Prop pitch & vibrations

Looking for other's experiences on this topic. I seem to have excessive vibration at propeller RPM frequency. I have re-pitched the prop twice so the blades are within 0.1 degree of each other. After an hour or two of flight the pitch is unequal again. Most recently off by 1.3 degrees. Not sure the vibration is related to the unequal pitch, or just out of balance weight-wise.

I'm not sure if the vibration is causing the pitch change, or the unequal pitch is causing the vibration. I REALLY don't understand how the pitch can change itself.

I am going to call Sensenich tomorrow to see what they say. Anybody have any experience with something like this?

Hey John - -

Did you follow the post Larry Geiger made about the prop and hub having a problem in some cases. Once you tighten the bolts, the pitch should not change, vibration or not. ? ? ?

John Bender

Hi John, thanks for the reply. I checked my prop when Larry's post first came out, and didn't detect any movement. I just re-read the thread, and will check for that fore and aft movement again tomorrow. John

Hey John - -

Again - if you check the pitch AFTER the bolts are all tight, and then you run it, neither blade should shift - ANY ! Have you measured the height of the blade from the floor each time to be consistent ? I'm sure you have. You may not be able to feel a very slight looseness, but under power, a blade might shift. Larry took a picture of the hub. You could see the wear marks. ? ? ? ? ? ?

John Bender

Spoke with Mike at Sensenich this morning. He suspects I have one of the bad hubs, and gave me specific instructions on how to test for it. He was VERY helpful and promises a quick turnaround if I send the prop back. I will have to send the whole thing blades and all, so he can personally check it out.

This afternoon I went to the airplane; First checked pitot alignment, blade tip tracking, and bolt torques (with a different torque wrench). All within specs.

Then checked for blade movement as instructed. One blade has a nearly imperceptable, and yet real, movement fore and aft. And - it takes quite a strong pull on the beefy part of the blade to make it move.

In the AM I will call Mike back for shipping instructions. The bad news is it looks like I got one of the bad hubs. The good news is that hopefully the mystery will be solved and I'll have a new hub before the really nice flying weather gets here!

Tomorrow after I remove and pack the prop I'll post the serial number of the hub.

In the interest of clarity and non-duplication I will post any further updates on my prop/hub on the original thread at: http://www.vansairforce.com/community/showthread.php?t=66335