City darling Rolls-Royce is gearing up plans to dish out bumper returns to investors this week as the firm delivers its annual results. The FTSE 100 giant is set to launch a buyback worth as much as £1.5bn, which will come on top of the company’s final dividend as the aircraft engineer looks to reinforce the size of its cashflow. It follows the spectacular turnaround under boss Tufan Erginbilgic, former BP chief, which has seen the company’s value double to over £112bn. The fresh buyback – as reported by Sky News –…