![]() ![]() The objective is to make the moments (due to thrust, drag, and lift) as small as possible and, by proper location of the tail, to provide the means of balancing the airplane longitudinally for any condition of flight. However, the one item over which they have the greatest control is the size and location of the tail. If the thrust line is designed to pass horizontally through the center of gravity, it will not cause the airplane to pitch when power is changed, and there will be no difference in moment due to thrust for a power-on or power-off condition of flight.Īlthough designers have some control over the location of the drag forces, they are not always able to make the resultant drag forces pass through the center of gravity of the airplane. (A moment arm is the distance from a datum to the applied force.) For airplane weight and balance computations, “moments” are expressed in terms of the distance of the arm times the airplane’s weight, or simply, inch pounds.Īirplane designers locate the fore and aft position of the airplane’s center of gravity as nearly as possible to the 20 percent point of the mean aerodynamic chord (MAC). In aerodynamic terms, the mathematical measure of an airplane’s tendency to rotate about its center of gravity is called a “moment.” A moment is said to be equal to the product of the force applied and the distance at which the force is applied. The use of these controls is explained further down on this page.Ī study of physics shows that a body that is free to rotate will always turn about its center of gravity. Roll is controlled by the ailerons pitch is controlled by the elevators yaw is controlled by the rudder. The three motions of the airplane (roll, pitch, and yaw) are controlled by three control surfaces. In light of the adoption of nautical terms, the motion about the airplane’s longitudinal axis is called “roll” motion about its lateral axis is referred to as “pitch.” Finally, an airplane moves about its vertical axis in a motion, which is termed “yaw”-that is, a horizontal (left and right) movement of the airplane’s nose. They have been adapted to aeronautical terminology because of the similarity of motion between an airplane and the seagoing ship. In fact, the names used in describing the motion about an airplane’s three axes were originally nautical terms. ![]() The airplane’s motion about its longitudinal axis resembles the roll of a ship from side to side. The axis, which passes vertically through the center of gravity, is the vertical axis. ![]() The axis, which extends crosswise from wingtip to wingtip, is the lateral axis. The axis, which extends lengthwise through the fuselage from the nose to the tail, is the longitudinal axis. At the point where all three axes intersect, each is at a 90° angle to the other two. The axes of an airplane can be considered as imaginary axles around which the airplane turns, much like the axle around which a wheel rotates. Whenever an airplane changes its flight attitude or position in flight, it rotates about one or more of three axes, which are imaginary lines that pass through the airplane’s center of gravity. Flight controls: How an airplane is controlled. ![]()
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