Читать книгу Flight Theory and Aerodynamics - Joseph R. Badick - Страница 17

A force is a push or a pull tending to change the state of motion of a body. A resolution of the typical forces acting on an aircraft in steady flight is shown in Figure 1.1, while Figure 1.2 shows the four separate components of aerodynamic forces during straight‐and‐level, unaccelerated flight. The component that is 90° to the flight path and acts toward the top of the airplane is called lift. The component that is parallel to the flight path and acts toward the rear of the airplane is called drag; while the opposing forward force is thrust and is usually created by the engine. Weight opposes lift and as we will see is a function of the mass of the aircraft and gravity.

The sum of the opposing forces is always zero in steady flight, but this does not mean the four forces are equal. In future chapters of this textbook, we will further demonstrate the following statement regarding forces acting on an airplane in steady flight: The sum of all upward component of forces equals the sum of all downward components of forces, and the sum of all forward components of forces equals the sum of all backward components of forces.

Figure 1.1 Forces on an airplane in steady flight.

Figure 1.2 Resolved forces on an airplane in steady flight.

Source: U.S. Department of Transportation Federal Aviation Administration (2008a).