# Why does speed lose out to capacity?

The Concorde had a maximum speed of 2.05 Mach, carrying about 96-128 passengers. The Airbus A380 can achieve a top speed of 0.95 Mach with more than 500 passengers on board. This means roughly 5 times more passengers can be accommodated by compromising half of the top speed. So, why does speed lose out so much to capacity that it ultimately becomes unfeasible to operate a supersonic airliner?

• There is somewhat flawed logic in your question, implying there is relation between speed and capacity. The ATR-42 has a top speed of Mach 0.55 and can carry about 42 passengers. Comparing it to the Concorde we see that it goes 4 times faster with twice as many passengers. This must be a quadratic relation. We therefore know that the A380 should be able to fly Mach 7 if they only tried a bit harder. – DeltaLima Jun 19 '15 at 8:10
• @DeltaLima Based on your numbers, it seems that faster-than-light travel should be possible for any vehicle containing more than about 77,000 passengers. Why are large sports stadia so slow? – David Richerby Jun 19 '15 at 9:58
• @DavidRicherby: Compatibility with existing runways. Most are just not long enough to get a sport stadium up to speed. – MSalters Jun 19 '15 at 10:02
• @DavidRicherby If the OP's logic is correct those large sports stadia should be moving with the speed of the tectonic plates which is indeed so and hence proves he's right. I retract my comment :-) – DeltaLima Jun 19 '15 at 10:03
• @DeltaLima: actually on these numbers, a sports stadium moves faster than a tectonic plate, as demonstrated by the fact that both the Giants and the Jets move faster than New York City. Similarly, the 49ers stadium has recently left San Francisco. The long-term record is either the Cards or the Rams, I forget which, and the Raiders stadium is migratory. – Steve Jessop Jun 19 '15 at 10:22

## 5 Answers

Which means, roughly 5 times more passengers can be accommodated by compromising half of the top speed. So, why does speed loses out so much to capacity that it ultimately becomes unfeasible to operate a supersonic airliner?

I think you are asking, "why do supersonic aircraft have such low capacity"?

To travel faster than the speed of sound you need to have a very sharp nose and minimal area exposed to the forward direction, to minimize the generation of shockwaves. Shockwaves are bad for people on the ground (the 'sonic boom' effect) and they are terrible for fuel efficiency. Second you really do not want to trap air on flat surfaces facing forwards, because the air will get squashed in the supersonic flow and heat up a lot (like when you blow up a bicycle tyre or a football it is warm afterwards, or when the space shuttle re-enters the atmosphere). Again this is an enormous drag and having hot air flowing around your aircraft causes problems with the structure (Concorde used to grow by 300 mm during flight because of the heat).

Since you cannot be wide and you cannot be tall (without being aerodynamically inefficient), you need to be very long if you want lots of people. And then you have other problems.

The design and construction of Concorde was never a commercial project, it was funded by two governments almost as a vanity project, as a prototype or as an experiment. Then it was given for free to two airlines to use as they wanted.

So unlike the A380 and the B747, no one has ever said "now we try to maximize the economics and the capacity of our design": that never happened. All they ever asked was "How do we make this work!?"

Whereas the subsonic aircraft get a lot of time, money and thought spent on how to make them more economical to use by filling them with more passengers.

For more information I recommend this interview with a former Concorde pilot: http://omegataupodcast.net/2015/02/166-flying-the-concorde/

Also, Concorde was developed 40 years ago. Are some more efficient supersonic Airliners possible today?

I am sure that these days a far more fuel efficient supersonic engine could be built for passenger operations. And I do believe there would be a market for it on say LON-NYC or even maybe LON-DXB. But designing supersonic aircraft is quite different to designing subsonic ones; and then you have all the difficulty of modern safety regulations without being able to demonstrate you are relying on old, proven designs; and then there are very few routes where it could work profitably so you have very high development and maintenance costs spread over a small number of airframes.

Basically, it isn't worth the risk to anyone to make it.

