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NASA Chat: Quest for the Holy Grail of Laminar Flow
March 30, 2011

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For years, people who fly or design or build airplanes have been on a quest for aviation's holy grail – laminar flow.

Laminar flow means the smooth, uninterrupted flow of air over an aircraft's wing. If you can achieve it, wonderful things happen. You become incredibly aerodynamic. You fly farther on less fuel. The really challenging part of this quest is that laminar flow is very hard to do, thanks to seams and rivets and hinges and flaps and anything that sticks out or moves. All those objects break the flow and create tiny pockets of turbulence.

Ethan Baumann of NASA's Dryden Flight Research Center is a key character in today's laminar flow story. He's the chief engineer for NASA's SubsoniC Research Aircraft Testbed, or SCRAT, and for the DRE Laminar Flow Glove Experiment, or DRELFGE.

Under SCRAT, Ethan is working with other researchers to transform a Gulfstream GIII aircraft into a flying laboratory. In about two years they'll fly the DRELFGE onboard - a large "wing glove" with the funky-sounding "Discrete Roughness Elements," along the leading edge. DREs, which are tiny bumps that actually stabilize airflow, have shown great potential to reduce aircraft drag on future aircraft.

On Wednesday, March 30, at 3:00 p.m. EDT, Ethan answered your questions about the quest for laminar flow and what it means for all of us if he succeeds.

  • How do you turn a regular aircraft into a flying laboratory?
  • What can laminar flow mean to the flying public?
  • Why is achieving laminar flow so hard to do, exactly?
  • How do you know if it's working?

More About Ethan Baumann
Ethan is an aeronautical engineer in the Flight Controls & Dynamics Branch at NASA's Dryden Flight Research Center. He started at Dryden as a co-op and has been there full time since 1999. Prior to his work on SCRAT and DRELFGE, Ethan worked on the Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) project; he was a team member on the X-43 hypersonic project, the Phoenix Missile Hypersonic Testbed, and an assistant to the chief engineer for the Space Shuttle Program. He has degrees from Purdue University and UCLA, and is a native of Indiana.

More Information
› Blog: Laminar Flow and the Holy Grail
› Feature: NASA Laminar Flow Tests, Supersonic (2009)
› Video: NASA Laminar Flow Tests, Supersonic (2009)
› Image: Laminar Flow Wind Tunnel Test

 

Chat Transcript
Quasar920: What's the maximum speed range a laminar flow airplane can fly?

Ethan: Laminar flow is something that can occur at all speed ranges, though the challenges in obtaining laminary flow vary with speed.

HeatherD: Reading over laminar flow, does this mean that it would help with removing the feelings of turbulence? There was an article online lately how turbulence really shouldn't scare people.

Ethan: Not exactly. The turbulence that passengers encounter during flight is due to the airplane flying through unsteady air. When we talk about turbulent air in the context of laminar flow, we're only talking about the air that is directly touching the wing. Passengers cannot tell if the airflow over a wing is laminar or turbulent.

Dominic: Hello, Ethan! I would like to know, how do you plan to achieve laminar flow? And when will this method be applied to airliners?

Ethan: Great questions. We're investigating a new technology called Discrete Roughness Elements or DREs for short as a way to help us achieve laminar flow. DREs are a series of small bumps that are placed along the leading edge of a wing and are used to help mitigate something called crossflow transition. DREs are a technology that Professor Saric of Texas A&M University has been developing and we are looking forward to trying them out on our aircraft.

Eblood: Ethan, great work, so far. What is your ultimate end goal? Are you looking to control just the flow over the wings of an airplane, or over the entire aircraft? If it is the latter, how will you go about doing that for the traditional tube-and-body aircraft design? Would a BWB design, much like the X-48B, be a better candidate for whole-aircraft laminar flow control?

Ethan: Our ultimate goal with this project is to determine whether or not the DRE technology works as a method of laminar flow control. If successful, this technology will help to maintain laminar flow over most of a wing's surface and significantly reduce drag. This technology could be applied to a new wing design for either the traditional tube-and-wing aircraft or for a BWB.

Jason (Moderator): Do you have a question you've been waiting to ask? Go for it! To submit your own question, please type it in the box at the bottom of the window and click the 'Ask' button on the right side of the box. Thanks for your patience as we answer your questions.

Mik: What kind of active laminar control methods has NASA developed?

Ethan: NASA has developed both active and passive methods of laminar flow control in the past. For example, several years ago, we flew the F-16XL here at NASA Dryden Flight Research Center, which sucked air through the surface of a wing glove in order to obtain laminar flow. With this experiment, we are examining a passive method.

Heather: Less fuel would be huge, is there any idea of the kind of savings? Would this hopefully mean cheaper airfares?

