On 29 March 2008 Lisa and I again helped out at the Science Olympics Bottle Rocket Contest.
In this contest students must construct a rocket based on a softdrink/soda bottle. The bottles are “launched” by partially filling them with water, and then adding compressed air which will force the water out of the bottle, propelling it upwards. The winner of the contest is the rocket that stays aloft the longest and doesn’t separate into parts at any time before touching down. There are 2 main strategies to getting a rocket to stay up:
- have a parachute deploy that will let the rocket drift back to earth;
- get the rocket up, and then have it lay on its side and float slowly down using just air resistance on the rocket itself to hold it up. These rockets tend to be very long in order to have the maximum area for wind resistance
On a windy day both types are difficult to launch as they need to sit vertical on the launch pad, with the parachute hidden away balanced only on the neck of the bottle prior to the launch. Once launched, the parachute should stay packed away until the rocket gets to the top of its flight, then deploy quickly to catch the rocket before it has fallen too far. For the floater rockets, they need to get up to the top of their flight, then lay on their side properly horizontal so that they can drift back down “flat”. This requires that the centre of mass be the same as the centre of air resistance on it. Since the rockets have to weigh between 150 and 400 grams the rockets that are built large to float have to be built of very light material.
At the end of the event it was the parachute rockets that took the top times.