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This page is intended for college, high school, or middle school students. For younger students, a simpler explanation of the information on this page is available on the Kid's Page.

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Aircraft Pitch Motion

Glenn
Research
Center

Computer animation of an airliner in which the nose
 moves up and down in response to changing the elevator angle.

In flight, any aircraft will rotate about its center of gravity, a point which is the average location of the mass of the aircraft. We can define a three dimensional coordinate system through the center of gravity with each axis of this coordinate system perpendicular to the other two axes. We can then define the orientation of the aircraft by the amount of rotation of the parts of the aircraft along these principal axes. The pitch axis is perpendicular to the aircraft centerline and lies in the plane of the wings. A pitch motion is an up or down movement of the nose of the aircraft as shown in the animation.

The pitching motion is being caused by the deflection of the elevator of this aircraft. The elevator is a hinged section at the rear of the horizontal stabilizer. There is usually an elevator on each side of the vertical stabilizer. The elevators work in pairs; when the right elevator goes up, the left elevator also goes up.

As described on the shape effects slide, changing the angle of deflection at the rear of an airfoil changes the amount of lift generated by the foil. With greater downward deflection, lift increases in the upward direction. With greater upward deflection, lift increases in the downward direction. The lift generated by the elevator acts through the center of pressure of the elevator and horizontal stabilizer and is located at some distance from the center of gravity of the aircraft. The change in lift created by deflecting the elevator generates a torque about the center of gravity which causes the airplane to rotate. The pilot can use this ability to make the airplane loop. Or, since many aircraft loop naturally, the deflection can be used to trim or balance the aircraft, thus preventing a loop.

On many aircraft, the horizontal stabilizer and elevator create a symmetric airfoil like the one shown on the left of the shape effects slide. This produces no lift when the elevator is aligned with the stabilizer and allows the combination to produce either positive or negative lift, depending on the deflection of the elevator. On many fighter planes, in order to meet their high maneuvering requirements, the stabilizer and elevator are combined into one large moving surface called a stabilator. The change in force is created by changing the inclination of the entire surface, not by changing its effective shape.

You can view a short movie of "Orville and Wilbur Wright" explaining how the elevator was used to control the pitch of their aircraft. The movie file can be saved to your computer and viewed as a Podcast on your podcast player.

Here is a still slide of the animation:

Computer drawing of an airliner showing the motion.
 about the pitch axis.


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Editor: Tom Benson
NASA Official: Tom Benson
Last Updated: Sep 10 2010

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