Have the exact same problem(on windows).

http://www.wimp.com/helicopterflying/

Not a littlebird, but shows some mobility from a helicopter that we DON'T have right now.

What more info do you need?

https://www.youtube.com/watch?v=Q4nIk7y9wfs

Look @ ~ 0:45sec and @ 3:18... And this game takes place +30 year into the future surely a "modern" littlebird must be faster than it is now.

Climb rate in-game atm is around 8.7m/s and according to wikipedia a Boing AH-6 has a rate of climb: 10.5m/s.

Also tried from 100-0m and it gave me roughly the same time, around 11.5-12sec.

AH9 feels like a "balloon" now, once in air it takes a loooong time to descend. Previous patch the AH9 felt AWESOME.