Banana blade

I was given a tip by a learned fan design guru, who might have designed fans for the secret military drones keeping you in check. The tip was to add dihedral to the blade, this is when the wing of an aircraft is canted up at an angle, which affects the stability of an aircraft.

Although its got the same name, the effect it has on fan blades is nothing to do with stability. Its to with reducing the stress on the root of the blade, and reducing the amount that the blade will deflect under load. And possibly more important than the latter if i ever planned to sell my blades (which i don’t), it gives the blades a cool 3D curved shape to make it look different to the competitors (doesnt show very well in the CAD screenshots).

This applies only to fast spinning fans andĀ propellers that have a dominating centrifugal load- slow turning wind turbine blades are coned forward to prevent the blades hitting the tower and self destructing.

So how does twisting the blade do this? I will try to explain with a few pictures of the structural model of the blade, when applying centrifugal and aerodynamic loads on their own, and together as the blade would see in real life.

The model is of the whole blade including the skin and foam cores, but they have been greyed out to show only the spar laminate material. Its important that everything is included and the densities and thicknesses are accurate, because for centrifugal loading the weight distribution is key.

Posted in: Fan design, General on December 19th by admin

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