Thank you both for your comments and suggestions! However, I realize that I've been a bit unclear about what I want to do. The actual flight simulation is going to be provided by X-plane (Laminar Research) and/or Flight Simulator 2004/FSX (Microsoft), so that part is not something I plan on writing myself (atleast not until everything else is working). What I'm going to put together is the cockpit and a visual system. The actual feel of the helicopter, flight dynamics and such, I'll pretty much have to settle for what they can provide, but the hardware feel I can contribute to. I'm slightly involved in a project in this category (recreational sims of complicated aircraft), so I know so much as to say that much can be done to get a fair, not totally unrealistic simulation of the real deal in many cases. I wish to make the EC135 one such case.
So, to make things even more clear (I hope), I will add that I have a pretty good sense of how the mechanical and hydraulic systems of the flight controls are designed in this particular aircraft, I know how the trim actuators are put together and some things like that. What I know nothing about is how these systems feel. I'm looking for statements from the community of pilots here to somehow quantify this, in order for me to build a good representation.
On the SAS, I basically know where the SAS is located in the control loop, I have figures for actuator authority and such, what I would like get a feeling for is the control laws and what sensory inputs the SAS has, also to get a somewhat good representation of the real thing. In this type of simulation, SAS and AP systems are easily put "between stick and simulator" so to say, but in order to write this software, I need some input on how the helicopter feels in this respect.
I've been planning on getting some simulator time, but I plan on waiting a bit longer with that. For one, I suspect it will be hideously expensive, and this is basically a hobby project. Furthermore, I think it would be more productive if I already have a working implementation of my own, to compare to the "reference" simulator the day I've managed to collect enough money and courage to try the real (simulated) thing.
So, further comments are greatly appreciated!