Water Rocket Computer Model Problems

Here is the seventh Water Rocket Computer Model Problem.

This Right Click and Zoom In to see better or Left Click to show full screen.is a water rocket with a fairly large T-Nozzle and uses a fairly high pressure. Otherwise, it is normal.

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 Flight Time as the output variable with Mass of water (80g to 1600g) on the Y axis and Mass of Rocket Empty (30g to 500g) on the X axis with a post-thrust integration interval of 10ms.

The graph shows two maxima, each with different reasons for being there, one is at the top left and the other is where the cursor is.

Water Rocket Computer Model Problem 07    
Mass of Rocket Empty 120   g
Capacity of Pressure Vessel 2050   cm3
Rocket Diameter 9.5   cm
Rocket Coeff of Drag 0.56    
Nozzle Diameter 21.5   mm
Constant K for nozzle 0.16    
[X] Launch Tube in use Used    
Duration of air impulse 200   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
[X] T-Nozzle in use Used    
T-Nozzle Diameter 8   mm
Diameter opened out flat 0.25   m
Parachute Coeff of Drag 0.9    
Deploy () Apogee.( ) Timer 4   s
Delay in opening 3   m
Mass of Water 850   g
Pressure in Vessel 150   psi
Height 1.3   feet
Angle of Elevation 90  
Speed at Angle of Elevation 0   m/s
Temperature 10   C
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.

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