BLUF: I have a vibration I hear and really feel in my feet when the RPM is above approximately 2450 RPM.
My RV-4 has a slightly over pitched 3 blade Catto on my 150 hp O-320. The prop is on a 4” Saber extension and has a 20 pound crush plate on the front; I’m using a 12” Catto spinner with the front bulkhead removed to accommodate the large crush plate (the crush plate touches the inside of the spinner and provides a bearing surface). I recently had the a dynamic balancing performed and for full throttle static conditions, the results were great - I started at 0.454 IPS and we got it down to 0.005 IPS on the third iteration. In flight however, I still feel a vibration above 2450 RPM up to the max RPM I can achieve. I emailed Catto and Nicole recommended trying to reclock the propeller 1 or 2 bolt holes. I reclocked one hole (60 degrees) CCW (looking at the tail) and also checked the tip tracking when I did so (it was within Catto’s 1/8” tolerance). I left the balance weights in place and flew for an hour, and still had the high RPM vibration. When I landed I took the prop back off and reclocked it another 60 degrees CCW (120 degrees total); I haven’t test flown this configuration yet.
Why am I posting this in engines instead of propellers? Based on all the above, I believe the prop can be ruled out as the cause unless this latest reclock proves to be the silver bullet. I downloaded the EMS data and reviewed the traces - I didn’t see the signatures of either a bad exhaust valve or a pair of cylinders down on power from a cam/intake issue.
I want to think it’s something on the engine that I haven’t considered causing this, although I’m not able to positively rule out something on the airframe. I did check the obvious (loose fairings) and in the past such defects manifested as a high frequency audible buzzing rather than a low airframe rumble.
I’d very much appreciate any insight on where to look next, especially if this latest reclock isn’t the solution.
My RV-4 has a slightly over pitched 3 blade Catto on my 150 hp O-320. The prop is on a 4” Saber extension and has a 20 pound crush plate on the front; I’m using a 12” Catto spinner with the front bulkhead removed to accommodate the large crush plate (the crush plate touches the inside of the spinner and provides a bearing surface). I recently had the a dynamic balancing performed and for full throttle static conditions, the results were great - I started at 0.454 IPS and we got it down to 0.005 IPS on the third iteration. In flight however, I still feel a vibration above 2450 RPM up to the max RPM I can achieve. I emailed Catto and Nicole recommended trying to reclock the propeller 1 or 2 bolt holes. I reclocked one hole (60 degrees) CCW (looking at the tail) and also checked the tip tracking when I did so (it was within Catto’s 1/8” tolerance). I left the balance weights in place and flew for an hour, and still had the high RPM vibration. When I landed I took the prop back off and reclocked it another 60 degrees CCW (120 degrees total); I haven’t test flown this configuration yet.
Why am I posting this in engines instead of propellers? Based on all the above, I believe the prop can be ruled out as the cause unless this latest reclock proves to be the silver bullet. I downloaded the EMS data and reviewed the traces - I didn’t see the signatures of either a bad exhaust valve or a pair of cylinders down on power from a cam/intake issue.
I want to think it’s something on the engine that I haven’t considered causing this, although I’m not able to positively rule out something on the airframe. I did check the obvious (loose fairings) and in the past such defects manifested as a high frequency audible buzzing rather than a low airframe rumble.
I’d very much appreciate any insight on where to look next, especially if this latest reclock isn’t the solution.