Thank you, this software has shown me that my dyno spreadsheet arrives at the same correction factor when using the same barometric pressure and temperature. My spreadsheet uses the same SAE 1990 standards. This is the first time that I have been able to verify the accuracy of my spreadsheet. Do you have any idea where I can find the formula for calculating the humidity correction factor?
The molecular weight of water is considerably less dense than dry air, and the humidity transforms moist air into a slightly different type of gas with a lower molecular weight.
The comparison of density altitude between completely dry air and 100% saturated air on an ISA sea level day is 0 vs. 221’. However, consider the same comparison done at 4000’ and 35 degrees, results in 7121 vs. 7923’ (about a 2.5% decrease in density ratio).
There is an additional factor to consider for engine performance, due to moist air displacing some O2 content. By my calculations, using the above examples causes the engine to experience (or “see”) equivalent densities of 582’ and 9268’.
The above comparisons are for academic purposes.
See “Performance of Light Aircraft,” John T. Lowry, and if interested I could give you the mathematical derivations of the above.