The DYI GO-kart Project: Rocket design
Posted: 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.
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 ). 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.
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.
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 ). 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.