• The technical (size) constraints feed into economic/business ones as well: Something like Concorde costs a lot more per seat-mile which comes with correspondingly higher ticket costs (and if you don't fill the plane you may be operating the flight at a loss). By comparison a 787 hauls more people and has a lower per seat-mile cost: You can attract more people at a lower ticket price, and reach a profitable capacity more easily. – voretaq7 Jun 18 '15 at 19:55
• @voretaq7 I agree, but on a small number of routes such as LON-NYC, the operating costs were not hard to meet. The famous story at BA is that they used to do surveys of Concorde pax to find out what they should charge, but almost no one knew how much they had paid in the first place! So BA increased the price with zero effect on demand. – Calchas Jun 18 '15 at 19:57
• @Calchas even better, BA originally charged the same for Concorde as for their regular service and couldn't sell the tickets. When they raised the price, and launched a campaign promoting it as a "premium service" and built an image of Concorde as the ultimate in luxury and class, people started buying the seats and Concorde became profitable. Those people hadn't wanted to fly in the cramped Concorde seats before the price went up, but now they could brag about buying the expensive premium service their friends/competitors couldn't afford... – jwenting Jun 19 '15 at 5:37
• @jwenting Actually that makes perfect sense. Underpricing a premium service is the same as trying to sell an overpriced value service. The pricing must match the market segment. And knowing what it is you are selling does help... Not in marketing, and I have still run to people wondering why making their products cheaper dropped sales... It really does happen, weird as that sounds. – Ville Niemi Jun 20 '15 at 16:18
• @jwenting Well, on a competitive market you generally get what you pay for. Meaning if you buy more expensive, you are less likely to get fired for buying a lemon. There used to be saying "Nobody got fired for buying IBM" to that effect in the early neolithic when IBM still sold PCs. Additionally, more expensive the decision was, the more committed your bosses are to it and less likely there is to be failure that you will get blamed for due to inadequate budget or leadership failure. Failures caused by saving money are generally very expensive. – Ville Niemi Jun 21 '15 at 0:32

There are a few questions here but ill mainly address this one

Also, Concorde was developed 40 years ago. Are some more efficient supersonic Airliners possible today?

First off there is at least one company who has said they are working on this mainly for the high end market but working on it none the less.

Boeing took a crack at it years ago but the program was eventually stopped.

The primary reason that no super sonic aircraft have been developed since the Concorde is because the FAA prohibits super sonic flight over land. This means a few things. First off you limit your self to routes that are primarily if not only over water. Which means that you limit who you can sell the craft too. This of course makes it unattractive to a company from a production/cost stand point. Now you are probably thinking, why not fly sub sonic over land then hit the throttle when we turn out over water. This sounds great but generally the aerodynamics that make a super sonic plane a super sonic plane are not great at the lower speeds in the spectrum. Could something maybe be designed, sure, but the market is clearly limited.

Cost is the main driving factor in aviation. It is cheap to develop a new car and bring it to market but planes require a much more stringent process which reflects in their price. As such airlines (and even GA consumers) want to get as much out of a plane (time wise) as they can. Supersonic aircraft experience stresses and heat that their subsonic counter parts don't. This makes them unattractive to potential buyers since the planes need more support to be kept in the air.

• Modern (as in the last 30 years or so) fighter jets are designed specifically for desirable trans-sonic performance at both high subsonic and supersonic speeds. the F-22 can supercruise (supersonic speed at military power, no afterburners). So you're right on both counts here; we have the technology, but cost and U.S. federal law are huge reasons it hasn't been done since Concorde. – KeithS Jun 22 '15 at 22:28
• Most other countries prohibit supersonic flight over land, too (some, but not all, have exceptions for military aircraft). – Toby Speight Mar 23 '18 at 13:35

I think this is a question about "how to design/build an airplane"... First of all, the Concorde was designed to have a 2.05 mach velocity and carry on 96-128 passengers, and the A380 was designed to have a 0.95 mach velocity and carry on ~500 passengers. This does not means that the A380 compromisses velocity over capacity. Someone could design and build an airplane to carry on the same amount of passengers as a A380, but fly as fast as the Concorde did. This hypothetical airplane must be VERY dificult and expensive to build and very expensive to operate, and surely non airport on Earth has ben build to handle it. When you design an airplane, the first thing you must have in mind is "what is this plane for?", because you are trying to "supply a demmand", and not trying to see "who would buy this s***t?". When an airline buys a plane, they have in mind

• This plane is going to fly from this airport to that specific airport in that specific path.
• XXX amount of passengers are going to buy tickets.
• To maximize the incoms and minimize the outcomes the plane I should by is: ***

The main reason that no commercial supersonic flights are aviable today is because the are very expensive and don't have many routes to cover. I mean, althou some airlanes would buy 3 or 4 "Concorde like" planes, any plane manufacturer will design and build just a houndred planes. It's just not profitable.

