• Question: Hi, my name is Alberteinstein12, and I wanted to ask you a question: what happens to the trails left in the air by aeroplanes?

    Asked by to Dre, Charli, Heather, Oliver, Becky on 20 Jun 2014. This question was also asked by .
    • Photo: Oliver George

      Oliver George answered on 20 Jun 2014:

      The trails left behind planes are called contrails (which is short for condensation trails). They are man-made clouds! They are usually caused by water released from the exhaust of jet plane engines but can also be caused by pressure changes at the tips of the wings. Depending on the weather they may stay around for a few seconds or they could even last for hours! When they disappear the water is spread out into the atmosphere.

      Planes can also cause distrails (which is short for dissipation trail) when they fly through a cloud, clearing a path which looks like a tunnel!

    • Photo: Charlotte Flavell

      Charlotte Flavell answered on 20 Jun 2014:

      Hi Alberteinstein12,
      The trails left in the air by aeroplanes are actually man-made clouds. That means they are made of lots of tiny water droplets suspended in the air. This is because when you burn aeroplane fuel, you get carbon dioxide and water and the water is the bit that forms the cloud. Usually these trails will just disappear as the cloud gets warmed up and the water turns to a gas instead.

    • Photo: Rebecca Williams

      Rebecca Williams answered on 20 Jun 2014:

      Hi alberteinstein!

      The trails left behind aeroplanes are like man-made clouds. They are made up of water, just the same as clouds are.

      Planes release water vapour (water gas) from their exhausts, like cars do. Very high in the sky, where planes fly, the temperature is cold enough that this water vapour condenses – this means that it turns from gas into water. You can make water condense by breathing onto a cold mirror or window. If its cold enough, this water also freezes. This makes the cloud behind planes.

      The trail will stay there for as long as the cloud is frozen – it takes a long time for the ice to turn back into gas. Sometimes it gets blown away by the wind.

    • Photo: Andrea Cristini

      Andrea Cristini answered on 20 Jun 2014:

      Hey Albert,

      Oliver, Charli and Becky have answered this really well. So I’ll talk about something slightly related to the trails left by aeroplane wings. That is why a wing helps the plane to fly.

      According to Bernoulli’s principle (named after Daniel Bernoulli), if a wing is shaped so that the top is curved and the bottom is flat, then air passing over the top must travel faster than the air on the bottom – makes sense if you think about it.

      It turns out (must be true though as planes don’t fall out of the sky) that if the speed increases the pressure that the air puts on the wing must decrease. So for a wing the pressure at the bottom will be higher than at the top, giving the wing lift against gravity.

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