Water Rocket
Computer Model Problems
Here is the second Water
Rocket Computer Model Problem.
The screen shot below is from the 3D optimisation of a
2 litre water rocket with an
unusually light body weight.
Again 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 flight time as the output variable
with Mass of Water (20g to 1444.5g) on the Y axis and
Mass of Rocket Empty (1.1g to 19.7g) on the X axis.
It is clear that the longest flight times will be
gained from a moderate weight that is greate enough to
pull the rocket through the air but not so great that the
rocket cannot achieve a good enough height. This maximum
is off to the right.
Variables 
Water Rocket Computer Model Problem 02 


Rocket 
Mass of Rocket Empty 
120 

g 
Capacity of Pressure Vessel 
2050 

cm^{3} 
Rocket Diameter 
9.5 

cm 
Rocket Coeff of Drag 
0.78 


Nozzle Diameter 
21.5 

mm 
Constant K for nozzle 
0.16 


[ ] Launch Tube in use 
Not Used 


Duration of air impulse 
50 

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 
[ ] TNozzle
in use 
Not Used 


TNozzle
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 
850 

g 
Pressure in Vessel 
75 

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/m^{3} 
Density of Liquid in Rocket 
998 

kg/m^{3} 
Acceleration due to Gravity 
9.81 

m/s^{2} 
Atmospheric Pressure 
1013 

mBar 
Density of Air at STP 
1.293 

kg/m^{3} 
The problem here
is . . . 
1. 
to
find an explanation for the maximum at the top
left; and, 
2. 
the
maximum at the lower left. 
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.
