This photo shows the X-29 during a 1991 research flight. Smoke generators in the nose of the aircraft were used to help researchers see the behavior of the air flowing over the aircraft. The smoke here is demonstrating forebody vortex flow at a high angle of attack. Angle of attack, or high alpha, refers to the angle of an aircraft's body and wings relative to its actual flight path.. The tufts that can be seen in this photo attached to the fuselage and wings of the X-29 were also used to help researchers visualize the air flow over the plane.