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Shaping a propeller . . . help!

  1. Oct 27, 2003 #1
    How do you shape (shape in meaning-> bending angles that will catch air, not shaping the design itself) a propeller out of a paper that will catch air (I got a Lou-vee Air car but it won't move b/c it is not pulling any air when spinning or pushign the air)?
     
  2. jcsd
  3. Oct 27, 2003 #2

    russ_watters

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    Staff: Mentor

    The same way as a fan is shaped.
     
  4. Oct 27, 2003 #3

    LURCH

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    Your prop is made of paper? I have trouble thinking of a way to shape a piece of paper so it will push any appreciable amount of air; the paper would rather just bend to relieve the pressure. I'll give it further thought but in the meanwhile, how about cardboard for the prop?
     
  5. Oct 27, 2003 #4
    Re

    the best or hardest material I can use is manila folders . . . I am not sure how to create the angle of attack for the propeller to scoop air

    http://www.phs.provo.k12.ut.us/~ericr/aircarsix.html

    (its not mine, but I want it to work like it)

    I wound up my Lou-vee Air car but it wouldn't budge.
     
  6. Oct 28, 2003 #5
    Interesting.

    Have you tried:
    First, buy a metal/plastic fan with the right size that you want.

    Soak your cardboard in a mixture of warm water and starch. Some experimentation required to get the mixture 'wet' enough to soak the paper but fluid enough so that it doesn't leave gobs of starch on the paper.

    Put your soaked paper on the fan's blades. It should fit easily like a paper-mache. Wait for it to harden.

    Voila :smile:
     
  7. Oct 28, 2003 #6

    russ_watters

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    Angle of attack too high - add more twist at the leading edge. The trailing edge should be straight. As an added benefit, a correct twist will make even a single layer oak tag propeller quite rigid. The angle of attack at the tips should be near zero. Again, just like a fan (or actually, yours looks more like a propeller).
     
    Last edited: Oct 28, 2003
  8. Oct 28, 2003 #7

    GENIERE

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    The high angle of attack shown in the photo may be needed to compensate for the flattening of the prop at speed.
     
  9. Dec 12, 2003 #8

    ken

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    Hi

    You need to get the whole length of the prop blade working at the same pitch for maximum efficency. Pitch is the distance a prop will travel forward into the air in one revolution, much like a screw thread. The tip of the blade is going around a much larges circle than the middle but still advancing forward by the same amount so
    the middle of the blade must be angled more steeply than the tip.
    The centre of the prop is not going around a circle at all, it is advancing straight forward and so the blade there is aligned along the prop shaft.

    Lets take for example a prop of 200 mm dia and 100 mm pitch.
    The radius to the tip is 100 mm the circumferance for 1 rotation is:
    2 x Pi x R
    where R = radious

    we get 2 x 3.141 x 100 = 628 mm

    Now in 628 mm the tip advances 100 mm and the angle between the prop shaft and blade is 90 - invTan (P/C)

    where P = pitch and C = circum (628)

    we get 90 - invTan (100/628) = 81 deg

    Using this we get "

    Rad 50, angle 72 deg

    Rad 10, angle 32 deg

    If you can make a prop so the blades twist somthing like that, it will work fine.
     
  10. Jun 17, 2008 #9
    I had to build a wind turbine for one of my nieces years ago and I cut the blades from an old spackle bucket, mounted them on a hub and ran a wire through all the blades at about halfway out from the center to hold the pitch. I couldn't believe how strong it was. If your dealing with a small car try a plastic cup instead. the changing radii of these containers makes the blade change angle of attack as you go from the hub out.
     
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