B-52 from inside the bomb bay
rhomboidus: Commercial airliners fly just under the speed of sound, and have for a while now. They do this because supersonic flight is *much* more expensive. It requires very expensive new aircraft, burns a ton of fuel, and is outlawed over land in many places because of sonic booms.
A few supersonic commercial aircraft have been tried, but they were not successes. Turns out most people aren’t willing to pay five times as much to get there twice as fast.
BaKdGoOdZ0203: Flying faster uses more fuel. Fuel is by far the most expensive cost to the airline. They fly at the planes best fuel efficiency. This is the “same” as decades ago because as you get close to breaking the sound barrier, it’s physically more difficult to go faster (uses more fuel than its worth).
The deciding factor for the vast majority of travelers is cost, not time. Airlines care about costs, to keep prices competitive.
Edit: I’m half asleep, and poorly summarized [this video](https://youtu.be/n1QEj09Pe6k) check out their other videos on airplanes and airlines. It’s fascinating (to me at least)
Flying_pig2: The short answer is this, when a aircraft flies faster then the speed of sound it suddenly becomes a lot more expensive to operate. Even though it spends less time in the air it still costs a ton more to fly above the speed of sound then just below it, so in the interest of reasonable ticket prices airliners stay just below the speed of sound.
Here’s the long answer, sorry if I don’t simplify this enough as it is more advanced. Sound is pressure waves moving through matter, whether that be wood, rock, metal or air. This speed at which this pressure waves moves can vary between material and how tightly packed that material is but what’s important for us is that it’s always around 343m/s in our atmosphere. Now well that is the speed the wave moves at, what’s more important is why it moves at that speed. That reason is because a pressure wave (sound) moves by particles being hit in a constant direction and hitting other molecules of air and transferring energy to them, in a way similar to a [Newtons Cradle](https://d2t1xqejof9utc.cloudfront.net/screenshots/pics/3caab7ab1b658c3218a521cb7a6e73c3/large.gif). The closer, or more dense the air is the faster this can occur.
The way this all relates to aircraft is that, wave speed is constant regardless of how fast the input (an aircraft) is moving, this in effect makes it so that the speed of sound also is the speed at which air moving away from an object it collides with. This result of this is that as an aircraft goes faster then the speed of sound the molecules of air move away slower then the plane moves forward. As a direct result of this, the pressure of the air in front of the wing suddenly increases dramatically because instead of moving away in sound waves it’s now bunched up in one spot forming an area of much higher pressure which creates the distinctive sonic boom. Higher pressure does more then just create a nice boom though, it also creates considerably more drag since the aircraft now has to push more air out of the way then it did before, which results in higher fuel costs since the engines have to burn more fuel to maintain said speed. There’s also a lot of other REALLY weird effects that going supersonic has but that’s the jist of it.
The above is why airliners don’t go supersonic, however most airliners actually cruise at Mach ~0.85 (mach is % speed of sound) instead of literally just below it (Mach 0.99). The reason for this is actually pretty straight forward, wings work by having lower pressure on top of the wing and lower pressure on the bottom of the wing. The way this pressure differential is achieved is by having the air on top of the wing moves faster then air on the bottom of the wing (The physics behind that are far beyond the scope of even this wall of text, so just [watch this](https://youtu.be/QKCK4lJLQHU) if you need to know more). This means that the air on top of the wing will go faster then speed of sound before the entire aircraft does, along with the increased drag that incurs (and even worse stuff like control surfaces tending to not work). This are is called the transonic region (trasnition and supersonic combined) and well planes can and do fly in this speed range it’s simply easier and slightly cheaper to keep them that little bit slower.
ok, so that was the aerodynamic side of the issue, here’s the governmental side of the issue. Sonic booms are loud. really loud. Like 60,000ft isn’t enough to not make them annoying loud. Therefore it’s illegal to fly supersonic over the US (except in certain designated corridors). This means that any supersonic aircraft could only service overseas routes like the Concorde’s New York to London route. In reality this isn’t actually *that* bad since long haul routes are what really fast planes are good for, what does make it bad is that it cuts off the entire trans-continental market. Even then though it wasn’t, and isn’t the sonic boom that makes supersonic transports non-viable.
