How to change the yaw angle in ROS

edit

Hi guys, I have been working on the ar.drone flying robot and what I want is to have the ar.drone takeoff, change the yaw angle by 90 degrees while holding that hover position and then land. I tried to write some code to achieve this but what happens is the ar.drone keeps on spinning all throughout the take off and landing. Here is my method:

void DC::Yaw(){
    ros::NodeHandle nh;
    ros::Publisher flyF = nh.advertise<geometry_msgs::Twist>("/cmd_vel", 1000, true);
    geometry_msgs::Twist yaw;

    yaw.angular.x =0;
    yaw.angular.y = 0;
    yaw.angular.z = 1.57;

    flyF.publish(yaw);
    ros::Duration(1).sleep();  
}

My takeoff and land functions work well but it is just this yaw function that is causing me issues.

Thanks!