Thu Apr 21, 2011 8:24 pm #956686
CaptCrispy wrote:Thanks for this mo0g.
I don't like not understanding something so I will look into this in more detail when I have time (especially as I will be flying a great deal in Switzerland soon!).
Np. In terms of density & humidity & performance, just think of the o2 molecules contained in a packet of air.. If its warmer, the air is expanded, so less o2 molecules in the same cube of air. If it is humid then there are more h2o molecules in that packet of air, taking up space where the o2 was. In any situation where you have less o2 in that packet of air, you need less fuel for optimum combustion = leaner mixture
A different way, cold/dense/dry air has the most o2. Any warmer/less dense/more humid means less o2 and therefore needs less fuel. So in lycoming engines they state a density altitude of 5000 before you need to actually lean the mixture for takeoff.. and density altitude is the EFFECTIVE altitude you are at taking the temp, altitude, pressure AND humidity into account. Anyway, hope that helps cement the logic behind it!
Anonymous shanonymous - the name is Mark...