Boundary-Layer Ingestion Key To MIT/NASA D8 Hopes

Commercial aircraft designs that depart from today's tube-and-wing shape demand equally innovative propulsion systems if they are to stand any chance of breaking the mold and providing the benefits anticipated by their creators.

With its engines flush-mounted beneath a pi-shaped tail, the Massachusetts Institute of Technology's (MIT) D8 concept with its “double-bubble” lifting fuselage is no exception. Sized to replace aircraft in the Airbus A320/Boeing 737 category around 2035—a time frame NASA calls “N+3 generation”—the D8 promises fuel burn more than 70% lower than the 737-800's. And while the wide, twin-aisle fuselage has more drag than the 737's, its overall shape enables a lighter wing and landing gear and a smaller tail.

The make-or-break aspect of the D8 design, however, is whether the embedded engine location is feasible, and whether smaller, lighter turbofans will be able to operate in the challenging flow conditions over the aft fuselage. To answer these questions, research is underway at NASA, MIT, Aurora Flight Sciences, Pratt & Whitney and the United Technologies Research Center (UTRC) into how closely the airframe and propulsion system can be integrated and what fuel benefits are possible from ingesting the fuselage boundary layer.

MIT has just completed four weeks of tests of the D8 in a 14 X 22-ft. wind tunnel at NASA Langley Research Center, Va., aimed a quantifying the benefit of boundary-layer ingestion (BLI) through back-to-back comparison of the same 1:11-scale, 13.4 ft.-span model with embedded and conventional podded engines. Initial results show a benefit close to that predicted, with a measured 5-8% reduction in the electrical power required to drive the 6-in.-dia. fans in the embedded engines at the same cruise condition, says Alejandra Uranga, technology lead for MIT.

BLI is not new a new idea; it is already being used in torpedo and ship propeller design. When a podded propulsor is in freestream airflow, like a turbofan in a wing-mounted nacelle, the excess kinetic energy in the jet is wasted. But when the propeller is immersed in the slower-moving boundary-layer flow there is no excess kinetic energy, and less energy needs to be added to achieve the same thrust. The benefit comes from the propulsor reenergizing the wake and reducing drag.

The question regarding the D8 is whether the same principle can be applied to an aircraft-engine fan operating under higher propulsive loads, and whether that fan can withstand such a turbulent environment without its efficiency being overly compromised.

“The primary question is, 'Can you get a fan that can operate in that distortion?' Secondly, by ingesting the boundary layer, are we reducing drag, as most people believe we are? It is drag versus efficiency and whether the summation of the two is still positive,” says NASA Fixed Wing project head Ruben del Rosario

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People Who Design and Build

Aerodynamicist:

During the design process, the aerodynamicist works hard with the other design engineers to make sure that the airplane, missile, car, boat, or truck moves easily through the air or the water. He or she does this by building a model of the object to be designed and then testing it. One way to do this is to build a scale model and place it in a wind tunnel or a water tunnel. This way the engineer can observe and measure the way the air or water behaves when the object is moving. Click on one of our interviews to hear about some of the projects some NASA aerodynamicists are working on! Another way to test a model is to build it on the computer and use math to predict how the air or water will behave. This kind of aerodynamicist is called a computational fluid simulation specialist, and he or she is discussed in a later section. Most aerodynamics engineers have at least a BS in engineering.

Aircraft Conversion Specialist:Do you know someone who rebuilds cars and then resells them? An aircraft conversion specialist can do the same thing with airplanes. Maybe the remodeling is just a series of improvements in a regular private plane - better instruments or adding a satellite positioning system. Or maybe he or she will rebuild and redesign an old military or cargo plane into a fancy executive aircraft! Either way, this specialist must have a solid understanding of aviation principles and components, as well as have good sales and customer relations!

Chemist: Why do airplanes use a different fuel than cars? Why do some rockets use solid fuels, while others use liquid fuels? How do you clean up after you use toxic chemicals? A chemist could tell you the answers to these questions! He or she analyzes the molecular makeup (sometimes atom by atom!) of fuels, plastics, or ceramics for use in aviation. Why not click on our interview to learn more about it? Your average chemist has at least a BS in chemistry, and many often have additional degrees in chemistry.

Computational Fluid Dynamicist: The CFD (computational fluid dynamics) engineer is an aerodynamicist who specializes in testing a model on a computer. He or she uses math equations and formulas to model the flow of air or water in and around objects such as airplanes, missiles, boats, cars, or submarines. We have interviewed several people who have worked on some really neat problems. Click on the interviews to see what they have to say! A CFD engineer usually has a MS or a Ph.D. in math or engineering.

