Static test of N2O liquid / solid hybrid rocket motor.

1. PRV. The active pressure release valve (PRV) worked, enabling the hybrid rocket motor to work correctly at a blustery 30 degF temperature.
2. Igniter In previous tests a section of thermalite cord was glued onto a slice of APCP propellant. I believe the glue inhibited ignition of the thermalite. (strange) This time, a small hole was cut through the APCP slug and the thermalite was jammed into the hole with no glue. Ignition worked fine.
3. Horizontal test stand A new test stand was built. See pictures here. Despite the tilted setup (due to simple laziness), the test stand was solid and the horizontal orientation did not seem to affect the results. This test stand weighs much less than the vertical test stand used in previous tests, and it is simpler to setup.
4. Chamber pressure In the past, the sensor connected to the combustion chamber would routinely burn-up ($$$). A 6 inch standoff was added between the combustion chamber and its sensor. In addition a T and a plug were put in-line so a 1/2" layer of oil could be added to protect the sensor. This seemed to work.

   

5. Stats:
   18" length x 3" diameter N2O tank (5 lbs)
   18" length x 2.75" OD x 2.25" ID PVC grain
   Graphite nozzle, 1" throat, 15 degree egress, 60 degree ingress
   Tank pressure actively regulated to 400 PSI
   Target size baby "M"

Results

Unfortunately the connector to the load cell amplifier/conditioner was broken. The connection allowed a sane impedance reading during setup, but no data were received during the test.

Approximately 1 pound of PVC burned and 5 pounds of N2O. Most likely the motor was a baby "M."

Internal chamber pressure was approximately 100 PSI which is too low. A smaller nozzle throat will raise the pressure. I see no signs of combustion instability even at this low pressure.

Small wisps of vapor can be seen from the bottom of the N2O tank. One of the fittings must have been loose.

Test Stand Output Test 1

Test Stand Output Test 2