I've recently finished writing a program that runs alongside MS Flight Sim and plays with the flight dynamics at run-time, adding in a lot of missing behaviours.
The default coefficients are tuned to give a roughly half-decent response to the standard Flight Simulator X Bell 206. (For Flight Simulator 2004 you should set the general realism in the sim to about 90% and use my default settings.)
If anyone wants to give it a go, you can download it here:
http://www.mediafire.com/?9zjcu5zeenc
You'll also need to google for and download FSUIPC.dll. (Note that you don't need the registered version.)
Since my program is free to use (for non-commercial use) I hope this doesn't constitute advertising!
Regards,
Si