3 blade vs. 2 blade on M20J

[MReitz]

I have a 1980 M20J and am close to needing a new prop. I have heard a lot of good things about 3 blades but have not heard many negatives. Can anyone give me some advice on which is best suited for the 4 cyl Lycoming in the M20J?

 

Thanks!

[rbridges]

I'm just parroting what I've heard, but I thought there were concerns about potential vibration issues with 3 blades on the 4 cylinder lycomings.  It may be just on the 180hp motors.  Given the extra weight and slight deficit in cruise, I'd go with a 2 blade.  Of course, I live in one of the flattest parts of the country and climb is not much of an issue.

[clh]

I have a three blade and I know quite a few folks that have two blades.

The consensus of opinion is that:

3 blades...

Have a better climb, but slower cruise,

may be quieter but could have vibration issues,

Three blade (except the MT composite) props are heavier than two blades.

three blades are more expensive to overhaul, but look better.

(The last was my opinion and has no more merit than that)

[dooleypster]

I have a 3 blade (because I bought the airplane that way).  I do think the 3 blade looks cooler, and in my humble opinion, it is smoother to fly behind.......BUT, as has already been said, it costs more to overhaul/replace, and it weighs more.  I have an '88 J model.  I believe the 3 blade gives me better climb performance off the runway, but slightly less cruise speed.  My ship is really heavy, so the added weight of the 3 blade subtracts from my passenger carrying capability.  If and when I need to replace the prop....I'm going to put on a 2 blade!!  If I were in your shoes right now, I'd buy the 2 blade...... work with me here....I'm trying to save you some AMUs.

 

[OR75]

I am curious to know why you think you may need a new prop soon ?

Cannot yours be overhauled ?

What type of prop do you have right now ?

[PTK]

I would go with what Mooney and Lycoming put on the airplane originally.

I would not experiment and second guess!

[Seth]

I'm overhauling mine right now - though it is a three blade and also a different engine setup (IO-550 300 HP).  What is wrong with your prop where it needs to be replaced vs overhauled?  

 

Isn't there a three blade that has minimized drag so that it does not hurt the cruise performance yet gives you the additional climb performance off the runway?   I thought there was one out there.

 

Also, take a look at the two and three blade Top Prop.  

 

Stock is fine too.  

 

Was there a gouge or corrosion issue trashing your prop?

 

-Seth

[Hank]

My 3-blade runs smoothly. It's slowness must be cancelled by the 201 windshield, because I still make book speed and am close to book fuel (block time, no fuel flow installed). I do climb pretty well, though.

Regardless of what new prop you install, get it dynamically balanced.

[Shadrach]

I have a 2 blade, have known others with a 3 blade, sometime installations are smooth and some vibrate.  I don't think any Lyc 4 bangers are especially smooth engines and would not want to risk making one less so.  I have heard that it is difficult to make them work smoothly because a 4 Cyl makes 2 power pulses per RPM does not transmit well through 3 blades.  I've alway wondered why the inverse was not true with a 6 Cyl (3 power pulse per RPM) through a 2 blade (I see lots of old 2 bladed Bos).  Anyway, vibrations notwithstanding, as a general rule, a 2 bladed prop is more efficient at turning HP into thrust and it does weigh less.  No one has ever explained the science behind the claims of increased climb performance with a 3 blade, perhaps it has to do with diminished P-Factor.   The 3 blade will accelerate the plane faster (how much I don't know), so perhaps increased short field performance.

 

Th MT Composites may have totally different characteristics.

 

I would never spend more money to go slower and lose payload. However, they sure do look cool!

[Piloto]

The main justification for having a three blade prop is for higher power engine coupling. Since the RPM is limited the only option is to increase the torque load by adding another blade.

Three blade props makes handling the plane on the ground a little bit more difficult. A blade is more prone to interfere with the tow bar. You have to be more careful when removing the cowlings. Your head is more prone to hit a blade. You cannot have two guys pull on the prop to pull the plane.

As for esthetics; once the prop is turning there is no difference, it looks the same.

José

[N1026F]

Three blade props look cool and if engineered correctly, give you quicker takeoffs and climbs. But they're heavier, more expensive and not as fast in cruise. The Ovation actually lost a few knots when they went from two blades to the scimitar 3-blade.

I would stick to a two blade on an IO 360; its already the most efficient version of a single engine aircraft. My old 78 M20J had every speed mod available installed by its previous owner, Dave Burden.(Gap seals, wingtip extensions, plexiglass over the light, Lopresti gear door covers, tail fairing where it meets the fuselage, Iridium plugs (He even removed the step!).

He left the two blade in place and it had an honest 165 kts in cruise. I never thought it was a big deal until several people who had flown in other J models told me that 165 kts was something special.  Sanjeev owns that bird now and flies it out of Las Vegas.

[bonal]

As for esthetics; once the prop is turning there is no difference, it looks the same.

José          

 

Visually this is true, but there is a big difference when heard from the ground and a three blade sounds different and in my opinion way cooler than a 2 blade. You can always tell when a 3 blade is departing and often even when one is flying overhead. a very nice sound.

[PTK]

...it is difficult to make them work smoothly because a 4 Cyl makes 2 power pulses per RPM does not transmit well through 3 blades. I've alway wondered why the inverse was not true with a 6 Cyl (3 power pulse per RPM) through a 2 blade (I see lots of old 2 bladed Bos). Anyway, vibrations notwithstanding, as a general rule, a 2 bladed prop is more efficient at turning HP into thrust and it does weigh less...

