I was reading Wikipedia page about hot air airship and another Wikipedia page about the first powered and steerable airship which was powered by a steam engine. So I ask myself "why didn't they use the exhaust steam from the steam engine as lifting gas?"
After quick research, I found this home made experiment of steam used as the lifting gas. This website even gives a comparison with other lifting gasses:
+-------------+----------+------------+-----------------+--------------------+--------+-----------+-------------------+------------------+ | GAS | M.W. | Temp. (°C) | Density (kg/m3) | Lift (N/m3) in ISA | Safety | Cost | Ease of provision | Buoyancy control | +-------------+----------+------------+-----------------+--------------------+--------+-----------+-------------------+------------------+ | H2 | 2 | 15 | 0.084 | 11.19 | bad | fair | fair | no | | He | 4 | 15 | 0.169 | 10.36 | good | very high | very bad | no | | CH4 | 16 | 15 | 0.676 | 5.39 | bad | low | fair | no | | NH3 | 17 | 15 | 0.718 | 4.97 | fair | low | fair | no | | hot air | 29 (avg) | 110 (avg) | 0.921 (avg) | 2.98 (avg) | good | very low | good | yes | | steam (H2O) | 18 | 100 | 0.587 | 6.26 | good | very low | good | yes | +-------------+----------+------------+-----------------+--------------------+--------+-----------+-------------------+------------------+
(source: http://flyingkettle.com/jbfa.htm)
Given the conclusion of this website, steam should now be more widely used as a lifting gas:
- it is available since the first lighter-than-air (plenty of time to develop the technology)
- it has a good lifting power
- it is cheap and safe
Yet, on 2020, almost all airships and balloons use helium or hot air, and no other lifting gas. So there must be drawbacks I fail to imagine. I hope finding those drawback will orient my research for my first question ("why didn't they use exhaust steam as lifting gas on airship fitted with steam engines?"). Moreover, there may be advantages I also fail to imagine.
Thus, what are pro and cons of using steam as a lifting gas?