 Design Engineer:The Boeing 757 and 767 use the same basic design and parts, but the 767 is a much larger plane that can hold up to 120 more people! The design engineer decides how long a plane has to be to hold a certain number of people, how wide it should be, where the wings need to be, and how strong the materials need to be. He or she calculates how the insides of the airplane and wing should be built to carry the predicted loads. Have you ever seen the inside of the fuselage skin or a wing? Click on our interview to meet a design engineer who can tell you all about it! Design engineers usually have at least a BS in mechanical, civil, or aerospace engineering.

Electronics Engineer:Have you ever wondered how those buttons, dials, and gages in the cockpit work? A lot of us know WHAT they are, but we don't always know how and why they work. An electronics engineer is a person who designs the sensors and connections that tell the pilot of an aircraft that things are fine, or that there is a problem. He or she also designs the connections and devices that translate the motion of the pilot's hand on the stick, for example, into impulses that are sent to the flap mechanism. These impulses are then translated into the motion of the flap. An electronics engineer can have a BS degree or higher in electrical, mechanical, or aerospace engineering.

Equipment Engineer: Whew! It's hot in here! Lets get an equipment engineer to design an air-conditioning system to cool us off. He or she would have to make it both efficient and inexpensive, as well as size it so that it is neither too big, nor too small for our room! These engineers design heating, pressurizing, hydraulic, and/or oxygen-equipment systems for airplanes, cars, and buildings. Equipment engineers usually have BS degrees in mechanical, electrical, or systems engineering.

Mathematician: Mathematicians can work in many different areas of aviation, although it's mostly behind the scenes. They develop the math formulas that engineers use to design their work, and help the engineers develop solutions to their problems. For example, a mathematician might work with an aerodynamicist to help formulate the equations to calculate the behavior of the fluid over a body. Or they might help record and analyze the wind tunnel data. Some mathematicians work with chemists or meteorologists to help them with the mathematical equations in their work. Click on the interviews to hear two mathematicians tell you about their work. One works in CFD, the other worked as a test engineer! Mathematicians study math all through high school and college, and most of them have graduate degrees in math as well.

Todd Levine

Metallurgist:Have you ever had a toy that looked like it was made of strong metals, but when you played with it it broke right away? Well, a metallurgist is a specialist who works with metals and metal alloys to develop and test strong compounds to be used in airplanes and cars. He or she tries to ensure that the parts will not break even after years of use. The metallurgist may work separately in a laboratory in another part of a company, or he or she may be a part of an engineering design team. Either way, he or she tries to make strong parts to last a long time. Metallurgists have a background in hard science, and may have degrees in chemistry, physics, or materials engineering.

Physicist: The physicist is another behind the scenes part of a design team. He or she may work in many different areas in aviation. A physicist might work by himself or herself, analyzing a scientific problem for aircraft or missiles such as overcoming the heat barrier or computing a trajectory, or he or she might be working closely with a design team. Some physicists work with metals and materials and might interact with chemists or metallurgists, while others are more mathematical and collaborate with aerodynamicists or failure analysis engineers. Most physicists have a solid background in math and science in high school and college, and go on to earn masters or PhD's in physics before going out to work.

Power Plant Engineer: Hey... Listen to that engine purr, or roar, as the case may be! A power plant engineer may work with piston engines, ramjets, scramjets, turbojets or turboprop engines, or rocket engines! He or she may design the whole engine system, or specialize by concentrating on a single component or part of an engine. Perhaps the engineer might get his or her hands dirty building and testing the engine, or maybe he or she will analyze the engine performance using the computer. Any way you look at it, a power plant engineer has an interesting job! We have one engineer for you to meet: Click on the interview to meet her! A power plant engineer usually has a BS degree in mechanical or aerospace engineering, and many have masters or PhD's as well.

Structures Engineer: How does the pilot know that the wing of the plane won't rip off when he or she flies really fast? Or how does a trucker know if a bridge is strong enough to hold his or her truck? A structures engineer designs and tests components and materials to see that they are strong and will last a long time. He or she may do vibration tests (a whole lot of shaking!) or stress and strain tests (bending and twisting and pulling!) to make sure that a suggested design will do the job. The structures engineer is an important member of the design team. Most structures engineers have at least BS degrees in civil, aerospace, or mechanical engineering.

Weight and Balance Engineer: Most people don't realize that when they and their luggage get on the plane, a weight and balance engineer has already determined where they should sit and where their bags should be placed to make sure that the plane is properly balanced. This may not seem very important to you, but the pilot and the design team think it is. The plane may not fly well or may break if it isn't balanced right! Think about it - have you ever tried to float a boat in water, but you put all the weight on one side of the boat? It probably sank, didn't it? So, the weight and balance engineer studies the loads on a plane or a missile, and he or she works with the other design engineers to ensure that the balance points on the plane or missile coordinate with the controls and structural systems. Then the plane or missile will perform as designed! These engineers usually have BS degrees in civil, mechanical, or aerospace engineering.

