Taking Cues from Birds to Green the Airline Industry

Three airlines fly in formation to increase fuel efficiency
Three airliners fly in formation to increase fuel efficiency

Stanford University research group takes biomimicry to whole new heights

At this summer’s Airbus “Fly Your Ideas” competition, an international call for sustainability innovation in the airline industry, one Australian team of graduate students walked away with the first place cash prize of 30,000 euros for a green passenger cabin concept. Derived from castor oil, their bio-composite cabin is an attempt to reduce dependency on non-renewable resources in the construction of airplane interiors.

While the majority of the finalists at the competition—including the winner—focused on materials and biofuels to offer eco-friendly alternatives to flight travel, one team garnered a significant amount of head-turning by looking at how planes fly. A team of doctoral students from the Aeronautics and Astronautics program at Stanford University conceptualized a way for commercial planes to save fuel by flying in formation. “In principle, the idea of flying aircraft in formation is the same as for migrating birds,” said Tristan Flanzer, one of the team members. “While in formation, birds experience lower drag and therefore can fly further. Aircrafts can take advantage of the same principles to reduce their drag.”

The Stanford students’ idea isn’t necessarily new or revolutionary. In fact, scientists since the early 20th century have studied how birds experience lower drag and consequently fly farther because of formations. “The challenge for us was developing ways to make this technology safe for commercial aircrafts, and analyzing the fuel burn and environmental savings that would result from an airline adopting formation flight,” said Flanzer.

Not quite this close. The study says 3-5 miles would be sufficient to save fuel. (image from flightglobal blogs)

How it Works

When aircrafts are in flight, they leave behind a significant wake. The wake is made up of two rotating vortices, one that induces downward velocity, which ultimately creates drag, and the second that creates a region of rising air that is known as upwash. Drag is usually thought of the physical forces that impede or oppose the motion of an object. “By positioning a trailing airplane to fly through this region of upwash, the amount of lift induced drag can be significantly lower,” noted Flanzer. “For a two aircraft formation, this can translate to a 15-20% total drag reduction for the rear airplane.”

NASA piloted (yes, pun intended…) a similar program in the early 2000’s, but the Stanford group’s idea is different in that it involves spacing aircrafts much farther apart to make formations more realistic in a commercial setting. Both domestic and international airways are often littered with planes, and spacing poses a significant safety solution as well.

To determine fuel burn savings, the team examined 32 trans-Atlantic routes from the US to the UK—16 to the US and 16 to the UK—over one 24 hour period for a single existing airline. They then computed the optimal number of planes within the formations (either 2 or 3 aircrafts) as well the optimal rendezvous and split locations. For example, flights from Los Angeles, San Francisco, and Las Vegas were simulated to depart at roughly the same time, rendezvous over the western US, fly the vast majority of their flight to airports near London in formation, and then at the end, split formation as each aircraft descended to their respective destinations.

The team concluded that arranging aircrafts in a three plane inverted-V formation is inherently more stable than others, and that an airline could save 12% of fuel compared to what it would burn if each aircraft flew alone. To put things in perspective, HowStuffWorks calculated that a plane like a Boeing 747 uses approximately 1 gallon of fuel every second. Over the course of a 10-hour flight, it can burn up to 36,000 gallons.

A 12% reduction would save thousands of gallons of fuels, not to mention the related greenhouse gas emissions, a factor for the industry’s constant vilification. “Airlines really kill for a one percent improvement in fuel burned,” said Geoff Bower, another team member in an earlier interview. “Twelve percent is actually very large.” In addition to saving fuel, formation flight can cut emissions of the greenhouse gases known as nitrogen oxides by one fourth.

The team has returned from France, where the finals were held, and are currently tweaking the concept to make it more commercially viable.

Ashwin is an Associate Editor of Triple Pundit. He recently returned to the Bay Area after living in Argentina, where he wholeheartedly missed the Pacific Ocean. He is a freelance editor and media and marketing consultant.After a brief stint working in the wine world, when not staring blankly at a computer screen, you'll find him working on Anand Confections or at 826 Valencia, where he has been a long-time volunteer.

25 responses

  1. Did these students ever take into account the dangers of having commercial airliners flying information? There is a reason why air traffic controllers use a separation distance of 5 miles in the enroute environment and 3 miles in the TRACON environment. Once again a perfect example of people only using numbers and not taking a step back and thinking about the situation in real life.

    1. why so gloom, all it would take for this to work in the commercial field is for the flight crews to pay attention to their surrounding. Military’s around the world fly in formation, and they have very few if no recorded collisions. so a little responsibility on the flight crews shoulders and this would help lower the cost of tickets, lower the emissions, and shorten the flight times. don’t be so pessimistic

        1. Wingtip vortices don’t dictate instantly. I have been tossed around in a light plane minutes 5 after a 757 landed. At 600 MPH, that s less than 5 minutes….

    2. Stepping back even further, Andrew, and one could imagine a change in communication protocol where the planes act as a unit, changing protocol. It’s not unrealistic.

  2. I wonder if perhaps this same effect could be replicated by an upwash-inducing drone plane that flies ahead of jets and creates the upwash, leaving no need to fly in formation. If the drone was highly efficient, it may be able to do this for far more planes, or for long-haul flights that burn a lot of fuel on each trip but don’t have much in the way of companion flight traffic.

    1. Maybe I’m stating the obvious here, but if you put a drone up to create a wake you’re wasting even more fuel on a passengerless aircraft. Even if you successfully get your 12% reduction in fuel from the wake, the drone plane will need to have less than 12% of the fuel consumption of the passenger plane to be a net fuel saving. If drone planes could be this efficient, why not passenger planes?

