The Roswell Report: Fact vs. Fiction in the New Mexico Desert

weight of equipment and balloon, the distribution of density in the atmosphere and the buoyancy of the lifting gas. Assuming that the lifting gas is helium, Graph 3 in Appendix II summarizes the relationship between gross load and floating level for balloons of several diameters. To use this graph to find the floating level of a balloon of given size and load, enter with the required buoyancy (equal to the gross load). Go vertically to the diagonal line corresponding to the balloon size and then horizontally to the extreme left-hand edge and read the altitude. The volume of the balloon is related to density by the use of the molar volume in this chart. Assuming observed pressure and temperature distributions over selected stations and the N. A. C. A. standard atmosphere, the molar volume is given as well as the altitudes. Table 1 of Appendix II gives the N. A. C. A. Standard Atmosphere relating pressure with altitude, and Table 2 gives the variation of temperature with altitude. For local conditions more exact measurements may be made using the temperature and pressure distribution indicated by a sounding rather than the standard. To do this, it is necessary to compute the molar volume from this relationship

$$
\mathrm {m o l a r v o l u m e} _ {z} = 3 5 9 \mathrm {f t}. ^ {3} \mathrm {x} \frac {\mathrm {T} _ {z}}{2 7 3 ^ {\circ} \mathrm {C}} \mathrm {x} \frac {1 0 1 3 . 3 \mathrm {m b}}{P _ {z}}
$$

Example: Find the molar volume at 30,000 feet MSL where the reported temperature is $ - 3 0^{\circ} \mathrm{C} $ , and the reported pressure is 300 mb.

$$
\mathrm {m o l a r v o l u m e} _ {3 0, 0 0 0} = 3 5 9 \mathrm {f t}. ^ {3} \times \frac {(2 7 3 - 3 0) ^ {\circ} \mathrm {C}}{2 7 3 ^ {\circ} \mathrm {C}} \times \frac {1 0 1 3 \mathrm {m b}} {3 0 0 \mathrm {m b}} = 1 0 8 0 \mathrm {f t}. ^ {3}
$$

This is the volume of a pound mol of any gas at those conditions.

By plotting several points of this curve of molar volume versus altitude, it is possible to locate very exactly the altitude which corresponds to the molar volume to which the balloon will go (found from Graph 3 or as follows). This density or molar volume to which a balloon will rise is given by the following formula:

$$
\text{Molar volume} = \frac{\text{Balloon volume}}{\text{Gross load}} \quad \text{Gas Lift/mol}
$$

$$
\mathrm {G a s l i f t / m o l} = 1 1. 1 \mathrm {k g / m o l} (\mathrm {u s i n g H e l i u m})
$$