Why does a force on a propeller act 90° "ahead" due to gyroscopic precession?
If I say &quot;my brother was born ahead of me&quot;, you might reasonably assume that my brother is older than me.  That his birth took place at an earlier point in time.
You seem to be assuming that &quot;ahead&quot; refers to the position that any given blade of the propeller occupied at an earlier point of time.  I.e., a position displaced opposite to the direction that the propeller is rotating.
But if you are driving a car and your passenger says &quot;the light's green, go ahead&quot;, would you take that a suggestion to go backwards?  Or to go forwards?
The meaning of &quot;ahead&quot; in the passage quoted in the original question is correct and reasonably unambiguous-- it means forwards along the direction that the propeller is rotating.
Note that the original passage did not contain the word &quot;before&quot;.