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I had a chance to fly a simulator of the Beta Technologies VTOL airplane (they're a PartsBox customer). I went from horizontal flight into hover, and my guide s

by jwr 5mo ago

I had a chance to fly a simulator of the Beta Technologies VTOL airplane (they're a PartsBox customer). I went from horizontal flight into hover, and my guide said "oh, by the way, you are consuming a megawatt right now". A megawatt. To hover. That really opened my eyes to the reality: unless we have unlimited, clean and nearly free fusion power, flying cars are not going to be a thing.

tekacs 5mo ago
This conclusion is... kinda absurd. In any reasonable setup, hovering would be a rare, rare operation (like 30-60 seconds during takeoff and landing), with most of the time spent in wing-borne forward flight – which'd be _wildly_ lower power usage, more like 200-250kW tops. About ~par with staying in continuous acceleration in an EV. More for sure, but not nearly as insane as what you're pointing to. ... and this is exactly where better batteries would help – being able to hold that power level for longer so you could actually go places in earnest without untenable mass.
- scottLobster 5mo ago
  Is it? If we're talking about a future where EVTOL takes over for passenger cars, there will be air traffic jams with delays that require extended circling and likely hovering. There's a reason all the EVTOL startups show individual vehicles landing in pristine fields, and it's the same reason car advertisements show one car on a closed course instead of I-95 at 3pm on a Friday
  - tekacs 5mo ago
    ... air traffic jams? The air is _much_ bigger than the corresponding ground. Certainly there'd be density _at_ take-off and landing, but even that's manageable by having e.g. arrival/departure locations at multiple heights. It also seems vanishingly unlikely (at this point) that we'd have EVTOL that's not fully autonomous, further reducing the odds of this - ~perfect and coordinated driving, as well as foreknowledge of what's happening between you and the arrival location drastically reduces traffic.
    - dmbche 5mo ago
      Do you know how planes land at an airport? They circle waiting for their turn. Why would that problem vanish?
      - tekacs 5mo ago
        ... because the entire point of VTOL (which is what the parent commentary was about) is that you can take off and land vertically and therefore don't need one of a few, scarce, super-long runways? ... and the waiting you're talking about is entirely because of those? On top of that, small VTOL craft that can hover and would be at lower speeds closer in (esp. autonomously flown) would just need less mutual clearance compared to jets, which also have an altitude band they have to stay in, as well as no ability to slow to a crawl and coordinate finely.
        dmbche 5mo ago
        Gotcha, just spitballing - my mistake taking it seriously
        tekacs 5mo ago
        You asked me why the problem of circling waiting for your turn would vanish when using VTOL aircraft. I don't know how to respond to that with anything other than, "That's the entire point of VTOL. It doesn't need one of those scarce runways that planes circle waiting for.".
        dmbche 5mo ago
        That's fine sir, you don't need to know everything about a subject to spitball. On you go
        tekacs 5mo ago
        My bad! You do list that you're an aeronautics person. I would genuinely genuinely love to understand what I'm missing – I'm sure there's some context here that I'm lacking!
Manuel_D 5mo ago
Two things here: one, hovering is actually much more energy intensive than horizontal flight. Two, a megawatt isn't that much energy in the context of aerospace. A 737 engine produces nearly 100 megawatts at peak output (the engines are rated in terms of pounds of force, so the conversion is a bit wonky).

by jwr 5mo ago

tekacs 5mo ago

This conclusion is... kinda absurd. In any reasonable setup, hovering would be a rare, rare operation (like 30-60 seconds during takeoff and landing), with most of the time spent in wing-borne forward flight – which'd be _wildly_ lower power usage, more like 200-250kW tops. About ~par with staying in continuous acceleration in an EV. More for sure, but not nearly as insane as what you're pointing to. ... and this is exactly where better batteries would help – being able to hold that power level for longer so you could actually go places in earnest without untenable mass.

scottLobster 5mo ago
Is it? If we're talking about a future where EVTOL takes over for passenger cars, there will be air traffic jams with delays that require extended circling and likely hovering. There's a reason all the EVTOL startups show individual vehicles landing in pristine fields, and it's the same reason car advertisements show one car on a closed course instead of I-95 at 3pm on a Friday
- tekacs 5mo ago
  ... air traffic jams? The air is _much_ bigger than the corresponding ground. Certainly there'd be density _at_ take-off and landing, but even that's manageable by having e.g. arrival/departure locations at multiple heights. It also seems vanishingly unlikely (at this point) that we'd have EVTOL that's not fully autonomous, further reducing the odds of this - ~perfect and coordinated driving, as well as foreknowledge of what's happening between you and the arrival location drastically reduces traffic.
  - dmbche 5mo ago
    Do you know how planes land at an airport? They circle waiting for their turn. Why would that problem vanish?
    - tekacs 5mo ago
      ... because the entire point of VTOL (which is what the parent commentary was about) is that you can take off and land vertically and therefore don't need one of a few, scarce, super-long runways? ... and the waiting you're talking about is entirely because of those? On top of that, small VTOL craft that can hover and would be at lower speeds closer in (esp. autonomously flown) would just need less mutual clearance compared to jets, which also have an altitude band they have to stay in, as well as no ability to slow to a crawl and coordinate finely.
      - dmbche 5mo ago
        Gotcha, just spitballing - my mistake taking it seriously
        tekacs 5mo ago
        You asked me why the problem of circling waiting for your turn would vanish when using VTOL aircraft. I don't know how to respond to that with anything other than, "That's the entire point of VTOL. It doesn't need one of those scarce runways that planes circle waiting for.".
        dmbche 5mo ago
        That's fine sir, you don't need to know everything about a subject to spitball. On you go
        tekacs 5mo ago
        My bad! You do list that you're an aeronautics person. I would genuinely genuinely love to understand what I'm missing – I'm sure there's some context here that I'm lacking!

Manuel_D 5mo ago

Two things here: one, hovering is actually much more energy intensive than horizontal flight. Two, a megawatt isn't that much energy in the context of aerospace. A 737 engine produces nearly 100 megawatts at peak output (the engines are rated in terms of pounds of force, so the conversion is a bit wonky).