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.

Tuesday, May 15, 2007

Flight Computer V1.3

We have finished the V1.3 Flight computer code and also took some photos. The full details of the design is available here:

While retaining the same functionality of V1.2, the new flight computer is lighter ( 37 g with battery), uses a single battery design and has a greater selectable range of delays ( 3 - 11 seconds in .25 second intervals.)



Anonymous said...

Hello, I hope I'm not being too annoying, but I am in a high school physics class and was interested in the methods you use to find the center of lateral area/center of mass/center of pressure of a plastic soda bottle. I have a few basic ideas, but felt it might be best to hear it from someone who has actually done this before. That way, I hope I can minimize any unstable flights. Any help and advice would be appreciated - Thank you!

George Katz said...


When we started with water rockets we measured the Center of Gravity simply by hanging the rocket on a string and moving the string until the rocket was level. We measured the Center of Pressure using the silhouette method where you project the silhouette of the rocket onto cardboard and trace it and then cut it out. Repeating the string balancing act with the cut out roughly gives you the center of pressure.

We only did this a few times, as eventually we learned to eyeball the weight distribution and fin size and location. Sometimes when we find the stability marginal we usually add a little weight to the nose and that fixes it up.

We are finding that with foam the rockets tend to be more unstable. We put this down to the length of time it takes the water mass to leave the rocket. A heavy tail is undesirable for long periods after launch. In this instance you need to factor in the weight of the water into your CG calculations. You need more aggressive (larger/further back) fins with foam rockets.