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2 blade vs 3 blade on a O-360?


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Hey all! 

I’ve seen some talk in various places about 3 blade props not doing that well on O-360 engines.  Specifically, I have been told about some vibration. Has anyone else found this to be the case? If you had the choice to put a 3 blade or a 2 blade on your 4 cylinder Mooney, which would you chose? 

Location will be southern part of the country, Arkansas in particular.  Possible flights out west at some point but I will not be frequenting the Rockies every month or anything. Most areas I will be flying in are pretty normal terrain. 

Thanks for the help! 

J

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I have an IO360 with 3 blade McCauley.  It’s fine, no vibration, looks good.  I have no data to support this, but I think I’d be a couple knots faster on 2 blades.  Not sure if I takeoff or climb better with 3 blades but that’s the claim.  

Get it balanced and try out different cruise settings to see what works.  2500 rpm is nice on mine.

If I bought a new prop, I’d get a 2 blade Top Prop and hope for 2 extra knots.

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I have a 1975 M20C with a McCauley 3 blade. It is vibration free, very smooth.  That said, I would not spend extra money to change from a two to three blade.  Or vice versa.  When mine was changed, the previous owner spent the extra money to relocate the battery from the firewall to the rear radio bay.  Going to a 3 blade, let's see: extra weight, possible weight and balance consideration, extra cost of acquisition, additional overhaul cost, possible speed penalty versus cooler look (debatable) , slightly better acceleration and climb.

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As part of the 'repair' to my plane I chose to switch back to a 2 blade from the 3. Save a bit of weight and not much change based on the discussions here.

I'm still waiting for some stuff to become clear, but I might switch to an MT 3 blade instead since the 2 blade is not yet ordered, same or better weight than the 2 blade and a smaller diameter, the problem is lead times are long, which I thought would be a problem when this mess started.

But like many have said, absent some event I'd not switch props just to switch props.

 

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Lots of us have 3-blade props  ecause new 2-blade supply dropped and 3-blade.prices were lower for a while.

My C has had a 3-blade Hartzell for my 12 years of ownership, and a few years before that. It runs smoothly (checked dynamic balance at annual last year, it was still 0.01 from the original installation).

There are many naysayers, but dynamic balance data is proof. Oh, I get ~147 knots True Air Speed on my supposed-to-be 140 knot airplane, so it doesn't slow me down . . . . 

Although it's heavier, and pushed CG forward. Still have not had any problems with that, either.

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Thank you guys for the responses!  Cody has been a big help in this process and is actually the guy that I’m working with. I’ve been more than pleased with his assistance.  I was just looking to hear other opinions but it sounds like his is the only one that matters. :)  thanks for the responses guys! 

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Previous owner installed a 3-blade McCauley in the mid-90s.  He didn't like the vibe.  Got the dynamic balance done, which helped, but still didn't like the vibe.  Installed a plexiglass cover over the landing light, vibe went away.  Smooth as a sewing machine.  He liked the 3-blade prop for operating off his half-mile grass strip.

Tom

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10 hours ago, Steve W said:

As part of the 'repair' to my plane I chose to switch back to a 2 blade from the 3. Save a bit of weight and not much change based on the discussions here.

I'm still waiting for some stuff to become clear, but I might switch to an MT 3 blade instead since the 2 blade is not yet ordered, same or better weight than the 2 blade and a smaller diameter, the problem is lead times are long, which I thought would be a problem when this mess started.

But like many have said, absent some event I'd not switch props just to switch props.

 

Make sure the MT 3 blade is truly smaller diameter if that’s what you’re buying it for... although 3 blade props are smaller in some applications, the Mooney 3 blades I know of are same diameter as the 2 blade props they replaced.

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21 minutes ago, Ragsf15e said:

Make sure the MT 3 blade is truly smaller diameter if that’s what you’re buying it for... although 3 blade props are smaller in some applications, the Mooney 3 blades I know of are same diameter as the 2 blade props they replaced.

The STC Mooney MT (M20J) is smaller, it's the only smaller diameter prop that I'm aware of for the M20J.(71 for the MT vs 74 for everything else)

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I may have a bias Opinion when it comes to this Topic. An that Comes from my experiences, weather flying behind certain props, or all the Dynamic balances I have performed.

The 3 Blade Hartzell is just rougher than a 2 blade or a C424 McCauley 3 way prop. Why? Hell I don’t know. Could be airframe related, or just the fact that a 4 Cylinder Non-Counterweight Engine doesn’t like them. But with that being said I can balance one to where is a smooth at a Turbo-Prop on the ground, But when it’s in the air is when I sometimes get some Lack Luster Pireps.

I spent many hours flying a 67F for my previous employer with a 2 way Hartzell. It was smooth as you could ever ask for. Then one day he sold the prop off the plane, an I had to build a 3 blade from Serviceable parts we had. Once it was on the plane it was balanced just like the 2 way was.

It just wasn’t as happy in the air, an it was a tad slower. But it made up for that in the climb.

Talking about that same Propeller, I Ferried a J Model with that Propeller an it was Turbine Smooth.

Long Story Short, It’s happier on some planes than others.

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10 minutes ago, Steve W said:

The STC Mooney MT (M20J) is smaller, it's the only smaller diameter prop that I'm aware of for the M20J.(71 for the MT vs 74 for everything else)

1.5” extra clearance is definitely nice if you’re operating off dirt or bumpy grass/old pavement.  And lighter than a 2 blade, huh?  Nice.

