Simulation Packages Expand Aircraft Design Options

NASA Technology

When engineers explore designs for safer, more fuel efficient, or faster aircraft, they encounter a common problem: they never know exactly what will happen until the vehicle gets off the ground.

“You will never get the complete answer until you build the airplane and fly it,” says Colin Johnson of Desktop Aeronautics. “There are multiple levels of simulation you can do to approximate the vehicle’s performance, however.”

altWhen designing a new air vehicle, computational fluid dynamics, or CFD, comes in very handy for engineers. CFD can predict the flow of fluids and gasses around an object—such as over an aircraft’s wing—by running complex calculations of the fluid physics. This information is helpful in assessing the aircraft’s aerodynamic performance and handling characteristics.

In 2001, after several years of development, NASA released a new approach to CFD called Cart3D. The tool provides designers with an automated, highly accurate computer simulation suite to streamline the conceptual analysis of aerospace vehicles. Specifically, it allows users to perform automated CFD analysis on complex vehicle designs. In 2002, the innovation won NASA’s Software of the Year award.

Michael Aftosmis, one of the developers of Cart3D and a fluid mechanics engineer at Ames Research Center, says the main purpose of the program was to remove the mesh generation bottleneck from CFD. A major benefit of Cart3D is that the mesh, or the grid for analyzing designs, is produced automatically. Traditionally, the mesh has been generated by hand, and requires months or years to produce for complex vehicle configurations. Cart3D’s automated volume mesh generation enables even the most complex geometries to be modeled hundreds of times faster, usually within seconds. “It allows a novice user to get the same quality results as an expert,” says Aftosmis.

Now, a decade later, NASA continues to enhance Cart3D to meet users’ needs for speed, power, and flexibility. Cart3D provides the best of both worlds—the payoff of using a complex, high-fidelity simulation with the ease of use and speed of a much simpler, lower-fidelity simulation method. Aftosmis explains how instead of simulating just one case, Cart3D’s ease of use and automation allows a user to efficiently simulate many cases to understand how a vehicle behaves for a range of conditions. “Cart3D is the first tool that was able to do that successfully,” he says.

At NASA, Aftosmis estimates that 300–400 engineers use the package. “We use it for space vehicle design, supersonic aircraft design, and subsonic aircraft design.”

Technology Transfer

To enable more use of Cart3D for private and commercial aviation entities, the Small Business Innovation Research (SBIR) program at Langley Research Center provided funds to Desktop Aeronautics, based in Palo Alto, California, to build a plug-in to Cart3D that increases the code’s accuracy under particular flow conditions. Aftosmis says Desktop Aeronautics delivered valuable results and made Cart3D more applicable for general use. “Now they are bringing the product to market. This is something we never would have had the time to do at NASA. That’s the way the SBIR process is supposed to work.”

In 2010, Desktop Aeronautics acquired a license from Ames to sell Cart3D. The company further enhanced the software by making it cross-platform, incorporated a graphical user interface, and added specialized features to enable extra computation for the analysis of airplanes with engines and exhaust.

“I think it’s going to be game-changing for CFD,” says Aftosmis. “Cart3D is the only commercial simulation tool that can guarantee the accuracy of every solution the user does.”


Benefits

altToday, Desktop Aeronautics employs Cart3D in its consulting services and licenses the spinoff product to clients for in-house use. The company provides commercial licenses and academic licenses for research and development projects.

The software package allows users to perform automated CFD analysis on complex designs and, according to the company, enables geometry acquisition and mesh generation to be performed within a few minutes on most desktop computers.

Simulations generated by Cart3D are assisting organizations in the design of subsonic aircraft, space planes, spacecraft, and high speed commercial jets. Customers are able to simulate the efficiency of designs through performance metrics such as lift-to-drag ratio.

“It will assemble a spectrum of solutions for many different cases, and from that spectrum, the cases that perform best give insight into how to improve one’s design,” says Johnson. “Cart3D’s preeminent benefit is that it’s automated and can handle complex geometry. It’s blazing fast. You push a button, and it takes care of the volume meshing and flow measurement.”

Without building an aircraft, engineers can never be completely certain which design concept will perform best in flight. However, they now have a tool to make the most informed prediction possible.

