IMHO,the following system works best. I always set the AI at the IAS that I intend to use if either:
a. Planned IFR transit - Cruise speed.
b. VFR, but with a possibility of an IFR abort. Approach or comfortable IMC manoeuvring speed.
It's quite simple to set it on departure pre entry into IMC or at a known datum, later refined at the desired IAS to give s&L flight at the appropriate power setting.
This is obviously dependant on a/c type as some have marked differences in pitch attitude in cruise and approach speeds.
dm - I don't think that accepting whatever it shows in flight is likely to be of much assistance as it may well give you an attitude markedly different from the optimum IFR speed. Again this is type dependant.
Lu - I think you've missed the point, I can't think of any helicopter pilot who would willingly try to hover IMC, unless it was for the most compelling of reasons and with the benefit of a full hands off autopilot hover facility. There ain't many of them about!!
