Propeller moment parameters? accuracy query

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by zk-jkw, Oct 5, 2009.

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  1. Oct 5, 2009 #1

    zk-jkw

    zk-jkw

    zk-jkw

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    I'm running through the yaw stability calculations (still... if only I had more time!) and calculating the propeller yaw and normal moment coefficients.

    Obviously there are a lot of educated guesses which are made around the propeller that will actually be installed as small propeller manufacturers provide little data.

    So given that the coefficients will vary based on what is actually installed I would assume there is a resource that is typically used for design purposes. And how much do these values really change by? (not having iterated several results myself). Can anyone with more experience comment on the accuracy/validity of calculating propeller coefficients in the real world?

    Zk
     
  2. Oct 14, 2009 #2

    zk-jkw

    zk-jkw

    zk-jkw

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    OK I realize (from the lack of response:depressed) that if your not designing a twin some may not worry about the propeller moment when sizing their rudder.

    So what I'm doing is calculating the propeller yaw moment coefficient. You essentially have to know the propeller you are using i.e. diameter, pitch and sectional characteristics throughout its length (CL & CD). At this stage this is a bit like calculating a whole lot of assumptions to 5 decimal places!
    Can anyone help with a reference on how this is traditionally dealt with? (is it ignored?)

    Propeller yaw side force; CYp,beta (or CNp,alpha) can be approximated from various quick charts in Raymer if you dont calculate it. However I haven't seen a similar approach to the propeller moment coefficient (Cnp or Cnp, alpha).

    Perhaps I'm missing something?
     
  3. Oct 14, 2009 #3

    orion

    orion

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    Assuming a reputable source, propeller mass moments should be able to be supplied by the prop manufacturer.
     
  4. Oct 14, 2009 #4

    zk-jkw

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    Propeller yaw moment parameters? accuracy query

    Orion: Sorry the original thread title is misleading/ ambiguous in retrospect. It should probably say "yaw moment" parameters
     
  5. Oct 14, 2009 #5

    Norman

    Norman

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    Like this?
     

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  6. Oct 14, 2009 #6

    zk-jkw

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    Looks like a start with those Technical Reports, TR819 & TR820.

    It appears as though they refer more to the side forces (Yp) rather than the moment (np) but I'll have a proper read first... cheers
     

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  7. Oct 16, 2009 #7

    Othman

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    For stability derivative estimates your best bet is to start with Jan Roskam's "Airplane Design Part VI".

    Another good reference for stability analysis is "Dynamics of Flight: Stability and Control" by Etkin and Reid.
     
  8. Oct 16, 2009 #8

    zk-jkw

    zk-jkw

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    I will have a look... interestingly Mechanics of Flight, Phillips seems to be the only text (I've found) that even uses the term for propeller yaw moment and a separate term for the propeller normal force...
     
  9. Oct 20, 2009 #9

    zk-jkw

    zk-jkw

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    Just to close this topic off in case someone searches it in the future. (I've had rare moment of clarity:gig:). Cnp,alpha is more commonly known as the p-effect...
    Apologies to anyone who suffered through my confusion!
     

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