Hybrid Rocket Motor Aerospike Nozzle Tests

This was the first fire of an Aerospike nozzle for my Senior Project in Aerospace Engineering from California Polytechnic State University in San Luis Obispo.

The test bed hybrid uses gaseous oxygen, GOX, and a 2" dia Plexiglas tube as the solid fuel. The Oxygen is at 100psi.

This test run was not choked, which was expected for the throat area is ~10 times greater than what the ideal area should be. The ideal gap between the spike and the compression cowl needed to be .003", yes, 3 thousands of an inch. However, if this were too small, this could produce a thermal choke well in front of the actual physical choke, which would reduce the performance of the rocket. I machined the compression cowl to have a gap of .053" instead. This would have allowed me to re-machine it smaller to maximize the thrust of the rocket.

I planned to fire the test for only 10 seconds, however I got distracted and allowed it to fire for 20 seconds, 2-3 seconds shy of turning the two piece nozzle into 3 or more pieces, thats what all the sparks are at the end.

This nozzle was machined out of 4140 Chrome-Molly. What took over 32 hours of CNC machining only took 20 seconds to destroy.

Now you know why they call this rocket science.

Category:

Science & Technology

Tags:

• aerospike
• hybrid
• rocket
• motor
• diamonds
• space
• engine
• cal
• poly
• oxygen
• propane
• plexiglas
• nozzle
• aerospace
• engineering

[whotookmeethed]

wow. that's awesome!

how is it both the combustion chamber and the solid fuel at the same time?

[ragobgar]

Well, its the solid fuel that acts like the combustion chamber, however if it were to burn through, then we'd have some problems. But it is the combustion chamber, thats where the fuels mix and burn.

[whotookmeethed]

but if it's the solid fuel and the chamber then it's burning inside itself?

i'm so confused. but it's cool!!

[ragobgar]

lol, yes, the inside is burning away while the outside acts like the chamber. The fuel grain has a 2 inch outer diameter with a half-inch diameter hole at the center.

[PurintonSFC]

looks great

this is only the 2nd aerospike i've ever seen. this is definetely the first hybrid i've seen. i'm curious if you've tried the nozzle on any other motors? I don't think plexi and Gox will get you very far if you're seeking to make thrust... tried LH2/LOX yet?

[ragobgar]

Thanks. And no, I haven't tried this nozzle on any other motors, it was designed only for this set up, however I do have another hybrid rocket motor that I machined that uses NOS and polypropylene with an Aerospike nozzle, though I haven't gotten to fire it yet, it should have the thrust of around 100 lbs. But this plexiglas and GOX setup is for a class lab demonstration so its not designed to be all that powerful. No I haven't tried LH2/LOX we don't have cryo here at school would be fun though.

[ragobgar]

Yes, the clear side is the combustion chamber, its clear plexiglass which is also the solid fuel for the rocket. If this were to burn through, there would be a problem. This set up is for a class demonstration in which they want to be able to see the combustion as it takes place.

[SolarWebsite]

I can't understand why the left part of the device is transparent. Is that the combustion chamber? What is it made of?

Cool clip!