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

ture difference between the lifting gas and free air. Evidently the effect of ventilation as the balloon moves through the air causes the lifting gas to remain at a temperature approximating that of the air, and the increase of lift due to temperature variation is small in magnitude.

Since changes in the value of free lift appear incapable of causing any appreciable increase in rate of rise, other possible variations such as a change of the drag, or fluid friction, effect must be considered.

The equation of Korff is based upon the assumption that the effect of the change in Reynolds number and the change in size are of equal magnitude, but in opposite directions. Therefore, these variables are eliminated to obtain the simple engineering formula of Korff. With a non-extensible balloon, however, the change of drag effect is probably less than the effect of change of Reynolds number. Therefore, it is likely that the rate of rise would increase with altitude. The change in drag effect may be realized by a decrease of relative size of the flabby, unfilled portion of the balloon. Thus there will be a decrease of the drag caused by flow of air past this flabby portion as the shape of the balloon changes; the result will be an increase in the rate of rise of the system.

## C. Superheat and Its Effects

The effect of the heating of lifting gas by the sun's rays has long been of interest to those using balloons for atmospheric investigation. In cosmic-ray studies using freely extensible balloons, this heating effect was used to advantage in extending the length of flights. These flights were often released at night using the heat added at sunrise to replenish lift lost during the night by diffusion and leakage.

In constant-level balloon work, using non-extensible balloons, the effect of superheat of the lifting gas is more often a disadvantage than an advantage. The disturbance of the flight is not great when the gas acquires this superheat but may be disastrous when the superheat is lost. It is at this time that a large amount of ballast is required to keep the balloon system afloat.

Let us investigate the effects of gain and loss of superheat on a full, non-extensible balloon. We shall try to explain these effects in terms of percentage loss or gain of lift of the balloon system by use of simplified engineering formulas. First, the general formulas:

$$
(1) \mathrm {L i f t}: \quad L = V _ {b} \left(d _ {a} - d _ {g}\right), \text {w h e r e}
$$

$$
V _ {b} = \mathrm {b a l l o o n v o l u m e}
$$

$$
d _ {a}, d _ {q} = \text {d e n s i t y o f a i r a n d l i f t i n g g a s , r e s p e c t i v e l y}
$$