Replace my 3-blade for a 2-blade? Stupid idea?

[AndreiC]

I took my plane (1970 M20E with 3 blade McCauley prop) to the annual, and the shop gave me a ride back in their 1965 M20C with a 2 blade prop. I was amazed at how much smoother their engine was. Mine has a continuous vibration that makes reading my iphone difficult at most times. It does not bother me as I sit in the plane, but I wonder if it is not even bad for the plane to be constantly shaking like this.

What are the advantages of the 3 blade prop? I was told it is getting better ground clearance (the blades are shorter). Is this true? 

If it is true that a 2-blade will work better on my 4-banger IO-360, do you guys think I can find someone willing to trade a 2-blade prop for my 3-blade? I don't have the money in the near future for a straight up prop replacement.

[aggiepilot04]

1 minute ago, Andrei Caldararu said:

I took my plane (1970 M20E with 3 blade McCauley prop) to the annual, and the shop gave me a ride back in their 1965 M20C with a 2 blade prop. I was amazed at how much smoother their engine was. Mine has a continuous vibration that makes reading my iphone difficult at most times. It does not bother me as I sit in the plane, but I wonder if it is not even bad for the plane to be constantly shaking like this.

What are the advantages of the 3 blade prop? I was told it is getting better ground clearance (the blades are shorter). Is this true? 

If it is true that a 2-blade will work better on my 4-banger IO-360, do you guys think I can find someone willing to trade a 2-blade prop for my 3-blade? I don't have the money in the near future for a straight up prop replacement.

The 3-blades look better (imo), but as you experienced, 2-blades will provide a much smoother ride on a 4-cylinder engine. My J model always vibrated (regardless of balancing efforts), and Maxwell always leaned on me to move to a 2-blade. It's not just comfort...obviously vibration is hard on everything.

[kortopates]

Other than ramp appeal, the advantages of the 3 blade are improved climb. But when engine power is lost the extra blade is an effective air brake and noticeably reduces float on landings.

Edited September 14, 2023 by kortopates

[Hank]

Some 3-blade props are shorter than the equivalent 2-blade props. But on out Mooneys, they are the same, so no change in ground clearance. 

Have you tried getting your prop dynamically balanced? The 3-blade Hartzell on my C is quite smooth, it balanced to 0.01 ips. No noticeable vibration. 

[mike_elliott]

5 minutes ago, kortopates said:

Other than ramp appeal, the advantages of the 3 blade are improved climb. But when engine power is lost the extra blade is an effective air brake and noticeably reduces float on landings.

When I had my F, I lost 5 kts in cruise with a 3 blade hartzel, and it wasnt able to be balanced smooth, in spite of Piqua (Hartzell) having 3 swings at the plate to do it. Finally, ordered a 2 blade and it was night and day. I probably wouldnt have noticed the vibration if I had not previously had a 2 blade on it, much like a helo pilot doesnt notice the vibration of those things. But what Paul says for advantages were true. Better climb, built in speed brake when chopping power. Extra 17# hanging in front of the main bearing on the engine to deal with.

[KSMooniac]

The MT prop for Mooneys is the only one with a smaller diameter/increased ground clearance. It is also much lighter than the 2 blade metal and far smoother than all of them when balanced. I love mine, and would only consider switching to the upcoming 2 blade composite Hartzell for even more weight reduction and perhaps faster cruise.

In your case, I'd try a good dynamic balance first, and if that doesn't get rid of the vibes then I'd find a way to swap for a 2 blade or MT.

Sent from my LM-V600 using Tapatalk

[DCarlton]

I'm no expert but I've never thought my 3 blade McCauley vibrated.  It does shudder crazy some times when you start or shut down the engine but I think it's smooth in flight.  Never had it balanced although I've thought about it.  I just got a quote this week for a MT and it was $17250 plus shipping.  The estimate I got for the two blade Hartzell was $12K if I traded the McCauley.  The 2 blade composite Hartzell does sound interesting; wondering if those will handle chips and dings better/worse than a metal prop.  

[EricJ]

3 hours ago, Andrei Caldararu said:

I took my plane (1970 M20E with 3 blade McCauley prop) to the annual, and the shop gave me a ride back in their 1965 M20C with a 2 blade prop. I was amazed at how much smoother their engine was. Mine has a continuous vibration that makes reading my iphone difficult at most times. It does not bother me as I sit in the plane, but I wonder if it is not even bad for the plane to be constantly shaking like this.

