Download on the Stabilizer, Increasing the Angle of Attack Still Further
COURSE MATERIAL SCHOOL OF MECHANICAL DEPARTMENT OF AERONAUTICAL ENGINEERING SAE1304 - AIRCRAFT STABILITY AND CONTROL UNIT – I - BASIC CONCEPTS 3 Degrees of freedom Degrees of freedom (mechanics), independent displacements and/or rotations that specify the orientation of the body or system Degrees of freedom (statistics), the number of values in the final calculation of a statistic that is free to vary Six degrees of freedom Refers to motion of a rigid body in three-dimensional space, namely the ability to move forward/backward, up/down, left/right combined with rotation about three perpendicular axes (pitch, yaw, roll). As the movement along each of the three axes is independent of each other and independent of the rotation about any of these axes, the motion indeed has six degrees of freedom. Notice that the initial conditions for a rigid body include also the derivatives of these variables (velocity and angular velocity), being therefore a 12-DOF system Figure 1. Motions of aircraft Figure 2. Directional axis Static stability As any vehicle moves it will be subjected to minor changes in the forces that act on it, and in its speed. If such a change causes further changes that tend to restore the vehicle to its original speed and orientation, without human or machine input, the vehicle is said to be statically stable. The aircraft has positive stability. . If such a change causes further changes that tend to drive the vehicle away from its original speed and orientation, the vehicle is said to be statically unstable. The aircraft has negative stability. . If such a change causes no tendency for the vehicle to be restored to its original speed and orientation, and no tendency for the vehicle to be driven away from its original speed and orientation, the vehicle is said to be neutrally stable.
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