Ethan: Our work here is being funded by NASA's Environmentally Responsible Aviation (ERA) project which has the goals of reducing aircraft noise and emissions. Studies show that laminar flow can help to reduce fuel burn for aircraft by ~8%-10% which results in a significant savings.

Ace: Are different paints or even paint schemes resulting in laminar changes?

Ethan: Very good question. It turns out that laminar flow is very sensitive to the roughness of a wing which can depend on the paint scheme. With this experiment, we are going to make the smoothest glove surface possible for the researchers. Then we are going to paint the glove surface and "rough it up" in order to see the DRE technology works with different paint schemes.

Ace: Small bumps? Out of paint or glue? Are the bumps in a pattern?

Ethan: I think of the small bumps or DREs as being very, very tiny pieces of scotch tape that are applied in a line along the front of the wing. The DREs are a couple of millimeters in diameter and much shorter in height than a human hair.

aish_: What can laminar flow mean to the flying public?

Ethan: Airplanes with laminar flow wings will have less drag and as a result burn less fuel than current airplanes. This will result a cost savings along with the environmental benefits of using less fuel.

Eblood: Even with stabilizing roughness features on the leading edge of the wings, can vibrations caused by unsteady ambient conditions trigger the transition to turbulent flow?

Ethan: Very good questions. Noise and vibrations in the wing can cause the airflow to transition from laminar to turbulent. Researchers and engineers have a way to shape the wing in such a manner that this is less of a concern.

Ace: I guess by "glove" you mean smooth? I don't understand "sucked air through the surface of the wing glove."

Ethan: By "glove", I mean the test section that we're placing on one of the wings of our airplane. There's an image of what the glove will look like on the chat page website. The glove is a structure that we're placing on the aircraft wing to change the shape of the wing. Our experiments with the DREs will be conducted on this glove. When I talk about air being sucked through the surface of the glove, I'm referring to a previous experiment on the F-16XL. In the F-16XL experiment they also placed a glove on their aircraft's wing to change the wing shape and were able to pull air through the gap between the wing.

smoothie2: In an earlier response, you said you're using a "passive method." What does that mean?

Ethan: We use the term "passive" to let people know that we're not using any mechanical or moving parts in order to obtain laminar flow. This is different than "active" control methods which usually consist of either sucking air through very small holes in the surface of a wing or by blowing air across the surface of a wing.

Orfalism: What is it like; working for NASA? Is it as awesome as I think it is?

Ethan: Working for NASA is really awesome. It is very rewarding working on exciting projects like this one which are developing technologies that could one day change how airplanes are designed. Plus it's fun working with all of the smart people at NASA and that we work with at Texas A&M University.

Beckette: Is the purpose of the line of "bumps" across the leading edge to create very small or "micro" streamlines for the airflow?

Ethan: It helps if you think of the air flowing over the wing as a series of ocean waves with different wavelengths. What the DREs or bumps do is to excite certain types of waves which then interfere with the waves which cause transition from laminar to turbulent flow. I know it's a little hard to imagine these tiny bumps affecting the wing flow, but researchers at Texas A&M University have demonstrated that they work in wind tunnels and in smaller scale flight tests than what we have planned.

Mik: How does laminar flow affect total lift?

Ethan: There's really very little impact on total lift. What laminar flow really does is to reduce skin friction drag.

Ethan: In addition to the laminar flow experiment that we're working on, we're modifying our aircraft to use it as a testbed for flight research experiments in the future.

Jason (Moderator): Do you have a question you've been waiting to ask? Go for it! To submit your own question, please type it in the box at the bottom of the window and click the 'Ask' button on the right side of the box. Thanks for your patience as we answer your questions.

Mkuester: Do you test only applique DRE? Or do you also test pneumatic units as part of your program?

Ethan: Right now, we are planning on testing only applique DREs. Researchers at Texas A&M University have tested pneumatic DREs in the past. Pneumatic units are something that we might consider looking at in the future, but not at this time.

Dominic: Can you accurately test DREs in a wind tunnel?

Ethan: It is very difficult to test DREs in a wind tunnel. Wind tunnels do not completely replicate the flight environment, which is why we still need to do flight test.

Ethan: To clarify, pneumatic DREs are basically small bumps that rise and fall as air is blown at them. Think of them as being small balloons inside the wing and the top part poking slightly above the wing when inflated.

uri101: Is the laminar flow research intended for travel uses or just airplanes in general?

Ethan: The laminar flow research we're conducting is for airplanes only. Unfortunately, we can not use this work to reduce drag on our cars.

Orfalism: Have you ever been in space?

Ethan: Not yet.

Dominic: What are the steps you need to take to modify a normal aircraft into a testbed for future technologies?

