Originally Posted by
peekay4
There are two different concepts here:
1. Fuel degassing (deaeration). This is the release of dissolved gasses, including oxygen, from the fuel.
2. Fuel weathering. This is the release of lighter / more volatile hydrocarbons from the fuel -- changing the composition of the fuel itself.
The author quoted in the first post seems to have mixed the two.
Peekay, while not directly in my area I worked with the people who worried about suction feed (aka gravity feed). I never knew them to differentiate between deaeration and evaporation of the more volatile elements of the fuel - they just wanted to know if suction feed would work. They simply referred to if the fuel was 'weathered' or not. As a rule of thumb, one hour after takeoff fuel was considered weathered (which would work out to be ~30 minutes at cruise). I recall a small number of flameout events where the crew was reconfiguring the fuel feed at top of climb and got the sequence wrong - inadvertently going to suction feed with fuel that was not yet 'weathered'.
In other words, while your differentiations may be technically correct, within the industry it's generally all referred to as 'weathered fuel'.