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Comment by bscholl | Hacker News Reader

Unfortunately, there's a ban on supersonic travel over land in the US since the 1970s. When this is reversed, we can fly SFO-JFK in about 2:20.

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Would it make sense for you to fly West from SFO, turn around, go super-sonic over the ocean and fly towards NY — then again, decelerate over the Atlantic, and turn back?

i.e. what is the distance from the shore you can boom?

Sonic booms are continuous while going faster than the speed of sound. It isn't just something that happens when you cross the barrier.

... Sonic booms happen anytime you're going supersonic speeds, it's not limited to when you cross the boundary.

https://en.wikipedia.org/wiki/Sonic_boom

Everywhere the plane is supersonic, it emits the boom. Your question implies that the only boom is when you "go super-sonic."

http://physics.stackexchange.com/questions/68354/is-a-sonic-...

Would a Mach 1 plane hear a boom if overtaken by a Mach 3 plane?

http://aviation.stackexchange.com/questions/17243/does-a-mac...

I understand why you got downvoted, but I don't think the question was actually repellant. If it were at the top of the thread it would be annoying but here I find it a fun thought experiment.

Didn’t get down-voted overall so fine on that end.

I actually never though of the existence of a continuous cone of focus outside of the plane — the graph I had seen were all focused on the whether the plane heard it.

I guess an alternative option would be to find routes above the polar circle, or through the narrow of Central america — but the increased distance would make it less interesting at “just” Mach 2.2.

The sonic boom isn't created when the aircraft transitions through the speed of sound. Although I never hear it explained this way, I believe it is caused when the velocity of the aircraft with respect to the listener transitions the speed of sound. That's when the sound waves approaching the listener bunch up and cause the boom.

When the aircraft is directly above a listener on the ground, the relative velocity is zero, so you can see how the velocity changes from greater-than-sound to less-than-sound (twice) as the aircraft is approaching and then departing with respect to the listener. Thus the listener hears 2 booms.

The boom is usually explained in terms of shock waves emanating from the aircraft, but I think my description explains the phenomenon just as well, but more intuitively.

slight correction to the above: there is no second boom heard by the listener when the aircraft is flying away from the listener faster than the speed of sound. The listener the would simply hear no sound.

As others have said, the boom is continuous. However, what you could (and presumably would) do is gain altitude at sub-sonic speed, then go supersonic only once cruising altitude is reached. That should help with volume. Also presumably they would avoid flying over major population centers.

Is the boom attenuated by flying through much less dense air?

Possibly! Certainly if the plane was traveling in a vacuum it would produce no boom, so one would assume that the boom would be reduced as the air became less dense. However my understanding is that most of the advantage from altitude comes from the attenuation (or really spreading out) of sound with the square of distance.

Since hearing response is logarithmic, the inverse square law probably isn't as helpful as you'd expect.

What's the regulatory situation in countries other than the US? Europe, Asia, Canada, Mexico, South America?

It's complicated and unclear, unfortunately. We'll have to see how things unfold when the airplanes are flying.

Might be an idea to spend a little more time on that.

The engineering is not the hard part here.

Without regulatory support and approval you don't have a product or a market, so "Let's worry about that after we get the prototype working" may not be a fully viable strategy.

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