During a field deployment exercise during the Cold War, I returned to our flight's refuelling point in a German farmer's field for a rotors running refuel. I'd already refuelled there before that morning. As we approached the bowser in the hover and at an altitude of about ten feet, it all got very exciting. The driver had "cammed up" his vehicle by laying a large sheet of black hessian (probably 10 by 8 feet) across the windscreen and trapping it in the cab doors. Unfortunately, rather than fool the Warsaw Pact army, he had done it so he could sit inside the cab and sleep. He woke up with a start and threw open the driver's door, whereupon the hessian flew free and got sucked straight into the middle of our main rotors, where it hung up on a blade. The rotors immediately went out of balance in a massive way and the aircraft out of control (the cyclic stick was stirring me around the cockpit, rather than the other way round) and Sod's law said that the aircraft moved closer to the bowser so that the main rotors were now right above it. The next few seconds were very exciting indeed but thankfully the hessian worked its way to the end of the blade, where it flew up again then recirculated back into the disc a second time but this time near the tips, where it was shredded into small pieces. I did manage to regain control and move clear and immediately landed and shut down. The leading edge strips of the main rotor blades were imprinted with a back hessian pattern, the dye had been forced out from the impact.
Thankfully the aircraft was undamaged and after an extra strong mug of NAAFI tea and a sincere apology from the bowser driver we were sent on our way to carry on with the task.