Hybrid rockets

[dharak1]

I want to start a discussion on hybrid rockets. Are they viable for every stage or just boosters? I understand how they have lower ISP but are pretty much throttle-able solid rockets. I plan to build a hybrid rocket similar to the one at the end of this video:

my grandfather said he would find some roofing tar for me and help build a test table 7 feet long to put the rocket on rails to see how much thrust it would produce. Its going to be 1 inch in diameter and use GOX for the oxidizer.

[Nuke]

this is worth a look:

http://hackaday.com/2012/09/26/hybrid-rocket-engine-uses-acrylic-as-fuel/

[dharak1]

I love the look of acrylic rockets, but with my grandfather being a drywall contractor its easier for me to get roofing tar. I also heard that roofing tar is better.

[K^2]

For anything you'd build at home, one fuel is as good as another. Mythbusters built a hybrid rocket out of a salami.

Hybrids are good for any stage, but not for any rocket. As you said yourself, they have slightly lower I_SP than liquid rockets. So for large rockets, that's the deciding factor. If you need over 9km/s of delta-V, for something like LEO launch, going from 400s of a hybrid to 480s of a liquid rocket can save you almost 50% in fuel. In practice it will be less, but it's still considerable.

On the other hand, when you are building a small rocket, weight is a huge factor, and liquid rockets have many heavy components. These components also tend to make liquid rockets less reliable. Hence the use of hybrid rocket on Space Ship One and similar projects.

[dharak1]

I understand the minuscule difference but roofing tar is also easy for me to get for free. I also Dont plan on putting this in a rocket anytime soon. Maybe in 1 or 2 years after i have developed it enough to make a good use of it. My first plan is just a pipe with roofing tar having GOX run to it and light it on fire. As you can see at the end of the video I posted The roofing tar far outpreforms the polyethylene.

[Nuke]

you could probibly turn a piece of firewood into a rocket engine if you bore a hole through it, attach a nozzel and inject pure oxygen.

im curious if the tar would hold its shape under heat. at room temperature the stuff is practically a solid. but warm it up and you have something thats more or less a fluid. this is probibly going to be undesirable in a hybrid rocket, as large clumps of fuel would be expelled out the back without actually being burned in the combustion chamber. but im curious to see what your actual results will be. thats why its called rocket science.

[K^2]

It will melt, of course, but so do most hybrid fuels. The point is that it burns away faster than it melts. So it's not a problem.

[dharak1]

That's why I need to use pure oxygen from welding tanks for the thing to burn fast enough.