Check the small hose underneath the vacuum is fitted correctly and isn't ripped. Also make sure the clear housing which holds the brush, it has 2 pivots, you need to basically squirt WD40 or some lubricant on these pivots to make it less stiff. This will ensure that the head stays in good contact with the floor at all times.
The brush may flick the feather out but that's normal, because when the vacuum is on the floor, the suction and airflow spread out evenly.
The DC27 isn't the best at hard floors if you're sucking up things like crumbs etc which are large because it has no large debris channel. a DC14 with a clutch, DC15 or DC33 or any modern dyson ball is much better at hard floors.
I presume when you say it feels "heavy" you mean that you can feel it sucking to the floor?