This is something I made for placing RCS thrusters in the right positions in the first try without having to go back and forth between the VAB and the hacked gravity launchpad.
Features:
Display thrust and torque forces caused by RCS or engines.
ΔV readout for monopropellant RCS.
Dry center of mass marker (DCoM).
"Average" center of mass marker (ACoM).
Center of drag marker (CoD) for assisting in parachute placement.
Ability to resize editor's overla