The propeller on the Dash-8 can change the angle it cuts into the air. See http://hartzellprop.com/understanding-variable-pitch-propellers/ (vid) for more, but as a summary, the fixed-blade prop (prop cannot change the angle it cuts into the air) is more inefficient than a variable pitch prop as it must be optimised for all stages of flight while the variable pitch one can change to suit the conditions.
In the event of a engine failure, this prop is now causing huge amounts of drag as it is angled against the flow of air. This can be solved by “feathering” the props to turn them towards the direction of the incoming air, thus reducing drag and allowing a turboprop with a double engine failure to glide further. https://en.wikipedia.org/wiki/Tuninter_Flight_1153 this was a ATR72 that would have possibly made it to safety if the pilots had remembered to feather the prop.
If I remember correctly Rolls is developing a variable pitch turbofan where the blades on the N1 fan can be changed but I might be wrong.
EDIT: went to check and its here https://www.rolls-royce.com/products-and-services/civil-aerospace/products/future-products/ultrafan.aspx