Each time I want to take-off I get a "wobbling" effect. Like your chopper is on a roller coaster. The ground itself 'moves'. I am not joking (this time). There is something wrong (at least with my eech.ini settings).
When the mission starts it is as if the chopper (comanche) is lifted from below the soil (just for a split second).
That would be the suspension modelling. Though it hasn't been tested much in other helicopters than the Mi-24, it was sort of a last minute addition to the other helicopters. So if it causes trouble use flight_model=0 for the other helicopters. Or you could try to tweak the suspension settings in common\data\dyn\rah-66-suspension.txt