• "An engineer is a person that can build with a dollar what any idiot could build with ten". If you subscribe to this definition of "engineering", the Concorde wasn't even engineered. – Jörg W Mittag Jun 18 '15 at 21:04
• Planes aren't necessarily bought for the specific purpose of flying a single route their entire careers, especially when you talk about U.S. domestic air traffic. It happens with the big widebody airliners largely because there are very few routes that call for such a large plane in the first place (ultra-long-haul, mainly). On domestic routes, it's usually more economical to fly more, smaller jets than fewer larger ones. It also creates some convenience for the passengers, as they have their choice of flight times. – KeithS Jun 22 '15 at 22:53
• @KeithS You are totally correct. But I think you are missinterpretating a little my words. Planes are not necessarily bought for an specific purpose, but are bought to supply specific necessities. I mean, an airline wont buy a plane that result very small or very big. They know what they need. – algolejos Jun 23 '15 at 3:59
• Very true, and correct. Airlines buy what they need to service the routes they plan, taking into account flight range, passenger demand, flight frequency, airport capacity (fewer flights per day between two congested airports with a widebody might be a sound plan, but some airports just can't accommodate one) etc. Right now, airlines are more or less keeping the "smaller planes, more flights" model, but Airbus predicts that airport congestion will require a switch to widebodies on major U.S. domestic routes in the next couple of decades, – KeithS Jun 23 '15 at 4:03

Mainly, cost.

Flying supersonic consumes a vast amount of fuel. In this day and age of bargain airfares, a London-NYC round trip ticket on Concorde would set you back anywhere from USD8k-20k, depending on what sort of discount you could get. At the same time, the bargain airlines were offering $500 round trip tickets over the same route. A good deal of Concorde's passengers were first class who used frequent flyer miles to upgrade to Concorde. The 787 has become a best seller, because it offers 15-20% better fuel economy than older models. That's what the customers want, not half the time at 10-20 times the cost. Also, due to the fact that most nations have banned supersonic flight over their land due to the sonic boom, for reasons that the Oklahoma City supersonic tests revealed in 1964, supersonic flight is limited to over ocean flights only. It couldn't be used on the very busy long over land routes, such as transcontinental US, or Europe to Asia. Building a very complex aircraft that could only operate on a few routes limits the number of aircraft that could be sold, which adds considerably to the development and operational costs. It is no coincidence that the Concorde, TU144, and Boeing 2707 were originally envisioned when oil was$3/barrel, in the early 1960's. When oil prices shot up in the early 70's, making supersonic flight hideously expensive, the 2707 was killed off and the TU144 sort of killed itself. Since the Concorde was already built at that point, they put it into production, but rising energy prices limited it to 14 aircraft for the flag carriers of Britain and France. The rest of the airlines bailed due to the very high cost.

It's not that we have regressed technically since the 1960's. More that the price of energy increased to the point where a supersonic airliner isn't economically feasible.

The social environment and world events also came into play for the Concorde. Read 1/2 down in this article: https://www.theatlantic.com/technology/archive/2015/07/supersonic-airplanes-concorde/396698/

Whereas most Concorde takeoffs and landings were warmly attended, others became protest sites. Money aside, Concorde had other challenges. Noise and environmental concerns shrunk the open skies. Many countries banned it from their airspace because of the loud sonic boom it produced. As a result, nearly half the planned routes, notably those over land, were off-limits. The crucial “Blue Ribbon” route between New York and London was miraculously approved in 1977. Whereas most Concorde takeoffs and landings were warmly attended, others became protest sites, with signs reading: “Ban the Boom” and “Save the Ozone Layer.” The Anti-Concorde Project founder Richard Wiggs was the face of this movement, publishing advertisements, organizing demonstrations, and calling Concorde “elitist and inherently unsafe.” Aviator Charles Lindbergh, the first to fly transatlantic in 1927, became an active environmentalist later in life and lobbied against supersonic travel. Ozone emissions and atmospheric pollution were the greatest environmental concerns and turmoil over the loud, disruptive boom that had the power to break windows were constant contentions.