The DYI-KART: Build log

[DYI]

After seeing the responses in my original thread on the topic, we've decided to use a hybrid rocket design for the kart. At this point, we're still in a design phase, and the actual construction won't start until July, but here's what we have so far:

Engine:
Type: Fluid oxidiser/solid fuel hybrid
Inside Diameter: 4.5"
Length: 72"
Fuel: Paraffin
Oxidiser: N₂O (50L of the liquid, to be precise)
Mass of casing: ~650lbs
Mass of oxidiser tanks: ~200lbs

Body:
This thing's essentially a very large engine with 4 wheels and a guide on the bottom to keep it on course. The frame will be built from structural aluminum tubing and welded, and we think we can keep its total weight well under 200 pounds, probably a lot less that that.

Guidance:
Rings on the bottom, which a steel cable is passed through. The cable will be anchored at the height of the rings off the ground and tensioned, causing minimal friction during normal operation.

We're melting down steel for the rocket casing using charcoal being burned by a high pressure, high volume, high flow air supply, with supplemental oxygen for throttling the burn rate. The steel will be melted down in high temperature rated ceramic containers in 5L batches, then poured down to the bottom of the concrete mold. After the whole thing is cast, we wait for it to cool, and then smash away the brittle concrete, which will have been severly weakened by the molten steel. The outside can be done with a sledgehammer, and the inside will use slightly more creative means.

Valving should be a minimal concern, as this thing won't have any throttling capabilities whatsoever (or any steering, braking, or overpressure safeties ).

This thread will be kept updated with details of the build. Input from any of the resident rocket scientists is, as always, greatly appreciated.

[Maniac]

Valving should be a minimal concern, as this thing won't have any throttling capabilities whatsoever (or any steering, braking, or overpressure safeties ).

Sounds unsafe I know you know what you are doing though I think.
Just one question what kind of speeds do you think you will be able to achive with this kart, or is that yet to be determined.

[DYI]

Sounds unsafe I know you know what you are doing though I think.
Just one question what kind of speeds do you think you will be able to achive with this kart, or is that yet to be determined.

I'm waiting for the rocket scientists to give me a rough idea of the maximum speed, but I can almost guarantee that it will be WELL over 100mph.

[Maniac]

I can almost guarantee that it will be WELL over 100mph.

Hmm i was thinking way higher than that, but im no rocket sciencetist. Who will be "driving" this you or will you get another poor soul to test it out. Also where will you be driving this you must have soe very long stretch of lightly used road near you.

[clide]

Sounds like an unmanned cart, I don't think he is insane enough to ride in something like that.

How do you plan on stopping it?

[DYI]

It will be on a long stretch of private road. We've got lots of volunteers who don't seem to care that they might get smeared all over the road. The owner might not like that very much, but any remains would be so charred that we could probably scrape them up pretty easily. Of course, someone would start asking questions eventually...

And as for stopping: It'll stop when it's damned good and ready

[starman]

Hmmm let's see here....no throttle, no steering, no brakes, no safeties...basically straddling a NOS/paraffin bomb... ...I'm voting with the unmanned crowd, at least until a few "proving runs" are performed.

Did you happen to catch the Mythbusters NOS/paraffin confederate rocket episode? The burn and acceleration on that thing was vigorous to say the least. They also did a followup episode where a NOS/meat rocket detonated on the launch pad.

Considering the risks, are you sure this particular form of locomotion is really that worthy an experience?

[TurboSuper]

Huh...so you did use the hybrid rocket after all

[Fnord]

You're going to have problems with casting the steel. Which problems, exactly, I can't say, but you'll have problems (I know from personal experience).


As for overall "danger" factor, I'd give this about a 6/10 unmanned, and 37/10 manned.
A rocket that size could get the thing moving more than 100 mph, but how much more, I can't say. You're going to have get some solid numbers down before much experimentation is done.

[DYI]

Okay, a small change has been made to the method:

Apparently the concrete mold would have a strong likelihood of exploding violently and spraying molten steel everywhere because of bubbles of water that could be trapped in it. So, we'll use a specifically designed high temperature casting compound instead of concrete.

As for overall "danger" factor, I'd give this about a 6/10 unmanned, and 37/10 manned.

A 370% chance of at least one violent death? Sounds about right. But we'll have quite a few people at the launch, and I can almost guarantee that the 3.7 of them that die won't include me.

Considering the risks, are you sure this particular form of locomotion is really that worthy an experience?

What could be more worthy an experience than a group of 4 teenagers spending thousands of dollars to make a horribly dangerous rocket cart that can kill them in 42 different ways at any given time without warning, and will probably explode violently on ignition?

[starman]

What could be more worthy an experience than a group of 4 teenagers spending thousands of dollars to make a horribly dangerous rocket cart that can kill them in 42 different ways at any given time without warning, and will probably explode violently on ignition?

Uuummm....surviving it?....

[DYI]

Uuummm....surviving it?....

EXACTLY! But you can't have the experience of surviving it if you don't build it in the first place. Which is, I would assume, why we're building it.

[rp181]

how big is it? i think your rocket is way too big. Have you even made a small one yet? thats like making the pipe dream for your first cannon. Ok, so a big exagerated, but you get the point.

How big is the core going to be? remember, as it burns thrust will rise exponentially.

Ide start with some static tests of the motor to be safe.

[joestue]

Casting a steel rocket casing? wtf?

buy a 4 inch schedule 160 pipe.

[Lentamentalisk]

so a 4 inch schedule 160 pipe is the shape of a rocket motor?
Last time I checked it was the shape of a pipe, and didn't have a nozzle or cap on the other end.
Feel free to correct me if I am wrong, but I also doubt that it would be strong enough to hold a rocket engine...
Think, then post.

oh ya, and I don't think 4" pipe has an INSIDE DIAMETER of 4.5"...