Gliders are more susceptable to adverse yaw by virtue of long wingspans and ailerons well out on the wing. Adverse yaw is mainly produced by the fact that if you have more lift, you have more drag. One way to get around this is to have differential ailerons where the upgoing aileron goes up more than the downgoing aileron thus producing more drag and hopefully equalising the excess drag produced by more lift produced by the downgoing one. Glider pilots have to use their feet wheras in most powered aircraft the rudder bar is mainly for steering on the ground and resting your feet on