These days, a sedan that only runs 5 miles per gallon would be laughed off a car lot.
Yet in the air — where Boeing 747s get about .2 miles to the gallon — that kind of gas mileage would be revolutionary.
Like their automobile counterparts, airplane engineers have been looking for ways to safely send those 70-ton metallic birds into the air on a leaner fuel diet to cut down on carbon emissions and rising transportation costs.
Earlier this year, engineers Geoffrey Spedding at the University of Southern California and Joachim Huyssen at Northwest University in South Africa put their heads together to tackle that airplane fuel efficiency conundrum.
After reconfiguring the typical plane design in order to maximize the plane’s aerodynamics, they came up with a brilliantly basic answer: Airplanes should look more like birds.
A more aerodynamic plane would reduce drag (resistant friction) as it cruises through the air and increase lift (upward propulsion), which translates to better fuel economy.
“The design of an aircraft is a complex and large system design problem, with many interacting components and constraints,” Spedding said. “Our logic is to first of all look at the aerodynamic consequences alone of this proposed aerodynamic improvement. If that does not work, then there is no sense in going further.”
It turns out that Spedding and Huyssen's ideal airplane design looked a lot more avian than current planes. Think longer, leaner wings and a more streamlined body.
But it was a birdlike tail that really amped up the aerodynamics, dampening the drag from the body and wings, as well as boosting the lift that lags under vehicle weight and cargo load.
“The small, stubby little tail has a much bigger effect than one might imagine because it’s effectively tailoring the flow over the entire (plane) body,” Spedding said. “More technically, by setting the trailing edge stagnation point, we also modify the forward stagnation point, and hence the entire body flow. Thus, the body becomes a lifting body.”
Although the engineering team’s research suggests that airplane structures should more resemble birds, the beneficial biomimicry probably stops there, according to James Usherwood from the University of London’s RVC Structure and Motion Laboratory.
Usherwood has studied birds’ flapping motions and energy expenditures extensively and doubts that they could effectively translate to human flight.
“I would argue there is good evidence to indicate that slow flapping animal flight is aerodynamically inefficient – rotorcraft (helicopters) would be much better, presumably because they do not have to cope with repeatedly accelerating the wings,” Usherwood said. “At higher or ‘cruising’ speeds, things are far less certain. Under these conditions, flapping, birdlike flight might well have some benefits over propeller-driven or helicopter flight.”
As for imitating avian anatomy to amplify airplane aerodynamics, Usherwood isn’t wholly convinced – but he doesn’t rule out the possibility, either.
“When it comes to other aspects of birdlike design, I am aware of colleagues who would argue for theoretical benefits of bird tails,” Usherwood said. “Details of feathers are often suggested as being beneficial, but their actual function in birds is often unclear. And whether any aerodynamic effects could scale appropriately for aircraft sizes and speeds is another matter.”
Engineers Spedding and Huyssen certainly aren’t the first to suggest a more aerodynamic, birdlike airplane design, but they hope to be the first ones to actually get the idea off the ground and into the sky.
“What's next is to confirm these wind tunnel results on a few more configurations — different angles between components, different tail shapes and sizes — and at the same time to pursue the more applied issues above,” Spedding said. “To do that, we need funding (this study was internally supported by a USC Research Innovation Fund), and so I plan on approaching various companies to ask if they wish to be involved.”
Photo: RJ Huyssen/NU,RSA