What are the advantages of the 3 blade prop? I was told it is getting better ground clearance (the blades are shorter). Is this true? 

If it is true that a 2-blade will work better on my 4-banger IO-360, do you guys think I can find someone willing to trade a 2-blade prop for my 3-blade? I don't have the money in the near future for a straight up prop replacement.

Something less expensive to try might be getting a balance job done.    If a balance job corrects a significant misbalance it can make a noticeable difference.

[Ragsf15e]

3 hours ago, DCarlton said:

I'm no expert but I've never thought my 3 blade McCauley vibrated.  It does shudder crazy some times when you start or shut down the engine but I think it's smooth in flight.  Never had it balanced although I've thought about it.  I just got a quote this week for a MT and it was $17250 plus shipping.  The estimate I got for the two blade Hartzell was $12K if I traded the McCauley.  The 2 blade composite Hartzell does sound interesting; wondering if those will handle chips and dings better/worse than a metal prop.  

Curious, who was going to take your current prop in trade?  Hartzel?

[DCarlton]

3 hours ago, Ragsf15e said:

Curious, who was going to take your current prop in trade?  Hartzel?

My current prop is a 3 blade McCauley.  I discussed the possibility of a trade with Roy at:  https://ottosenprop.com

Also discussed the possibility of overhauling my McCauley. 

[AndreiC]

Ok, are there any recommended prop shops around the upper Midwest (I am in Madison) to go to for prop balancing?

 

 

[Fly Boomer]

11 hours ago, Andrei Caldararu said:

Ok, are there any recommended prop shops around the upper Midwest (I am in Madison) to go to for prop balancing?

 

 

Not exactly "upper" Midwest, but our resident prop guy is @Cody Stallings.

[EricJ]

11 hours ago, Andrei Caldararu said:

Ok, are there any recommended prop shops around the upper Midwest (I am in Madison) to go to for prop balancing?

You don't need a prop shop to do a good balance job.    Some A&Ps do it.   The guy that did mine isn't even an A&P and usually just does experimentals.    I supervised him doing mine and signed it off myself.   He did a good job.

[LANCECASPER]

12 hours ago, Andrei Caldararu said:

Ok, are there any recommended prop shops around the upper Midwest (I am in Madison) to go to for prop balancing?

 

 

@Rmnpilot isn’t too far from you - he may have used someone up there to do a prop balance that he could recommend

[Rmnpilot]

2 hours ago, LANCECASPER said:

@Rmnpilot isn’t too far from you - he may have used someone up there to do a prop balance that he could recommend

Just had mine done.  @Andrei Caldararu, send me a message.  Im based at ATW and there’s a local guy here that does it
 

[Hank]

I had my balance checked during annual several years ago, more than a decade after the initial balance. The IA charged $50 extra, since the spinner, cowling, etc., was already off.

You really just need someone with the equipment. Quick, easy.and pretty painless.

[AndreiC]

OK, I'll ask the shop that does my annual now (Mooney Service Center in Willmar, MN) if they can dynamically balance the prop as well while at it. If not, I'll talk to Ryan @Rmnpilot. BTW, @Rmnpilot, did you see a big change after the balancing?

[A64Pilot]

A three blade should be smoother than a two blade, but I had an Avia Engineer who rode with me in my Maule say that some motors that had a lot of hours on a two blade just won’t run smooth with three, I don’t know, maybe? But the greater the blade number the smoother the prop as a general rule..

I think your crazy, unless you have to buy a new prop buying one is well crazy, balance the one you have, normal limit is .2 IPS (inches per second) but I try to balance to less than .1 myself, some props you can get real low, some you can’t I don’t know why, perhaps it’s the engine. Even if you get a few kts with a different prop are a few kts worth tens of thousand of $$?

The other possibility is blade track, which is real easy to check, pull your plugs so it’s easy to turn the motor and put a folding chair or anything so it just touches the prop, rotate the prop it should touch at exactly the same place on all blades, if not you have an issue and need a prop shop to look at it.

You want to balance with the spinner on, because of course it could affect balance.

[cliffy]

My 3 blade balanced out real nice.

How old are your engine mounts?

Is anything "hard" touching the engine mount causing the vibration to transfer to the airframe? 

One that might be missed is "how hard " is your baffle rubber? It might be transferring vibration to the cowl.