Two different manufacturers unveiled supersonic jets at this year's Paris Air Show, eight years after the Concorde stopped flying. The introduction of the new planes got the Explainer thinking—why hasn't commercial air travel gotten any faster over the last few decades?
Fuel efficiency, among other things. Commercial airlines have slowed down over the last three or four decades. Today, flying from New York to Denver takes 19 more minutes than in 1983, and a flight from Washington, D.C., to Miami takes 45 more minutes than in 1973. The primary reason for such sluggishness is the cost of fuel. By the laws of physics, drag is approximately proportional to the square of the speed, so even a slightly faster flight requires a lot more fuel. Hiking a plane's velocity by 10 percent takes 21 percent more energy. * Speeding up by 40 percent approximately doubles fuel consumption. Shorter flights can save airlines money on labor, but not enough to offset the loss in efficiency. (Fuel represents about 35 percent of the cost of a flight, whereas personnel expenses constitute 30 percent.)
Fuel isn't the only reason for the slowdown. In the 1960s and 1970s, most personal and corporate planes were propeller or turbo-prop aircraft, which fly at a lower altitude than jetliners. That kept them out of the way of large commercial aircraft. Today, most bigwigs fly jets, and their gain is our loss: Not only are more planes using U.S. runways, but passenger jets must reduce their airspeed when they get caught behind a corporate CEO.
There have also been changes in the way airlines report flight times, which makes them seem longer than they actually are. When airlines started disclosing their percentage of on-time flights in the mid-1980s, they added a few extra minutes to the scheduled times to increase their apparent punctuality, a practice known as block padding.
Manufacturers are technically capable of producing faster planes, but there isn't much demand for them outside of the military. In 1961, American manufacturer Convair released a commercial jet that could reach Mach 0.91, meaning 91 percent as fast as sound. That's significantly faster than current design speeds, which range between Mach 0.78 and Mach 0.82. Even though fuel cost less than 50 cents per gallon back then, few airlines were willing to give up fuel efficiency for the sake of speed.
As for the supersonic planes introduced at this week's air show—they fly more than 25 percent faster than the average jetliner. But even if they make it to market soon, don't expect to be zipping around the country at the speed of sound. Supersonic flights are allowed only over water—and are thus limited to connecting wealthy cities separated by an ocean—because sonic booms can damage things and annoy people on the ground.
Got a question about today's news? Ask the Explainer.
Explainer thanks Robert W. Mann of R.W. Mann & Company Inc. and Tim Neale of Boeing.
Correction, June 28, 2011: The original stated that the increase in drag is equal to the square of the increase in speed. (Return to corrected sentence.)