Ethan: Very good question. Our airplane is a Gulfstream III business jet, so it is configured to carry passengers. We are adding an instrumentation system to record data from our experiment and the aircraft systems. We are also placing sensors all over the aircraft to help out with our flight tests. In addition the aircraft didn't have a lot of electrical outlets on it to plug in our computers, so we are modifying the electrical system. When we're done, we will have an aircraft that is capable of supporting a wide range of flight test experiments.

Ace: I saw the "glove" are you moving it up and down the wing or is this the only spot?

Ethan: The "glove" is going to be fixed in one location on the wing and not be moved. It's in what we call the "sweet spot" on the wing. It's far enough away from the engine that we don't have to worry about the engine affecting the experiment, and it's far enough away from our control surfaces that the aircraft will fly like it normally does.

K: Ethan, how can you tell that the DREs are doing their job and reducing drag? Are there force transducers or some other instrumentation on the glove?

Ethan: Very good question. We are actually not going to measure drag or force. We will primarily use an infrared video camera to detect laminar and turbulent flow. There are very small temperature differences between laminar and turbulent flow that the infrared video camera will see. In addition, we will place a number of sensors on the glove which will measure air pressure and temperature.

smoothie2: Do you know how you'll know whether the DREs work? Is it something you can know right away or will it take a whole series of tests? Like, at what point can you say "Eureka!"

Ethan: There're really two answers to this question. We will have video from our infrared camera which will detect the amount of laminar flow that we have in real-time during the flight test. This will give us an indication that things are working or not. Then after we land, the real work begins. The researchers will comb through the data recorded in flight to understand why we had laminar flow and to compare the data with their predictions. It will really be after the researchers have studied the data that we will have the definitive answer as to whether the DREs work.

Aerognome: What other types of flight test experiments are you hoping to conduct in addition to the laminar flow experiments?

Ethan: In addition to the laminar flow experiment, we are working on a project with the Air Force Research Laboratory (AFRL) to flight-test a compliant trailing edge. A company called FlexSys, Inc. has developed a flight control surface which is different than those currently in use on airplanes. These compliant structures simply deform or flex in flight similar to the way that a bird changes the shape of its wing in flight.

Ace: Do you calculate the " sweet spot" for every type of wing?

Ethan: The researchers and aerodynamicists on our team use Computational Fluid Dynamics (CFD) tools to predict the airflow over the wing. They looked at their CFD results and decided to place the wing glove at its current location. In order to come up with the best experiment possible, they chose the location for our glove.

Jason (Moderator): We've got about ten minutes left in today's chat. Do you have a question you've been waiting to ask? Now's the time to ask it. To submit your own question, please type it in the box at the bottom of the window and click the 'Ask' button on the right side of the box. Thanks for your patience as we work on answering your questions.

Ace: Oh, a Gulfstream III! Are you taking volunteers? (hah, hah)

Ethan: Unfortunately, no. It wouldn't necessarily be a very comfortable ride anyways. We had to take out the nice, fancy seats and most of the interior in order to put in our computers and seats which are rated for flight-test.

smoothie2: Your bio on the chat page mentions a bunch of other work you've done; is there anything you learned on these other projects (and sometimes they're space-related) that you've applied here?

Ethan: Good question. My background is actually in the area of aircraft flight controls, and I'm more comfortable with aircraft simulations and software than with laminar flow. So much of my technical background is a little out of place on a laminar flow project. What I've learned that is most useful is how to work with people with different technical backgrounds and skill sets. That's also part of what I find really fun about working at NASA. I learn something new every day and I get to interact with a lot of great people both at NASA and with our partners like Texas A&M University.

Jason (Moderator): We've got time to answer just a couple more questions in today's chat...

Ace: Can you recommend some reading to be more familiar with this?

Ethan: I'd recommend doing an internet search for "DREs, Texas A&M University, Professor Saric." That should come back with links to a number of papers that Professor Saric and his students have written on DRE technology.

Dominic: One last question: Do you think that the aircraft of tomorrow will have DREs and/or other anti-flow separation devices? (like flaps on today's aircraft)

Ethan: I really believe that the aircraft of tomorrow will have wings designed for laminar flow. DRE technology looks like a very promising technology to help us get there, but we first need to gather more data and prove that it works.

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NASA engineer Ethan Baumann standing in front of the Gulfstream GIII testbed aircraft.
NASA engineer Ethan Baumann and the Gulfstream GIII testbed aircraft.
Image Credit: 
NASA / Tony Landis
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Aerial image of the Dryden's Gulfstream GIII aircraft.
The area where the DREFLGE wing glove will be placed on Dryden's Gulfstream GIII is outlined in green.
Image Credit: 
NASA / Tony Landis
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Computer generated image of an airplane showing what the wing glove looks like.
This computer simulation shows what the wing glove looks like and how it will be placed on the testbed aircraft.
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