      1. If the space between planes could be 5 miles then the drone might be able assist 9 or more planes (each 5 mi apart?) and could save fuel. (9 times 12 would be 108% savings and only 100% spent on the drone.)
        I would like to see the data.

    2. I like the concept, but Connor is probably correct. The first plane acts as the lead anyway for any number of planes, then they can switch places, evening it out.

  3. This is brilliant thinking but I worry about the wake turbulence that this would cause, even at that distance. AA587 Went down in Queens, apparently due to wake turbulence from the plane in front of it – probably at about that distance. Maybe it’s totally different at high altitude and full speed?

    1. AA587 crashed due mostly to pilot error. There was wake turbulence but it was the pilot’s overreaction using the rudder to try to correct it that caused the failure of the tail.

      1. That’s a great point though, especially with all the accidents that have happened this summer. If AA587 crashed due to pilot error, the chances of accidents only increase when you start bringing in multiple planes into the fold. I believe the researchers account for plane separation when they drop elevation as they near their destinations, but there’s still a good amount of coordination that needs to happen (and unfortunately—seemingly—a significant amount of opportunity for more pilot error).

  4. Ok to all of you calling me out about how I didn’t read the article and was only looking at the picture…well you are all very wrong. First of all to Michael, yes flying like that is called formation flights like what the military uses. However, never will a group of commercial jets ever act as one unit. There would be far less efficiency in the air traffic and do you really think that different companies will be willing to loss money compared to a competitor? If any of you have ever experienced a thing called wake turbulence, it is a nasty little thing. Planes crash because of it or loose total control. Tom, no the idea of “drafting” like what NASCAR cars do to each other and wake turbulence are very different. Wake turbulence is partially caused by the aircraft effecting the trailing airflow but the primary cause is the air moving over the wing, the shape of the wing and wing tip voticies. Also, each air carrier in the world has its own idea about how to deal with unknown problems in the air; weather, emergencies, reroutes ect. Supposed you have a group of only 3 aircraft flying in formation and in there route of flight there is a storm beginning. With a storm comes wind and vertical pressure differences, these are what cause both chop and turbulence. The first plane feels that his/her best course of action is to climb the second plane’s idea is to deviate to the right and the third plane feels that slowing down and deviating to the right is the best course of action. If the lead aircraft, aircraft number 1, begins to climb its wake turbulence will be magnified and its effects on the other aircraft would be felt 10 times as much putting the trailing aircraft in serious danger. You then take into account the increased wing surface area that would be effected by the new wake turbulence with the trailing aircraft banking for their turns and once again the effects of the wake turbulence would be increased even more. Another problem what if an emergency happens to an aircraft int he middle of the formation? Would it simple dive out of formation, no it wouldn’t the formation would have to break and the time it takes for this to occur can mean the difference for a safe our a horrible outcome to occur. Also, I am not just some guy commenting on this, my job is to control aircraft, I am an air traffic controller.

    1. A lot of the problems you brought up aren't that relevant. You're assuming all the planes have to be in formation all the time. If there's a storm or something let them go by themselves.

      Also the wake from one commercial jet will not crash a plane behind it. Even the autopilot could handle that.

  5. This is brilliant and needs a serious investment right away. Airplanes use a surprisingly large percentage of the world’s fossil fuel – a single transcontinental trip can double an American’s energy footprint. The substantial benefit is and obvious to a physicist who thinks about it for a minute. Sure there are some challenges. But air traffic controllers are using a control system that was designed and built many decades ago and is extremely antiquated; projects to replace it keep failing and in desperate need of replacement. We have systems to control particle accelerators where particles are moving at light speed. We know how to build systems to do this today. Don’t think we can’t just because your computer crashes periodically. There are important computer systems that can run reliably for decades at a time because they (unlike home and office desktop computers and software) were designed to be reliable. (The Apollo Moon Lander’s computer was designed with triple-redundant systems to achieve extreme reliability even given unreliable parts.) The autopilot in a new plane alone is far more reliable than a pilot and copilot team alone.
    But yes, new technology will lead to Air Traffic Controllers needing to find new (and far less stressful) jobs. On land, there’s been a fair bit of work done on having cars drive nose to tail in convoys safely. It’s much more practical in the air. And a commercial cross-country flight is already much safer than a cross-country drive. I’d love to work on building these systems.

  6. The idea of grouping airplanes is interesting concerning how birds migrate. If these researchers actually spoke with Dr. David Cimprich (An Endangered Bird Field Biologist, from the Nature Conservancy based in Killeen, Texas), they would find out that the birds usually also travel in storms. While working for him for a seasonal period, the Black Capped Vireos arrived from their Mexico wintering grounds in groups after storms. If the storms and wind velocity of such were calculated from weather data, it could also be shown that the airplanes could save a huge amount of fuel through hitching a ride on wind jets like the birds did.

    First the older birds and males arrived, then the younger birds and females arrived; Possibly due to getting lost or stronger currents earlier in the season (About 2-5 weeks apart). Both arrived after huge storms hit the Killeen area.

    Maybe airplanes could use the same advantage that ships at sea and birds in the air have used for centuries(?).

  7. A lot of the problems you brought up aren't that relevant. You're assuming all the planes have to be in formation all the time. If there's a storm or something let them go by themselves.

    Also the wake from one commercial jet will not crash a plane behind it. Even the autopilot could handle that.

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