Thats one thing to consider, my 3 blade added ~30 lbs?  Maybe I need to look that up again, seems high...

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When looking to purchase a 20c I flew a few. One had a 2 blade McCauley the other two were hartzell one 3 blade the other new 2 blade scimitar. The slowest of the bunch was the two blade McCauley and worse climb. The 3 blade looked cool was nose heavy in landing but that could be other factors as well.  Due to aircraft specifics I went with the new 2 blade scimitar aircraft. It was smooth and similar speed and climb as three blade. Got it home after the prebuy and my AP did a lot of research with Don Maxwell prior to my getting home. First oil change he checked and corrected engine alignment and did a repair on the dog house as well as aileron rig check. Maybe my imagination but that made it smoother, faster and better climb. I would say I have to be within 25fpm of the three blade I flew. But this all leads me to the question. "What did those other planes also need that was not prop related?" No matter what, it was still 3 different airframes. I would love more ground clearance, not for grass but because I'm new to mooney and just nervous/respectful of narrow margins.  If you're curious about performance data, a flight with full fuel and one 170lb human ballast at 6500 msl 30.17" baro 52F MP 23" almost wide open prop 2425 true airspeed 150.8 kts.  GPS ground speed data on 10 mile leg triangle confirmed the above with .6 kts.  The flight home from purchase was similar conditions, cooler and I thought the 146kts I was getting was good on a little more than 9 gph!  Look out wife, i have a mistress and I'm going to tell you all about her. Lol.  Seriously i really appreciate the AP taking his own time to research the plane and not do what many AP told (they are hell to work on, you're going to pay me a lot). Ed researched and as he worked, he found a lot about the plane he liked, thought superior, "if you stop, think plan, execute it's not bad at all, if you insist on working on it like a Cherokee you have problems, the biggest of which, you're a lousy mechanic".  I really appreciate him letting me get involved "learn your airplane.  If you're somewhere and need an AP I want you to know your plane chances are he wont".  He gives me the bill and theres no labor on it, just filter, oil, and some misc hardware $65, then fuel $400. I ask if fuel was supposed to be labor, he said, "no the labor is my plane warming gift to you. I would rather see you fly it and that's the fuel charge, I dont want this thing to be the typical mooney around here that flies 5 hours a year. I want you to have no excuse to not fly it at least 6 hours a month.  Shes solid now, fly her she will be kind, neglect her she will bite you hard".   Then he went back to work on the MIG 17 he is chief mechanic on.  Would engine alignment and doghouse make that much diffrrence?

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3 hours ago, Tcraft938 said:

When looking to purchase a 20c I flew a few. One had a 2 blade McCauley the other two were hartzell one 3 blade the other new 2 blade scimitar. The slowest of the bunch was the two blade McCauley and worse climb. The 3 blade looked cool was nose heavy in landing but that could be other factors as well.  Due to aircraft specifics I went with the new 2 blade scimitar aircraft. It was smooth and similar speed and climb as three blade. Got it home after the prebuy and my AP did a lot of research with Don Maxwell prior to my getting home. First oil change he checked and corrected engine alignment and did a repair on the dog house as well as aileron rig check. Maybe my imagination but that made it smoother, faster and better climb. I would say I have to be within 25fpm of the three blade I flew. But this all leads me to the question. "What did those other planes also need that was not prop related?" No matter what, it was still 3 different airframes. I would love more ground clearance, not for grass but because I'm new to mooney and just nervous/respectful of narrow margins.  If you're curious about performance data, a flight with full fuel and one 170lb human ballast at 6500 msl 30.17" baro 52F MP 23" almost wide open prop 2425 true airspeed 150.8 kts.  GPS ground speed data on 10 mile leg triangle confirmed the above with .6 kts.  The flight home from purchase was similar conditions, cooler and I thought the 146kts I was getting was good on a little more than 9 gph!  Look out wife, i have a mistress and I'm going to tell you all about her. Lol.  Seriously i really appreciate the AP taking his own time to research the plane and not do what many AP told (they are hell to work on, you're going to pay me a lot). Ed researched and as he worked, he found a lot about the plane he liked, thought superior, "if you stop, think plan, execute it's not bad at all, if you insist on working on it like a Cherokee you have problems, the biggest of which, you're a lousy mechanic".  I really appreciate him letting me get involved "learn your airplane.  If you're somewhere and need an AP I want you to know your plane chances are he wont".  He gives me the bill and theres no labor on it, just filter, oil, and some misc hardware $65, then fuel $400. I ask if fuel was supposed to be labor, he said, "no the labor is my plane warming gift to you. I would rather see you fly it and that's the fuel charge, I dont want this thing to be the typical mooney around here that flies 5 hours a year. I want you to have no excuse to not fly it at least 6 hours a month.  Shes solid now, fly her she will be kind, neglect her she will bite you hard".   Then he went back to work on the MIG 17 he is chief mechanic on.  Would engine alignment and doghouse make that much diffrrence?

Not looking for a fight and perceptions are reality, but maybe lighten up on the “3-blade is nose heavy in landing”?  Trim is your friend and the weight of a 3-blade does not make the short body “Nose heavy” in landing...The 3-blade does shorten ground run and climb better than a 3-blade with a speed and weight penalty.  More $ to overhaul.  Nice to have options...Speed or ground run and climb.  Choose your “winner”.

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Could the ignition system affect the “3-blade-hate”? I had my mags overhauled and after the IA installed and timed them, my helicopter-like vibration mostly disappeared. I have a 3-blade Hartzell.


Sent from my iPhone using Tapatalk

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