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How Air Speed Indicators Work

  1. Oct 12, 2011 #1
    The title here may not be descriptive enough....I know how pitot-static systems work: difference in total pressure and static pressure yields dynamic pressure which is equal to 1/2*rho*v^2. My question is, why is it that the dial on the air speed indicator's gauge has linear markings? If I am measuring pressure to get velocity, but pressure increases with the square of the velocity, I would expect the markings on the dial to be very close together in the low range and then get gradually farther apart in the high range.

    Clearly, there is a mechanical system inside the gauge that handles this, but it must be more than a torsion spring system because springs have linear expansion rates (kx). What mechanically is happening inside the gauge here?
     
  2. jcsd
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