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Clocking a 3 blade prop

wcalvert

Well Known Member
Anyone have an opinion (hopefully with some data to back it up!) regarding the clocking of a 3 blade prop (IO-360, Catto, RV7)

I'm getting some pretty solid drumming/vibration in the floor board area, dominantly on the pilot side, when at higher power and speed.

The prop combo (weighted crush plate) has been balanced to .02IPS, so that doesn't seem the issue.

Just wondering if there is an affect from the power pulse and the prop blade position, thereby making the idea of clocking important.

Anyone please?
 
I had a similar issue, and it ended up that the primary culprit was one of my exhaust pipes vibrating it’s way into physical contact with part of my engine mount. It was only about 10 hours worth when I found it but it was already enough to remove material from the mount tube in question. Check your exhaust hangers and see if you can move the pipe into anything by hand.

In my case, just adjusting the hanger wasn’t enough; I had to shim my engine in relation to the mount to rotate the exhaust pipe away from the mount.
 
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Floor Vibration

It's more likely turbulent flow against the floor panel. Could be from the exhaust - some say the angle at which it exits the plenum is crucial.
Turbulence could be developing from the cowling / fuselage interface if this isn't smooth - when in flight.
Others I know have attached bitumen pads to damp out the vibrations / noise
 
I do plan to do a simple extension on the existing pipes (about 4") to see if that causes any change in the vibration.

Next is installing the gear leg fairings and pants to check for any turbulence from the round gear leg interacting with the fuse floor.

Last, sound dampening panels covered with the carpet of the day ... :(

Onward !!
 
Looks like I'm finally onto something ...

I had left the lower cowl exit tunnel (the part that drops down around the exhaust pipes) about an inch long thinking it looked "better" when building the lower cowl. This in effect made the tunnel area larger and the "drop" larger as well. And the aft edge of the tunnel isn't super stiff at mid span.

So I trimmed the tunnel at basically a right angle to the lower cowl surface, even with the back of the lower cowl.

After trying tailpipe extensions, air dams, vortex generators on the lower cowl, prop balancing and gear fairings, this seems to be the source of the vibration.

Now I'm looking for the optimal trim to make the pounding go away... maybe lean the tunnel cut forward to make it even smaller ... :rolleyes:
 
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