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Comment by hugs | Hacker News Reader

I haven't seen anyone directly address it in the comments here (or in the video): was an audible sonic boom noticeable on the ground during today's test flight?

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this plane doesn't look like it was made to produce a low boom. It has a very distinct von Karman ogive [1] fuselage and typical delta wings. I would guess that it's shape is primarily optimized for fuel efficiency at 1.5 mach or above.

If you take a look at NASA's low boom demonstrator [2], you can see that it's much skinnier and the nose is crazy elongated. This is intended to break up the bow shock into multiple parts, thereby decreasing the amount of energy each one has.

[1] https://en.wikipedia.org/wiki/Nose_cone_design#Von_K%C3%A1rm... [2] https://en.wikipedia.org/wiki/Lockheed_Martin_X-59_Quesst

Silly question, but would it be feasible to just equip a plan with a telescoping nose merely for this effect that could be deployed prior to supersonic flight?

Weight would kill the economics. It's not a fighter jet. But maybe it will be fine for drones. You should apply to YC.

Given that they were only authorized to fly in the "Bell X-1 supersonic corridor", I'd wager that sonic booms are fairly commonplace there. I doubt there are any residents around.

https://www.afmc.af.mil/News/Photos/igphoto/2003098938/

There are residents for sure in that corridor, but the residents are on Edwards AFB, and are fairly used to sonic booms. When I was on Edwards, there was still the last operating SR-71, and that boomed any time it flew.

Noticeable is certainly a way of putting it.

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

>However, in the first 14 weeks, 147 windows in the city's two tallest buildings, the First National Bank and Liberty National Bank, were broken.

If a sonic boom is "noticeable", that's one thing. But the problem is that even from cruising altitude they're shockingly loud. If the sonic boom is merely bearable, that's quite an improvement.

Right, and making an improvement is a big part of Boom's marketing. (It's in their name?!) I'm surprised I didn't hear them make any comments about it in the video during the flight as they crossed the sound barrier each time. Unless I missed it?

It's not something they probably want to draw attention to (despite the name), because it is a barrier to allowing these kinds of flights over land.

No, it's the whole point of Boom. They won't be able to keep the sonic boom a secret. They whole company's future hangs on making that sonic boom minor enough that supersonic flights will be allowed with few restrictions. Therefore asking what the boom was is perfectly fair.

Now, Boom might say (have they? I'm not following them) that the XB-1 is a demonstrator that they can do supersonic flight, and that the sonic boom reduction work will follow on. In that case asking what today's boom was is not that interesting.

The chase planes also went supersonic, so they would have contributed to the sonic boom, which might complicate that analysis (well, there would be at most 3 pairs of sonic booms, and it should be possible to tell which ones correspond to which planes).

I'm not criticizing anyone for asking how loud the boom was. I'm telling you why they didn't provide that answer unprompted.

GP was asking about this flight's sonic boom. That's the whole point of Boom: to make supersonic airplanes with small sonic booms.

First confirmation I've found so far on this exact question: "XB-1 is supersonic! (No boom audible here, as expected)" - Jon Ostrower https://bsky.app/profile/jonostrower.com/post/3lgsvea6zbs2x

Raises more questions though, because there were two other chase planes. Did the other planes stay below the sound barrier at all times?

Edit to add: Was no audible boom expected because of the planes themselves or because of where the people were watching from?

With planes being long enough away from the demonstrator, and speed of sound relatively low (about 330 m/s), the booms of all three planes should be separate enough, e.g. a good 100 ms away from one another, even if all three went supersonic and were dragging their respective shock waves.

The distance between the planes appeared to be around 30-50 m at the supersonic transition time, as much as I can estimate the size of the planes. A sound recording made under the flight path should allow to measure how many dB was the demonstrator's boom.

I don't see the problem? I was just saying that "not noticeable" is a really high bar to set for a supersonic flight.

But your first sentence reads like a direct answer to the question:

> Was the sonic boom noticeable?

> Noticeable is certainly a way of putting it.

As in, "Yes it was noticeable, and then some." At least, that's how I read it.

That's not even close to what I intended.

This doesn't say anything about today's flight though?

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