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Comment by sandworm101 | Hacker News Reader

Delays happen. That is normal. I am more worried about the slip in speeds. "Traveling at Mach 2.2" becomes "could fly at Mach 1.7". That is a radical loss of performance. It is more than just 0.5. It is a switch from traveling at a speed to "could fly", a theoretical top speed for the same aircraft. I think they are facing solid engineering challenges and are having to reduce expectations.

FYI, most airliners already fly at or above 0.85 Mach. 1.7 is faster than 0.85 but operationally it will only be only an incremental decrease in total travel time.

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The sweet spot for civil supersonics from an aircraft design standpoint is less than Mach 2. You can maintain good propulsion system performance without variable geometry inlets, boom strengths are lower, aeroheating loads are lower, fuel burn is lower, etc. Operating expenses will be significantly lower for such an aircraft. Maybe Boom is finally realizing the importance of all this as well.

Whether that's enough travel time reduction to make these aircraft worthwhile is definitely a valid question. The low-boom technology that NASA is pursuing is for sub-Mach 2 aircraft (I don't believe Boom is pursuing a low-boom design, but I haven't followed closely as I don't consider them a credible organization either).

A halving in speed sound amazing!

A halving in speed would be surprising, at least.

Even if we say doubling instead of halving, I assume that the total portion of a transatlantic flight that it could travel at top speed would be pretty small, so the total time might still be more than half.

other than lower speeds during approach and departure around controlled airspace with speed restrictions, the overwhelming majority of a transatlantic flight will be at full speed.

of course, there are exceptions with congestion, hold patterns, excessive vectoring, etc, but this is generally true.

another thing to keep in mind is headwinds/jetstream. when going west across the atlantic; they can often be 100+mph. so the delta between boom and eg. a 787 becomes even more pronounced in this situation.

It’s not like the 787 can’t also make use of the jetstream.

Typical height of the polar front jet stream is 30-40,000ft, that's great for a 787 that's most efficient exactly in that altitude range. But doing mach 1.7+ you want to be much higher for efficiency, so it's entirely likely that the Boom plane will miss the jet stream.

They're talking about going against the jetstream, so that doubling air velocity means more than doubling ground velocity. If the boom plane gets to miss the jet stream entirely that only improves the situation.

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