Page:Dictionary of aviation.djvu/261

 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,

�� �