I would never spend more money to go slower and lose payload...

This is wisdom!

I was unclear on the reasons. Thank you for explaining it Ross!

[Piloto]

As for esthetics; once the prop is turning there is no difference, it looks the same.

José          

 

Visually this is true, but there is a big difference when heard from the ground and a three blade sounds different and in my opinion way cooler than a 2 blade. You can always tell when a 3 blade is departing and often even when one is flying overhead. a very nice sound.

Yeap. Same as when a Vespa pass by versus a Harley. The girl on the Vespa wears a suit while the guy on the Harley wears a heavy jacket with a bunch of patches.

José

[par]

My 63 C has a 3 blade prop and that is how I purchased it. It is actually being overhauled right now. I normally climb at 110mph and I routinely see 1500 FPM with just me in the plane and 1000 FPM with a passenger. I have never flown in another C with a 2 blade prop so I don't know if i'm doing better or worse but maybe someone can chime in. By the same token, it feels smooth enough to me without having anything to compare it to.

[PTK]

Vespas are cool!!! Early 60's vintage especially!

[Guest]

50% more parts at overhaul, 50% more chance of leaks, 50% more induced drage from the extra blade, not quite 50% more weight.

I had the 3 blade MT on my E model and went back to the 2 blade Hartzell, cool sound is only heard when your plane is flying and you are not!

Clarence

[KSMooniac]

The 3 blade MT has a few advantages over the metal choices... it is lighter than all of them, it has a greater ground clearance (metal 3-bladers are the same as the 2-bladers for Mooneys!), and it is much smoother.  It will also reduce the likelihood of crank damage in a prop strike scenario since the blades will splinter/shatter, but unfortunately it won't eliminate the need for a tear-down inspection.  Removing the lower cowl with a 3-blade is a bit of a PITA compared to the 2-blade.  Ditto for hand tow bar use.

 

I don't believe it is as fast in cruise as the Hartzell Top Prop, though.  

 

The light weight and smoothness are the biggest advantages, IMO.  It can theoretically last longer since the leading edges have a replaceable stainless steel protector, so you don't end up filing it away like an aluminum blade.  The light weight is especially helpful for the K models that typically have CG's pretty far forward.

[aaronk25]

So O.P. What are you gonna do considering the info above?

[M20F]

The main reason I am aware of for three bladed and larger props (like those turned by some of the older geared engine set ups like a GO-480) is high altitude performance. The bigger prop or the additional blades take more of a bite so you can get higher than you would with a smaller prop or two blades. For most modern set ups I really don't think there is a lot of advantage or you would see people flying around with 10 bladed props as opposed to majority flying with two bladed.

[Rustler]

I replaced the prop on my 1980 M20J with an MT 3-blade because of unrepairable damage to the original. The new prop was 8 pounds +/- lighter than the 2-blade prop. The MT provided increased climb, quieter and smoother operation at altitude, and no discernible loss in cruise speed. It came to me balanced better than any dynamic balancing I've had on any prop. The aesthetics of the 3-blade vs. the 2-blade never entered into the decision. I never experienced any of the problems with the MT that are raised in postings regarding this subject.

 

I think if you search the database, you might be able to find the original report I wrote on this conversion.

[rob47v]

I can't speak for the Mooney's but I had a Bellanca Super Viking with a  3 blade prop and this thing was a speed monster, climbed like a rocket, and a true 170k cruiser, but it drank fuel like a sailor. I took a flight on an acquaintance similar viking with a 2 blade prop climb and it was very noticeable, slower that is to me, but cruise speeds tho slower weren't so bad. Oh the engine was absolutely smooth from start-up, idle to full power. I wish Lycoming would offer the IO-390 with increased stroke instead of larger bore. That would be of much added benefit. One might see hp gains of maybe 25-35 hp. Our little birds could highly benefit from such improvements. Just my thought!!!!     

[d0tnet]

3 blade engine out is a much different experience than with a 2 blade... I would put that in the cons column for the 3 blade.

[mike_elliott]

I replaced the prop on my 1980 M20J with an MT 3-blade because of unrepairable damage to the original. The new prop was 8 pounds +/- lighter than the 2-blade prop. The MT provided increased climb, quieter and smoother operation at altitude, and no discernible loss in cruise speed. It came to me balanced better than any dynamic balancing I've had on any prop. The aesthetics of the 3-blade vs. the 2-blade never entered into the decision. I never experienced any of the problems with the MT that are raised in postings regarding this subject.

 

I think if you search the database, you might be able to find the original report I wrote on this conversion.

on a 6 cylinder turbo charged engine, the 3 blade is the way to go, on a 4 cyl Lycoming, get ready to replace your fillings, lose TAS, gain climb performance and have a speed brake when you pull power. 

[MyNameIsNobody]

Wash-rinse-repeat. This is like comparing a banjo to a guitar. They are different, but both have advantages. I would go with a 2-blade for two reasons. Faster&Cheaper.

Now a statement like "Vespas are cool"....Chic? O.K. Neato? Yup. Groovy? Yes. Cool? Not so much.

Vrooom....Vrooom.

Like comparing a Mustang experience to a 152.

Are 152's cool?