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Primary Motions | |
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An airplane can basically move in six different ways; these are called the six degrees of freedom of motion. An easy way to demonstrate the motions is to use the right hand rule. This is a technique engineers use to help them define the orientation of an object and the ways it can move. Using the right hand, extend the thumb and point it forward. Point the index finger to the right, but even with the thumb so that they are on the same level. Then point the middle finger downward (see sketch below). These are the three axes of motion for the airplane. Envision the airplane with its nose pointing out along the thumb and the wing out along the index finger. The plane can move forward or backwards along the thumb (the x axis). It can move left or right along the index finger (the y axis), and it can go up or down along the axis of the middle finger ( the z axis). These three motions are known as translations or movements along the axes. In addition, the airplane can rotate about the thumb; hold the thumb steady and rotate the hand about it. This is called roll, and it is the fundamental motion used for turning the aircraft. As the hand is rotated about the thumb, the index finger is rolled up or down, just as the wings are rolled up or down, or banked, in a turn. If the hand is rotated about the index finger, or the y axis, that is called pitch. The nose of the plane moves up and down in a pitch rotation. The pitch angle contributes to the angle of attack of the plane and becomes a part of the lift calculation. A rotation about the middle finger (z axis) is called yaw; it is a sideways motion. The nose and wings are rotated to either side. These three rotations: roll, pitch, and yaw, combined with the three translations, define the basic motion of an airplane.
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