D. Ballast Requirements
For a 20-foot General Mills balloon, a flow of ballast of at least 200 grams per hour is needed to keep the balloon aloft. Flow of the compass fluid used varies (through a sharp-edged orifice) with the head, or vertical distance between the free surface of the liquid and the orifice. It is not affected by the temperature or pressure, so long as the reservoir is properly vented.
Flow also varies with the size and shape of the orifice. Using round spinnerette orifices, the flow of various heads has been computed and is shown in Table 3, Appendix II. From a knowledge of the minimum head to be expected (depending on the construction of the ballast reservoir and its connection to the orifice), the desired rate of flow can be obtained by proper selection of orifice size. While 200 grams per hour has been used successfully for the usual floating altitudes of the General Mills 20-foot cells, this figure should be considered as an absolute minimum. A short period check of the flow rate through each ballast assembly prior to flight is recommended.
E. Altitude Sensitivity
The altitude gained by a balloon when its load is reduced by one kilogram is called its altitude sensitivity. This amount is affected by the density of the atmosphere at the floating level; for 20-foot balloons between 40,000 and 53,000 feet, it is roughly 1000 feet per kilogram of weight lost. This weight is normally lost by ballast dropping. The altitude sensitivity and the ballast drop control the rate of rise of the ceiling. Graph 4, Appendix II gives more exact values for this figure at various altitudes.
F. Forms and Records
For the purpose of making standard pre-flight computations, a series of computation sheets have been drawn up. These are shown in Appendix I. Reward tags attached to components of the flight train have encouraged the finders to protect the equipment and report its location for recovery. The tags, questionnaires, and the warning notices which are used on appropriate gear where squibs or acid are used are shown in Figures 20 and 21.
V. BALLOON INFLATION
A. Preparation of Balloon
From the moment the protective packing of the balloon is removed, great care must be exercised to prevent tears
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