Hacker News Reader

Comment by JumpCrisscross | Hacker News Reader

> other being the geopolitical issues that arise from negotiating flight paths over various country's air space

Overture targets ICAO Stage 5 noise levels, the most stringent international noise standard [1].

[1] https://hmmh.com/resources/news-insights/blog/stage-5-aircra...

Boom is trying to build their own engine for the full size aircraft. That's tough. The number of groups that have built a reliable high-performance jet engine is very small. China still has trouble doing it.

The XB-1, the 1/3 scale model, uses standard General Electric J85 engines.[1] Old, reliable, not too expensive, and used by many prototypes over many decades.

[1] https://en.wikipedia.org/wiki/General_Electric_J85

> Boom is trying to build their own engine for the full size aircraft. That's tough

It echoes my criticism of Virgin Galactic checks notes ten years ago.

That said, Boom started dancing with the DoD in ‘22. That’s a deep pot of cash, and could help make up for inexperience.

Surely there is somebody with enough brains in the Pentagon to diversify their supplier base away from the moribund Boeing-esque incumbents, right? If they haven't learnt this lesson post-SpaceX, when are they going to figure it out?

A couple billion bucks is pocket change to the DoD, they literally "lose" it in their couch cushions, and it could eventually be the difference between "viable domestic defense aerospace industry" and "buy threaded steel nuts for $9000 each, with an 18 month lead time and 5000 pages of paperwork."

> Boom is trying to build their own engine for the full size aircraft.

Hahahaha. No.

That China still has trouble is one thing. The fact that Russia also has issues, with around 80 years of experience, tells you everything you need to know about how non trivial the task is.

Then again, SpaceX managed to pull their thing off, using modern tooling and some of the world's best rocket engineering teams. Russia and China, with all of their expertise don't have SpaceX's capabilities either. Supersonic jet engineering isn't exactly the same thing as rocket engineering, but they're related.

Appreciate the reference, I wasn't familiar with the ICAO noise standards.

If I'm reading things correctly it looks like Stage 5 caps out at 50dB, whereas a cursory search on the decibel levels for a supersonic boom comes up with 110dB.

That seems like a pretty large divide! Am I missing something?

Edit: A sibling comment appears to have addressed my confusion.

My understanding is that Boom is planning to implement technology that prevents sonic booms as we think of them.

IIRC their goal is to deflect it upwards with their wing and fuselage design.

> cursory search on the decibel levels for a supersonic boom comes up with 110dB

Short answer is we aren’t able to predict how loud a sonic boom will be [1]. Raw decibels produced at source is one thing. But you also have components like direction, dispersion (spatially as well as temporally) and frequency and how altitude and even moisture effect all that.

We’re making progress [2]. But the conventional wisdom is you need a perceived loudness on the ground that matches subsonic airliners to have a hope in hell of FAA approval. (Would note that a sonic boom in this context is not a physical phenomenon but summary of perceptions. There will always be an acoustic reaction to supersonic flight. But the far field effects that characterise a “boom” aren’t inherent to supersonic flight.)

[1] https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1...

[2] https://www.sciencedirect.com/science/article/pii/S037604212...

This is a lie. They write "Overture’s takeoffs will blend in with existing long-haul fleets, resulting in a quieter experience for both passengers and airport communities, meeting or exceeding ICAO (International Civil Aviation Organization) requirements for all subsonic aircraft operating over land and at or near airports."

Note that they are talking about takeoffs (and presumably landings) only where there isn't any sonic boom anyway, not cruising.

> This is a lie

Hell of a claim with zero evidence. By your logic, I could disprove the Sun by not observing it at night.

Yes, the ICAO rules are for takeoff and landing. When subsonic planes are the loudest. Concorde, for example, couldn’t have met these requirements.

We don’t know what Boom are targeting for in-flight noise. But we can guess, based on its parity with ICAO take-off and landing requirements, that it aims to match subsonic noise levels on the ground. There is strong evidence we can soften and disperse a high-altitude boom [1]. Whether it’s doable by Boom is an open question.

So no, it’s not a lie.

[1] https://www.nasa.gov/centers-and-facilities/langley/nasas-su...

What? I cited their own document to show that your claim was not about the sonic-boom noise (which is what people are worried about). You say yourself "we don’t know what Boom are targeting for in-flight noise".

What do you mean about "its parity with ICAO take-off and landing requirements"?

Reply on news.ycombinator.com