APPLICATIONBRIEFS

Geographic information system Attack helicopter designplans environments aided by computer graphics

Ware MyersContributing Editor

To Ron Walters the environment comesfirst; a computer system is just a tool for plan-ning its use in such a way that all those af-fected-government agencies, developers,and area residents-benefit. In 1971 hestarted a consulting firm in environmentalplanning and resource management. It iscalled Comarc Systems and is located in SanFrancisco. Along the way he discovered that acomputer-based geographic information sys-tem would greatly facilitate the firm's work.The Comarc system now combines the

capabilities of computer graphics, automatedcartography, information management, dataanalysis, and modeling. It accepts data fromaerial surveys, satellite images, existing maps,and ground surveys. It can connect directly tothe machine-readable files of other compuitersystems. After appropriate analysis, the sys-tem can output its results on a display terminalor in the form of reproducible maps. It canalso provide color prints or separations, and itcan generate reports or transmit its informa-tion directly to a client's computer system.

The most obvious use of the system is toproduce maps. Input data may be in differentmap scales and in different projection andcoordinate systems. The user can changescales, projections, and coordinates and edit,add, or delete data. The system generates sym-bols, as well as different types of lines,shadings, and other presentations that helpthe map communicate to the viewer.

In addition to mapmaking, the system canreference all kinds of information to geo-graphic coordinates. It can be applied to anyproblem that is spread over a geographic area.For example, the Palm Springs area had Co-marc prepare a master environmental impactstatement. Walters believes that individual en-vironmental impact statements, preparedafter investment funds have already beencommitted, put the cart before the horse. Thetemptation then is to use the statement tojustify,the project. It is much better, he says,to do an area-wide study first into which in-dividual projects can later be fitted. The com-puter system makes this approach economi-cally feasible.

"The AH-64A Apache is a very compli-cated structure containing 10,000 degrees offreedom, 4500 structural elements, and over1600 nodes," said Grant Parker, a senior dy-namics engineer at Hughes Helicopter, as hewas discussing some of the design problemsassociated with Hughes' forthcoming ad-vanced attack helicopter for the US Army.

The Apache, a two-seater, twin engine heli-copter intended for use in future antitank war-

fare, is now nearing the end of a full-scale en-gineering development program at Hughes. Inthe course of the aircraft's development, engi-neers at Hughes made use of both McDonnellDouglas Automatioq Company's Fastdrawinteractive graphics modeling system and afinite element program for structural analysiscalled MSC Nastran (MacNeal-SchwendlerCorporation Nasa Structural Analysis). Bothof these run on McAuto's CDC computers:Fastdraw on a Cyber 175 and Nastran on aCyber 176. Hughes uses McAuto's DaclItime-sharing service to edit the model on in-teractive CRT graphics terminals in its ownoffices.

Again referring to the Apache's compli-cated structure, Parker said, "With Fast-draw, we can solve this huge problem, as wellas a number of smaller ones, by constructingthe model [of the Apache] in substructures. Indoing this we can identify and correct errors inthe geometry of each substructure before put-ting them together and running a Nastrananalysis. This saves a tremendous amount oftime and money."

Hughes also uses Fastdraw extensively totest vibration levels on the Apache. "The bigthing with Fastdraw is that we can move thedeflected shapes around in Cartesian space,"Parker stated, "allowing us to study the dy-namic characteristics of the airframe to ensuretHat Army vibration requirements are met."

Designed with the help of McAuto's Fastdraw interactive graphics modeling system (inset), theApache advanced attack helicopter is now completing its development program at HughesHelicopters, Inc., in Culver City, California, for eventual deployment with the US Army.

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