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The DYI GO-kart Project: Rocket design

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The DYI GO-kart Project: Rocket design

Unread postAuthor: DYI » Thu May 15, 2008 6:44 pm

Me and 3 friends are building a human scale rocket propelled vehicle, likely unmanned. We've set out to achieve at least 150km/h with it, more if funds allow. I'm not going to be discussing the frame here, as we already have that sorted. What I will be discussing is something a bit closer in spirit to our collective hobby: The rocket.

We've had several rocket designs, but for the final version, we settled on 3 different designs to choose from:

1. CO<sub>2</sub> rocket. Judging by the fuel:weight ratios of the tech class liquified gas rockets, we'd need about 200lbs of CO<sub>2</sub> to propel even our lightest design up to a decent velocity. Just in case you didn't know, 200 pounds of CO<sub>2</sub> ain't exactly cheap. Or even reasonable. The advantage of this design is the simplicity, safety, and ease of construction. Liquified carbon dioxide won't run much past 1000psi even on a really hot day, meaning that the containment vessel wouldn't be very difficult to build - simple SCH 40 4" steel pipe would be fine. Of course, the very low pressure and low speed of sound means that thrust isn't the greatest.

2. Liquid O<sub>2</sub>/gasoline rocket. Probably the best thrust:weight of any of the options, but also rather difficult to construct. The fuel would be cheap compared to option 1, but the materials required to build it would likely end up nullifying any savings on fuel. It would certainly be entertaining, but it could be a pain to get it working, and could end up a bit over our rather low budget of only $2.5k or so.

3. My personal favourite, and the one I'll be discussing here: Superheated H<sub>2</sub>O rocket. :twisted:
The fuel is free, the design is fiendishly simple, and the available power is enormous.

Essentially, it uses superheated water to create a steam explosion when the pressure is dropped below a certain level.

My design calls for filling the chamber 95% full with water, and pressurising the remaining space to 1000 psi with nitrogen, after which the gas supply will be disconnected. The chamber will then be heated to 300 degrees Celcius with a resistance heating coil, at which point the pressure in the chamber should be at slightly under 2000psi, and the H<sub>2</sub>O will still be in the liquid state. At this point, the heater is disconnected, and a firing valve connected to the gas space at the top of the chamber is opened (remotely, or course :roll: ). The pressure will vent until it drops below the boiling pressure of the water in the chamber. When this happens, the water in the chamber will flash boil, and vent out the nozzle (directly after the firing valve) as fast as the flow rate will allow. Something like this should happen very soon afterward...

Before anyone asks, I can handle the pressure generated. We're probably going to be casting our own chamber for this thing. Any suggestions on how to reduce overall weight, fine tune for greater performance, or simply improve the design should be posted. Comments explaining to me the gruesome details of my imminent demise are neither required nor appreciated.
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Unread postAuthor: ammosmoke » Thu May 15, 2008 6:53 pm

Well, it seems to me that you have already decided what you want to do.... Steam. I think that steam is a very good idea. Although, where the heck are you going to do this, and why?
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Unread postAuthor: judgment_arms » Thu May 15, 2008 7:00 pm

ammosmoke wrote:and why?

Well that was a dumb question… :wink:


Sounds slick DYI, if you going to make you own chamber I recommend at the very lest remote testing if not hydro testing… to me it sounds like a good way to remove stumps…
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Unread postAuthor: igpay » Thu May 15, 2008 7:01 pm

Holy Jeezcats Batman!(I <3 saying that)
Thats some serious stuff youre planning there!
Suggestion to lower weight: All Carbon Fiber!!! :D
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Unread postAuthor: DYI » Thu May 15, 2008 7:11 pm

Hopefully, we'll be able to do a hydrostatic test on the finished chamber. Either way, it's going to be done very remotely.

The where will be a long, straight road which we'll block before the test, the when will be early morning on a day in the late summer, and the why?
Because I can, of course :D

And to anyone who didn't read the first post but wants to answer anyway: Our budget is not unlimited. We cannot build the entire thing from titanium alloys and carbon fiber. Unfortunate as this is, we are not NASA.
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Unread postAuthor: Acdcmonkey1991 » Thu May 15, 2008 7:11 pm

first off, I can't wait to see this built, simply because I have been drooling over the subject of high powered water rockets for a year or two now. to reduce the wieght, I would suggest an aluminum frame. How heavy is this going to be and how large do you plan to build your chamber?
I am still not getting the flash to steam part though...
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Unread postAuthor: igpay » Thu May 15, 2008 7:14 pm

try looking at this ACDC
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Unread postAuthor: TurboSuper » Thu May 15, 2008 7:22 pm

I think this is what the O2/Gasoline rocket was doing, but why not a hybrid rocket motor?

You don't have to use gasoline, ABS shavings or even cardbard would work perfectly fine.
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Unread postAuthor: DYI » Thu May 15, 2008 7:24 pm

The frame is already being made from aluminum. I'm talking about the rocket itself. The frame has already been optimised as far as our funds will allow.

I'm hoping for a few cubic feet of chamber. As far as we know, we'll just use concrete for the mold.

At 2000psi and 300 Celcius, the water still won't have reached its boiling point, although the entire volume will be heated to 300C. When the pressure drops, so does the vapourisation temperature, and the entire volume of water will suddenly be above its boiling temperature (i.e. superheated), and will flash to steam as fast as the flow through the nozzle will allow.

We already designed a hybrid rocket motor, and decided that it wasn't feasible. It was actually one of our first designs.
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Unread postAuthor: igpay » Thu May 15, 2008 7:28 pm

I get the superheating process now, sounds awesome.
But how do you stop the steam from escaping when you open the valve?
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Unread postAuthor: ammosmoke » Thu May 15, 2008 7:33 pm

Well, it certainly was a dumb question in that sense. (Because you can, duh!) But, I was kinda wondering if you were doing it for a competition or something.

Well, I suppose you can use an aluminum foil burst disk, then shoot it with a 22' rimfire....
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Unread postAuthor: DYI » Thu May 15, 2008 7:46 pm

When I open the valve, there is no steam. You obviously don't get it yet. The steam is created when the pressure of the water drops to the point that it can begin to boil, as it is already fully heated to 300C.
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Unread postAuthor: igpay » Thu May 15, 2008 8:07 pm

I know, but isnt the valve still open as it flash steams? Oh, and i forgot to ask, what type of valve will you be using?
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Unread postAuthor: FordGtMan » Thu May 15, 2008 8:11 pm

I think you are going to need something with a little more juice...lol

http://youtube.com/watch?v=JtosxwPAV2E&feature=related







:D :D :D
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Unread postAuthor: turbohacker » Thu May 15, 2008 9:22 pm

Well your in luck! I just stumbled apon a new interesting rocket engine idea that i decided to test.

I just tested this crude prototype and it produced an impressive amount of thrust for its size. It is constructed of a peice of half inch pipe about 6 inches long. I welded a 1/4" plate with a small hole in it to one end of the pipe and i threded the other end with a standard 1/2"pipe tap. I then threded a "t" into this and plumed up the oxygen bottle. (i had to plumb up the acetylene bottle too just to ignight the rubber, but i can turn off the acetylene after it starts running.) I have only run it off of fuel hose because that is what i had. Anyways i thaught with a little experementation this could be a viable propultion system for your project- heck it worked on spaceship one...

Image

Image

I dont know if the video will work, and if it does than sorry for the poor quality...

[youtube]http://www.youtube.com/watch?v=qrzQrgmdY-4[/youtube]
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