I am writing to inquire about the pitch specifications for the following McCauley propeller models:

  1. IC235/LFA7570 with a maximum diameter of 75 inches and minimum diameter of 74 inches.
  2. IA170E/JHA7660 with a maximum diameter of 76 inches and minimum diameter of 75 inches.

Both models have 2 blades. I would appreciate it if you could provide me with the detailed pitch information for these propellers.

Thank you for your help.


1 Answer 1


The suffix numbers are the propeller diameter followed by the geometric pitch at the .75 radius station. So they are 70 inches of pitch and 60 inches of pitch, respectively, at a point 75% of the radius from the center of the blade (28.1 inches and 28.5 inches, respectively).

The pitch in inches is how far forward a propeller of that pitch would go forward in one revolution if you imagine air were a rigid substance. It is related to the actual blade angle at the .75 radius station by the following formula:

$$\text{pitch}=\frac{3\pi}{4}\text{diameter}\times\tan\left(\text{blade angle}\right)$$

Using this formula, the blade angles are about 21.6° and 18.5° respectively.

  • $\begingroup$ Ah! LFA7570 means LFA = something; 75 = inches in diameter, and 70 = inches of pitch at 75% of radius (52.5 inches). What does "70 inches of pitch" mean? I'd expect pitch to be in degrees. (Yes, it took me some head scratching to figure out how to interpret your text description...) $\endgroup$
    – FreeMan
    Commented Jun 13 at 13:30
  • $\begingroup$ @FreeMan Imagine air as a rigid substance, and the propeller as a screw screwing through the air. The geometric pitch in inches is how far forward a propeller of that pitch would go through the air in one revolution. $\endgroup$
    – Chris
    Commented Jun 13 at 17:01
  • $\begingroup$ Ah, got it. Thanks, that makes sense now. $\endgroup$
    – FreeMan
    Commented Jun 13 at 19:04

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