This next list of jobs features positions that require less formal education, but still may rely heavily on math and science classes in high school or at technical schools:

Assembler: The assemblers are featured throughout the production line of an aircraft or missile. They put together various parts of the aircraft, or they monitor the machines that are putting it together. An assembler needs to be good with his or her hands and with tools.

Draftsman/CAD Operator:Throughout the design and production process, many, many drawings are made to detail the design and building of an aircraft. The draftsman used to sit over a large board and draw the piece of the aircraft to the engineer's specifications, but these days, most drawings are done on a computer using a CAD (computer-aided-design) program. A draftsman (male or female!) must be a good artist, with a strong sense of proportion. Experience with computers is a good plus also.

Electronics Installation Technician: This technician works with the assemblers, but specializes in electronic equipment. He or she will install the various electronic instruments in the cockpit such as air navigational aids (like radar or the MLS - microwave landing system) and communications equipment, and also do the landing and cruise lights on the outside of the plane.

Jig and Fixture Builder: The assembly of aircraft and missiles requires very specific frames and cradles, or jigs, to hold the pieces of the aircraft as they are being worked on. Most of the time, these jigs must be made at the production facility; they can't be bought from a catalog. The jig and fixture builder is in charge of creating just the right frame or jig for a part or procedure. These builders are very good mechanics, and often contribute to the design process because of their experience. While they may not be formally trained in engineering, they often have a natural intuition for design.

Model Builder: When the aerodynamicists need to run a wind tunnel test, they go to a model builder with the specifications of the aircraft and commission him or her to create a scale model. Not only does the model builder have to recreate the aircraft in detail, but he or she also needs to be able to build into the model the necessary instrumentation for the test data. A strong background in math and science helps the model builder to be a full partner in a successful wind tunnel test sequence.

Mock-up Builder: While the model builder and the aerodynamicists are working on their small-scale tests, it is often important for a design engineer to work with a full-size mock-up of the aircraft. For example, the designer of the cockpit needs to be able to see the full design to ensure that seats are positioned properly, there is head room for all sizes of pilots, and important switches and instruments are easy to see and reach. In an inflight emergency, the pilot doesn't have time to fumble about to find the right switch to throw! So the mock-up builder works with the engineers to develop full-scale models of the design. Again, these builders have a solid background in math and science, along with good mechanical skills.

Sheet-Metal Fabricator: Many parts of aircraft or missiles are cut or formed from large sheets of metal. The sheet-metal fabricator will work with the metal and the machines that manipulate it to see that the proper parts are created. Good mechanic skills and some computer experience will help someone train as a fabricator.

Technical Illustrator: Illustrations or drawings of the aircraft parts are very helpful to have in an instruction manual. This manual may be a maintenance manual for up-keep, a how-to manual for an operator like a pilot, or a record of the design process for the design engineers. The technical illustrator helps researchers, engineers, and maintenance personnel by drawing the technical figures necessary to demonstrate a point in the record. Illustrators generally have artistic backgrounds, but the ability to understand basic math and science concepts helps them translate the desires of the technical people to easy-to-follow figures for publication.

Tool Designer: Highly specialized tools are necessary for the building of aircraft and missiles. They usually can't be bought in stores or from catalogs. So, the production facility foremen must create their own tools. The tool designer may be an engineer, or he or she may be an extremely experienced mechanic who has great insight into exactly the type of tool needed for a job. Nowadays, a lot of the assembly is preformed by computerized machines, so tools must fit into the machine as well as suit the job.

Tool and Diemaker: Once the tool designer has arrived at a set of specifications, the tool and diemaker must make the requested part. This tool might be machined, or cut down from a raw piece of metal, or it may be cast by pouring hot liquid metal into a mold called a die. A die is the reverse of the tool, and it must be made very carefully so that the finished tool is exactly what was ordered.

Wind Tunnel Technicians: These technicians work in a wind tunnel facility, operating the tunnels and the data-gathering devices. Since computers are used now for retrieving data, many people are needed to watch the tests to ensure they are running smoothly and that nothing breaks down. Wind tunnels take a lot of energy to run various tests, and the small detailed models can be very expensive. If a test run is stopped because something is broken, something isn't working properly, or a model breaks down, it can be very costly. Technicians may not have engineering degrees, but many have engineering experience. Engineering students often work part-time or full-time as technicians to make money and gain experience while they are still in school.

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