Page:Dictionary of aviation.djvu/199

 DICTIONARY OF AVIATION 175

in a square manner, as in aerodynamic experimentation; foll^en presentation of a square plane. pressure 'pse$9z n.

1. posh or thrust, as of the gas inside of a balloon, or of the air upon an aeroplane, airship, or other object.

center of pressure, see under center.

forced pressure, an increast pressure or density which is forced upon the air or other fluid adjacent to an aerofoil or other surface which is acting upen it. compare forced vacuum, under vacuum.

negativ pressure, pressure in a negativ sense or di- rection, as that produced by rarefaction of the air in front of a revolving propeller; suction.

tangential pressure, pressure in a direction tangential to the surface of an aerocurv or curvd aerofoil; posh or thrust upon a curvd sustaining^surface in the direction of a tangent to the curv of that surface parallel to the line of the direction of the impinging air^current or to the di- rection of flight.

vapor pressure, see vaporfpressure.

2. the elastic pressure of the atmosfere; atmosfenc pres- sure; barometric pressure.

belt of high pressure, a belt or long narrow region of high barometric pressure, as between two areas of high pressure, or as the belt nearly encircling the earth near the Tropic of Capricorn.

equatorial belt of low pressure, a belt or long narrow tract nearly encircling the earth in the equatorial region and characterized by low barometric pressure due to the northeast and southeast tradewinds and the deflecting force resulting from the rotation of the earth.

high pressure, unusually high pressure of the air as indi- cated by a barometer; atmosfenc pressure which is greater than the normal.

highfpressure area, an area or region of the earth's surface over which the barometric pressure is high.

low pressure, unusually low pressure of the air as indi- cated by a barometer; atmosfenc pressure which is less than the normal.

pressure-anemometer 'p5e$9z-aeni,m0mi-tez n. an anemom- eter for mesunng the pressure of the wind. pressure-gradient 'p3e$9z,gzee-di-3nt n. the gradient of pressure, as of the atmosfere; the rate at which the air^ pressure changes in value.

pressure-height 'pse$9z,hait n. the atmosfenc pressure in terms of the height of a vertical column of fluid of uni-

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