Water Rocket Modeling Sean Munson Ben DonaldsonAlex Dillon
Design Goals RangeRange AccuracyAccuracy AestheticsAesthetics These tell us little about how to build a rocket!
The Model
What happens to the rocket? Boost Phase Water leaving rocket under pressure Air Thrust Phase remaining air pressure leaves rocket Coast Phase Gravity, drag act on rocket until it smashes to the ground
Boost Phase
Boost Phase: Thrust
Coast Phase
Coast Phase: Drag
“Whoa, what about the Air Phase?” Us: “We neglected it, sort of.” You: “You can’t just do that…” Us: “Well, actually, since we made some other assumptions…”
What’s Important? Cross Sectional Area (Nozzle, bottle)Cross Sectional Area (Nozzle, bottle) Coefficient of Drag (C D, Surface area)Coefficient of Drag (C D, Surface area) Mass of RocketMass of Rocket PressurePressure Volume of WaterVolume of Water
Validation of the Model & Experiments
A Preface Rocket for tests was constructed in ~20 minutes, with cardboard finsRocket for tests was constructed in ~20 minutes, with cardboard fins Launchers don’t work most launches required a kick to free the rocket, making it difficult to measure the angleLaunchers don’t work most launches required a kick to free the rocket, making it difficult to measure the angle
Mass vs. Range Pressure: 70 psig Volume H 2 0: 0.7 liters Angle: 35° Observations: Launch without ballast (rocket mass: 70 grams) highly erratic Stability problems above or below 0.11 kg Determined C D to be 1.8
Volume H 2 O vs. Range Mass: kilograms Pressure: 70 psig Angle: 30°
Pressure vs. Range Mass: kilograms Volume H 2 0: 0.8 liters Angle 30° Observations: Last set of tests. Fins mush Data unreliable Clearly, more pressure is good so long as you do not exceed safety margins What the #&$% ? The stout kick required likely changed the angle to 20° or 25°.
Design Goals: Low C D, ALow C D, A –Parabolic, smooth nose –Experiment with multiple 1L bottles Mass: ~115 gramsMass: ~115 grams Experimentation with nozzle area?Experimentation with nozzle area? –Difficult with these launchers Tight but loose fit on launcher?Tight but loose fit on launcher?
Questions?