Apologies for being a bit thick here - but I'm still not 100% in the picture.
I understand the concept of aerodynamic contrails and the basis of cjam's explanation of condensation contrails. The bit I am unsure about (for condensation contrails) is to where the extra water vapour comes from...
The story as I understand it so far...
The air in front of the engine at -50 degrees has a RH of x% (less than 100%). It passes through the engine and exits at a much higher temp which would allow it to hold more vapour invisibly (but the vapour was invisible at -50 degrees anyway). It then cools to its original temp but the RH is now 100%. Since aviation fuel contains no water (I would hope not anyway), where has the extra moisture come from?
look forward to your assistance / abuse
