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Unformatted text preview: Definitions Chapter 11 Reference path: A path followed by an airplane in steady flight. Perturbed path: The path followed by an airplane after being disturbed from the reference path. Reference angle of attack: The angle of attack of the airplane along the reference path. Nondimensional stability derivatives. The perturbed aerodynamics are linearized about the reference path. This process requires derivatives evaluated on the reference path. These stability derivatives are expressed in terms of force and moment coeffcients. Linearized equations: The perturbed path is assumed to lie in the neigh- borhood of the reference path (small perturbations), and the equations of motion are expanded in a Taylor series about the reference path. Only the first order terms are kept so that the resulting equations are linear. Small perturbation equations: See linearized equations. Dimensional stability derivatives: The linearized equations are written in the simplest form. In doing so, the coeffcients of the small perturba- tions become dimensional. Characteristic equation: After the linear equations are transformed, the system matrix is the coeffcient of the states. The determinant of the system matrix set equal to zero is the characteristic equation. Modes: The response of a linear system is composed of several sub- motions. These sub-motions are called modes. Time constant: The response of a first-order system is characterized by a single constant called the time constant. Natural frequency: The oscillatory response of a second-order system is characterized by two constants one of which is the natural frequency. It is the distance of one root from the origin. Damping ratio: The oscillatory response of a second-order system is characterized by two constants one of which is the damping ratio. It is related to the angle that the line from the origin to one root makes with the real axis. Short-period mode: The typical longitudinal response of an airplane to a dis- turbance is composed of two modes. The short-period mode has a high frequency and a high damping. Phugoid mode: The typical longitudinal response of an airplane to a disturbance is composed of two modes. The phugoid mode has a low frequency and a low damping. Approximate short-period mode: If the velocity is assumed to be con- stant, the response of the airplane is governed by a second-order equa- tion which gives the approximate short-period mode. Approximate phugoid mode: If the angle of attack is assumed to be constant, the response of the airplane is governed by a second-order equation which gives the approximate phugoid mode. Spiral mode: The characteristic equation for lateral-directional motion of an airplane yields two real roots and one complex root. One real root gives the spiral mode, which is usually unstable....
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This note was uploaded on 09/18/2011 for the course ASE 367K taught by Professor Staff during the Spring '10 term at University of Texas.
- Spring '10
- The Land