whole amount of gas in well less then a second or it will never pressurize the tube enough for ejection. The valve would have to

1. Hold up to 1000 psi.
2. Have a large flow when open
3. Open with minimal electrical energy (MAWD cap discharge)

This is not a simple engineering problem and in all likelihood, is not something that can be build in even well equipped home shops due to material and tolerance requirements.
I would guess the cost of the valve, in the number of quantities that would be used by "some" of the hybrid motor users, would be in the $200 - $300 range at best.

Not to throw cold water on the idea, but the valve is really the key to the whole thing. In fact, if someone can design a valve that would work that way, I suspect there are a lot of applications where it could be used in industry and a patient might be very valuable.

Maybe look into the methods used to release the high pressure air used to launch torpedos and missiles out of submarines. Maybe they can be downsized.

 

[Shade]

Maybe look into the methods used to release the high pressure air used to launch torpedos and missiles out of submarines. Maybe they can be downsized.

They used large diameter ball valves and a surge tank located
nearby with minimal piping, well they did in the WWII subs when
the torps were ejected out of the sub with impulse air, they do
it differently today.

The problem as I see it if you use a valve is getting a servo with
enough torque to open the valve fast enough. I think it is do-able
but will take some experimental work.

Another option, is a frangible (ceramic) burst disc, then you could
use some sort of spring loaded firing pin to shatter it. Like using
a snap punch to break shatter glass. The firing pin then would be
actuated via a timer or altimeter. If you make it a stand alone system
just have 2 of them for DD.


Just pick your problem a materials problem or an engineering problem.

 

[kramer714]

not saying it is easy but....

The key to the valve is not to use a direct loading valve but use a piloted valve, a diaphram valve (tough at these pressures), a metal bellows valve, piloted toggle valve or a simple reset-able cartridge valve. All these use the service pressure to help hold the valve shut, releasing a small amount of pressure opens the valve.

Actuation can be done by a small solenoid that opens a small valve (small = low force). A simple 9 volt linear low stroke solenoid is what I had in mind. Remember I'm not opening the valve as much as reliving the pressure on one side of the valve.

I had thought about a burst disk, one of my goals is for the system to act like a motor topper without having to install parts each time. Kind of tough with the burst disk.

 

[DaveHein]

I had thought about doing a non-pyro CO2 ejection a couple of years ago. The animation shown below demonstrates how it would work (click on the picture to see the animation). The CO2 cartidge is screwed into the valve to pierce the end of the cartridge. An o-ring maintains the pressure seal on the cartridge. At the time of ejection a solenoid or servo pulls up on the top lever. This releases the other lever, which allows the cylinder and o-ring to slide to the right. The CO2 gas escapes out of ports on the sides of the valve.

I never built this, but maybe there is someone else out there that might be interested in building it. The main drawback to using CO2 or nitrous for deployment may be the weight of the cartridge and the valve. It's hard to beat the energy density of a black powder charge.

Dave

 

[kramer714]

I like the concept, this is like the toggle valve I was talking about.

From a weight standpoint, I think the weight hit would be pretty low if you start off using a hybrid motor. A bunch of the valve could be built into the upper closeout of the motor.

 

[Lentamental]

A site that could prove very useful to you would be Spudfiles.com, which as the name suggests, is a spudgun forum. There you will find some of the smartest, and most advanced home made pneumatic designs around, and many of them could be modified to fit this exact purpose. There is one person in particular, "Brian the Brain" whose work you will definitely want to check out. He has done a lot with CO2, in very small and efficient cannons.
Kramer was right when he talked about diaphragm valves. Piston and diaphragm valves (known in the industry as QEVs, short for Quick Exhaust Valve) have a small pilot that, when vented, releases all of the air quickly. On spudfiles you will find all sorts of ways people have scratch built their own valves from standard pipe parts, and some good L type copper pipe should hold well over 1000psi. I would highly recommend the use of some other type of compressed propellant however, with a much lower vapor pressure, such as propane, or something of the sort, because it is really much easier to deal with 120psi than 830psi (CO2s aproximate pressure at room temperature).

Best of luck, and keep us informed on what you decide to do.