The engine of an Airbus A320, or that of a Boeing B737, moves about 600 litres of air per second. That’s a lot, isn’t it?
Well, imagine a Boeing B777, which is capable of moving up to 1900 litres per second, and all that air shoots out at high speeds towards the back of the plane.
In addition, the design of the aircraft creates very turbulent vortices at the wingtips which, together with the jet stream, create a turbulent wake behind the aircraft.
But don’t confuse the turbulent wake of an aircraft with contrails or condensation trails because they are not the same thing. Don’t know what they are? We tell you all about it in the linked post.
Like almost everything in aviation, it depends on the intensity.
There have been cases where private jets have looped after entering the turbulent wake of an Airbus A380, the world’s largest airliner. But, as a rule, it is not much more than light turbulence.
There are several techniques to avoid wake turbulence. The first, and most obvious, is separation between aircraft.
At airports, air traffic controllers know the minimum separations between aircraft due to wake turbulence, which are based on the time it takes for the wake to dissipate. In turn, separation times are estimated based on the size of the aircraft and the take-off or landing position.
For take-offs, it is advisable to rotate beyond the point where the previous aircraft landed, while for landings, it is better to take off further than the previous aircraft, as once the aircraft touches down, the wake disappears.
The other technique for avoiding the turbulent wake, this time in flight, is to stay above the path of the preceding aircraft and to the side the wind is blowing.
As explained above, high intensity turbulent vortices are generated at the wings, which generate most of the induced drag in aircraft.
To minimise this, aircraft manufacturers are developing new designs for aircraft wings, including winglets or sharklets, i.e. where the end of the wing is folded upwards.
This new design reduces fuel burn by 3.5-7%, minimises the turbulent vortices generated and also the noise pollution produced by the aircraft.
As mentioned above, turbulent wake is largely due to induced drag.
As a general rule, induced drag is higher the lower the speed of the aircraft, but in turbulent contrails, it works differently.
The reality is that an aircraft generates more turbulence the larger it is, the faster it flies and when it is in a clean configuration, i.e. without extended flaps or landing gear.