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Winglets Save Billions of Dollars in Fuel Costs

Aside

Originating Technology/NASA Contribution

KC-135 aircraft
During the 1970s, the focus at Dryden Flight Research Center shifted from high-speed and high-altitude flight to incremental improvements in technology and aircraft efficiency. One manifestation of this trend occurred in the winglet flight research carried out on this KC-135 during 1979 and 1980.

Anyone who has made a paper airplane knows that folding the wingtips upward makes your plane look better and fly farther, though the reasons for the latter might be a mystery. The next time you snag a window seat on an airline flight, check out the plane’s wing. There is a good chance the tip of the wing will be angled upward, almost perpendicular. Or it might bend smoothly up like the tip of an eagle’s wing in flight. Though obviously more complex, these wing modifications have the same aerodynamic function as the folded wingtips of a paper airplane. More than an aesthetically pleasing design feature, they are among aviation’s most visible fuel-saving, performance-enhancing technologies.

Aerodynamics centers on two major forces: lift and drag. Lift is the force that enables a plane to fly. It is generated by unequal pressure on a wing as air flows around it—positive pressure underneath the wing and negative pressure above. Drag is the resistance encountered while moving through the airflow. A significant source of drag is actually derived from the high pressure under the wing, which causes air to flow up over the wingtip and spin off in a vortex. These vortices produce what is called induced drag and are powerful enough to disrupt aircraft flying too closely to one another—one reason for the carefully monitored spacing between flights at takeoff and in the air. Induced drag hampers aircraft performance, cutting into fuel mileage, range, and speed.

In 1897, British engineer Frederick W. Lanchester conceptualized wing end-plates to reduce the impact of wingtip vortices, but modern commercial technology for this purpose traces its roots to pioneering NASA research in the 1970s. At the time, NASA’s Aircraft Energy Efficiency (ACEE) program sought ways to conserve energy in aviation in response to the 1973 oil crisis. As part of the ACEE effort, Langley Research Center aeronautical engineer Richard Whitcomb conducted computer and wind tunnel tests to explore his hypothesis that a precisely designed, vertical wingtip device—which Whitcomb called a “winglet”—could weaken wingtip vortices and thus diminish induced drag. Less drag would translate into less fuel burn and better cruise efficiency. The winglet concept provided a better option than simple wing extensions which, while offering similar aerodynamic benefits, would require weight-adding strengthening of the wings and could render a plane too wide for airport gates.

After evaluating a range of winglet designs, Whitcomb published his findings in 1976, predicting that winglets employed on transport-size aircraft could diminish induced drag by approximately 20 percent and improve the overall aircraft lift-drag ratio by 6 to 9 percent.

Whitcomb’s research generated interest in civil and military aviation communities, leading to flight testing that would not only confirm his predictions, but help popularize the winglet technology now found on airplanes around the world.

Partnership

In 1977, NASA, the U.S. Air Force, and The Boeing Company, headquartered in Chicago, initiated a winglet flight test program at Dryden Flight Research Center. Whitcomb’s Langley team provided the design, and Boeing, under contract with NASA, manufactured a pair of 9-foot-high winglets for the KC-135 test aircraft provided by the Air Force.

Whitcomb was validated: The tests demonstrated a 7-percent increase in lift-drag ratio with a 20-percent decrease in induced drag—directly in line with the Langley engineer’s original findings. Furthermore, the winglets had no adverse impact on the airplane’s handling. The Dryden test program results indicated to the entire aviation industry that winglets were a technology well worth its attention.

The 1970s were an important decade for winglet development for smaller jet aircraft, with manufacturers Learjet and Gulfstream testing and applying the technology. Winglets for large airliners began to appear later; in 1989, Boeing introduced its winglet-enhanced 747-400 aircraft, and in 1990 the winglet-equipped McDonnell Douglas MD-11 began commercial flights following winglet testing by the company under the ACEE program.

In 1999, Aviation Partners Boeing (APB) was formed, a partnership with Seattle-based Aviation Partners Inc. and The Boeing Company. The companies created APB initially to equip Boeing Business Jets, a 737 derivative, with Aviation Partners’ unique take on the NASA-proven winglet technology: Blended Winglets.