The other two hurdles that aren’t the laws of physics (at least not directly) are the ozone layer and takeoff noise. Supersonic transports typically need to fly really high in order to reduce drag and dissipate heat better, that alone isn’t a problem. What is a problem is that they fly so high that, at least in the 60’s when the Concorde was coming out, people believed that they might make a hole in the Ozone layer. I don’t know if there’s scientific truth to that statement, but it did hurt the development of the Concorde so I feel it should be listed if only briefly. The other factor was noise at takeoff and landing, long story short the Concorde used jet engines that were much louder then jet engines used on normal airliners (and it goes to reason any new supersonic plane will need them as well), to be more specific there were straight up afterburning turbojets which is as loud as you can get jet engine wise (I used to have a old ELI5 for this but I can’t find it). These engines were so loud that pretty much every airport the Concorde was planning on servicing banned it, minus the ones on the trans-atlantic route between New York/London, and a few other cities (not that they didn’t try). This caused everybody who wanted a Concorde to suddenly not want a Concorde and Air France/British Airways got stuck with it.
So those are the problems facing a supersonic transport as well as why we don’t have them anymore. But why is nobody trying to make one? Well, some people are, but those companies are dubious at best (not saying they won’t succeed, just saying we’ll see the Spanish inquisition coming before I predict it). Thankfully this is the one part of this topic that is simple (hallelujah). Developing an airliner, or even a business jet is stupid expensive. For example, Boeing barely turns a profit from it’s 787 (at least I think they did) and that’s a conservative guaranteed to succeed type design. A supersonic transport is a massive gamble in an industry where there is no room to gamble. Bar government funding of some sort or a massive improvement in drag reduction (among other things) making these things feasible we’re really not likely to see a supersonic transport anytime soon.
That’s why airliners stay at about that max speed, but why don’t we go even slower to save more money? Simple answer: people thought that would happen but it’s all around better to go faster until drag starts getting exponentially higher. Long answer: it’s time for a history lesson. After WWII and the invention of the jet engine it didn’t take long for people to figure out how to make very powerful propeller engines that used a jet engine to spin the propeller instead of a piston engine (commonly known as a turboprop). When these came out aircraft manufacturers thought that these engines would simply replace the increasingly complex piston engines airliners were starting to utilize since the turboprops were far more reliable and all around simpler. They were aware of straight jet engines (called turbojets) but simply thought they were to unreliable and inefficient to catch on. This gave rise to planes like the [Lockheed Electra](https://en.wikipedia.org/wiki/Lockheed_L-188_Electra). Inevitably people tried putting turbojets into airliners but, that ended up in the [Comet](https://en.wikipedia.org/wiki/Comet) which was… not a good plane (it had an issue of breaking apart mid-air). So people still thought turboprops would be the way of the future, then Boeing released it’s (https://en.wikipedia.org/wiki/Boeing_707) which was hugely successful and resulted in other companies rushing to catch up with planes such as the [DC-8](https://en.wikipedia.org/wiki/Douglas_DC-8) (To be fair, this was just as much a way for Boeing to make a jet tanker as well). After the success of both of these planes a turboprop simply couldn’t compete since jet’s were faster and about as expensive, though they still are sometimes used on short routes where speed is less of an issue .
beardedengineer7: The Concorde was a super sonic jet that cut travel time significantly. However, the cost to operate was a huge drawback. Also, flying super sonic above the continental U.S. isn’t allowed by passenger planes. The Concorde required an additional engineer in the cockpit raising operation costs. Overall it’s cheaper to operate as is. I believe that Boeing is pursuing super sonic flight again though so maybe in the future that will change!
thegreedyturtle: Since the reasons have been pointed out already, I’ll mention that Elon thinks the next advance will be bug fuckin rockets. (His term btw.)
kouhoutek: The speed of sound forms a natural barrier to aircraft speed. The amount of energy needed to go fasters increases significantly as you approach the sound barrier, as do the stresses on the aircraft. It takes a completely different design to fly at supersonic speeds, and about three times as much fuel.
morbidlyobesemarcus: You’ll be suprised because the majority of commercial planes flying today were designed before the new century. But that’s irrelevant. The biggest reason is that on shorter and more dense routes with higher traffic, regardless of how fast a plane can go max speed, they may need to slow down for sequencing. However on longer and less populated routes these routes have gotten faster.
Edit: Cost index is something to look into also.