As the month of May came to a close, a team of Boeing engineers were putting the finishing touches to a one-of-a-kind flying machine at an outpost of that company’s “Phantom Works” just outside the sun- and sand-blasted southwestern Arizona town of Yuma. Unpiloted and powered by a Williams International F112 jet, the X-50A Dragonfly will, if successful, knock off one of the last of aviation’s landmark goals–the successful flight of a wing that can transition from rotary to fixed airfoil flight and back without landing.
The advantage? Elimination of the helicopter’s “roll over” tendency at high speed, an effect caused by the asymmetric lift that results when a helicopter gains significant forward speed. As it does so, the airflow over the rotor blade advancing forward in its rotational arc speeds up, becoming the sum of its advancing rotational speed and the forward speed of the entire aircraft. At the same time, rotor blades on the retreating side develop less lift, since the flow of air over their surface is the forward speed of the helicopter minus the retreating rotational speed.
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