Why does propeller slip (efficiency) change during the flight (fixed-pitch)?
The reason that efficiency is reduced during phases of flight that are flown at high airspeeds is because the angle of attack between the propeller and relative wind is reduced. If an aircraft is stationary on the ground, its propeller is taking a larger &quot;bite&quot; of air because there is no relative wind. When there is more air moving past the prop, it takes a smaller &quot;bite&quot; of air, therefore producing less thrust and being less efficient. The advantage of a constant speed prop is that you can change the pitch of the prop depending on your airspeed, so it maintains a constant angle of attack, and is more efficient in every phase of flight. I'm not totally sure that's what you are asking, but that's what I got :)