Bell Helicopter engineers have resolved a performance anomaly that test pilots had discovered when flying the hybrid aircraft in conventional flight mode, also known as the zero-degree position of the nacelles. The BA609 is a six- to nine-passenger corporate aviation tiltrotor, a product the companies expect to begin delivering in 2011. According to Roy Hopkins, Bell's chief test pilot for the BA609, both prototype aircraft had been exhibiting a differential torque between the two prop-rotors in flight tests, causing a left-turning tendency at cruise speeds. The companies are flight testing one aircraft at Bell in the USA and the other...