What does prop vibration feel like?

Yes, I know this is a stupid question, but hear me out.

I discovered a good-sized nick in the prop while doing the annual, I suspect from the winter detritus that was around the ramp when I pulled it out to heat up the oil a few weeks ago -- the aggregate on the ramp outside the hangar is just falling apart.

Mike Hilger was kind enough to lend his experience yesterday and filed it out.

Now, I had the prop balanced during Phase One but to be honest with you I didn't notice a huge difference, I suspect because I didn't have enough time in the plane when I had it done to have, literally, a good "feel" for things.

I pulled the plane out, sans cowling, afterwards and started the engine. Everything worked fine. The engine monitor showed nothing unusual, but I felt a pulsing vibration that I can't recall feeling before.

Basically, I would get about 10 seconds of that smooth sound and feel --.that sound and feel of a humming aircraft engine that's better than sex for men of a certain age.-- and then about 10 seconds of slight vibration. That would repeat over and over.

There was nothing noticeable on RPM or other readings from one to the next, just a vibration.. A runup showed everything is fine.

I realize that after filing out a nick (and you can certainly tell where it was on the prop) the thing will have to be rebalanced at some point, but I'm curious about whether this sort of vibration is typical in this condition, or am I just highly sensitive?

I flew a 172 yesterday that had just been through a bad rain storm on its previous flight. The prop had a ton of paint chipped/peeling off, so much so that I almost didn't take the plane. Idling at 900-1000rpm there were some pretty bad vibes, which felt similar to what you described. At any normal operating speed it felt/sounded fine. Can't help with a way ahead. I would have a mechanic or someone experienced see it and feel it to help make that decision on a case by case basis, but I can't imagine noticeable vibes are particularly good for a plane.

Keep in mind these pulses, I'm pretty sure, wouldn't likely be noticeable to people unless I pointed them out. They're that subtle.

I know this isn't the exact same scenario, but maybe another data point for you. I have felt that pulsing feeling when flying at full throttle and full rich mixture (0-360 and a brand new wood prop). I couldn't see anything happening on the gauges. No RPM change in the slightest. I leaned the mixture and the pulsing feeling went away.

Cowling

LettersFromFlyoverCountry said:

Yes, I know this is a stupid question, but hear me out.


I pulled the plane out, sans cowling, afterwards and started. Everything worked fine. The engine monitor showed nothing unusual, but I felt a pulsing vibration that I can't recall feeling before.


There was nothing noticeable on RPM or other readings from one to the next, just a vibration.. A runup showed everything is fine.

I realize that after filing out a nick (and you can certainly tell where it was on the prop) the thing will have to be rebalanced at some point, but I'm curious about whether this sort of vibration is typical in this condition, or am I just highly sensitive?

Click to expand...

Bob,

While vibrations can come from many places.....before I would look at all the possibilities, I would put the cowling back on and run it again. It could be a cable, wire bundle or any number of things being affected by the prop blast and resulting in vibration feedback. If its still there during runup with cowling on(and I would face it into the wind...if there is any) then you can start the troubleshoot process INMHO.

Bon chance!

Skykingbob said:

Bob,

While vibrations can come from many places.....before I would look at all the possibilities, I would put the cowling back on and run it again. It could be a cable, wire bundle or any number of things being affected by the prop blast and resulting in vibration feedback. If its still there during runup with cowling on(and I would face it into the wind...if there is any) then you can start the troubleshoot process INMHO.

Bon chance!

Click to expand...

Yes, the direction of the wind is very important... it causes many new sounds, vibrations and feels during runups or other ground runs.

And the wind was fairly gusty at the time. After I repack the nosewheel bearings today, I'll button her up and try it again.

It has to fly to the paint shop on Saturday.

Points to ponder

1. Is this a fixed-pitch prop?

2. If two-bladed, when the nick was filed out, was a similar amount/weight of material removed from the opposite blade?

3. When you noticed the pulsing, was the engine at a steady RPM?

IF, it's fixed pitch, and the RPM was steady, it would be very interesting to determine what could make the prop "pulse" cyclically.

Suggest you find an EAA chapter with a dynamic balancer and check your prop/engine combo. I balanced mine last week, and it's easy, if repetitive
(start, idle; max static RPM, measure, shut down; add weight; lather, rinse, repeat until satisfied...)

Put another way,

Buttoned everything back up yesterday and did not notice any pulsing.

Will run it down to get the prop balanced as soon as I get the medical back.