Water Rocket
Computer Model Problems
Here is the sixth Water
Rocket Computer Model Problem.
Someone  wrote to the water rocket
group saying that they knew of a steel tube rocket, powered
with steam that had a capacity of 33 litres and weighing 40kg.
The water rocket computer model does not deal with the vapourisation of
water so I wondered how the rocket would perform with just water and air at
ambient temperatures. This is what happened. I guessed a rocket diameter of 20cm,
a pressure of 300psi and an air impulse of 4 seconds.
As always, I have included the file details so that
you can reproduce it yourself to investigate the peculiar
nature of the maxima displayed in the screen shot on the
right.
It is a plot of Height as the output
variable with Mass of water (1000g to 26000g) on the Y
axis and Nozzle Diameter (10mm to 50mm) on the X axis with
a post-thrust integration interval of 1ms (the picture is
the same using 10ms as well).
The graph shows an area of viable flight and on the right is an area
of short impulse and on the left is an area of low thrust.
The maximum on the right of the viable flight area is echoed
to the left and less obviously again (where the cursor is).
| Variables |
| Water Rocket Computer Model
Problem 06 |
|
|
| Rocket |
| Mass of Rocket Empty |
40000 |
|
g |
| Capacity of Pressure Vessel |
33000 |
|
cm3 |
| Rocket Diameter |
20 |
|
cm |
| Rocket Coeff of Drag |
0.56 |
|
|
| Nozzle Diameter |
21 |
|
mm |
| Constant K for nozzle |
0.16 |
|
|
| [ ] Launch Tube in use |
Not Used |
|
|
| Duration of air impulse |
4 |
|
ms |
| [ ] Parachute in use |
Not Used |
|
|
| Launch
Tube |
| Length |
20 |
|
cm |
| External Diameter |
21 |
|
mm |
| [X] Hollow Launch Tube |
Used |
|
|
| Wall Thickness |
2 |
|
mm |
| Length of Tube Empty |
25 |
|
cm |
| Distance of Vent from End |
0 |
|
cm |
| [ ] T-Nozzle in use |
Not Used |
|
|
| T-Nozzle Diameter |
4.75 |
|
mm |
| Parachute |
| Diameter
opened out flat |
1.2 |
|
m |
| Parachute
Coeff of Drag |
0.9 |
|
|
| Deploy ()
Apogee.( ) Timer |
4 |
|
s |
| Delay in
opening |
5 |
|
m |
| Initial |
| Mass of Water |
10000 |
|
g |
| Pressure in Vessel |
300 |
|
psi |
| Height |
1.5 |
|
feet |
| Angle of Elevation |
88 |
|
° |
| Speed at Angle of Elevation |
0 |
|
m/s |
| Temperature |
10 |
|
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 maxima that occur. |
The variables are in the table on the left...
If you give up or you think you know what is going on,
look at the answers.
|
Back to the Computer Model
Page 
