Delta will invest $1 billion to curb climate change, NBC News reported. The airline’s endeavors to reduce its carbon footprint will include funding clean-air technology while reducing waste. The choice of aircraft purchases depends on flight range and fuel efficiency.
According to NBC News, Delta Air Lines is the first airline to make a such a large monetary commitment to fighting climate change. “The aviation industry accounts for roughly 2 percent of global carbon dioxide emissions and has set out a plan to achieve carbon-neutral growth from 2020, even as air travel is set to accelerate,” the article said. “Facing increasing demands from customers, individual airlines like Delta have taken additional steps to mitigate their carbon impact with measures ranging from eliminating single-use plastics to investing in biofuels and purchasing more fuel-efficient aircraft.”
When airlines decide which planes to purchase, flight range and fuel efficiency play a major part in the choices they make.
Fuel Burn of Airplanes
The only time most passengers on a jet engine think about fuel is when they hope the plane has enough for the trip. Passengers rarely consider how the fuel itself changes the mechanics of flight, including lift, or upward force on the plane; drag, or wind resistance; and the plane’s overall weight.
“As the jet aircraft burns fuel, its weight decreases, and we must maintain lift equal to weight for equilibrium flight,” said Dr. James W. Gregory, Professor of Mechanical and Aerospace Engineering at The Ohio State University. “So, the lift produced by the aircraft must go down throughout the flight.”
Additionally, the sheer amount of fuel a jet airplane holds and uses is staggering. Dr. Gregory used a Boeing 747 as an example.
“The combined fuel burn for the four engines on a 747 is one gallon per second, which for a 10-hour flight is 36,000 gallons, or 238,000 pounds of fuel burned,” he said. “The weight of a fully loaded Boeing 747-8 is 987,000 pounds, and the fuel weight is 416,000 pounds.”
As the weight of the plane changes, the physics of its flight range do, too.
One idea of how the aviation industry can combat climate change is to make aircraft more fuel-efficient: the less fuel needed, the less carbon dioxide emitted. Based on the large consumption of fuel that an airplane requires, it initially seems like gaining fuel-efficiency would be an unrealized task.
“The aircraft cruises at a rate of one mile every five seconds, giving a fuel burn of five gallons per mile. This is a measly 2/10 of a mile per gallon,” Dr. Gregory said. “That sounds horrible compared to the most fuel-efficient cars out there, which might have a fuel economy of 40 miles per gallon.”
However, Dr. Gregory said that the fuel efficiency of a car would be an unfair comparison because we aren’t taking into account the number of passengers in the car versus in the plane.
“A typical American car carries only one and a half occupants, on average,” he said. “If we define a metric of fuel burn per person, then we’re doing a much better comparison. [Let’s] express this in terms of person-miles per gallon.
“In this case, the car with two people at 40 miles per gallon achieves a normalized economy of 80 person-miles per gallon. But a 747 can easily carry 500 people, achieving a normalized fuel economy of 100 person-miles per gallon. On top of that, the 747 travels at a speed nearly 10 times faster than an automobile and can easily traverse inhospitable terrain.”
The next decade for Delta will consist of finding ways to improve those numbers while reducing waste.
Dr. James W. Gregory contributed to this article. Dr. Gregory is Professor of Mechanical and Aerospace Engineering at The Ohio State University. He received a bachelor of science degree in Aerospace Engineering from Georgia Tech and a doctorate in Aeronautics and Astronautics from Purdue University.