Over this past weekend we completed another round of testing of our 3" hybrid rocket motor testing!
This burn was very similar to the one we performed in November. However, upon attempting to increase the oxidizer flow rate, we discovered we needed to plumb our solenoid and control valve in series to achieve the flow and control we desired. The specifications & requirements were:
Nitrous Oxidizer & HTPB (rubber) Fuel
Single, circular fuel port
Port Diameter: 1.6 inches
Fuel Core Length: 34 inches
Target Oxidizer Flow Rate: 0.9 lb/s (Ideal: 1.2 lbs/s)
Actual Oxidizer Flow Rate: ~0.3 lb/s
Expected Thrust: 200 lbs (Ideal: 225 lbs)
Actual Thrust: 40 lbs
Thrust & Combustion Pressure data recorded
In-house Rocket M&C System to control all aspects of the firing.
As you can see, we saw a decrease in expected oxidizer flow rate. We are currently troubleshooting what the root cause of this could be. While this led to a very fuel rich burn, it helps show the robustness of hybrid rocket motors, able to perform (albeit not very efficiently) even in extreme ranges of O/F. Everything else about this motor performed well, and the burn would have been excellent had our oxidizer rate been where we targeted.
One great step forward with this test was the inclusion of a bottle scale, which now gives us a continuous oxidizer flow rate measurement. This is a great piece of data to use for analysis, and will also help troubleshooting.
We'll be doing more testing next weekend. I'm shooting for an early January update to talk about the rest of progress made based on our December schedule (Update#14).
I hope you all have a safe and very happy holidays!