Propeller Beta vs. Twist

[EM]

I think I am understanding this correctly now, but can anyone confirm that beta 3/4 is not an absolute angle but rather a relative rotation angle which is used to uniformly rotate the twist distribution that was specified on the blade tab.

For example, one can set beta 3/4 to zero and then go to the blade tab and input a twist angle at each station. Then if the beta is changed to 2 deg, then every section is rotated 2 degrees more than the assigned twist value.

Its just a little confusing to me since in typical propeller literature beta is an absolute angle. 

Take care,

Ed

[Rob McDonald]

For a variable pitch prop, the angle of the blade at 75% r/R (or sometimes 70%) is typically used as a number to represent the position of the blade.  This number is given as Beta3/4 in OpenVSP.

The twist distribution graph presents the twist in a global frame.  The default blade's twist is such that the twist is 20deg at 75% of r/R.

The default value of Beta 3/4 is also 20deg.  Consequently, the default position of the blade is in its 'natural' position per the design.

If this is a variable pitch prop, increasing the pitch by 5 deg can be affected by changing Beta 3/4 to 25.

If you would rather work with the variable pitch angle in an absolute frame, then the 'Feather' variable just below Beta 3/4 is for you.  Click the yellow radio button to the left to make Feather active instead of Beta 3/4.

Rob

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[EM]

Thanks for clarifying. That makes perfect sense. 

[Cibin Joseph]

Ed,

Just to add to that, you might want to check out this discussion on this forum quite a while back.

Cibin

To view this discussion on the web visit https://groups.google.com/d/msgid/openvsp/CAEppYpGi6p4_1rF4C-6QcrQ3_1aiomH4Bw1DZjiH97-nP5nGOQ%40mail.gmail.com.

[EM]

That additional discussion is helpful also. 
-Ed