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Comment by d_silin | Hacker News Reader

Blended-wing body makes a lot of sense for cargo/tanker aircraft. No issues with emergency evacuation procedure for passengers.

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Has it been evaluated whether any real-life evacuations were time sensitive enough to where a wide bodied plane would have resulted in more deaths? Doesn't seem like a real problem intuitively, but I don't really have any data to back that up.

Do they do all those evacuation tests with able-bodied volunteers? How would they evacuate for example five wheelchair users within the 90 seconds or whatever is required for the test?

That's what I'm getting at though. There are imagined criteria for these tests, but what has the real life situation been in actual emergencies? Have there been enough real life evacuations where getting everyone out within 90 seconds vs 3 minutes was the difference in saving many lives?

All airliner safety features are objectively pretty pointless given that cars remain legal and routine with like 100x the lethality. But yes, there have been at least a handful of cases where some but not all of the passengers were able to get out of a plane in time, particularly when the plane caught fire on landing (e.g. Air Canada 797).

> 90 seconds vs 3 minutes

That's a huge difference in case of a fire. Ninety seconds of smoke filled, oxygen deprived, or hot air, and many people will make it out alive. Three minutes and most will have passed out.

There's quite a few instances of burning planes being evacuated where not everybody, but a sizeable portion, made it out. Seconds matter*.

* Almost always there was some idiots slowing everything down by grabbing their luggage.

That's obvious. But I just made those numbers up - they aren't important to my point, which is that I'm asking if there is any real world data on evacuation timing.

All those instances where not everybody - but some - made it out of a plane that caught fire but where the passenger cabin was otherwise intact, physically allowing the evacuation of conscious passengers.

Here's a good example because it has a clear cutoff point: "Less than 90 seconds after touchdown, the interior of the plane flashed over and ignited, killing the remaining 23 passengers on board, who died from smoke inhalation and burns from the flash fire."

https://en.wikipedia.org/wiki/Air_Canada_Flight_797

It seems obvious that a faster evacuation would have saved more people and a slower one less, roughly proportional to speed of evacuation.

Not only is the test with able bodied people, they also are permitted to practice first to make the time.

But - the test handles this by only giving them 90 seconds. In the real world it would take far longer, but rather than testing a longer, more realistic test, they do a really fast one instead.

The test is about whether such an evacuation is theoretically possible, not if it is realistic under any conceivable circumstance (half the plane gone, blocked exits, plane resting at an incline, smoke and/or fire and/or water in the cabin...).

If the happy-path evacuation isn't possible to begin with, e.g. for design reasons, the more complicated realistic ones will be negatively affected as well.

Aircraft fires can escalate extremely quickly, and in an enclosed space like an aircraft there's nowhere for smoke to go. Accidents also often result in less than optimal evacuation conditions. Fire may block exits, doors can jam, slides can fail to deploy, all of which slow down the evacuation. I've spent way too much time watching the Air Disasters show [0] and off the top of my head remember at least half a dozen or so accidents portrayed in the show where a plane was evacuated in minutes but some passengers were killed by fire or smoke because they couldn't get off in time. I'm not saying that wide body planes couldn't be evacuated quickly or safely (haven't really looked into them at all) but I don't think it's a situation where you can just say, wide bodies are more slow to evacuate and that's no big deal.

[0]: https://www.smithsonianchannel.com/shows/air-disasters

Also no issues with passengers caring that they don't have a window seat, or aren't even anywhere near in the view of a window.

So I flew Emirates First the other day. They now have virtual windows in some suites, which are linked to cameras outside of the plane. That worked surprisingly well, and after a few moments I forgot about having booked an aisle seat.

I would expect this to eventually be rolled out more widely and later replacing real windows, which are structural weak points of the hull and heavy. Also, for our Ryanair no-frills flyers: they are screens where you can show ads.

For the Emirates experience, see https://www.youtube.com/watch?v=VdDzaNlGSmk

I thought that the main disadvantage with flying wings for passenger traffic was that any kind of roll is made much worse the further you get from the main roll axis, so turbulence etc becomes more uncomfortable in the wing part.

I believe that is somewhat offset by having larger rotational inertia as more mass is further from the center. That does however, necessitate larger control surfaces achieve the same roll performance.\

Also, anecdotally from my flying (I'm a private pilot, small, single engine planes) turbulence tends to create much more vertical translation and pitching movement than it does roll movement.

I wonder if the design of blended wing body aircraft means that airlines will be more weight constrained by volume constrained. If that is the case, it would be economical for them to have much wider aisles (faster boarding) and exit rows which could offset the negative impact that having more than 2 aisles would have on evacuation time.

Could it make sense for a fighter?

Possibly, depending if you think it needs to dogfight or not. The F35 actually can dogfight pretty much fine, due to the semi lifting body (after they fixed the software, old articles, pre 2016 really, are outdated), but blended wing is not the same thing. If you see the stuff the US is doing with NGAD concepts that pretty much only do beyond visual range and don't have guns it could be fine. Some of them are more fighter/stand off weapon delivery "bombers" like the B52 are becoming now.

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