I found out that it will still be over a week before I receive my Hangar Pack in the mail, so will be a while yet before I'm able to try out what I wrote about further up.
To those who have installed Hangar Pack 1:
Have you tried re-applying the Heli update (and then after that re-applying the 1.0.9 update)
after installing the Hangar Pack?
Quote from the FSOne download page:
This heli performance upgrade patch updates all existing heli models to improve the flight performance and realism. .... Pre-existing heli models are retained in a new folder for access unmodified by the performance upgrade patch. .....
Clearly the Heli patch alters the files that are specific to the individual Heli models themselves (it does not just replace core software files like most patches do). And you can tell that it's doing something like that (not just replacing a few common files) when you run the Heli update (and there seems to be heavy cpu processing going on during the update).
So therefore the Heli patch might need to be re-applied for
any newly installed Heli's.
If that does not work (if the Heli update can't be re-applied), then it's worth trying with a
fresh install of FSOne like I described in my earlier post above.
Again I'll try all this myself as soon as I have the Hangar Pack.