Propeller Pitch gauge calibration

[Nat Penton]

Anyone  would have (lengthy) difficulties trying to measure the pitch distribution without a pitch guage similar to the Prather. The only problem with the Prather is that it was designed for props of max diameter of 16 ins and with it you can only measure out to 5.5 ins max ( about 70% of 16 ). I referred to the pitch distribution as being proprietary however it is there for anyone to measure. The blade area distribution would also come into play in determining pitch distribution, and also probably the section distribution, so I suspect it is more art than science. We can thank APC for perservering.
  ----- Original Message ----- 
  From: Rcmaster199 at aol.com 
  To: discussion at nsrca.org 
  Sent: Saturday, October 16, 2004 9:52 PM
  Subject: Re: Propeller Pitch gauge calibration


  Nat, so if someone were to reverse engineer the famous APC prop blade pitch distribution, one could start by making a bunch of cardboard right triangles fit under the blade, at, say, 1" intervals, moving out from center. Then one can determine what the pitch at each station is by simple graphical means from the triangles, and plot that against radius (stations). I would hazzard to guess a parabollic distribution.

  Of course, if one isn't so inclined, he can always call Tony and buy the sucker, but what has he learned?? LOL. Tongue planted firmly in cheek.

  MattK, pontificating again, but what the hell. BTW isn't that what the rubber band wielding free flighters do with the props they build from sticks?



  Matt, you are correct. Feel free to help clarify my comments.                   Nat
      ----- Original Message ----- 
      From: Rcmaster199 at aol.com 
      To: discussion at nsrca.org 
      Sent: Saturday, October 16, 2004 12:02 AM
      Subject: Re: Propeller Pitch gauge calibration


      Nat, taking a hypothetical example of a 20x10 prop, the radius is 10 inches and coincidentally so is the pitch at the 70% station of the prop. 
      The 70% point is 7" from center. 
      The circumference of the circle at that station is 2x(7")x Pi. 
      The right triangle would then have a base of 2R x Pi and a height of 10"(prop pitch). 
      The hypotenuse inscribes angle which is the true pitch angle at the 70% station. 
      (Reducing the triangle down to say 5% of the original makes it manageable.)
      Is this what you mean?


      Matt


        Peter,
        Prop pitch is measured at the 70% station.Pitch distribution along the span ( deviation from true pitch ) is proprietary and is, in the case of APC, what accounts for their excellent performance and low noise.

        A way to calibrate your gauge is to make a template , a triangle with the x axis equal to the circumference  at a given blade station and a slope of ,say, 10 inches and check this against the guage reading at that station.

        i.e. at each station a prop will "twist" forward the same amount in one revolution if it has true pitch ( no slippage ).

        You do not need to express inches of pitch as degrees.
        When are you going to give me a report on the Alliance trim !!
          ----- Original Message ----- 
          From: Peter Pennisi 
          To: discussion at nsrca.org 
          Sent: Friday, October 15, 2004 5:18 PM
          Subject: Propeller Pitch gauge calibration


           

           

           

          Hi Guys,

           

          I have modified a propeller pitch gauge to accommodate larger propellers. The gauge I have is a very old prop shop model.

           

          I have decided to check my APC props because I was getting mixed performance results between all my prop sizes.

           

          Anyway I thought I would check my gauge with a new prop to see how accurate it was and the numbers I got were different to what was on the prop. I tried another new prop of exactly the same size I got a different result again. Anyway I am shocked to find that what is displayed on the prop is different to my measurements.

           

          What part of the prop should I be measuring my pitch as this varies slightly over the length of the blade?

           

          Secondly, how would I go about calibrating my unit because I can’t do it with new props because there all different.

           

          How do I express for example 13 inches of pitch as degrees?

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