Contrails

[cromwell]

Those things left by jet planes in the sky.
Am I remembering this correctly, but in the past they seemed to disappear after a while?
Now they seem to hang around forever, spread out and become long clouds.
Odd.

[Workingman]

From my "Theory of Flight" classes in the RAF. Two factors re contrails: the altitude of the aircraft and the relative humidity of the atmosphere. The higher the aircraft the more likely contrails will form and the more moist the air the bigger and longer lasting they will be - the basics.

A few modern things might make things different. As the atmosphere warms, as it is doing, the more moisture it can hold - that relative humidity thing - so bigger contrails. Another is the efficiency of modern engines. They are huge and gulp in more air then burn it hotter - more exhaust air to cool down and hot vapour to condense. The third is that modern aircraft fly much higher than previously.

It is all a combination of the basics and modern life. We see more of them on clear days like today, but they are always there.

[Suff]

Pretty much everything I would have said WM however I hadn't considered the ever increasing size of the engines.

That being said the days of super massive wide bodied jets appears to be waning. The A380 is no longer being sold, the 787 dreamliner is significantly smaller than the 777.

So we may see a time where these contrails reduce again. Where we live in France is a major crossroads for international flights. Depending on weather etc there can be as many as 30 contrails in the sky at the same time.

[Workingman]

Contrails are more to do with flying altitude and atmospheric conditions than the size of the plane and engine.

We are screwing the atmosphere with our, not so, net-zero crap, so contrails are not likely to reduce any time soon - if ever - unless we stop flying everywhere. We are seeing that phenomenon with hurricanes and typhoons.

When it comes to comparing planes, size is secondary. The 787 might be (a bit) smaller than the 777 but its range and litres of fuel per hour of flight are way ahead. Per passenger per mile it wins hands down. Ultra-wide bodies fell out of favour because few airports could accommodate them.

[cromwell]

Two factors re contrails: the altitude of the aircraft and the relative humidity of the atmosphere. The higher the aircraft the more likely contrails will form and the more moist the air the bigger and longer lasting they will be - the basics.

A few modern things might make things different. As the atmosphere warms, as it is doing, the more moisture it can hold - that relative humidity thing - so bigger contrails. Another is the efficiency of modern engines. They are huge and gulp in more air then burn it hotter - more exhaust air to cool down and hot vapour to condense. The third is that modern aircraft fly much higher than previously.

Thanks WM. That's much clearer now.