Why does a jet plane let off the white colored smoke., and what is it?

Answer 1

The "smoke" is actually water vapour that condenses in the cold air of high altitude.
The water vapour itself is a by-product of the combustion of jet fuel. You get the same effect on your car when the weather is cold.

Answer 2

If you are talking about the "smoke" from the wingtips... then it's not smoke.

It's water vapor. The leading edge of the wing heats the air as it comes into contact with it through friction. The warmer air cools as it leaves the wing tip and the water in the air as humidity "steams"

It's called a condensation trail or "con-trail".

Answer 3

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 pollution as such.
Contrails are created in one of two ways:

1. First, the airplane'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 steam emerges into a cold environment, (as altitude increases, the atmospheric temperature drops) which lowers the temperature of the steam until it condenses into tiny water droplets and/or desublimates into ice. These millions of tiny water droplets and/or ice crystals form the contrails. The temperature drop (and therefore, time and distance) the steam 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 outide air temperature around the aircraft is at or below -57 degrees centigrade.

2. The wings of an airplane cause a drop in air pressure in the vicinity of the wing (this is partly what allows a plane to fly). This drop in air pressure brings with it a drop in temperature, which can cause water to condense out of the air and form a contrail but only at higher altitudes. At lower altitudes, this phenomenon is also known as Ectoplasm. Ectoplasm is more commonly seen during high energy manouvers like those of a fighter jet, or on jet liners during takeoff and landing, at areas of very low pressure, including over the wings, and often around turbo-fan intakes on takeoff. See also Wing tip vorticies.

Exhaust contrails tend to be more stable and long-lasting than wing-tip contrails, which are often disrupted by the aircraft's wake and are commonly very short-lived.

Answer 4

It is water vapor in the exhaust. The warm, moist exhaust hits the very cold air at altitude and condenses into clouds.

Answer 5

It's the exhaust of the engines burning fuel and turning it into carbon dioxide. It is extremely cold up there so you are seeing the vapor trail.

Answer 6

It is water vapor condenstating at high enough altitudes
that is why they are called "con trails"

Answer 7

It's water vapor (condensation)