by pietromarx » Fri Mar 16, 2018 5:09 am
Having just replaced a Hartzell composite prop due to an undisclosed lightning strike that happened before purchase, I can tell you that I have closely examined what Hartzell, my A&P, and everyone else says about a prop. Unexpectedly spending $20k on something focuses the mind.
Hartzell and my A&P are extremely clear: at least 3 times is the thing to do. I've seen props which are sluggish until the 3rd, even 5th time through. The goal isn't the number inasmuch as making sure that the prop changes pitch smoothly.
Deaken is somewhat ambiguous as his pieces says, "How many times should you cycle the prop? If the RPM drops smoothly and properly, once is enough. The fresh oil will probably cause the piston to move a good deal and when it comes back to the low pitch stops, most of the "old" oil will be pushed out. If you really want to feel good, do it twice, to get even more of that "old" oil out of there. Three times is gross overkill, in my opinion, but a lot of people do three times, or more. In reality, there are tiny bleed holes that allow a constant flow of warm oil to both sides of the prop piston, so even if you take off with cold oil in there, it will quickly be replaced with nice slippery warm stuff. On some of the big old props on the radials, in extreme Arctic conditions, the oil would congeal faster than the bleed ports could replace it, but I doubt you'll find any modern props with this problem. I should note for completeness that many of the props on the big radials might require many more cycles to achieve a smooth RPM drop when cold. In freezing temperatures, it may take up to ten cycles. There's a lot more to the mechanism, and a lot more oil involved."
Having just replaced a Hartzell composite prop due to an undisclosed lightning strike that happened before purchase, I can tell you that I have closely examined what Hartzell, my A&P, and everyone else says about a prop. Unexpectedly spending $20k on something focuses the mind.
Hartzell and my A&P are extremely clear: at least 3 times is the thing to do. I've seen props which are sluggish until the 3rd, even 5th time through. The goal isn't the number inasmuch as making sure that the prop changes pitch smoothly.
Deaken is somewhat ambiguous as his pieces says, "How many times should you cycle the prop? If the RPM drops smoothly and properly, once is enough. The fresh oil will probably cause the piston to move a good deal and when it comes back to the low pitch stops, most of the "old" oil will be pushed out. If you really want to feel good, do it twice, to get even more of that "old" oil out of there. Three times is gross overkill, in my opinion, but a lot of people do three times, or more. In reality, there are tiny bleed holes that allow a constant flow of warm oil to both sides of the prop piston, so even if you take off with cold oil in there, it will quickly be replaced with nice slippery warm stuff. On some of the big old props on the radials, in extreme Arctic conditions, the oil would congeal faster than the bleed ports could replace it, but I doubt you'll find any modern props with this problem. I should note for completeness that many of the props on the big radials might require many more cycles to achieve a smooth RPM drop when cold. In freezing temperatures, it may take up to ten cycles. There's a lot more to the mechanism, and a lot more oil involved."