Half Cat Static Test 4 - March 9, 2021

• Partial success (test stand fell over)

• Partial data acquired

• Changes from previous test: None with the engine

Test 4 was necessitated by the lack of data in test 3, attributed to a bad microSD card. This time a CO2 purge was added to the vent assembly to extinguish the chamber following shutdown, and it did perform as expected. However, what was not expected was the test stand suddenly reconfiguring itself into a horizontal position despite its rigidity in prior tests. This led to a very odd burn that invalidated the data past the first couple seconds.

The data itself does have some interesting points. At the exact moment where the fluid level in the nitrous tank is expected to dip below and expose the oxidizer inlet to only gas (due to the tank no longer being upright under gravity), there is an immediate decline in chamber pressure and thrust. Also, immediately afterward, the tank pressure spikes when the stand hits the ground and the liquid nitrous sloshes into the pressure transducer at the top.

Due to the anomalous circumstances, the fuel was expended before oxidizer (since the piston will continue pushing the fuel out regardless of orientation). For a brief time, the engine operated in oxidizer-only, nitrous-decomp mode. The three brass fuel fittings on the bottom side of the injector (relative to the Earth, as the engine was now laying sideways) partially melted from the lack of fuel flow actively cooling them.

Sudden decrease in amplitudes correlates with test stand ground impact