Why can't aeroplanes fly faster?

23 November 2014

Question

Love your show; listen to it on podcast. Also thank you for answering a few of my questions in the past (survival time in sealed car, coughing while cleaning ear).
I was on an interminable flight from New York to Hong Kong a few days ago, and I don't understand why are Boeing and Airbus not working on increasing the speed of air travel? They have worked hard to improve the seat comfort, entertainment and food, but heck, if they just shortened the trip by 50% that would please me 500%. Are we going to be forever stuck in this air speed? What are the constraints of aerodynamics? Are noise rules the issue? Can a supersonic jet be ever built with "decent" fuel economy? Will we ever see another "Concorde" in our lifetime?

Answer

Sara - This week, we buckle our seat belts ready for takeoff with this question from listener, Paul Jenn.

Paul - I was on an interminable flight from New York to Hong Kong a few days ago and I don't understand why airplane manufacturers aren't working on increasing the speed of air travel.

Sara - So, why can't we fly just a little bit faster? Is it a case of better design and engineering or will we be stuck at this slow speed forever? Well, we're off to a flying start as Neil Scott, head

of engineering at Airbus shot back fast with this answer...

Neil - In short, speed costs fuel and money. If you're driving your car at 40-mile an hour and then accelerate to 80 miles an hour, what happens to fuel consumption? It goes up. The same is true on an aircraft. The faster you go, the more fuel you burn. Drag, which causes the increase of fuel burn, is actually proportional to the square of the speed [addendum: energy to overcome drag is proportional to the cube of the speed]. So, drag increases at a faster rate than increasing speed. So, you can't just get there more quickly, you have to pay for it. One of the biggest costs for an airline of course is fuel, therefore the likelihood of us designing a supersonic aircraft for major commercial flying is probably not going to happen anytime soon.

Sara - Basically, more speed means more air resistance, means that cheap holiday flight you were planning on booking won't be so cheap anymore.

Neil - Another advantage of decreasing fuel burn of course, is there's less CO2 emissions, less nitrous oxide emissions and less noise, so we all win.

Sara - Well, it's good to hear that we all benefit from flying slower, but is it a flight fancy to think I won't be stuck in the air for 13 hours at a time as a jet setting grandma?

Neil - At the moment, it's not possible to build a super efficient plane that's also super speedy and cost-efficient. But with future innovations in propulsion systems, that's engines, based for example on hydrogen or electricity, it might well be possible in the future.

Sara - Thanks, Neil. Maybe someday then. In the meantime Paul, maybe try to get some shuteye on the redeye. For next week, Matthew Boniface wrote in this yawn first of a question...

Matthew - Why do I yawn and why do cats yawn and can I catch a yawn from a cat?

Sara - What do you think?

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