<p>How are the coloured vapour trails made?
</p><p>The vapour trails begin life as diesel fuel, contained in an extra fuel tank bolted on the underside of the Hawk fuselage. At the rear of the aircraft, immediately above the jet exhaust pipe, there are three small tubes through which the pilot can pump small quantities of this diesel. When the diesel meets the extremely high temperatures found in the jet exhaust (over 500 degrees Celsius), the diesel immediately vaporises creating an intense white cloud. With separate switches on his control column, the pilot can add red or blue dye to the diesel and produce the other two colours. During a 30-minute sortie each aircraft can produce vapour for a maximum duration of seven minutes.
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These vapour trails are essential for flight safety, allowing the Team Leader to judge wind speed and direction accurately, as well as allowing the Team Leader and Synchro Leader to keep sight of each other even when they are several miles apart. Trials have found no discernible hazard to health and the emissions are insignificant in terms of local pollutants.
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/48215073@N00">Santosh Puthran</a>
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<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/talk2santosh/9659060875/">Red Arrows Bournemouth Airshow 2013</a>