Once an aircraft defies gravity to leave the ground it is subjected to four basic aerodynamic forces known as weight, lift, thrust, and drag. How the aircraft relates to these forces is called flight dynamics and involves three axes of control, pitch, roll, and yaw which reflect the attitude of the aircraft as is moves through the air. For the purpose of this discussion we are concerned only with “fixed-wing” aircraft as the fight dynamics for helicopters is somewhat different.
To form a mental visualization of flight dynamics, imagine you are sitting in the center of the aircraft toward the back edge of the wing. Now visualize an imaginary line passing through the center of the fuselage from nose to tail which is referred to in aeronautical terms as the “center line of flight.” Your point on this line, in technical terms, is referred to as the “center mass” of the approximate aircraft from which two axes are projected forward and one is perpendicular. Pitch, roll and yaw are three axes of rotation relative to the center mass point in the aircraft and how the aircraft is positioned relative to this point describes its fight attitude.
Pitch is a term which describes the attitude from the prospective of the nose of the aircraft relative to center mass. When the nose of the aircraft is rotated above the center line relative to the center mass point this is known as a pitch up attitude, and conversely, when the nose is rotated below the center line a pitch down attitude. The equilibrium point(nose pitch equal to the center line of flight) is denoted as level flight. The pitch of the aircraft is controlled by a horizontal stabilizer(elevator) on the tail of the aircraft, and adjusted by the pilot pushing the yoke forward (pitch down)or aft (pitch up).
Roll axis of an aircraft is the dynamic which describes the motion or status of the starboard (right) and port(left) side wing tips of the aircraft with reference to the center mass with the wings paralleled to the ground denoting level flight. If the static wing position or motion is such that the starboard wing tip is rotated down towards the ground and port wing up, this is referred to as a right role attitude. Conversely, when the port wing tip is down, or moving in that direction, a left roll attitude is indicated. The roll attitude of the aircraft is affected by ailerons located near the tip of each wing and controlled by turning the steering yoke or moving the stick towards the direction of the intended roll attitude adjustment.
The yaw axis reflects the position of the nose of the aircraft left or right of the actual azimuth heading of the aircraft; again, relative to rotation of the aircraft from its center mass perspective. It would seem rational that under optimal conditions and level flight the yaw attitude should be neutral. In fact, if the aircraft is flying with any degree of crosswind it must fly with some degree of yaw to maintain its course heading. Yaw axis is affected by the vertical stabilizer on the aircraft tail and controlled when the pilot presses on left and right foot pedals.
Pitch, yaw and roll axis are the fundamental elements of flight dynamics and also a mind set a pilot must learn and instinctively respond to to maintain flight. There are limits to each of these aircraft attitudes which if exceeded will cause the wing to stall and the aircraft to no longer maintain a status of flight. In the following circumstance(posted to youtube) the roll of the B52 in question is increased to almost 90 degrees essentially eliminating wing lift while too close to the ground. The aircraft was executing a steep turn to port when lift was lost causing the nose to “yaw” left as well, but in this case left was down and there was no option for recovery. While in the AF, this Helium writer maintained a GCA radar system located about 100 feet away from this crash site. Fortunately, the GCA unit had been decommissioned by then, and nobody on the ground had to pay the supreme price for the subsequent instance of pilot error.
