The Micro Hybrid parts.
The Micro Hybrid mounted on the test stand.
The Micro Hybrid being fired.
Cut fuel grain.
Test stand and data logging by Tom Mueller, Thanks Tom!
This page shows my original work I did with my Micro Hybrid Rocket Motor.
Click here to see all the latest info on this motor including flight videos.
THE DISCLAIMER: By reading this you agree to proceed at your own risk
with any construction using any information provided on this page and release
me of any liability. If you don't agree, then don't do any building, just
watch and enjoy. Thank You
This is the original concept of my Micro Hybrid.
This is two views of a paper grain I made from a grocery bag.
Reading through the May 95 issue of High Power Rocketry I came across an article stating that with the weight considerations of hybrid hardware, it would be interesting to see someone build one in the E, F, and G range. Wanting to build a rocket motor of my own design, this was my cue.
My first task was to obtain a small oxidizer tank and design around that. Not looking at the time, as it sometimes seems to work out, I came across a small oxygen/butane torch at my local Radio Shack. The cylinders used are about the size of a CO2 cartridge. Checking on a replacement pack of oxidizer cylinders I found a label that said "Micronox". A safety data sheet from the Radio Shack faxback service confirmed that these are indeed nitrous oxide cylinders. Recently, I have found a new source for these cylinders at the cooking store in the mall. I can now get them in bulk for less than a dollar a piece.
With this information in hand, next came the selection of the fuel. Well as hybrids, you name it and it's probably been tried, anything from wood to plastic to tar paper and even a salami or two. Trying to keep this as simple as possible I first opted for an acrylic grain, but I didn't like the burnt smell it gave off so I decided on a rolled paper fuel grain instead. To make it I simply took a paper grocery bag, cut it up and rolled it around a 1/4" inch rod while brushing it with glue.
To test this fuel grain I made a simple injector from a Radio Shack butane torch frame. With a little bit of "micro pluming" I was able to attach it to the fuel grain. For a nozzle I simple peeled some of the paper from the other end and constricted the opening with a small hose clamp. Very high tech! In order to get oxygen from nitrous oxide it has to be heated above 500 degrees F. For this I used a fuse and a little piece of composite propellant with a hole hand-drilled in it at the top of the motor. Once the propellant started burning the nitrous was released from the cylinder, passed through the burning propellant, and started the combustion in the core of the fuel grain. To release the nitrous I took out the needle valve/knob from the torch and inserted a pencil eraser into the hole. I then put a nail into the eraser which resulted in a very simple piercing mechanism (another high tech item!). So the whole thing works like this: The frame is held in a vise with the fuel grain attached to the side port of the torch body. The nail head is sticking out the bottom. The vise is then tilted off-balance and held in that position with a clothespin (first thing I saw when I turned around to look for a stick). Once the fuse is lit and the propellant burning the clothespin is removed via a tug on a string and the vise falls, piercing the cylinder and releasing the N2O.
The test resulted in a nice bright flame about 2 inches long and a sound level about the same as an Estes "D" motor. Total burn time was less than two seconds. The fuel grain was later cut in two lengthwise, revealing a typical hybrid burn pattern. No measurements were taken as this was just a functionality test.
I am now working on the motor hardware which will use an aluminum injector/piercing
unit, a 1" diameter motor tube and a graphite nozzle. I hope to get some
thrust measurements and final grain dimensions from these firing tests
so I can optimize the size and be able to fly it in a small rocket.
This is the finished nozzle with
graphite insert.
My greatest apologies to Louie Diaz, who was very VERY kind to take these pictures using his digital camera, and I forgot to give him credit. I'm so ashamed!
For those of you that have questions on the injector unit, well, all
I'm saying is that it preloads the nitrous before flight. I'll have a more
detailed description after I do my firing tests and write the report.
It took three attempts to fire the motor. A design flaw showed itself as an ineffective seal at the pyrovalve/o-ring area. Two attempts to pre-load the nitrous resulted in venting the contents of the cylinder out the motor. Lots of helpful suggestions and a little epoxy helped make a seal that was effective. When the fire button was pushed there was a little wisp of smoke and then a long narrow burst of flame. Mach diamonds were clearly visible! The burn time was about 1 second, due to full oxidizer flow.
Initial inspection of the motor revealed no obvious damage to the hardware. Inspection of the fuel grain showed an increase in the core diameter from the initial 1/4" diameter, and an even burn from top to bottom. Later I will cut the grain in half to get a better view of the burn pattern. Below is the graph showing the thrust produced during this test. This graph compares very closely to a popular manufacturer's "E27" motor. The next step is to make the hardware smaller and lighter and to increase the motor's performance, yet still using the same size nitrous cylinder ( it's too easy to just flow more nitrous through it).
I hope to get some pictures and maybe even a short video here soon so keep a lookout.
I'd also like to thank the people who came up to me and said they saw
my homepage. I plan to continue working on this motor and maybe having
it ready for flight soon.
The Micro Hybrid parts.
The Micro Hybrid mounted on the test stand.
The Micro Hybrid being fired.
Cut fuel grain.
Test stand and data logging by Tom Mueller, Thanks Tom!
How to get more thrust and a longer burn time :-)