Product Outcome

Aircraft with winglets
Aviation Partners Boeing manufactures and retrofits Blended Winglets for commercial airliners. The technology typically produces a 4- to 6-percent fuel savings, which can translate to thousands of gallons of fuel saved per plane, per year.

Like other winglet designs, APB’s Blended Winglet reduces drag and takes advantage of the energy from wingtip vortices, actually generating additional forward thrust like a sailboat tacking upwind. Unlike other winglets that are shaped like a fold, this design merges with the wing in a smooth, upturned curve. This blended transition solves a key problem with more angular winglet designs, says Mike Stowell, APB’s executive vice president and chief technical officer.

“There is an aerodynamic phenomena called interference drag that occurs when two lifting surfaces intersect. It creates separation of the airflow, and this gradual blend is one way to take care of that problem,” he says.

APB’s Blended Winglets are now featured on thousands of Boeing aircraft in service for numerous American and international airlines. Major discount carriers like Southwest Airlines and Europe’s Ryanair take advantage of the fuel economy winglets afford. Employing APB’s Blended Winglets, a typical Southwest Boeing 737-700 airplane saves about 100,000 gallons of fuel each year. The technology in general offers between 4- and 6-percent fuel savings, says Stowell.

“Fuel is a huge direct operating cost for airlines,” he explains. “Environmental factors are also becoming significant. If you burn less fuel, your emissions will go down as well.” APB winglets provide up to a 6-percent reduction in carbon dioxide emissions and an 8-percent reduction in nitrogen oxide, an atmospheric pollutant. The benefits of winglets do not stop there, Stowell explains. Reduced drag means aircraft can operate over a greater range and carry more payload. Winglet-equipped airplanes are able to climb with less drag at takeoff, a key improvement for flights leaving from high-altitude, high-temperature airports like Denver or Mexico City. Winglets also help planes operate more quietly, reducing the noise footprint by 6.5 percent.

If all the single-digit percentages of savings seem insignificant on their own, they add up. In 2010, APB announced its Blended Winglet technology has saved 2 billion gallons of jet fuel worldwide. This represents a monetary savings of $4 billion and an equivalent reduction of almost 21.5 million tons in carbon dioxide emissions. APB predicts total fuel savings greater than 5 billion gallons by 2014.

APB, the only company to currently both manufacture and retrofit winglets for commercial airliners, is currently equipping Boeing vehicles at the rate of over 400 aircraft per year. It is also continually examining ways to advance winglet technology, including spiroid winglets, a looped winglet design Aviation Partners first developed and successfully tested in the 1990s. That design reduced fuel consumption more than 10 percent.

While winglets require careful customization for each type of plane, they provide effective benefits for any make and model of aircraft—even unmanned aerial vehicles. Consider other winglet designs on commercial carriers, as well as blended and other winglets on smaller jets and general aviation aircraft, and the impact of the original NASA research takes on even greater significance.

“Those flight tests put winglets on the map,” says Stowell.

Blended Winglets™ is a trademark of Aviation Partners Inc.

Detectors Ensure Function, Safety of Aircraft Wiring

NASA Technology

Engineer testing wiring in the Space Shuttle Discovery
A NASA engineer tests wiring in the rear engine compartment of Space Shuttle Discovery. To pinpoint the location of faulty wires, a NASA contractor invented the Standing Wave Reflectometer.

Pedro Medelius waited patiently in his lab at Kennedy Space Center. He had just received word that a colleague was bringing over a cable from a Space Shuttle solid rocket booster to test Medelius’ new invention. Medelius was calm until his colleague arrived—with about 30 other people.

“Talk about testing under pressure,” says Medelius. “There were people there from the Navy, the Air Force, and the Federal Aviation Administration.”

After the group’s arrival, Medelius took a deep breath and connected his Standing Wave Reflectometer (SWR) to the cable. He wiggled the cable around, and the display showed a fault (a short or open circuit in wire) about an inch and a half inside the connector on the cable. His colleague questioned the results, because he had already checked that area on the cable. Medelius used the SWR to check again but got the same result. “That is when we took the cable apart and looked inside,” Medelius says. “Lo and behold, that was exactly where the fault was.”

