1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

B Da Vinci's flying machine meets solar sail?

  1. May 12, 2016 #1
    so the question has been previously answered as to what would happen if a fan was in the vacuum of space. but the responses I seen all ask what the fan would push on or up against. what if the fan where to push against light? solar sails are able to have a force push against them in space?
     
  2. jcsd
  3. May 12, 2016 #2
  4. May 12, 2016 #3
    Could u not make a solar sail kinda like Davinci's flying machine ? Or does that just sound cool ... And then if the base must rotate then why not make it corkscrew shaped and also solar sail?


    ........... One word a day???? Today's word is procrastinanigans..... The act of procrastinating your shenanigans
     
  5. May 13, 2016 #4

    A.T.

    User Avatar
    Science Advisor
    Gold Member

    So the question here is: Can a spinning fan like solar sail produce more thrust, than a non spinning one, with the same surface area?
     
  6. May 13, 2016 #5

    phinds

    User Avatar
    Gold Member
    2016 Award

    Well, it seems to me that's hardly the only question. The big question I see is, what powers the fan? The OP clearly envisions the fan pushing against light, not passively being pushed BY light.
     
  7. May 13, 2016 #6
    That's something I have been wondering... Which I think if we could harness an extra thrust some how from the light.. I mean I doubt a fan will but maybe more a screw?
     
  8. May 13, 2016 #7
    With no resistance in space I guess it wouldn't really help
    The fan is powered by light of course... ?? Solar energy... Or does light work different in space?
     
  9. May 13, 2016 #8

    phinds

    User Avatar
    Gold Member
    2016 Award

    Sure, that works, but my point is that I don't think you can use the energy in the light twice, so all of the energy that goes into turning the fan does not go into moving the vehicle forward, so you get less efficiency than a plain old solar sail.
     
  10. May 14, 2016 #9

    A.T.

    User Avatar
    Science Advisor
    Gold Member

    Yes, but the first question is, if rotation can really increase the force on a propeller shaped solar sail. And unlike with a propeller in a tailwind of air, the answer is not that obvious to me for light.
     
  11. May 14, 2016 #10

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    What extra thrust? Consider a simple mirror. Light with momentum p comes in and light with -p goes out. How do you get any more momentum? That's all there is.
     
  12. May 14, 2016 #11

    phinds

    User Avatar
    Gold Member
    2016 Award

    My thought was that the amount of light energy arriving at the vessel is independent of whether or not the struck surface is rotating so the only difference would be the awesomely trivial amount of (possible) extra energy give to the impact by the speed of the sail. Thus you have essentially a tie, BUT you have to power a rotating sail and that uses up far more power than anything that could be gained from the fact that the sail is rotating.
     
  13. May 14, 2016 #12

    A.T.

    User Avatar
    Science Advisor
    Gold Member

    Only by interacting with more light. So the question is whether rotation can achieve this.
     
  14. May 14, 2016 #13

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    But an efficient solar sail reflects all the light in its path. How do you reflect more than "all"?
     
  15. May 14, 2016 #14
    I would love to find out... Thank u guys I was curious.. . I'd love to see a live test... That would be cool
     
  16. May 14, 2016 #15

    A.T.

    User Avatar
    Science Advisor
    Gold Member

    We talking about a fan-shaped solar sail, which doesn't reflect all the light that passes through the rotor disc. Something like the heligyro in the middle.

    Sail-design-types.gif

    The question is whether it's rotation can increase the amount of reflected light. It seems to me not. But a good and simple argument would be nice.
     
  17. May 14, 2016 #16

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    But it does reflect all the light that impinges the sail.
     
  18. May 14, 2016 #17
    I think it may be useful to think of the light as a kind of photon-gas tail wind. If the blades of the fan are flat, then I agree, rotating would not change anything. However if they are angled like fan blades, then thy could sweep a greater volume of the photon gas then flat, stationary blades would. The effect would be very slight though, unless the speed of the blades was a significant fraction of C.
     
  19. May 14, 2016 #18

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    I'm not sure this isn't zero. But in any event, by tilting the blades you reduce the forward thrust by cos(theta).
     
  20. May 14, 2016 #19
    That would be true for a stationary angled blade, but a moving angled blade would blue shift the reflected photons. I'm thinking you could gain a little more Δp from the blue shift then you'd loose to the change in angle.

    I'm pretty sure most of us could do the math to actually figure this out. I'm also pretty sure I'm feeling too lazy for anything deeper then a qualitative analysis right now. :-)
     
  21. May 15, 2016 #20
    It would be awesome if we could master light travel through a method like this... All though it would take lifetimes to get any real speed
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Da Vinci's flying machine meets solar sail?
  1. Solar Sailing (Replies: 7)

Loading...