航空術(shù)語(yǔ)詞典 Dictionary of Aeronautical Terms 上

時(shí)間：2011-03-11 23:11來(lái)源：藍(lán)天飛行翻譯 作者：admin 點(diǎn)擊：次

astatine. A highly unstable radioactive chemical element. Astatine’s symbol is At, and its atomic number is
85. Astatine is the heaviest of the halogen elements.
astern. A location or direction measured from an aircraft.
Astern means to the rear of, or behind. This term comes from “stern,” which is the aft, or rear part, of a ship.
ASTM (American Society for Testing Materials). An organization which sets various standards, called ASTM standards, used in the aircraft industry.
astrocompass. A navigational instrument that determines direction relative to the stars. Astrocompasses are not affected by the errors inherent in magnetic compasses and gyrocompasses.
astrodome. A transparent hemispherical dome in the upper skin of an aircraft, over or near the navigator’s station. The navigator uses the astrodome to make observations of the sun or stars when navigating by celestial navigation.
astronaut. A person who travels beyond the earth’s atmosphere.
astronautics. The branch of science that deals with space flight. Astronautics includes the design, construction, and operation of space vehicles and their related support equipment and activities.
astronomical twilight. The period of time before sunrise and after sunset when the sun is not more than 18° below the horizon.
astronomical unit. A unit for measuring distance in astronomy. One astronomical unit is the average distance between the earth and the sun. This is approximately 93 million miles.
astrophysics. The branch of science which deals with the physical characteristics of the heavenly bodies. These characteristics include their mass, density, temperature, size, luminosity, and origin.
ASU (altitude sensing unit — turbine engine fuel control). A subsystem in a turbine engine fuel control that regulates the fuel scheduling as a function of altitude changes.
asymmetrical. A condition of a body in which its shape is not the same on both sides of its center line.
asymmetrical airfoil. An airfoil section that is not the same on both sides of the chord line.
Asymmetrical airfoils are the most commonly used type for fixed-wing aircraft, but because the location of the center of pressure changes as the angle of attack changes, they are seldom used for rotary-wing aircraft.

asymmetrical lift (helicopter flight). A condition of uneven lift produced by the rotor system of a helicopter when it is in forward flight.
When a helicopter is hovering in still air, the lift is uniform across its rotor disk. But when it is moving in flight, the blade traveling in the same direction as the helicopter, the advancing blade, has a speed equal to its own speed plus the speed of the helicopter. The blade on the other side, the retreating blade, has a speed equal to its own speed minus the speed of the helicopter.
Since the amount of aerodynamic lift is determined by airspeed, the difference between the airspeed over the rotor blades on the two sides of the helicopter causes the lift on the side of the advancing blade to be greater than the lift produced by the retreating blade.

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