If you have the enviroment set up as the tutorial found here https://drive.google.com/open?id=1TP-kR2L8zDoeb2tTdHy4Co4Aqj2QQSS0wQGtv7M0Dlo
this is what you got to do

open three new terminals

terminal1: roslaunch simulation_control posix_sitl.launch

wait a little while

terminal2: roslaunch simulation_control px4.launch fcu_url:="udp://:14550@127.0.0.1:14557"

terminal3: roslaunch simulation_control simulation_control.launch 

have fun