How do they do it? - Growth Rotor Blade

[Graviman]

Thanks again to N.L. for helping me understand this stuff.

Phoinix,

The secret seems to be in the design process to determine number of blades for a given MAUW. It is not uncommon to chose an aspect ratio outside of the flapping hinge of 12, to keep blade 3/4 wave mode below 3P. The fewer the blades the less the vortex interaction, so the number of blades is a compromise between high solidity ratio and blade tip vortex interaction. BugDevHeli's rotor ring development may well change all this.

My guess is that Sikorsky are keen to push up the solidity ratio for higher figure of merit, without increasing vortex interaction. A great deal of development will have gone into the blade to control it's aeroflexural eigenmodes, at say 3P 5P etc. This means that the number of blades stays the same for a given rotor radius, hence the aspect ratio goes down.

So GRB is a package which gives you better rotor dynamics, and both higher hover and cruise efficiency. This last part is accomplished because Nr is beeped down for hover, and beeped up to counter cruise retreating blade stall. Again better rotor dynamics improves the Nr range.

Mart