M20C running 3-Blade McCauley Scimitar Prop Vibration...

[MaxwellSmart86]

I am a new user to MooneySpace but I have been referencing MooneySpace for the past 6-months while I pursued purchasing my first plane. I now am a proud owner of a very well kept 1965 Mooney M20C.

I am hoping to get some feedback from all of you since this is my first Mooney (I flew Cherokees, Archers, Cessnas, etc. in the past).

I have McCauley 3-Blade Scimitar prop with 200hours on it since new and about 800hours on the current engine.

Here's my question - What do all you M20C owners see for vibrations while you are cruising in your C? The reason I ask is that when I cruise at 7,500ft, WOT and 2,500rpm - I feel a noticeable vibration in the yoke and panel (you can visually see the yoke vibrating a bit). Not terrible like the wings are coming apart, but noticeable enough to almost be uncomfortable. If I back off to 2,400rpm/WOT it is less and at 2,400rpm reminds me of flying our Cherokee 180 - a slight vibration in the yoke and panel (sort of the hum of the engine).

The problem is that the plane is so new to me, I don't know what is "normal". I had the prop dynamically balanced last week to .065 IPS but that made zero difference in the vibration at 2,500rpm. I am going to have my A&P check some of the basics under the cowl to make sure we don't have something obvious touching/rubbing.

In the meantime, what do all you C owners experience?

Thanks so much! I love my new plane, just running down all these little loose ends.

[Danb]

Pictures please    Still wonder if it’s balanced ok. 

[MaxwellSmart86]

30 minutes ago, Danb said:

Pictures please    Still wonder if it’s balanced ok. 

What would you like pictures of?

if you fly a C, what do you feel for vibration at cruise speeds? Thanks!

[Jakes Simmons]

My ‘76 C had a three blade when I bought it. The vibration was noticeable at all rpm’s and like you mentioned, similar to older airplanes that lived on a school flight line I had flown in the past. One thought was a three blade prop is out of “sync” with a four cylinder engine. One thing to try is remounting the prop 180 degrees from its current position. That has helped some folks. What I did, and really only because my income was much higher then currently, was buy a new two blade scimitar prop from Hartzell, replace the engine mounts, and then had the prop guru at Maxwell’s dynamically balance the set up. REMARKABLE difference. Plus I never liked the three blade. Besides vibration I thought it was slower at cruise although quicker off the ground through the first 500 feet. 
     Vibration is fatiguing for the pilot and hard on the instruments. Try a dynamic balance first, check condition of your engine mounts, then maybe rotate prop mounting. If all else fails, work a WHOLE bunch of OT and get the more efficient two blade. 
     What’s funny is the smoothest flying Mooney I experienced had the original inspection ridden prop. Like a turbine…

[AndreiC]

When I got my 1970 E (3 blade McCauley, but non-scimitar) about 1.5 years ago it was vibrating badly enough that I could not read information from my yoke-mounted iphone. A rebalancing helped some. I don’t know what else also helped, since now it is quite a bit smoother, without me doing anything else in the meantime. I also was told at the time the theory that 3 blades on a 4 cylinder is not as smooth as 2 blades, but I don’t know if this is an old wives tale or not. 

[47U]

14 hours ago, MaxwellSmart86 said:

In the meantime, what do all you C owners experience?

I have a 3-blade McCauley which the previous owner installed in 1990.  Initially, he didn’t like the vibe at all.  His final solution was to put a lens over the landing light to make the front of the cowling smooth.  The recessed landing light well generated a weird harmonic (I guess?).

In Aug ‘21, I had accumulated about 40 hrs on a prop overhaul (third overhaul on this prop) and thought it felt different.  I had also replaced all the engine isolators.  I got it dynamically balanced down to 0.1 IPS (Dynavibe GX-2), but wasn’t really sure if it felt any different.  Then, a few months later, a buddy of mine got a MicroVibe II and we checked it again and it was dialed right in at both 2400 and 2000 rpm.  I still think it’s a little smoother if I run it at 2500 rpm, though.  I don’t have things perceptibly shaking.  

Some thoughts on things to check…

The STC for the prop should give you information on the proper index on the crank flange and any red/yellow caution RPMs on the tach.  (I had to remark my tach to match the STC, 20 years after the initial installation!)

Do an inflight mag check to make sure all the cylinders/plugs are happy at altitude/cruise settings.

