Does a three-bladed prop make for a rougher ride than a two bladed prop?

[BigD]

I recently flew a M 20 C with a three-blade prop. I was surprised at the rough ride the airplane offered. It almost seemed to be vibrating at the higher rpm’s. 400 when we will use the RPMs to 2400 it seems smooth out a little bit but was still rougher than I remember a two-bladed prop being. I was told by several people that this is normal when you put a three bladed prop on a four-cylinder engine. I am curious what other people have to say about this. I have flown the two bladed Mooneys and I do not remember the ride being this shaky. I am familiar with the rule that four-cylinders should have a two-bladed prop, and six cylinders should have a three-blade prop.

 

 

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[TTaylor]

My experience is the opposite, three blade runs smoother.

 

[L. Trotter]

Something is not right if the vibration is that noticeable. If all is well....dynamic balancing is in order.

[DonMuncy]

From what I read and hear, it depends on some weird engine harmonics that no one can predict. Some 4 cylinder engines do well and some don't. And the only way to know for sure is to try one.

[kerry]

When shopping for a prop I came across a good deal on a 3 blade McCauley Blackmac.  The prop shop I was dealing with highly advised against it.  They mentioned  every Mooney they put it on had bad vibration.  I decided to go with Hartzell top prop.  If it's worth anything I think the 3 blade prop looks pretty cool on a short body Mooney.

[Yetti]

Yes but only a polished spinner will show an increase in speed. 

[tigers2007]

I noticed a smoother ride with my 3x blade after both of my magnetos were replaced (1100HRS or so since last IRAN). Something new it felt like riding in a helicopter before. I bet that mag timing was the biggest factor.


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[pirate]

I added a three blade on my C and would never go back. Smooth when ( Properly ) balanced and  truley helps a C climb performance on hot days. 

 

[MyNameIsNobody]

I can give two data points.  1966 M20E. Three blade McCauley and newer version of same.  No sign of vibration beyond what I have experienced in many other GA aircraft.  Short ground run.  Strong climb.  150knots if you burn an extra gallon of gas an hour.

Not a C...

[neilpilot]

Operated a 3 blade on my 64E for 20 year, and on our 65C since purchase in 2012.  Both are smooth, and recent balance check on 65C indicated very low vibration at 0.05 IPS.

[Hank]

My C has a 3-blade Hartzell for climb, and a polished spinner for speed. At altitude, I get 146-148 KTAS on 9 gph block time (no fuel flow).

It was dynamically balanced by the PO at install ~2003; I checked it at annual last year, it was 0.01 ips so we just unhooked and left it alone . . . .

So much for "rough" and "slow."  

[Raptor05121]

I love my three-blade.  Its very smooth. I've flown/rode in three other Mooneys with two blade and some vibrate, some don't. I'd say mine is right in the middle, probably smoother than most, and thats with mags at 700SMOH and last balance in 2005. I'm sure I could spend some money and make it nicer but its perfect for me. If my instruments are any to believe, cruise anywhere from 145-147KTAS at 8,500ft and block-to-block fuel burn is 8.5-8.7gph. Solo with 20 gallons, I'll easily peak 1,500fpm, and at full gross is 750-800fpm

This Mooney has taught me three things: I'll never own a fixed-gear plane, I'll never own a fixed-pitch plane, and I'll never own a 2-blade. 

[BigD]

I love my three-blade.  Its very smooth. I've flown/rode in three other Mooneys with two blade and some vibrate, some don't. I'd say mine is right in the middle, probably smoother than most, and thats with mags at 700SMOH and last balance in 2005. I'm sure I could spend some money and make it nicer but its perfect for me. If my instruments are any to believe, cruise anywhere from 145-147KTAS at 8,500ft and block-to-block fuel burn is 8.5-8.7gph. Solo with 20 gallons, I'll easily peak 1,500fpm, and at full gross is 750-800fpm


This Mooney has taught me three things: I'll never own a fixed-gear plane, I'll never own a fixed-pitch plane, and I'll never own a 2-blade. 

