As I type this I’m still trying to figure out: a. What have I found out, and b. Is it relevant.
Yes, the humidity does make a difference to the DALT. I put various figures into the calculators on the web pages (your links need editing, they bring up a page
http:/// ) using standard atmosphere values and came up with the following. Using RH values of 5% and 95% respectivly the humidity changed the DALT as follows:
At 2000ft OAT 11deg c, 5% = 2100, 95%= 2267
At 10000 OAT –5 deg c, 5% = 10002, 95%= 10067
At 35000 OAT –55deg c, 5%= 35011, 95%= 35012
The differences in the Relative Air Density varies from 0 at 35000, 0.1% at 10000 and 0.4% at 2000. Even at 30deg c at 2000 the difference is only 1.5%.
Still not sure whether it makes a difference or not, especially as in aviation we use a graph based on the formula DA=PA+/-120T which makes no mention of humidity. The change of lift on an aerofoil is probably negligable. If you want to squeeze max power out of a piston engine then the humidity will make a difference, as humid air increases the weight of the charge drawn into the cylinder and increases the heat efficiency of the engine (I think!!). Both of which give an increase in power (I think!!!).
Phew, now I need to go and lie down for a while.