Military jet trails. What causes the streak in the sky, and why does it linger so long?

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Military jet trails. What causes the streak in the sky, and why does it linger so long?

In: Technology

Not just military jets, contrails are ice formed by moisture in the air flowing over the wing surface – the top side of a wing creates a different speed than air over the bottom of a wing surface, thus generating lift.

You’re probably thinking about the trails left by the military jets at air shows.
For those shows, there a machine that sprays oil into the exhaust.
The exhaust heats up the oil making smoke.
Sometimes that oil is even colored.
It stays up because it’s not much more denser than air, and much hotter.
I think the majority of the oil is what amounts to be liquid wax (paraffin-based smoke oil), but I’m not 100% sure.

When fighting a war, military jets really don’t want smoke trails.
It shows up really really well on radar and everyone can see it.
But in an airshow in peace time, you want everyone to see you, and look at how cool your moves are. So they put them in.

That being said, there are ways to unintentionally make a smoke trail.
The differences in air pressure caused by the engines and wings sometimes causes the water vapor to condense around stuff in the air. Often around the stuff left over from when they burnt jet fuel.
So that makes clouds.
You see this quite often in air liners, but it sometimes happens to military jets.
In war time this makes the pilot very very nervous.