Smooth transfer of power

With 5000 lbs of force pushing on the body of the rocket engine, you have to bolt it down securely or else you'll have a 300 lbs steel tank flying through your windshield and the car sitting there steaming.

Since a roll cage is really a necessity in a rocket car anyway, I figure that's really the best way to transfer that enormous amount of force to the chassis of the car. I haven't been able to find any exact dimensions of real 924 or 944 roll cages, but I've eyeballed some pictures on flickr and I think I've built a fairly accurate model. Everything is parametric anyway, so I should be able to change it around once I find some real dimensions.















Also, I came across a possible difficulty in manufacturing the design as it stands now.
The problem is that the exit diameter of the nozzle is larger than the bolt hole circle that connects it to the rocket. It's clearly possible to drill the holes for it from the far side, but all of these holes require counterboring (or spotfacing) as well:















My first thought was to use a normal counterbore, pushing the shank up through the hole and into the spindle of a mill, then cutting the spotface by pulling the counterbore upwards. Unfortunately, no counterbore I've ever seen has a ground cutting edge on the top. Also, very few have a shaft that would even fit through the M8 bolt holes.

So what I think I'm going to do is use a 5/16" boring bar (McMaster #32435A12) with a tiny nib of a cutting tool sticking out. It is going to be a pain in the ass to insert and remove to tool 20 times though.

As it stands

I've been messing around in SolidWorks with my design and I wanted to share what I have so far. The current design is based on 12" Type 304 Stainless Steel SCH40S Pipe. It has welded heads, a bolted-on nozzle, welded in ports for a fill plug, 3x 9kW electric immersion heaters, and a junction for the compressed air that will actuate the main valve.

If you have Solidworks, click here for the files.

Also, if anyone happens to have any CAD files for a Porsche 924 roll cage, that would be great too. Probably not, but it was worth it to ask.

This Crazy Project

During my Junior year of high school, I has a unique opportunity to do a science fair project to present at an event in Beijing. I ended up building a mono-propellant hydrogen peroxide rocket engine. It put out a thrust of about 500 newtons. Now, I'm in college, and I've decided to build another rocket engine, except that this one will produce about 22,000 newtons. At this point, all of this is really just an idea, and while I am continuing to work on it, I think completion is still years away.

Here's the plan:

An 85 Liter tank of water is heated to a temperature of 250° C (480° F). At the desired moment, the water is released through a piston valve to a Convergent-Divergent nozzle, generating steam moving at more than 1000 m/s. The reactive force pushes the tank and the Porsche 924 to which it is attached at huge acceleration.

That's the plan anyway. As I do this research the estimated costs for the project just gets higher and higher, so much so that I really don't even feel like talking about that part of it.

I've created this blog in an effort to document the design process, and hopefully a forum for people to speak up and correct me on anything that might have otherwise led to 3rd degree burns.