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How Software Reduced Fuel Burn on NASA’s Frankenstein F/A-18

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Research test pilots at NASA recently completed a series of tests aimed at reducing fuel consumption in airplanes by fine-tuning the software that controls the fly-by-wire system. The goal of the research is to develop flight software that can make small changes in adjusting the actual control surfaces on the wings and tail. By precisely controlling the position of the physical surfaces, the flight computer can reduce drag, saving fuel.

The NASA pilots at the agency’s Dryden Flight Research Center used the agency’s highly modified F/A-18 (number 853) that has been a mainstay of flight research for more than a decade. The former fighter jet has been used on numerous research projects including other flight-control surface experiments where test pilots were able to warp the wing to perform a maneuver rather than move the control surfaces. During our last visit to Dryden we were able to poke around and look at 853 while it was undergoing maintenance and modifications before the current round of research flights.

On a typical airplane there are three main flight-control surfaces. When a pilot moves a control stick from side to side or moves a control yoke like a steering wheel, the control surfaces known as ailerons on the wings move up and down, resulting in the airplane rolling left or right. When the control stick or yoke is moved forward and back, control surfaces on the horizontal part of the tail known as the elevator (or stabilator, in the case of the F/A-18) move up and down, and the airplane will pitch up or down (climb or descend). And on the floor the pilot can push a right pedal or left pedal that move the control surface on the vertical part of the tail left or right, helping to turn the airplane with a yawing motion left or right.

For the current round of tests, it was largely up to software engineers to make the changes to the airplane. The airplane uses an Airborne Research Test System (ARTS) computer that can be modified and programmed for research flights beyond the normal flight computer’s capabilities.

During normal flight on most planes – from fighter jets to big airliners – the pilot (or autopilot) will adjust the flight-control surfaces to compensate for wind or other issues that would cause the airplane to deviate from its course. These trim adjustments can increase the drag on an airplane, and continuous changes to the trim can lead to continuous increases in drag.

In this case the ARTS was programmed with a “peak-seaking algorithm” that resulted in very precise adjustments being made to the flight controls during cruise flight that minimized the amount the surfaces were deflected. NASA says the new computer code resulted in an impressive drag reduction, with a 3 to 5 percent reduction in fuel burn compared to the normal trim state used on the aircraft.

Many modern airplanes, including the Boeing 787, have highly refined flight-control computers today that also help minimize drag (and even reduce the effects of turbulence). NASA’s research could further improve the flight-control laws used on airliners and other transportation aircraft in the future

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How Software Reduced Fuel Burn on NASA's Frankenstein F/A-18 | Autopia | Wired.com
 
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The gist of the article is this: EVERY aircraft, no matter how aerodynamic, flies with some degree of aerodynamic inefficiency, most notably the 'out of trim' condition and create unnecessary drag.
 
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The gist of the article is this: EVERY aircraft, no matter how aerodynamic, flies with some degree of aerodynamic inefficiency, most notably the 'out of trim' condition and create unnecessary drag.

Gambit, is autothrottle feature available on latest US fighters? How does it help?
 
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Gambit, is autothrottle feature available on latest US fighters? How does it help?
None when I was active duty. Back then, it was not considered because of the technological immaturity of the full authority engine control system. But the newest block of the F-16 is slated to have auto-throttle. As for this new flight control trimming software, it is still in the exploratory stage, but I can easily imagine it controlling engine setting to get the maximum mileage.
 
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