Source: Travel 3Sixty
The contrails of a cruising aircraft
When I was a young boy, I often wondered about the white smokey streaks across the sky that could be seen on a clear day.
It wasn’t until I became a pilot that I realised what they were: condensation trails, also known as contrails, produced by jet engine exhaust from airplanes flying at cruising altitude. When water vapour in the exhaust condenses in the cold environment at high altitudes, contrails are formed.
Breath looks misty in cold weather
This is similar to when, in extremely cold weather, your breath looks like puffs of white smoke. The humidity in your lungs which is present in the air that you exhale when you breathe or speak, condenses in low temperatures, making your breath look misty.
The condensation trail that forms as a plane cruises above in the sky is no different.
The Cruise
Cruising at higher altitudes helps save fuel
A plane goes through various phases for each flight, which include the take-off, climb, cruise, descent and landing. The aircraft is at its safest phase when cruising in clear skies, as it is usually at its most fuel-efficient altitude.
An Airbus A330 on an eight-hour flight from Kuala Lumpur to Melbourne would carry about 55 tonnes of fuel, and at the cruise phase, it would consume between 80 and 85 per cent of its fuel. As the fuel burns, the aircraft becomes lighter and the optimum cruising altitude increases. The pilot takes advantage of this and normally requests permission to climb to a higher altitude in order to save even more fuel.
This is because the air at higher altitudes is less dense, providing less resistance, and thereby improving fuel efficiency.
Matter of Perception
On average, a commercial airliner cruises at an altitude between 35,000 and 40,000 feet, and travels at a speed of about 480 knots, or eight nautical miles per minute!
On a clear day, if you look out the window of an aircraft cruising over land, you would notice that cities, rivers and coastlines seem to ‘move’ very slowly. This is because although your body can generally feel acceleration, your perception of speed is greatly limited when you travel at a constant speed (when cruising), unless there is an external reference to help you gauge how fast you are moving.
For instance, when travelling in a car, the sound of the tyres on the road and the rush of the wind give you a good perception of the speed you are moving at.
However, when an aircraft is cruising, the cabin is fairly quiet and the speed is constant – so the body is unable to perceive speed. Plus, external objects (like cities and rivers) are at a great distance, making it more difficult for you to gauge the speed of the plane.
As a result, even though the Airbus A330 is flying at a high speed, your perception leads you to believe that you aren’t moving very fast at all!
Throwing a Curve
Have you noticed that flight paths in route maps are usually marked with curved lines?
There is an interesting explanation for this. Because the Earth is a sphere, the size of the areas located closer to the North Pole and South Pole are, in fact, inaccurately depicted in maps due to a type of map projection called the ‘Mercator projection’. So, Greenland, for example, being ‘stretched’ on the map, appears larger than it should be.
Imagine taking the surface of a sphere and ‘flattening’ it on a map to illustrate the geographical locations of countries around the world. The places that are closer to the two poles of the planet have to be ‘stretched’ to allow for a more consistent illustration.
As such, the shortest distance between two points on a sphere is an arc and not a straight line, which explains why flight paths on route maps are curved.
Wishing on a Star
A rarely seen shooting star
The renowned Italian artist, Leonardo da Vinci, who was fascinated with flight, said, “Once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return.”
Over 500 years later, humans still find the skies intriguing, and da Vinci’s words continue to inspire aviators and travellers alike to try and discover more truths about traversing the skies.
Posted: 19.9.18