DICTIONARY OF AVIATION 237
under-wind 'Andacr/wind n. a wind blowing in the under or lower airs; an atmosferic undercurrent: distmguisht from uppertwind.
underwork 'And3z,wi3:zk n. the framework or other con- trivances situated under or beneath the main part of an airship; the lower parts of a dirigible balloon, located underneath the gasbag; the understjucture ; the underbedy.
unmanned ,An'msend, (assumptivly} 'An,m3end adj. [also spelt unmand] net carrying a man or operator; having no aeronaut or aviator aboard : as, an *unmand balloon.
untoggle / An'tegal tr. unfasten, disconnect : as, to *unteggle the car.
up-and-down ,Ap3n'daon adj.
1. characterized by upward movement fellowd by down- ward movement; going first up and then down: as, a sen- sational *up-and-down flight.
2. related to, or controlling up-and-down movement; hav- to do with vertical steering: as, the *up-and-down and the stabilizing planes : distmguisht from sideztofside.
up-current 'Ap^szant n. a current or stream of air coming or going up; a rising or ascending atmosferic current; an rp-wind.
upper-wind 'Ap9z,wind n. a wind blowing in the upper or higher airs ; an upper wind or atmosferic current : dis- tinguisht from under-wind.
upright 'Ap,zait n. an upright or vertical stick or piece, as in a kite-frame : as, the cress-sticks and *uprights.
up rush 'AP,?A$ n. a rush, or sudden and forceful movement, upward or skyward, as of air.
up-stroke / Ap / st0ok n. the upward stjoke or siueep of a re- ciprocating part such as a flapping wing; a stroke or beat in an upward direction : the epposit of dowmstroke.
up-thrust / Ap / OsAst n. a thrust or posh in an upward di- rection; lift: as, the *upthrust of the wind upon a wing.
��vacuum 'vaekgu-am n. empty space; an enclosed space from which the air or other gas has been removed, by means of a pump or otherwise.
forced vacuum, a partial vacuum, or decrease of pressure or density which is forced upon the air or other fluid ad- jacent to an aerofoil or other surface which is acting upen it. compare forced pressure, under pressure.
valve vaelv n. [also spelt valv] a device or appliance designed to control the flow of a fluid, as gas or air, thru a pipe,
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