AR
 

My nephew treated me to a sim ride in the KC10. What a treat. I forgot to ask at the time, but why, when I was a little right of the centerline on the belly of our tanker, my instructor told me to input some right roll to get left, back to alignment? (We were receiving a refill).

Cool, sounds like fun :)

Does the KC10 exhibit noticeable adverse yaw?, I don't know, but it would explain the instruction.

Flown the 10 for a few hours (IP) and can only think it is to either stop a bit of PIO (moving left and right but having trouble stopping astern) or to shack your position once you've moved back to the centreline from out to the right. There was always a natural (if AAR can be callled such) push back towards the centreline if you wandered too far out to the side, and you would need to stop that movement when you approach the centreline in this case. And refuelling behind a 135 was always the devil's work!😰

Poor instruction? At EFT, we teach "bank ON, bank OFF" when adjusting lateral spacing formating behind another aircraft. The temptation is normally to maintain a roll input for too long thus precipitating a PIO so the bank ON/OFF technique usually negates this but as I have no experience of flying one heavy behind another, I'm not sure if this technique would be relevant. But it's what we teach.

The aerodynamic effects of the tanker tend to push the receiver towards the centre of the boom envelope. When your nephew says to use some right roll input to correct from a right-of-centre position, he is basically saying 'don't use left roll input'. Rolling left would initiate a PIO; centralising the yoke can do the same. Better, when right of centreline, to reduce the right roll input a little, stabilize, then reduce a little more.