Hello fellow aviators,

There seems to be varying experience with vibration/shake on different engine/prop combinations on some Cessnas (180's, 182's & 185's) specifically with three bladed propellers on 470's and 520's. There are other aircraft (bonanzas,etc) that I understand have experienced the same issue, which I'll describe as a nuisance. I'm trying to gather a set of data to see what the different experiences have been with this and any solutions people have found. Thus, I created a survey to gather more info. There's no identifiable information collected with this survey (anonymous), and I'll likely publish the results at some point, but I'd appreciate people filling it out. Thanks!

https://forms.gle/SogAyAQB8CFT3ZsH7

Done!

Thanks for all that have entered their experience. The data is quite interesting. Feel free to share the link with anyone else who has an experience to add to the dataset.

Can you update this forum thread with the feedback from the survey?

I definitely will in a few days. Still gathering responses to analyze.

Here's the results (44 responses) to date. The plots will update as more responses come in. The majority of vibe all seems to occur with 3 blades on 520's and is split between Hartzell and McCauley props (although I did not collect model # data). Some people found dynamic balancing helped. While most have the stock Cessna mount, some still report the issue even with a beefier mount. The worst rpm range is reported to be 2500 for IO-520 series and lower (2400) for the Pponk/Northpoint 470-50 engines. With more data points, one could probably pull more analytics out of it.

https://docs.google.com/forms/d/e/1FAIp ... wanalytics

Forgive me, I am a total noob. I've only touched a few engine engine mounts and propellers in my life... But they have all been two or four cylinder engines with indexed two blade props with side forces expressed at 180 degree intervals. And the mounts have all had four-points of connection to the airframe. With four dampners designed for those 180 degree side forces.

So if you have the pistons and crankshaft exerting force at 180 degrees, and the prop exterting force at 120 degrees there really isn't any way to avoid uneven loads, it's just a question of dynamically balancing the side loads, which won't be perfectly applicable at every rpm... Or did I miss something?

Naomi wrote:Forgive me, I am a total noob. I've only touched a few engine engine mounts and propellers in my life... But they have all been two or four cylinder engines with indexed two blade props with side forces expressed at 180 degree intervals. And the mounts have all had four-points of connection to the airframe. With four dampners designed for those 180 degree side forces.

So if you have the pistons and crankshaft exerting force at 180 degrees, and the prop exterting force at 120 degrees there really isn't any way to avoid uneven loads, it's just a question of dynamically balancing the side loads, which won't be perfectly applicable at every rpm... Or did I miss something?

By those physics it makes sense that a 2 blade should run smoother. But in general most people find a 3 blade smoother in my experience.