Quaternion orientation and Gazebo simulation reference frames


I am doing some simulation in gazebo classic and am wondering how the world frame and body frame of the aircraft are set up. I believe the aircraft is in NED frame by default, is this also the case for the Gazebo world frame?

My second question is if the scalar part of the quaternion given by the vehicle odometry topic is at the beginning or the end of the vector. (e.g. is [0 0 0 1] no rotation, or is [1 0 0 0] no rotation?)