Dave,
This is all textbook stuff. What i have described is the basic principle behind combined blade element and momentum theory. My vantage point is that i have also created a vortex panel method, which can be as accurate as CFD but without the computational overhead (mine should eventually cope with drag, trailing edge stall, and transonic flow). Integrating VPM and BEMT in one rotor/fan model has left me with the understanding about the helices described above. I think it is this lack of perspective which leads to a lot of misunderstanding (including my own a while back) about how flow alters the power required for a given thrust/lift.
Regarding X2, it does not matter where the prop is located relative to the rotor. If you think of the helicopter as being in a black box, it will require thrust power to cruise and to lift power to hover - This will not change significantly with configuration as long as rotor and prop area are constant. In some flight conditions puller prop will allow a slightly greater total area of induced flow, ie prop & rotor streamlines are kept apart, reducing power requirement. In power hungry conditions of hover and cruise-dash i doubt power requirements are any different with puller or pusher prop. Transition is one example of a single flight condition, but it a transient event requiring perhaps a brief blip in power increase for a given envelope.
Last edited by Graviman; 12th May 2009 at 18:28.