There’s an AD for the engine mount, but not sure if it applies to later C serial numbers.  Certainly verify the gussets mentioned in the AD are there, no cracks or broken tubes, and all the isolators and bolts to the firewall are good.  The C isolators are indexed to the engine mount with a pin.  If the pin is not aligned, the washers get misformed when torquing down the bolts.  I’d think that could affect the performance of the isolator(s).

 

Please let us know of your progress… and welcome to the fold!

[philiplane]

Change the engine isolators if they are more than five years old. You might find they're stiff, sagged, or cracking.

People hate changing them due to the cost, but it's the single best thing you can do for the plane, and yourself. They're only designed to last for 5-7 years before fatigue sets in. 

[MaxwellSmart86]

Thank you all for the feedback so far, this is all a helpful place to start. I believe I'm finding that even with a 3-blade prop on an M20C, I likely should not have significant vibrations... I called my A&P today as well, we are going to start digging together along with all the comments above (and any further comments here). Thanks much!

[Andy95W]

22 hours ago, MaxwellSmart86 said:

What would you like pictures of?

if you fly a C, what do you feel for vibration at cruise speeds? Thanks!

He was just trying to be friendly.  Most of us really like seeing pictures of each others’ airplanes, especially if it’s new to you.

[MaxwellSmart86]

[Hank]

I have a Hartzell 3-blade on my 1970 C, dynamically balanced at install around 2003 by the previous owner, and checked again but not adjusted in 2018. I've not noticed any undue vibration. 

I'm taking up a first-timer tomorrow, so will ask what he thinks about it.

[MaxwellSmart86]

1 hour ago, Hank said:

I have a Hartzell 3-blade on my 1970 C, dynamically balanced at install around 2003 by the previous owner, and checked again but not adjusted in 2018. I've not noticed any undue vibration. 

I'm taking up a first-timer tomorrow, so will ask what he thinks about it.

Thank you, this is all adding up to me digging more into the vibration I have. Based on everyone’s feedback, it’s not just a 3-blade prop versus 2-blade prop and it likely is not “normal” - I suspect something else. I hope my A&P can peak soon so I can report back.

[Andy95W]

3 hours ago, MaxwellSmart86 said:

@MaxwellSmart86- That is awesome!  Nice airplane.  I always love the original paint schemes.

As for your vibration- it sounds like you need a dynamic prop balancing done.  Decent prop shops can do it in a couple of hours.  Makes a huge difference.

[M20F]

@Jakes Simmons I feel made the most definitive post.  Fly any 4 banger (Mooney or otherwise) with a 3 bladed prop and then with a 2 bladed.  You will come to the same conclusion.  

[MaxwellSmart86]

I think I might have made progress last night. Took the plane out for 2hours, tried all different settings, 25-square on the ground holding the brakes, WOT with 2200, 2300, 2400, 2500 at low altitude, same thing at high altitude. All settings seem to have this vibration I feel present - some worse than others. Finally at WOT/2,500rpm/7,500ft we noticed the Left mag had much more of a rumble to it then the Right mag. On the right mag, you could continue to fly the plane and you almost couldn’t tell you were on one mag. On the left mag, there were noticeable hiccups and those hiccups had the same vibration/shake feeling as what I’ve been feeling in the yoke. Also, I only have a digital EGT but when I’d run the right mag my EGT would increase from 1325-1425 in a matter of 15 seconds. On the left mag, the EGT would go from 1325-1375 but also get there very slowly.

I'm thinking I have a left mag (plug, wire, whatever) not firing clean. I will call my A&P tomorrow and relay all of this.

i think I might be close to answer. Thank you all for the advise and suggestions.

Edited August 16 by MaxwellSmart86

[MaxwellSmart86]

Finally a small update… found one bad plug - figured we were on to something. But still a vibration. Compressions are all good, plugs are all tested/good. Both magnetos checked. Magneto timing checked. Prop was dynamically balanced 2 months ago. 
 

We dug through log books and we found the Lord motor mounts are 32years old. They don’t have tons of hours but 32 years is a long time if the logs are right. Motor is not sagging, mounts look ok visually and are squishy still. Bottom mounts maybe look a smidge sagged.

We decided to do motor mounts. It’s good maintenance no matter what. I’m curious what we learn, I will continue to post. I spoke to a 30-year vibration expert, he told me any mounts beyond 10-15 years can easily equate to doubling the vibration. He went through all details with me and agreed mounts are next on the list.

I’ll continue to post as we learn more…