I read some posts on the RedWing Discord channel (am I the only one who doesn’t like Discord? - it seems such a mess compared to a forum). One user was confused as to why people were complaining that they couldn’t get above 12000ft because he had taken it up to 27000ft with no difficulty. It turns out that you have to lean the mixtures a lot when at altitude…almost to cut out. I had leaned the mixtures a bit but not to that extent. Anyway, if you carefully lean the mixtures, the Connie climbs very well…superchargers are not even required.
This means that the aircraft can be flown over most mountain ranges. It also means that the bug where the fps bogs down after the superchargers are engaged can be worked around…ie don’t use them. I think RedWing have some work to do with the engine simulation though. 
