PayloadManagerX is available as a free download on the "DOWNLOADS" page (next-to-last at the bottom of the page).
With this tool you can:
- Attach any sim object anywhere on your aircraft at runtime
- Use simulated additional (external) fuel tanks that feed into your fuel system
- Perform aerial refueling
This app is currently only available for Prepar3D V4.x. THIS IS AN EXPERIMENTAL APP / PROTOTYPE - no promises as to when or if there will be further development. But you can expect all existing features to be fully functional.