Water Rocket Computer Model Problems

Here is the seventh Water Rocket Computer Model Problem.

This 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.

 Variables Water Rocket Computer Model Problem 07 Rocket 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 Parachute Diameter opened out flat 0.25 m Parachute Coeff of Drag 0.9 Deploy () Apogee.( ) Timer 4 s Delay in opening 3 m Initial 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 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.