Drucella Andersen
Headquarters, Washington, D.C.                                               
July 9, 1992
(Phone:  202/453-8613)

Peter Waller
Ames Research Center, Mountain View, Calif.
(Phone:  415/604-3938)


RELEASE:  92-105

NASA SCIENTISTS "FLY" COMPUTERIZED FIGHTER AIRCRAFT IN 3-D 

   NASA researchers have "flown" a complete three-dimensional, 
high-performance aircraft in a supercomputer for the first 
time.

   Dr. Yehia Rizk, a scientist at NASA's Ames Research Center, 
Mountain View, Calif., reproduced the complete flow of air 
around an F/A-18 jet fighter.  The air flow field, which 
duplicates high angle-of-attack (nose-high) flight, lets 
researchers analyze the unsteady air flow that causes sporadic 
buffeting of tail surfaces and lets scientists study improved 
control systems for the plane's forward fuselage.

   "This achievement is a milestone for the aerospace 
industry," said Dr. Paul Kutler, Chief of the Fluid Dynamics 
Division at Ames.  "It will be a long time -- if ever -- before 
supercomputers replace wind tunnels.  But supercomputers are 
ever more important.  For wind tunnel tests, an expensive 
fixed-design model must be built.  In a supercomputer, aircraft 
shapes can be altered frequently and radically, potentially a 
far cheaper research process."

   Aerodynamic studies of fighters such as the F/A-18 are very 
useful because these planes make extreme maneuvers, and 
findings can be applied to all other classes of aircraft.  

   Kutler said the new supercomputer techniques also appear to 
have promise in other areas where fluid flow is modeled, such 
as weather prediction, spacecraft entry, artificial heart 
design, ship and automobile concepts, jet and rocket engine 
design and studies of galaxies and interstellar gas.

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   The research is part of an effort to reduce wind tunnel 
tests of new aircraft designs.  Supercomputer design has the 
potential to be less costly and gives data not available from 
wind tunnels, such as greater detail on flight conditions.

   Developing the full F/A-18 flow took 2 years.  It now takes 
about 50 hours to enter the program and data into the computer, 
Rizk said, but he hopes to reduce program entry time to several 
hours within the next year or two and by the year 2000, to a 
few minutes.

   For complete flow-field simulations, data to recreate a 
particular aircraft shape in 3-D is entered in the computer.  
Researchers can view the design from any angle on the 
computer's color display screen.  Then, a three-dimensional 
grid is created around the vehicle.

   The grid for the F/A-18 has more than a million points at 
which the basic air flow equations are recalculated many 
thousands of times to reproduce the "real" flow around the 
vehicle.  From the computer display, researchers get 
information such as colored lines showing paths of individual 
air particles moving through vortices (whirlpools of air) and 
turbulence around the craft.

   Aircraft like the F/A-18 -- with twin tails, two jet engines 
and forward controls -- present interrelated problems.  Both 
the plane's complex shape and the physics of the resulting 
intricate air flow must be dealt with.  The wing leading edge 
creates a vortex, adding lift.  The vortex then intercepts the 
canted tail, providing better control.  But at the high nose-up 
flight position needed for tight turns, the vortex bursts, 
producing unstable flow.

   Rizk wrote new software to handle the complex geometry.  He 
then put together 10 different types of three-dimensional grids 
around the entire craft.  To make sure all the grids "talk" to 
each other, he uses a special Ames grid-integrating computer 
code.

   The multiple-grid approach allows different grid densities, 
equations and turbulence models as required.  Once the grids 
are in place, algorithms (computer arithmetic) are written to 
solve the flow equations at millions of points.

   Other Ames researchers have created the complete flow field 
around an F-16 fighter in level flight at 700 mph.  They now 
are seeking to control laminar (smooth) air flow around an F-16 
fitted with a delta-wing at speeds up to Mach 2 (1,400 mph). 
                             -end-


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EDITORS NOTE:  A 6-minute, 3/4-inch video clip is available to 
media by calling 202/453-8594.  The video will be played on 
NASA Select television at 1 p.m. EDT on July 9.  Photographs 
also are available to illustrate this release by calling 
202/453-8375.

Color:  92-HC-402 through -407
B&W:   92-H-452 through -457