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.