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Crunching Numbers

Posted by: box - Thu Aug 20, 2015 9:25 am
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Crunching Numbers 
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Post Crunching Numbers   Posted on: Thu Aug 20, 2015 9:25 am
I have been thinking about a rocket "concept" and I was wondering how one goes about to draw the design and crunch the numbers to see if the design has any merit.

The idea is a 3d printed whole rocket. The twist is going with old designs and putting the engine at the front of the body. The combustion chamber is a torroid and the exhaust is expelled along the "bottom" of the ring in a circle, and the rocket's body forms an aerospike.

The wall of the aerospike through channels that connect to the fuel tanks heats up the fuel to generate the pressure to drive the liquid into the combustion chamber. The initial burn is started off by solid fuel layer in the combustion chamber. So it is partially a two staged rocket, could potentially be one that starts as solid rocket, then transition into a hybrid system.

So it basically is just a flying aerospike. I am hoping to figure out a passive design that has very little moving parts and can be printed as one piece. The reason why I wanted to put the engine in the front is stability, and I thought with the body serving as the spike of an aerospike it can help with maximizing efficiency, and also creating the pressure to pump the fuel at the same time.

So the launch involves igniting the solid fuel, as it does the initial burn, it heats up the liquid fuel in the body, the valves open and the liquid stage takes over and does the rest of the work.

With 3d printing the whole body I was hoping to combine the functionality of structural elements, so for instance the tubing to carry out the heat transfer between the walls and the tanks also double up as features that make the structure stronger. Or the obvious one that the aerospike also serves as part of the system that pumps the fuel.

So how does one go about putting this into numbers and a proper drawing?


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Post Re: Crunching Numbers   Posted on: Fri Oct 23, 2015 7:33 pm
It would probably work, but probably not practically.

The large surface area of your combustion chamber "ring" and its cooling channels will weigh much more than a conventional one at the bottom. The geometry of an aerospike nozzle is pretty fixed. I'm not sure it would tolerate a long cylinder wall to follow and still act.... "nozzle-y". It would be an interesting experiment though. If it did work, the heat from the exhaust gas would be a handy way of heating and pressurizing the propellant tank for "free". Not having to carry big turbopumps might make up for the bulk of the combustion chamber.

As for numbers. There aren't any. All of the data for aerospikes is for "conventional" ones with discrete combustors and the curving nozzle profile. Anything would be just a guess based upon "first thoughts" like the above comments. You at least need to do some FEA gas dynamic simulations, or (better yet) build a test motor and see what it does.

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