>>> WHOOSH   >>>
Pop Bottle Rocket Flight Analyzer
Version 1.1

Written by R.Nakka  July 1993

This program was written to predict the performance of a pop bottle rocket as a reaction (rocket) engine. A "pop bottle rocket" is novel contrivance consisting of a plastic pop bottle (typically 1, 1.5 or 2 litre) partly filled with water and pressurized with compressed air. The pressure may be as high as 200 psi. Apparently, the industry standard requires that these bottles be capable of withstanding this order of pressure, although I have not confirmed this.  (the maximum pressure I have used is 150 psi).

The required input is:
Time step:        time (sec.) between successive iterations (calculations)  Default is 
                  0.005 sec.
Iterations:       Number of times the calculations are performed  Default is 20
                 (if insufficient, user is notified in output)
Volume of water:  Total volume of water loaded into vessel, litres (typically 0.1-0.8)
Volume of vessel: Total volume of the bottle, litres (typically 1.0, 1.5, or 2.0)
Charged pressure: Air pressure that bottle is charged with, psi (typically 50-150)
Throat diameter:  Diameter of the bottle throat at its minimum, cm (typically 2.17)
Vessel diameter:  Diameter of the bottle, cm (typically 11.1 for a 2 litre bottle)

The output is, at each time step:
Air Volume:       Volume of air remaining in the vessel , litre
dV/dt:            Rate of decrease of the volume of air in vessel, litre/sec.
Jet Velocity:     Velocity of the jet of water exiting from the bottle, metres/sec.
Pressure:         Pressure of the air remaining in the vessel
Thrust:           Propulsive force developed, newtons

Also outputted is:
Total Impulse:    Integral of the thrust over the operating duration, newton-sec
                 (basically, a measure of the total lifting capability of the rocket)
Specific Impulse: The impulse delivered for a given mass of propellant, in this case
                  water, newton-sec/kg
                  (a measure of the efficiency of the bottle rocket, the greater the 
                   specific impulse, the more efficient the design)

The output is printed to the screen, and is also written to a file,  WHOOSH.OUT

Inputted values are saved after each run, in a file called            WHOOSH.DAT 
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The units used in this program are all S.I. (metric), with the exception of air pressure, which is in pounds per inch. This rogue system of units  is a result of the air compressor that was used for charging, which was calibrated in psi, so I granted myself this one indiscretion.

Conversion of units:

Multiply    psi   x           6895  to get  N/m^2
            cm    x           0.3937 to get inch
            metre/sec   x     3.281	to get  feet/sec
            newtons     x     0.2248   to get    lb (force)
            newton-sec  x     0.2248   to get   lb-sec
            newton-sec/kg  x  0.1020   to get   lb-sec/lbm
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It is worth noting that, with some ingenuity, a rocket with rather impressive results may be achieved by connecting a number of bottles together, stacked one atop the other. My nephew, for his school project, built such a rocket with 3 bottles (1.5 litre), and fins for stabilization. The lower bottle was filled with water, the upper two stored the pressure charge. This rocket was even equipped with a parachute, released at the peak, using a clever pressure-operated ejection system. Although the exact altitude achieved was not measured, it went about three hundred feet high.  Later, with my help, we even attempted to launch one constructed with  four 2-litres bottles and a single 1-litre bottle at the top. This contraption, with which we were aiming to reach 500 foot altitude, did not get off the pad, however, as it experienced structural failure at the joint of a strut (connecting the bottles together) while being pressurized, resulting in my nephew getting a rather thorough soaking from the "fuel"  which was suddenly liberated !

