Everyday i saw jet planes crossing the sky leaving a white line from the engine behind,Why they do that?

Question

that's some kind of test?

Answer 1

to mark the houses to destroy...

your's is next

Answer 2

You can do a search on contrails, and please ignore the references that say anything about chemtrails or chemicals.  

It's just water vapor.  No test, just a product of combustion and heating air with water in it.  They are as harmless as clouds.

Answer 3

Lots of silly answers above but the truth is fairly simple.

For every gallon of fuel burnt a jet engine produces 8 gallons of water (in the form of steam) but at say 35000 feet the temperature is about -65 degrees centigrade so the steam converts almost instantly into ice crystals. This is what you can see. These crystals dissipate harmlessly in the atmosphere. Gravity says they fall, as they fall they get warmer and eventually melt., It's only water after all.

Contrary to what some so called "experts" try to tell you it has no effect on global warming.

Ian M.

Answer 4

Messages from outer space.

Only the chosen can see them.

Answer 5

It's called a exhaust.....

The "white line", also called a contrail, happens when the plane is flying at an altitude where the moisture content and temperature of the air is just right. The contrail is actually tiny ice crystals formed from water in the exhaust of the airplane.

Answer 6

Its moisture from the exhaust creating ice crystals. All combustion engines release a little bit of water which is formed from the chemical reaction between oxygen in the air and the hydrogen in the hydrocarbons (like gas, diesel, and jet fuel) being burned. Its just that water freezing in the sub zero temperatures up there.

The moisture coming off the wings of an aircraft that is making a high g turn is not the same thing, it is caused by inertial cavitation.

In other words, the air is being forced over the wing with so much force and momentum that it creates an actual cavity (like a bubble) of low pressure where the air cannot flow because of its own momentum, instead of just a small pressure gradient (gradually changing from high to low pressure), so the pressure is so low in that cavity of air that the moisture condenses.

Answer 7

the white line is gas emitted as a discharge,but you need to be careful if the line is getting shorter than you could be danger in case the line falls on you some day.

Answer 8

the Powerful jet turbines are turning so fast they break the moisture barrier therefor causing the "white smoke" you see.

you know at the airshows. the F-18s when they pull out of a dive or turn sharp you see the same thing forming on the wingtips.

Answer 9

thats a really long string and they follow it to get back home

Answer 10

They are marking their place in the sky - kinda like dogs do in the park.

Answer 11

Just training