Cars, cars and electric cars

Discussion in 'Just Talk' started by joinerjohn1, Jul 26, 2017.

  1. PhilSo

    PhilSo Screwfix Select

  2. I do understand where you think you are coming from.

    The best thing to do to any moving object to make it as free to move through the air as possible is to reduce its drag. That is key. Reduce drag.

    Obviously it's a compromise as vehicles also have to look good - they can't all be shaped like this: images.jpg for practical & aesthetic reasons, but that is the idea. That's what's aimed at as much as possible.

    If the design can be improved on further - to reduce air resistance a teeny bit more - then that is what the designer would do. Any everything they do in this respect would be an energy saving. If they could design a hole going through the body that would help this, they'd do it, 'cos that is a net gain.

    They would not, however, design this 'improvement' - holes or whatever - and then stick a turbine in there 'cos that would then be a net loss. The energy produced by this turbine would not overcome the losses caused by the turbine's air resistance.
  3. By all means have a removable turbine on your roof to charge your battery when your car is parked up - that is free renewable energy. But, before you drive off remove it.
  4. btiw2

    btiw2 Screwfix Select

    Greg Clark: Secretary of State for Business, Energy and Industrial Strategy
    "In industrial sectors – from automotive and aerospace to financial and professional services and the creative industries – the UK has built a global reputation."

    Mr HandyAndy: Director of Screwfix forums automotive research
    "Try this. Take a solid sheet of metal 3ft x 3ft and weld it upright to the car roof. That is gonna produce a lot of drag.
    Now cut the biggest hole in it that you can, and put fan blades in it. The drag MUST be less than the solid sheet of metal, and the fan will spin."

    Greg Clark: Secretary of State for Business, Energy and Industrial Strategy
    Deleted member 33931 likes this.
  5. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    Ok. You didn't say the motor was turning the blades. I misinterpreted that.
    And yes the free air is turning the blades and slowing the copter down.
    But as I said, not as much as a solid sheet of metal.
  6. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    DA, how would it be a net loss?
    A hole with a fan it is going to give less resistance than the solid. Some air will pass through. That is still a gain.
  7. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    Don't be silly.

  8. Its not a direct gain. The best you can claim is that its less loss of energy, but its still a loss.
  9. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    That is one way of putting it, but not correct. It's an overall gain.
  10. chippie244

    chippie244 Super Member

    If it was a gain, as has been said, you would have perpetual motion and losses through friction ensure this can never happen.
  11. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    It's not perpetual motion. The motion is powered by the forward movement of the car. The reverse air flow blows a fan. Any air that comes out the back and is unrestricted is a gain.
  12. chippie244

    chippie244 Super Member

    Any energy you get out of the fan will be less than the energy you put in unless you drive over a cliff.
  13. P J Thompson

    P J Thompson Active Member

    Funnily enough, we're not the first to discuss this. Here's an example:

    The turbine will create drag as a factor of it moving in the first place. You then have the extra resistance to movement created by the emf in the turbine when you're drawing load from it. You than have the inherent inefficiencies to add in. It's a great idea....if it worked but it doesn't for your average car. A flat faced bus or truck maybe could be designed to be slightly better but you'd be better off just sorting out the flat face of the vehicle.
    Or you could concentrate on harnessing some of the wasted energy, like my downhill idea :)
    longboat and btiw2 like this.
  14. btiw2

    btiw2 Screwfix Select

    Pointing HA to a physics forum. Genius! Please let this be the final word on this.
  15. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    No. You have to take away from the car some resistance, then add back LESS resistance. That is a gain.
  16. P J Thompson

    P J Thompson Active Member

  17. What you are effectively saying is, let's build a wall, a great big beautiful wall. It'll be a mile high. It'll be awesome. It'll completely block the wind. It'll have AWESOME wind blocking properties - it'll have a CD factor of 1.17 (I've Wikipediad).

    You then remove a single brick.

    YES, that has now less resistance than the solid wall.

    But the best scenario was to never have built the wall in the first place.

    In your car, the best thing to do for economy and energy savings is to reduce the drag as much as possible. If designers felt it was worth while, they would make a hole go right through the car. That would reduce drag and make the car more energy efficient. A GAIN.

    What they wouldn't then do is to spoil that gain by placing a draggy turbine in it 'cos that turbine's resistance would increase the overall drag again and consume more energy than would be delivered from it.

    But, wait - the OVERALL drag of this turbine in the hole would still be LESS than not having the hole in the first place and you WOULD also get something out of it! A DOUBLE GAIN!

    A hole with a turbine in what was originally a poorly dynamic surface is a WIN-WIN!

    Mr HA is right!

    I am now going to cash in all my savings and live in a commune in central America. I cannot cope with real life any more.
  18. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    Not sure which part of your post is most sarcastic.
    But the second part is spot on.
    The first part?
    I ain't building a wall.
    But if I were building a wall, it would have a hole in it with a turbine. A gain.
  19. Sparkielev

    Sparkielev Screwfix Select

    I had a Ford Fiesta with holes all the place in it don't think it went any faster tho
    Jord86 and P J Thompson like this.
  20. P J Thompson

    P J Thompson Active Member

    Aren't all fiestas full of holes though?

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