I quickly looked at the code and there is one thing I noticed, lines 72 and 127 in AirDensityCalculator.java, in the method getDryAirDensity:
That is a really bad idea. It means the whole program stops immediately if that line is reached. Much better would be to throw an exception instead, for example:
Also, the design could be better. The code is getting messy with all those switch statements. You could use a design
pattern such as the
strategy pattern for the different calculations that are necessary for the different types of units.