The impetus for Medelius’ new wire inspection technology came about in 1999 when one of the space shuttles lost power due to a fault somewhere in its more than 200 miles of electrical wiring. “The backup circuit was activated and prevented a major dysfunction, but nevertheless, there was a problem with the wiring,” Medelius describes.

Even though technicians used a device called a multimeter to measure the electrical current to find which wire had a fault, it could not pinpoint exactly where on the wire the fault was located. For that, technicians had to visually inspect the wire.

“Sometimes they would have to remove the whole wire assembly and visually inspect every single wire. It was a very tedious operation because the wires are behind cabinets. They go all over the place in the shuttle,” says Medelius. “NASA needed an instrument capable of telling them exactly where the faults were occurring.”

To meet NASA’s needs for a highly precise device to inspect electrical power bundles, wires, and connectors, Medelius devised the SWR. “It came down to what was affected when a wire is short circuited or opened,” he says. “We worked out a few equations based on physical principles.” The SWR proved very sensitive, and the technology was patented.

Technology Transfer

Kennedy made the technology available for commercial licensing. Corona, California-based Eclypse International was immediately intrigued by the technology, due in part to the 1996 explosion and crash of TWA flight 800. Eclypse had worked with the White House-led Air Transport Safety and Rulemaking Committee on the investigation of the accident, which, according to the National Transportation Safety Board, was most likely caused by a short circuit in its wiring. Chris Teal, marketing director at the company, says, “We were trying to find a technology to test the wiring without being intrusive or destructive.”

After obtaining an exclusive license for the SWR, Eclypse refined the SWR for commercial use by incorporating an easy-to-use keypad and making the device more rugged. “The first version was hard plastic that shattered if you dropped it. We made it tough, so none of the connectors or casing would break if it fell,” says Teal.

Benefits

Originally featured in Spinoff 2005, Eclypse has had many years of success with the NASA technology, which is now in widespread use by the military and commercial airlines, among others. As a small business that started with just 6 employees, Eclypse now employs approximately 30 people.

Helicopter maintenance
Eclypse International licensed NASA technology and then commercialized the EXP+ to identify the location of a fault down the path of wiring on aircraft, submarines, sea vessels, and helicopters. Here, a HH-60G Air Force Special Operations Command intercommunications subsystem is tested.

Called ESP+, Eclypse’s spinoff technology takes less than 5 seconds to locate a fault. “It’s the fastest and easiest to use hand-held wire tester available today,” says Teal.

“It is comforting to know that what 
we did helped to make flight safer.”

—Pedro Medelius, 
Kennedy Space Center

Available as a standalone piece of equipment or as part of Eclypse’s Electrical Component Analysis System (ECAS), ESP+ provides step-by-step instructions to guide a user on the type and location of an electrical wiring fault.

“Mechanics who have never touched wiring can now fix it,” says Teal. “All they have to do is start the test, and in a matter of seconds, it will tell them where the fault is within 18 inches. Electrical checks that used to take two folks 8 hours can now be done in 45 minutes with one person.”

According to the company, the US Army purchased 300 ESP+ devices to include in their helicopter battle damage and assessment repair kits. In addition, one of the military programs using ECAS reported a savings of $2.19 million on development costs.

ESP+ is currently employed throughout the United States and abroad to check the health of wiring in commercial and military aircraft, submarines, sea vessels, and even presidential helicopters. A sampling of commercial customers includes Sikorsky, Boeing, Raytheon, Qantas Airlines, United Airlines, Continental Airlines, American Airlines, and FedEx. Military customers include the United States Navy, the United States Marine Corps, Australian Defense, the South Korean Army, the Spanish Navy, and Portuguese Air Forces.

In the future, Eclypse plans to promote its technology for routine maintenance of system wiring. “Our core technology and philosophy is to handle the electrical from the date it is put in service to the date of its retirement,” says Teal. The company also aims to attract the interest of networking and mainframe distribution entities and similar complex electrical industries to help ensure normal operations for their electrical wiring.

Today, Medelius says he appreciates seeing how NASA technology helps not only NASA, but everybody—even himself. “I fly a lot, and it is comforting to know that what we did helped to make flight safer. It’s a good feeling, not only as an engineering accomplishment, but from a personal standpoint.”

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