This blog covers the day to day progress of water rocket development by the Air Command Water Rockets team. It is also a facility for people to provide feedback and ask questions.

Wednesday, November 21, 2007

Foam vs. Water-only flight test results

We have updated our main site with the results of the foam vs. water-only test flights.

In the analysis we show that foam flights were about 2-3% lower in altitude than the water only rockets. This was a little dissapointing but also encouraging in other ways and certainly gives us a direction for further research with foam. Since the update We tweaked the simulation's drag coefficient and nozzle loss factor so the simulation matched the highest observed water-only flight altitude. We then added the weight and drag of the attached camera, upped the pressure to 120psi and ran the simulation again. The predicted water-only altitude was 350'. The last camera mission on the day was a foam flight with the camera and the altimeter. The altitude measured was 353'. This would put foam on par with water-only.

The altitudes are too close together to be able to make any definitive conclusions one way or another, and a lot more flights are required.

There are a few reasons we want to pursue foam experiments further:

  1. It's a lot of fun.

  2. The residual foam weight issue, described in the update, could point towards a measurable advantage when solved.

  3. These tests were only carried out at low pressures, enough to get the rocket off the ground. As the pressures increase, the take-off and peak velocities will also increase. Due to the difference in velocities between water and foam powered rockets (water = faster & shorter burn, foam = slower & longer burn) the difference in drag will play a more signigficant role since drag is proportional to the square of the velocity. This should favour foam at higher pressures.

  4. Convergent/Divergent (DeLaval) nozzles are yet to be fully analyzed. Although initial tests showed them to be no better at low pressures, higher pressures and nozzle shape optimization are still yet to be tested.

  5. Use of foam may be more optimal for upper stages of a rocket than for the main stage. More simulation is needed.

  6. Efficient generation of foam. From foam thrust measurements we found that foam generated using the Jet Foaming technique produced about 14% less total impulse. We have yet to test alternative ways of generating foam that may be more efficient. A couple of new foam generation ideas are already on the drawing board.

  7. Foam optimisation. So far we have only been using the same ratio of bubble bath to water when mixed, but other combinations will need to be tested.

  8. Different foaming agents. So far we have only tested kids bubble bath to generate foam. There are much better foaming agents available and foam density and viscosity are likely to play key roles in the efficiency.

  9. The test results from all these experiments and data from other rocketeers may be used to build a foam simulation model for further research.
If all the above issues can be optimised for a particular application, then it still may turn out that foam can have higher performance in particular situations.

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