On Jan 16, 7:05*am, "Ken S. Tucker" wrote:
Humidity feeds into "density altitude" because water
vapour molecule H2O has density ~ 10 compared to
Nitrogen N2 ~ 14 *at equal pressures*

Not quite. The density is proportional to molecular weight, which
would be in the ratio of 18 for water to 28 for nitrogen ( g /mol )
But of course we are really interested in the density ratio between
water and air which would be 18 to 28.9

Ths simply comes from rearranging the Gas Equation we all learn in
high school
PV =nRT
substiute n =m/M where m is mass and M molecular weight , you
rearrange to get
m/V = PM / RT
m/V of course = density
( assuming ideal behaviour exists which is a pretty good assumption at
the pressures and temperatures involved in flying light aircraft ).

I'm guessing: but I get the impression that the onset
of turbulence over wings was also dependant on temp-
erature, even when the density altitude is the same.
* In Quantum Theory that makes sense.
To start, warm air is more chaotic than cold air at the
molecular level, and the chaos *seeds* the turbulence.
You know, hot fluids are less viscous than cold and so
less sticky. That's likely a secondary correction.
Regards
Ken- Hide quoted text -

So if warm air is more turbulent ( I think I can accept that ) wouldnt
that mean that at higher temperatures for the same density altitude
you would get less lift and require longer take off distance?
As previously stated the results are the other way around.

Cheers
Terry