Why do airplanes leave the white stream behind them sometimes and not other times?

Question

LT say Bamma make no sense :)

Answer 1

Contrails are condensation trails (sometimes vapour trails): artificial cirrus clouds made by the exhaust of aircraft engines or wingtip vortices which precipitate a stream of tiny ice crystals in moist, frigid upper air. Contrary to appearances, they are not air pollution as such, though might be considered visual pollution.

An aircraft engine's exhaust increases the amount of moisture in the air, which can push the water content of the air past saturation point. This causes condensation to occur, and the contrail to form.

Aviation fuel such as petrol/gasoline (piston engines) or paraffin/kerosene (jet engines) consists primarily of hydrocarbons. When the fuel is burned, the carbon combines with oxygen to form carbon dioxide; the hydrogen also combines with oxygen to form water, which emerges as steam in the exhaust. For every gallon of fuel burned, approximately one gallon of water is produced, in addition to the water already present as humidity in the air used to burn the fuel. At high altitudes this water vapour emerges into a cold environment, (as altitude increases, the atmospheric temperature drops) and the local increase in water vapour density condenses into tiny water droplets and/or desublimates into ice. These millions of tiny water droplets and/or ice crystals form the contrails. The energy drop (and therefore, time and distance) the vapour needs to condense accounts for the contrail forming some way behind the aircraft's engines. The majority of the cloud content comes from water trapped in the surrounding air. At high altitudes, supercooled water vapour requires a trigger to encourage desublimation. The exhaust particles in the aircraft's exhaust act as this trigger, causing the trapped vapor to rapidly turn to ice crystals. Contrails will only occur when the outside air temperature around the aircraft is at or below -57 degrees Celsius.

Answer 2

Contrail, Short for Condensation trail.

Breath out on a cold moist day and you see your breath as a fog in front of you. same thing.

Bigcountry... It's NOT exhaust smoke, though it is caused by the exhaust.

CG say Bamma is a joke

r w : They are NEVER called CHEMtrails. only CONtrails. Chemtrails are a joke. like Bamma. the stuff of weirdo conspiracy theorists with not one clue as to real life. Only people who believe in them is the same people who think the National Enquirer is a real news magazine.
The reason you do not see them behind prop planes is that they don't fly high enough. Usually somewhere around 25,000-30,000 ft or more depending on local weather conditions. Prop planes dont go that high normally. The few that can. yup they create them too. but you on the ground can't tell the diff between prop and jet at 30,000 ft.

A few of you have the correct answer, or at least part of it. Pilot Jock has the most in depth and correct answer. I agree with Chercham, Pilot Jock is the right answer.

Answer 3

so as that phenomenon is stated as a contrail ( a condensed version of "Condensation path") and your grandpa isn't too some distance off. actual while an plane is going with the aid of the sky the nice and comfortable exhaust from its engines could reason water to condense right into a path at the back of the airplane. If the air is chilly sufficient, and the airplane is severe sufficient then those trails become ice, and are available into sight to us, way down below.

Answer 4

Forget all the 'chem-trails' nonsense. Load of shyte!
What's happening is you have a turbine engine burning kerosene in a very cold environment. In most cases the temp is around minus 50C at cruising altitudes.
One of the by-products of burning hydrocarbons is water vapour. When the hot, water vapour laden exhaust hits the icy cold air ...it condenses and leaves a trail of steam..(a contrail) behind.
How long this contrail lasts depends on the relative humidity of the surrounding air, winds aloft, type of engine creating the exhaust amongst other factors. In some cases almost no contrail will form. Usually this is occurs when the engine is at reduced power, aircraft at a lower altitude or the air aloft is very dry or warmer than normal.
Forget the chem trails...makes for good late night radio....but the fact is...... it's all steam!

Answer 5

Pilotjock is the only one so far who has it right.
Vote for him.
BTW, you do get contrails behind piston aircraft, but they have to be flying VERY high for the air to be cold enough - higher than most piston aircraft go but you did see a lot of contrails in WW2 from high altitude bombers and fighters.
There is a TINY truth in the pollution answer, but only because the contrail needs a condensation nuclei to form on and the tiny exhaust particles are that nuclei. Without the nuclei, no contrail would form but there is often enough nuclei from natural sources (sand, dust, pollen, salt) for condensation to form.

Answer 6

an airplane leaves that white stream behind for the same reason you can see your breath (as a vapor) on a really cold day. the higher up you go, the colder it gets, approx 2 degrees C for every 1000 feet (300m) in elevation. up at 30,000 feet (10,000 meters), depending on the surface temperature, it can reach in excess of - 40 degrees C (-40 degrees F) and the fuel vapor condenses at really cold temperatures

Answer 7

They're called contrails and it depends on the atmospheric conditions if a plane makes them or not.

Answer 8

Condensation, hot engine + cold moist air = vapor trail.

Answer 9

it has to do with the moisture content in the air. when there is no moisture in the air the planes can't leave "vapor trails". the air has to have just the right temperature and moisture content to make them.

Answer 10

This blog has an explanation of contrails that should answer your question: http://privatejetcharter.spaces.live.com/