Solar Impulse lands in California after Pacific crossing

Re:Solar Impulse lands in California after Pacific crossing by Gravityloss on Sunday April 24, 2016 @01:20PM (#11560480)

Flight scales badly to slow speeds. Let me demonstrate with some very rough calculations:

Imagine three aircraft flying the same distance.

The first is a large airplane flying at 20 m/s. Solar impulse speed. The second is a large airplane flying at 200 m/s. Basic propeller plane. The third is a small airplane flying at 200 m/s.

    Slow plane:
    speed: 1x
    area: 1x
    lift: 1x
    payload: 1x
    drag: 1x
    thrust: 1x
    power: 1x
    distance: 1x
    energy: 1x
    
    Big fast plane:
    speed: 10x
    area: 1x
    lift: 100x
    payload: 100x
    drag: 100x
    thrust: 100x
    power: 1000x
    duration: 0.1x
    distance: 1x
    energy: 100x
    
    Small fast plane:
    speed: 10x
    area: 0.01x
    lift: 1x
    payload: 1x
    drag: 1x
    thrust: 1x
    power: 10x
    duration: 0.1x
    distance: 1x
    energy: 1x

You can see that you use the same energy per payload no matter how fast you go, but your plane can be a lot smaller if you go fast.

(This didn't take into account altitude. That means you can go even faster for the same energy expenditure.)

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Re:Solar Impulse lands in California after Pacific crossing by Retric on Sunday April 24, 2016 @01:37PM (#11560552)

Things are far more compex than you are suggesting. The tradeoffs for spead work out largely because you can increase altitude which is very useful.

I accept that Solar does not work to supplement the onboard generator used for electrical power on jets due to weight and night time flights. At the same time solar is ~1% the fuel cost for that amount of power for 20 years. They say they can scale this up 50x and carry 50 people. IMO, it would be better to build cargo only craft in that size range as this is far to slow outside of sight seeing in VFR.

Not to mention wind. That said if you can say double the solar power and add significant altitude and speed that's much more viable. I am assuming this is significantly worse than the best possible solar aircraft we could build in say 30 years.

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Re:Solar Impulse lands in California after Pacific crossing by Gravityloss on Sunday April 24, 2016 @02:40PM (#11560787)

Well, 1/100 the cargo and 1/10 the speed means you need 1000 solar planes for every kerosene plane for the same route revenue. If we assume they cost the same to buy since they are the same size. And that doesn't take into account night flying etc...

Much better to have the solar panels on land and do synthetic kerosene for planes.

Ships go half the speed of Solar Impulse, but they have a lot more payload per dollar invested.

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