The humidity of the air may also cause slight
variations in lift, but for rough calculations it may be ignored,
as the difference in lift is not likely to amount to more than
0.3 lb. per 1,000 cubic feet of gas.
The purity of hydrogen has an important effect upon the lift of
an airship. One of the greatest difficulties to be contended
with is maintaining the hydrogen pure in the envelope or gasbags
for any length of time. Owing to diffusion gas escapes with
extraordinary rapidity, and if the fabric used is not absolutely
gastight the air finds its way in where the gas has escaped. The
maximum purity of gas in an airship never exceeds 98 per cent by
volume, and the following example shows how greatly lift can be
reduced:
Under mean atmospheric conditions, which are taken at a
temperature of 55 degrees Fahrenheit, and the barometer at 29.5
inches, the lift of 1,000 cubic feet of hydrogen at 98 per cent
purity is 69.6 lb. Under same conditions at 80 per cent purity
the lift of 1,000 cubic feet of hydrogen is 56.9 lb., a resultant
loss of 12.9 lb. per 1,000 cubic feet.
The whole of this statement on "lift" can now be condensed into
three absolute laws:
1. Lift is directly proportional to barometric pressure.
2. Lift is inversely proportional to absolute temperature.
Pages:
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26