"Michael Calwell" wrote in message
...
Hello,

Question from a complete landlubber.

I work outdoors beneath the flightpath to Edinburgh Airport.

I take it that vapour trails are the condensed water contained in the
air ingested by the engines. My question is, how much air does an engine
ingest at cruise? How would you visualise that amount of air?

Yours in amazement at how you stay aloft,

Michael

It is not the vapor from the air you are seeing, it is the water that is
produced as a byproduct of burning hydrocarbons.

Ever see water dripping from your car tailpipe, especially in the morning
when you start it up? Water is being produced, and being condensed on the
cold sides of the tailpipe, then it drips out. When the tailpipe gets
warm, the water stays invisible, so you don't see clouds unless the outside
temperature gets very very cold, then you get clouds coming from the back of
the car, as the result of the exhaust cooling rapidly, and the vapor in
exhaust condenses to become visible.

This is similar to what is happening when you see contrails. They almost
always are very high, so the water vapor condenses and then freezes into ice
crystals almost instantly, so then it is harder for the water to
re-evaporate into the surrounding air. This is the reason con trails are
visible for a long time after the aircraft passes by.

The vapor that you see off the tips of props, or from the topside of fighter
jet wings when they are pulling high G-forces are from the pressure in the
air being reduced very quickly, which causes the water vapor to become
visible for an instant, then disappearing just as quickly when the pressure
is returned back to normal.

As far as the amount of air being passed through an engine, for a
reciprocating engine, the amount is much smaller than a jet engine. Gallons
per second for a piston engine, and hundreds of gallons for a jet engine?
Something like that.

I hope this has helped.
--
Jim in NC