displaced. Another advantage is that reproductions ofthe cut sheet can be given to construction supervisorsso that they may always have access to all the essentialconstruction data.AIRFIELD SURVEYSAirfield construction is of a special kind; for thisreason, it is discussed here under a separate heading.AIRFIELD ROUTE SURVEYSThe route for an airfield is the horizontal locationof the runway center line; if there is more than onerunway, there is, of course, more than one route. Theprincipal consideration regarding the direction of arunway center line is the average direction of theprevailing wind in the area, since planes must take offinto the wind. The azimuth of the center line will beas nearly as possible the same as the average azimuthof the prevailing wind. A study of the meteorologicalconditions is therefore a part of the reconnaissancesurvey. Other data gathered on this survey (which maybe conducted on foot, by ground surface vehicle, byplane, or by all three) include the land formation,erosional markings, vegetation, configuration ofdrainage lines, flight hazards, approach zoneobstructions, and soil types.From the reconnaissance data, one or morepreliminary center lines are selected for location bypreliminary survey. For quick preliminary stakeout,there may be two parties, working away from station0 + 00 located at the approximate midpoint of thecenter line. In such cases, stations along the azimuthmay be designated as plus and those along the backazimuth as minus.Level parties follow immediately behind thetransit parties, taking profile levels and cross sectionsextending the width of the strip, plus an overage forshoulders and drainage channels. From thepreliminary survey data, a plan and profile are madeof each tentative location, and from these, a selectionof a final location is made.AIRFIELD STAKEOUTAirfield runways, taxiways, hardstands, andaprons are staked out much as a highway is staked out.There are, however, certain special considerationsapplying to approach zones.As you know from chapter 3, an approach zone isa trapezoidal area beyond the end zone at each end ofa runway. It must be free of obstruction not only onthe ground but also off the ground at a specific glideangle. The size of the approach zone depends on thetype and stage of development of the field. Forpermanent naval air stations, the trapezoidal areamight be 10,000 feet long with a width of 4,000 feetat the outer end. For purposes of explanation only, wewill assume that these are the dimensions of theapproach zone for which you are surveying.The glide angle for most types of aircraft is 2percent, usually given as 50:1, or a rise (or drop) of 1vertical for 50 horizontal. Figure 10-25 shows, inplan, profile, and isometric, an approach zone and itsadjacent transition surfaces and end of runway. Youmust stake out this approach zone and check it forclearance by the following procedure:Figure 10-26 shows the approach zone in plan.The dotted line BC lies 750 feet from the center line.The angle at B can be determined by solving theFigure 10-26.—Plan view of approach zone.10-25
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