vibration on decent

[Dave in Eugene]

Recently installed an 8" prop extension...Noticed a good change especially to take off acceleration... I do not have a spinner. Also notice a relatively high frequency vibration when I push the plane over to descend...my guess is it is some kind of cavitation around the prop... I pull back on the rpm's and it subsides...any ideas?

Thanks,

Dave

[Kilo42]

Two blade or three blade?  Before I had my 3 blade I had something similar happen to me.  When I would begin my descent I began experiencing a vibration until I changed the RPM setting out of the effected RPM range.  

During the process of removing, reinstalling, retorquing and retracking my prop I came upon a 2" crack close to the hub area on the backside.

I grounded the plane and installed a Catto three blade and have had no problems since.  Plane has been flown with and without a spinner.

I would start with an overall visual inspection of the prop.  Retorque the extesion bolts to the fly wheel to insure proper torque and uniformity.  Retorque the blade bolts and re-track the blade.  You can find directions on how to track the blade in the articles section.  Also make sure that the mating surfaces between the blade and the extension are clean.  Any debris here can cause the blade to not track properly.


Kilo42
Long-Ez N81HM

[Dave in Eugene]

ok... I will pull the prop and take a look....I have had the prop off often...can't hurt.

Thanks,

Dave

[Kilo42]

Dave,

Any luck on the vibration search?



Kilo42

[Dave in Eugene]

No time to track it yet...maybe this coming week...thanks,

Dave

[Joe Person]

Dave,

Have you measured the runout on the extension's flange furthest from the prop?  As one goes to longer extensions, it becomes more important to make sure the extension itself is running true, with no "wobble".

[Dave in Eugene]

Good to hear ya Joe,

I will check that too.

Thanks,

Dave