 The 707's wings are swept back at 35°, and like all swept-wing aircraft, display an undesirable "Dutch roll" flying characteristic that manifests itself as an alternating combined yawing and rolling motion.Boeing already had considerable experience with this on the B-47 and B-52, and had developed the yaw damper system on the B-47 that would be applied to later swept-wing configurations like the 707.However, many pilots new to the 707 had no experience with this instability, as they were mostly accustomed to flying straight-wing propeller-driven aircraft such as the Douglas DC-7 and Lockheed Constellation.