Rule 5b. Never use single quotation marks in sentences like the previous three. Incorrect: I had a visit from my 'friend' the tax man. The single quotation marks in the above sentence are intended to send a message to the reader that friend is being used in a special way: in this case, sarcastically. Avoid this invalid usage.
Why do jets leave a white trail in the sky? Jets leave white trails, or contrails, in their wakes for the same reason you can sometimes see your breath. The hot, humid exhaust from jet engines mixes with the atmosphere, which at high altitude is of much lower vapor pressure and temperature than the exhaust gas.
An afterburner is nothing but a set of fuel injectors, a tube and flame holder that the fuel burns in, and an adjustable nozzle. A jet engine with an afterburner needs an adjustable nozzle so that it can work both with the afterburners on and off. The disadvantage of an afterburner is that it uses a lot of fuel for the power it generates. Therefore most planes use afterburners sparingly. For example, a military jet would use its afterburners when taking off from the short runway on an aircraft carrier, or during a high-speed maneuver in a dogfight.