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About Labs

070309-001 - Baffle to prevent blow-through
Date 9th March 2007      1:00pm - 3:00pm
Tested by GK and PK
Location Sydney, Australia
Test Procedure Static Fire Test
Related 070309-002 (Performed same day)
070309-003 (Performed same day)


  • To evaluate whether a baffle on a Robinson coupling can prevent the blow-through effect.

Experiment Setup

The 8L Polaron III  rocket was set up on the launcher and tied down for this experiment. The standard static test fire procedure was used. A video camera was set up to film the lowest bottle to see the water's behaviour.

The baffle being tested replaced the coupling nut and is essentially a plugged tube with four 6mm holes radiating out from the center. Because the baffle is so close to the base of the bottle, the bottle lobes help direct the airflow downward to the surface of the water.

Setting up for static fire tests.
The rocket is attached to the launcher with the 2 meter extension.
The baffle that screws onto the Robinson coupling, You can see the air holes on the side.
The rocket is manually fired.

Static Fire Tests #5 and #6 - Baffle

This test shows how water behaves inside the lowest bottle with the baffle in place. It seems to solve the blow through problem as well as the water being pushed up against the sides during the air pulse as was seen in the previous tests #1 and #2.

Launch Pressure (psi) Notes
1 110 9mm Nozzle, baffle on lowest coupling
2 110 7mm Nozzle, baffle on lowest coupling


Frame from the video showing just prior to launch.
Just after launch, there is no blow through.

 Water rocket with baffle in coupling

Conclusion / Analysis:

  • The baffle looks like it solves the blow-through problem, and doesn't allow air to pass directly into the nozzle from the lowest coupling.
  • The baffle also eliminated the water held in the lowest bottle during an air pulse.
  • At this point we don't know if and how much it reduces overall thrust from the rocket especially during the air pulse. - More tests are needed.

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