In case you don't follow the dev blog I'm happy to formally announce that Combat-Helo will be using Fred Naar's Helicopter Total Realism (HTR) physics module for the advanced flight-model.

The data driven flight model uses advanced blade-theory derived from works such as Wayne Johnson's Helicopter Theory and others. The model can process different helicopter configurations, standard, tandem, co-axial and it's flexible allowing for constant adjustments to CoG, payload shifting and stabiliser airflows.

HTR is currently available as an external module for FSX and interfaces via FSUIPC. Details in the forums at Hovercontrol.