The integrated band idea
bsieker
Hi bsieker and others,
Probably I didn’t explain the idea very well - think of the band as a rim and the fan blades as spokes of a rigid or semi rigid wheel.
This rim looks a bit like the metal tyre round a wagon wheel and is attached directly to the all blade tips.
In this way the blades are stabilised and supported by each other. There may even be an aerodynamic benefit due to the fencing effect at the tips.
Now imagine you are a blade, hanging on to the disk hub but also being held in there by this band. Before you can fly off you have to compress all the opposite blades which are supporting the band in turn. The band doesn’t have to take the 100 tons - the hub does that and the band provides support to stop it getting ideas.
It is the sum of the forces working like wagon wheel spokes in compression but like bicycle wheel spokes in tension. (Wagon sits on its spokes - a bicycle hangs from them)
So the blade doesn’t get much chance to get fatigued and won’t want to depart. If the blades expanded there would be a bending moment so the rim material should be the same as the blade material. If composite, then composite too.
A tight cord around the blade tips would be lighter and have a similar effect but could be more difficult aerodynamically.