TESTS BEGUN TO STUDY DECREASE IN AIRCRAFT DRAG; MAY PRODUCE SUBSTANTIAL FUEL COST REDUCTIONS FOR AIRLINES
Dwayne Brown, Fred Brown
NASA researchers have begun tests on an experiment they hope
will improve the efficiency of commercial aircraft by minimizing
aerodynamic drag. This, in turn, could mean a savings of up to
$140 million annually in commercial fuel costs.
Drag is the aerodynamic force resulting from air pressure and
friction that acts to resist the passage of an aircraft as it
flies through the air.
Called the Adaptive Performance Optimization experiment, the
tests will obtain data on applying an aircraft’s control surfaces
in the optimal position to reduce drag. The tests, which began
last week, will be conducted on a modified Lockheed L-1011 TriStar
by NASA’s Dryden Flight Research Center, Edwards, CA.
NASA’s Langley Research Center, Hampton, VA, is sponsoring
the testing, which is part of the Advanced Subsonic Transport
Aircraft Research program led by the Airframe Systems Program
Office at Langley.
“A drag reduction of only one percent translates into an
equivalent saving in fuel usage and fuel costs, a major factor in
airline operations when you improve the efficiency of transport
aircraft by minimizing aerodynamic drag,” said Dryden engineer
Glenn Gilyard, principal investigator and flight-test director for
“There are lots of data to indicate that a one percent
improvement is achievable,” Gilyard said. “The trick is
identifying very small changes in drag,” he added. Project
officials are hoping for drag reductions of up to three percent.
The modified Lockheed L-1011 TriStar jetliner is operated by
Orbital Sciences Corp. of Dulles, VA. The research team plans to
fly the aircraft approximately three or four times each year over
the next two or three years in both the current and follow-on
phases of the experiment. The follow-on phases could incorporate
the TriStar’s flaps into the system, as well as second-generation
computer software using artificial intelligence. Most of the
tests will be flown at speeds of about Mach 0.83 and at altitudes
of 30,000 to 40,000 feet.
Gilyard pointed out that all aircraft are designed to operate
most efficiently at a single point in their flight profile.
Unfortunately, they often do not fly at that design point, and
therefore fly at reduced efficiency.
“The experiment is designed to improve aircraft performance
during a given flight condition, based on real-time in-flight
measurements and analysis,” Gilyard said.
For the experiment, a team of engineers designed a software
program for the aircraft’s research computer that reduces
aerodynamic drag of the entire aircraft by changing the positions
of the aerodynamic control surfaces. The program incorporates
data such as airspeed, altitude, engine measurements and other
parameters to make instantaneous decisions on adjusting the
position of the control surfaces for the greatest aircraft
efficiency for each point in the flight profile.
In addition to developing the software, NASA engineers
developed flight-research systems that will record test data and
will allow on-board flight test engineers to make decisions and
analysis of research data while the flights are in progress.
“We are trying to achieve savings based on the difference
between what the manufacturer designed the airplane to be and what
the airplane actually is,” said Gilyard. “The bottom line is how
much fuel goes into that airplane over the course of a year. The
potential fuel cost savings for a single MD-11 in regular service
could be $130,000 per year and for a Boeing 747, the savings could
These tests mark the beginning of programs that will reflect
the enabling technology of one of NASA’s major aeronautics goals –
– to reduce the cost of air travel by 25 percent within ten years
and by 50 percent within 20 years.
A Photographic image is available to news media to illustrate this
release by calling the Headquarters Imaging Branch at 202/358-
1900. The photo numbers are: