Fan blade physics
All fan and compressor blades in a turbofan engine are airfoils, meaning they have an elliptical leading edge like a conventional propeller blade. The tapered shape follows Bernoulli’s principle, forcing the air to move faster over the curved ‘top’ of the blade, reducing pressure and creating lift or thrust from ‘below’. Turbofan blades are also long and wide, giving them a large surface area. When 20 blades with a six-metre (20-foot) diameter are spinning at the same time, they can move around 1,100 kilograms (2,400 pounds) of air per second, producing signifi cant thrust.
Turbofan blades are also ‘ducted fans’, which means the spinning blades are housed within a cylindrical duct rather than rotating freely. Ducted fans have the advantage of reducing a drag effect called wingtip vortices. When an elliptical wing cuts through the air, it leaves a spinning trail of air called a vortex. That vortex increases drag, vibration and noise. Ducted fans prevent this and, as a result, are quieter, run smoother and can create the same amount of thrust with shorter blades.