when a airliner flies overhead some times you see a smoke trail sometimes you dont why not?

Question

is it to do with temperature?

Answer 1

It is a condensation trail or contrail. There are different mechanisms at work. Jet aircraft fuel is a type of kerosene. When you burn kerosene, a lot of water vapour is produced. Water vapour is the invisible gaseous form of water. When the water vapour hits the cold air it freezes into ice crystals leaving a white trail behind the aircraft. If the air is dry, the trail quickly sublimes back to water vapour and disappears. (Sublimation is the change from the solid state, ice, to the gaseous state, water vapour, without going through a liquid phase.) If the air is very moist, the trail can persist for a while before it sublimes.

You can see a similar effect when you boil a kettle. The water vapour emerges from the kettle and condenses into a visible cloud of water droplets. These quickly evaporate back to water vapour.

Before water vapour will condense into water droplets or freeze into ice crystals it needs condensation or freezing nuclei. These are minute particles of dust, smoke, salt etc that are found in the atmosphere. If the air is very clean and there are no such nuclei, the air can become supersaturated. This means there is a lot of water vapour in the air but nothing on which it can condense or freeze. Enter one big aeroplane pumping out not only water vapour but also particles of soot, smoke and oil from the burning of the fuel. Instant freezing nuclei. The contrails these produce last a very long time and often spread out to form sheets of cloud.

Aerological soundings of the atmosphere are made every day all over the world by sending up weather balloons with a radiosonde attached that gives the temperature and humidity at different heights. From the sounding it is possible to work out at what height contrails are likely to form. These computations were very important during WWII. Bombers would fly just below the level where contrails formed. This meant that any fighters above them would be leaving contrails and would be more easily seen.

Answer 2

That's not a smoke trail - what you are seeing (or not seeing) is a vapor trail. The vapor trail is caused if the air is relatively humid, and the aircraft is high enough. The engines will super heat the air, and when the humid air cools it will form ice crystals (that why you see the 'smoke' behind the aircraft, but it's not really smoke it's a cloud of cooled down water in the air that is forming as small ice crystals like clouds). You will not see this coming from aircraft that are lower as the air is not as cold.

Answer 3

It's not a smoke trail.

It's a vapour trail and depends on the temperature and moisture levels at the height that the plane is flying.

Too little moisture or too warm and no trail.

It also is NOT condensing exhaust fumes, it is caused by the vortices of air spinning off the wing tips.

Answer 4

From your description it sounds very much like you live near an airport, i used to live next to the M4 motorway. The planes taking off, were bellowing pure smoke fumes during its thrust to acsend. On a descent to land the same happens when the plane throttles back!

Answer 5

Yes It has to do with the weather conditions at the altitude where they are flying, usually above 25,000 feet. the smoke trail is caused by the exaust freezing as it exits the plane.

Answer 6

Its not smoke, its water vapor.

It has to do with both temperature and the amount of humidity in the air, as well as the altitiude and speed of the plane.

Answer 7

i've got basically taken 2 journeys on an airplane & the two have been interior the previous 3 or 4 years! I nevertheless get worried! the only subject i think of of is that if there are human beings from The Mile intense club on it!!!

Answer 8

Not smoke, condensation. Depends on atmospherics and height of the aircraft. Higher up, more likely to be visible.

Answer 9

Yes. It is the moisture from the exhaust condensing, and it must be cold.