Momentum Theory gives simplistic but reasonably accurate data related to the activity of the helicopter rotor. Its primary shortcoming is that it considers the aerodynamically induced forces as being consistent over the disk area.

Blade Element Theory improves on the above method by calculating the local aerodynamic forces at segmented locations over the disk area.

Vortex Theory attempts to provide an even better representation of the aerodynamically induced forces by considering the effects of shed and trailing vortices of one blade on the on following blades.

This blade vortex interaction is a valid concern for helicopters with single rotors. It therefore must be a greater concern for helicopters with multiple rotors.

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I, pretentiously, suggest the following;

The diameters of the vortices are quite small in the region where the following blades will pass through or near them. Therefore, if helicopter blades were extremely rigidity the vortices' upward moments will partially self-cancel with their downward moments. The end result will simply be a modification to the lift and drag forces on the following blades, at specific locations.

This being the case, the vortex sheet can be considered simply as spiraling planes of 'areas' and the tip vortex as a spiraling filament of 'areas', through which the elements of the following blades will pass. The improvement upon 'blade element theory' will not be the complex 'vortex theory'. It will simply be 'blade element theory' with adjustments to the lift and drag on the blade's elements, as they pass through these 'areas',.