I hope I have similar experience with mine Raptor


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[cctsurf]

What about loading, with that big anchor up front (3-blade prop), do you find that you have difficulty keeping the cg from getting too far forward?  Just Curious

[ArtVandelay]

I assume the added benefit of 3 blade props on a J is no placard for RPM,MP restrictions.

[jaylw314]

34 minutes ago, teejayevans said:

I assume the added benefit of 3 blade props on a J is no placard for RPM,MP restrictions.

On my M20J with IO-360 A3B6, the installation of the 2-blade Hartzell prop removes the RPM and MP restrictions.  I think they only apply to the original 2-blade McCauley on the M20J

[Hank]

3 hours ago, cctsurf said:

What about loading, with that big anchor up front (3-blade prop), do you find that you have difficulty keeping the cg from getting too far forward?  Just Curious

My 200 lbs, my instructor's dozen or two more, full fuel and a 3-blade were never a problem. Close to the front but legal, and longer body styles should be easier.

It does make an effective air brake if you want to slow down quicker.  

Edited March 29, 2018 by Hank

[Alan Fox]

I have had both , I prefer the 3 blade...No real vibration problems....... Takes a while to get used to the feel sound of the 3 blade , if transitioning from a 2 blade...

[DXB]

Its maybe just a balancing issue on your 3 blade rather than an intrinsic feature of the prop?

[tigers2007]

If my instruments are any to believe, cruise anywhere from 145-147KTAS at 8,500ft and block-to-block fuel burn is 8.5-8.7gph. Solo with 20 gallons, I'll easily peak 1,500fpm, and at full gross is 750-800fpm

How are you guys getting 145-147kts? I have consistently calculated 138kts TAS on a regular basis. 20” and 2500rpm; leaned getting

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[MyNameIsNobody]

One two three four I smell a speed war...

 

[TTaylor]

19 hours ago, tigers2007 said:

 

How are you guys getting 145-147kts? I have consistently calculated 138kts TAS on a regular basis. 20” and 2500rpm; leaned getting

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It is the same way they claim their penis size .

[MyNameIsNobody]

3 hours ago, TTaylor said:

It is the same way they claim their penis size .

Is that a thing?

[Hank]

On 3/30/2018 at 9:06 PM, tigers2007 said:

How are you guys getting 145-147kts? I have consistently calculated 138kts TAS on a regular basis. 20” and 2500rpm; leaned getting
 

 

Two ways:

The OAT for this was 43°F, so you can check my math.

Here, on a later flight, I let Dr. Garmin WAAS do the math:

Please let me know if I did something wrong.

Easy way, from photo #1:  IAS = 144 mph; Altitude = 9500 ms

TAS = 144 + (2% x 144 x 9.5) = 144 + 27 = 171 mph = 148 knots 

From Photo #2, TAS = 147 knots in the bottom box. Takes a lot of knob twisting though . . . .

[Raptor05121]

On 3/29/2018 at 3:19 PM, cctsurf said:

What about loading, with that big anchor up front (3-blade prop), do you find that you have difficulty keeping the cg from getting too far forward?  Just Curious

IIRC the 3blade is about 20lbs heavier. With a PlanePower alternator and Skytec starter, it kinda balances out. CG and max gross are two things I never have to worry about in my plane. Volume is the limiting factor. I've loaded this plane with camping gear stuffed to the ceiling, 3 people and full fuel and I was 150 under gross. If it fits, it ships.

On 3/30/2018 at 10:06 PM, tigers2007 said:

 

How are you guys getting 145-147kts? I have consistently calculated 138kts TAS on a regular basis. 20” and 2500rpm; leaned getting

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I run WOT/2700rpm up to climb, pull the prop back to 2500 and lean until smooth. Trim trim trim, after a few minutes I'll run the numbers. The slowest I've ever seen is 143KTAS. It'll swim between 145-147 depending on how I leaned (non-vernier mixture).