Water Rocket & Parachute Competition

A water rocket uses water as its reaction mass. The pressure vessel—the engine of the rocket—is usually a used plastic soft drink bottle. The water is forced out by a pressurized gas, typically compressed air. It is an example of Newton's third law of motion.

Water and gas are used in combination, with the gas providing a means to store potential energy, as it is compressible, and the water increasing the mass fraction and providing greater force when ejected from the rocket's nozzle.

The seal on the nozzle of the rocket is then released and rapid expulsion of water occurs at high speeds until the propellant has been used up and the air pressure inside the rocket drops to atmospheric pressure. There is a net force created on the rocket in accordance with Newton's third law. The expulsion of the water thus can cause the rocket to leap a considerable distance into the air.

If aerodynamic drag and transient changes in pressure are neglected, a closed-form approximation for the peak height of a rocket fired vertically can be expressed as follows:

 = peak height reached, 

 = Initial mass of water only,

 = Rocket mass with water, 

 = Initial gauge pressure inside rocket, 

 = density of water, 

 = acceleration due to gravity.

Assumptions for the above equation: (1) water is incompressible, (2) flow through the nozzle is uniform, (3) velocities are rectilinear, (4) density of water is much greater than density of air, (5) no viscosity effects, (6) steady flow, (7) velocity of the free surface of water is very small compared to the velocity of the nozzle, (8) air pressure remains constant until water runs out, (9) nozzle velocity remains constant until water runs out, and (10) there are no viscous-friction effects from the nozzle

OBJECTIVE

The objective of the contest is for each team or individual to launch a rocket propelled by water and air and reach a maximum height. The launch angle will be kept the SAME for all rockets launching during the competition. The winning rocket will have the longest Hang-time. Hang-time is defined as the time from when the rocket leaves the launch pad until the time the main rocket body reaches the ground or strikes an object. This measurement will be taken using a stopwatch by at multiple judges; the average of the judges times will be used as the final “hang time”.

RULES & REGULATIONS

1. No commercially finished or model products may be used.
2. The pressurized portion of the rocket must consist of ONE plastic 1.5 liter soft drink bottle.
3. No materials will be allowed that can compromise the integrity of the plastic bottles (e.g. hot glues or super glues). Sanding or other abrasion of the plastic used for the pressurized body of the rocket is not allowable.
4. Do NOT use metal, glass, hard plastics, or spikes to construct the rocket. Any use of these materials will automatically disqualify the rocket from the competition.
5. The mass of the empty rocket assembly must NOT exceed 300 grams.
6. All energy imparted to the rocket must originate from the water/air pressure combination provided by the judges. No other potential or kinetic source of energy will be permitted.
7. Timing of the rocket stops when the first part of the rocket hits the ground, or when the rocket disappears from the judge's sight, or when the rocket impacts or gets entangled with an object (e.g. the rocket collides with a tree).
8. Though various rocket components may separate during the flight, all must remain linked together with a maximum distance NOT to exceed 3 meters. If a nose cone is used, it can separate, but should remain attached to the rocket body.
9. All rockets will be launched using the launching pad provided by the supervisor.
10. The use of parachute IS allowed.
11. There will only be TWO launches per participating team.

DIMENSIONS & LIMITATIONS

1. On the bottom of the rocket, leave 7.5 cm from the throat of the exit plane clear of any coverings (paint, markings, drawings, etc.), see Diagram.
2. Maximum total height of rocket is 76.0 cm, see Diagram.
3. Optional Nose-cone tip must have a minimum radius of 1.5 cm, see Diagram. (No sharp point is allowed)
4. Maximum fin width is 10.0 cm.

SHOULD THERE BE ANY AMBIGUITY OR CONFUSION OF THE RULES AND REGULATION, THE STRICTER (SMALLER DIMENSION) RULES WILL BE APPLIED. JUDGES' DECISIONS ARE FINALIZED.