subsonic flight

subsonic flight

[¦səb′sän·ik ′flīt]
(aerospace engineering)
Movement of a vehicle through the atmosphere at a speed appreciably below that of sound waves; extends from zero (hovering) to a speed about 85% of sonic speed corresponding to ambient temperature.

Subsonic flight

Movement of a vehicle through the atmosphere at a speed appreciably below that of sound waves. Subsonic flight extends from zero (hovering) to a speed approximately 85% of sonic speed corresponding to the ambient temperature. At higher vehicle velocities the local velocity of air passing over the vehicle surface may exceed sonic speed, and true subsonic flight no longer exists.

Vehicle type may range from a small helicopter, which operates at all times in the lower range of the velocity scale, to an intercontinental ballistic missile, which is operative throughout this and other velocity regimes, but is in subsonic flight for only a few seconds. The design of each is affected by the same principles of subsonic aerodynamics. Subsonic flow of a fluid such as air may be subdivided into a range of velocities in which the flow may be considered incompressible without appreciable error (below a velocity of approximately 300 mi/h or 135 m/s), and a higher range in which the compressible nature of the fluid becomes significant. In both cases the viscosity of the fluid is important. The theories which apply to compressible, inviscid fluids may be used almost without modification in some low-subsonic problems, and in other cases the results offered by these theories may be modified to account for the effects of viscosity and compressibility. See Transonic flight

A typical subsonic wing cross section (airfoil) has a rounded front portion (leading edge) and a sharp rear portion (trailing edge). Air approaching the leading edge comes to rest at some point on the leading edge, with flow above this point proceeding around the upper airfoil surface to the trailing edge, and flow below passing along the lower surface to the same point, where the flow again theoretically has zero velocity. The two points of zero local velocity are known as stagnation points. If the path from front to rear stagnation point is longer along the upper surface than along the lower surface, the mean velocity of flow along the upper surface must be greater than that along the lower surface. Thus, in accordance with the principle of conservation of energy, the mean static pressure must be less on the upper surface than on the lower surface. This pressure difference, applied to the surface area with proper regard to force direction, gives a net lifting force. Lift is defined as a force perpendicular to the direction of fluid flow relative to the body, or more clearly, perpendicular to the free-stream velocity vector.

The wing, as the lifting device, whether fixed, as in the airplane, or rotating, as in the helicopter, is probably the most important aerodynamic part of an aircraft. However, stability and control characteristics of the subsonic airplane depend on the complete structure. Control is the ability of the airplane to rotate about any of the three mutually perpendicular axes meeting at its center of gravity. Static stability is the tendency of the airplane to return to its original flight attitude when disturbed by a moment about any of the axes.

References in periodicals archive ?
Braun also points out that propulsion is an equally daunting challenge, noting that aircraft designed for subsonic flight (a Boeing 737, for example) have very different propulsion needs than supersonic fighter jets and hypersonic spy planes.
In 2016 NASA launched the "New Aviation Horizons X-Plane Initiative," one part of which is the "Ultra-Efficient Subsonic Flight Demonstrator" program.
The Yak-130 is the world's only training aircraft with the aerodynamic configuration and subsonic flight performance characteristics of modern jet fighters.
This occurs at sea level for low subsonic flight conditions and at cruise altitude for high subsonic flight conditions (transonic flight).
It also employs a Drop Scale Factor for transonic and subsonic flight as well as max and min wind zones.
We axed Concorde because it was not economically viable to maintain supersonic flight when subsonic flight had greater carrying capacity and, in many cases, business class offers a virtual office environment.
Among specific topics are buoyancy and stability, basic elastostatics, nearly ideal flow, action and reaction, gravity waves, and subsonic flight.
For subsonic flight, the propulsive efficiency, [[eta].
The test would be for the subsonic flight phase aerodynamics and the effectiveness of the control surfaces and some avionic systems.
Lunev (aero-physics and space research, Moscow Institute of Physics and technology) uses analytically treatable examples, similarity laws and asymptotic analysis to explain the general patterns and features of typical flows and how real gas affects them, providing physics and aerospace students with applications for supersonic and subsonic flight.
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The article states, "The recently retired supersonic commercial transport, the Concorde, tilted its nose downward for subsonic flight.