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Selection of airfoil and sizing of propeller

  1. May 8, 2015 #1
    Two problem to solve.
    1) I have 4 propellers built with different airfoils. I have the graphs of coefficient of thrust and efficiency in function of advance ratio. There is a mathematical method to select which one is the best or the only way is just look at graphs
    2)I know the maximum thrust necessary at my aircraft so I need to found the right dimension (diameter) and number of blade for a propellers .
    I can calculate the thrust produced by the propeller but this change with the advance ratio and the pitch angle so really i don't know how to select the best diameter and number of blade.

    I thank you in advance for the answers
     
  2. jcsd
  3. May 8, 2015 #2

    SteamKing

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    A propeller is a device which converts torque from an engine into thrust. Selecting a propeller is more than just picking one which produces the right thrust. You also must consider the engine driving the propeller and what its torque characteristics are.
     
  4. May 8, 2015 #3
    but in the ideal case that I can have always the best engine appropriate for the propeller ?
     
  5. May 8, 2015 #4

    SteamKing

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    That's not the point. You are selecting a real propeller driven by a real engine to add thrust for a real plane.

    If the propeller can't absorb the torque output by the engine at its speed of revolution, then the propeller also won't produce the amount of thrust you think that it will.
     
  6. May 8, 2015 #5
    yes you have right, but in the case that I can select the engine after the selection of propeller, in this way it's the propeller that give the characteristics to the engine.
     
  7. May 8, 2015 #6

    SteamKing

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    Good luck with that approach then.
     
  8. May 8, 2015 #7
    so if i don't know the characteristic of the engine I can't built a propeller ?
     
  9. May 8, 2015 #8

    SteamKing

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    You can build any number of propellers, but you want to build (or select) the propeller which is the most efficient at turning the available torque produced by your engine into thrust for your plane.

    This article discusses the key topics in selecting the best propeller for your aircraft:

    http://www.experimentalaircraft.info/articles/aircraft-propeller-selection.php
     
  10. May 9, 2015 #9
    the problem is that i have already small efficiency of the propeller because the velocity of fly is max 30m/s this mean a small advance ratio and a small efficiency and if i decrease the diameter of prop i don't have enough thrust .
    It's a loop where I don't found a solution for this I am doing some semplification like I can have the best engine for the propeller and considering only the condition where it spend the major part of time.
     
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