Water Rocket ModelingWater Rocket Modeling
Sean MunsonSean Munson
Ben DonaldsonBen Donaldson Alex DillonAlex Dillon
Design GoalsDesign Goals
• RangeRange
• AccuracyAccuracy
• AestheticsAesthetics
These tell us little about how to build a rocket!These tell us little about how to build a rocket!
The ModelThe Model
What happens to the rocket?What happens to the rocket?
Boost PhaseBoost Phase
Water leaving rocket under pressureWater leaving rocket under pressure
Air Thrust PhaseAir Thrust Phaseremaining air pressure leaves rocketremaining air pressure leaves rocket
Coast PhaseCoast PhaseGravity, drag act on rocket Gravity, drag act on rocket until it smashes to the grounduntil it smashes to the ground
Boost PhaseBoost Phase
Boost Phase: ThrustBoost Phase: Thrust
exhaustThrust mF
2surface
2nozzle
A
A - 1
a)h(t)+(g2+2P(t)
exhaustexhaustThrust mvF
nozzleexhaustexhaust Avm
Coast PhaseCoast Phase
Coast Phase: DragCoast Phase: Drag
2
2
1vACF airDDrag
maF
““Whoa, what about the Air Phase?”Whoa, what about the Air Phase?”
Us:Us: “We neglected it, sort of.” “We neglected it, sort of.”
You:You: “You can’t just do that…” “You can’t just do that…”
Us:Us: “Well, actually, since we made some other “Well, actually, since we made some other assumptions…”assumptions…”
What’s Important?What’s Important?
• Cross Sectional Area (Nozzle, bottle)Cross Sectional Area (Nozzle, bottle)
• Coefficient of Drag (CCoefficient of Drag (CDD, Surface area), Surface area)
• Mass of RocketMass of Rocket• PressurePressure• Volume of WaterVolume of Water
Validation of the ModelValidation of the Model& Experiments& Experiments
A PrefaceA Preface• Rocket for tests was constructed in ~20Rocket for tests was constructed in ~20
minutes, with cardboard finsminutes, with cardboard fins
• Launchers don’t workLaunchers don’t workmost launches required a kickmost launches required a kickto free the rocket, making itto free the rocket, making itdifficult to measure the angledifficult to measure the angle
Mass vs. RangeMass vs. Range
0.07 0.08 0.09 0.1 0.11 0.12 0.13 0.14 0.15 0.1685
86
87
88
89
90
91
92
93
Mass (kg)
Ran
ge (
m)
• Pressure: 70 psig
• Volume H20: 0.7 liters
• Angle: 35°
Observations:
• Launch without ballast (rocket mass: 70 grams) highly erratic
• Stability problems above or below 0.11 kg
•Determined CD to be 1.8
Volume HVolume H22O vs. RangeO vs. Range
0.2 0.4 0.6 0.8 1 1.2 1.4 1.630
40
50
60
70
80
90
Volume (l)
Ran
ge (
m)
•Mass: 0.150 kilograms
•Pressure: 70 psig
•Angle: 30°
Pressure vs. RangePressure vs. Range
50 55 60 65 70 75 80 85 9040
50
60
70
80
90
100
110
Pressure (psig)
Ran
ge (
m)
•Mass: 0.186 kilograms
•Volume H20: 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 #&$% ?
The stout kick requiredlikely changed the angleto 20° or 25°.
What the #&$% ?
The stout kick requiredlikely changed the angleto 20° or 25°.
Design Goals:Design Goals:
• Low CLow CDD, A, A– Parabolic, smooth noseParabolic, smooth nose– Experiment with multiple 1L bottlesExperiment with multiple 1L bottles
• Mass: ~115 gramsMass: ~115 grams
• Experimentation with nozzle area?Experimentation with nozzle area?– Difficult with these launchersDifficult with these launchers
• Tight but loose fit on launcher?Tight but loose fit on launcher?
Questions?Questions?
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