The Boomerang Vent & Ballast Calculator is a critical tool for operators of the 4th Generation Boomerang Balloon Flight System. Using launch site, target altitude, and flight system parameters, the calculator displays:
- The initial helium fill volume and corresponding weigh-off weight to achieve a desired ascent rate, typically about 5 m/s.
- The estimated total vent time at altitude necessary for the Boomerang Balloon Flight System to achieve neutral buoyancy.
- The new ascent rate and settling altitude after a ballast drop of specific duration, either during the ascent or after reaching float.
How the Boomerang Vent & Ballast Calculator Works
Ambient conditions of the launch site and target altitude are entered at the bottom of the calculator in the white boxes along with the balloon’s helium gas temperature and pressure. For planning purposes, conditions at altitude may be estimated from recent soundings. In the U.S., these soundings can be found at the National Weather Services’s Storm Prediction Center Observed Soundings site. During the flight, it is important to update the balloon differential pressure and temperature fields especially as Boomerang approaches the vent altitude.
The white boxes in the middle of the calculator under “Flight system properties” are used to enter balloon, flight system, and ballast masses along with key system-specific constants. The “Ascent targets” area is used to input the desired ascent rate and any mid-flight ballast drops.
Intermediate calculations are shown in the gray boxes. The “Launch free lift” value can be used to create a pre-launch weigh-off weight to achieve the desired ascent rate. Finally, the blue fields display calculation results, most importantly vent time to achieve float at the target altitude and the post-ballast drop ascent rate. Note, default values are shown for a Boomerang Balloon Flight System using helium as the lift gas.
Initial Ascent Rate Calculation
The desired initial ascent rate, typically about 5 m/s, is used along with the total launch mass to drive the calculation of the helium volume & mass loaded. The balloon drag coefficient can be adjusted to take into account different types and sizes of balloons. Drag coefficient assumptions affect the initial helium fill and vent time calculation.
Determining Vent Time for Neutral Buoyancy
The Boomerang Vent & Ballast Calculator determines the neutral lift helium mass required for the system to “float” at neutral buoyancy. The difference between the “Ascent rate helium mass” and “Neutral lift helium mass” is the mass of helium to be vented to achieve float. The at-altitude ambient conditions along with the balloon’s helium gas temperature and pressure are used to calculate the total amount of time to open the vent valve.
When the valve is open, helium gas vents from the balloon because it is at a slightly higher pressure than ambient due to the pressure exerted on the gas by the latex balloon. In general, vent times increase as altitude increases due to decreasing atmospheric and balloon gas densities. Procedures provided with the Boomerang Balloon Flight System guide operators on how to operationally use the total vent time calculation.