Water Rocket
Computer Model Problems
Here is the first Water
Rocket Computer Model Problem.
The screen shot below is from the 3D optimisation of a
250 ml water rocket with launch
tube and T nozzle.
I have included the file details so that you can
reproduce it yourself to investigate the peculiar maxima
displayed in the screen shot on the right.
It is a plot of speed (velocity along the axis of the
rocket - in this case, the launch angle is 90 degrees so
effectively, it is vertical velocity) as the output
variable with Mass of Water (20g to 140g) on the Y axis
and Mass of Rocket Empty (10g to 150g) on the X axis.
It is clear that the highest speeds will be gained
from the lowest combined weight of water and rocket, as
indeed they are as displayed in the bottom left of the
screen shot.
| Variables |
| Water Rocket Computer Model Problem
01 |
|
| Rocket |
| Mass of Rocket Empty |
25 |
|
g |
| Capacity of Pressure Vessel |
269 |
|
cm3 |
| Rocket Diameter |
5.7 |
|
cm |
| Rocket Coeff of Drag |
0.56 |
|
|
| Nozzle Diameter |
21.75 |
|
mm |
| Constant K for nozzle |
0.16 |
|
|
| [X] Launch Tube in use |
Used |
|
|
| Duration of air impulse |
1000 |
|
ms |
| [ ] Parachute in use |
Not Used |
|
|
| Launch
Tube |
| Length |
8 |
|
cm |
| External Diameter |
21.5 |
|
mm |
| [X] Hollow Launch Tube |
Used |
|
|
| Wall Thickness |
2 |
|
mm |
| Length of Tube Empty |
8 |
|
cm |
| Distance of Vent from End |
0 |
|
cm |
| [X] T-Nozzle in use |
Used |
|
|
| T-Nozzle Diameter |
1.3 |
|
mm |
| Parachute |
| Diameter
opened out flat |
3 |
|
m |
| Parachute
Coeff of Drag |
0.9 |
|
|
| Deploy ()
Apogee.( ) Timer |
4 |
|
s |
| Delay in
opening |
2 |
|
m |
| Initial |
| Mass of Water |
64 |
|
g |
| Pressure in Vessel |
94.3 |
|
psi |
| Height |
1.3 |
|
feet |
| Angle of Elevation |
90 |
|
° |
| Speed at Angle of Elevation |
0 |
|
m/s |
| Temperature |
20 |
|
C |
| Environmental |
| Gamma of Gas in Rocket |
1.402 |
|
|
| Density of Gas in Rocket |
1.293 |
|
kg/m3 |
| Density of Liquid in Rocket |
998 |
|
kg/m3 |
| Acceleration due to Gravity |
9.81 |
|
m/s2 |
| Atmospheric Pressure |
1013 |
|
mBar |
| Density of Air at STP |
1.293 |
|
kg/m3 |
| The problem here
is . . . |
| 1. |
to
find an explanation for the large central
maximum; and, |
| 2. |
the
maximum at the top edge towards the left. |
If you give up or you think you know what is going on,
look at the answers.
|
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