Hartzell 3-Blade on M20J

[ToddDPT]

I'm excited to hopefully be joining the Mooney ranks with the purchase of a M20J.  This will be my first Mooney and definitely a welcomed upgrade from the Archers I have been renting!  I also want to thank everyone for the wealth of information they have shared with me on this site in previous posts.  Many of them have greatly helped me with my Mooney search.  

I am looking at pulling the trigger on a 1977 model that I have heard about through some of my local pilot friends.  It is not yet listed on any website.  I don't have all the specifics with the aircraft, but one of the differences was the Hartzell 3-blade prop.  I have looked on the forums for any information and have just come across minor comments about a 3 blade prop.  I've heard of possible increased vibrations, too much strain on a 200hp engine, etc.  What are your thoughts regarding a 3 blade?  Are there any ADs or extra maintenance costs regarding these props?  For those of you who know, does the 3-bladers give you that much more climb performance and reduce cruise speed much?  Both engine and prop have about 600 hours on them.

Again, I want to thank everyone for their time.

Todd

[Guest Anonymous]

Hi Todd,

I have a G model and not an F or J, so I am only pulling with 180 horses, but I do have the 3-blade (McCauley in my case) and like it.  I have heard the claims about vibration, but I don't think it is any different if the prop is properly (dymanically) balanced.  Mine shook a little before I did that, but is pretty smooth now.  It gets rid of the AD that was on the two-blade, and also all RPM restrictions except for a restriction for continuous operation from 1650 to 2200 reduced power below 15" of manifold.  Noise is noticebly reduced during takeoff and climb.

As for performance, I reduced my takeoff distance (about 200' at OLM, which is almost sea level), and my climb is better, although I have never quantified it.  I have a hangar neighbor with a factory 2 blade on an Exec, and I can climb with him now.  I did loose about 2 knots in cruise, but that was offset by the Lake Aero cowling and other speed mods that I installed at the same time.

I cannot comment on maintenance -- I haven't had anything to do on the prop yet.  However, my A&P says that the 3 blade reduces the stress on some components in the hub, and should fare better unless the vibration claims mentioned above become a factor.  Not mine, soo far.

RFB

[hansel]

Maybe a more important question is "why was the J converted to a three-blader in the first place?" This often occurs after a gear-up or a prop strike... not always, but you should be extra diligent with your review of the logs.

My understanding of the 2 v. 3 blade for Js is that it's basically a wash. The IO-360 is not a powerful engine, so you might gain a little in climb and looks department, then lose a little at cruise. Wouldn't be a deal breaker either way for me as long as the plane's history looks good.

Good luck, and welcome to the wonderful world of Moonies!

[Jeff_S]

I'll preface this by admitting that I've owned my J for all of a week now, so take what I say with that in mind. As you can see, it has the Hartzell 3-blade prop. The only thing I've noticed is that the panel vibrates a little more noticeably when the prop is running at 2400 than at any speed lower or higher than that. I haven't done anything about this yet but suspect that balancing the prop will help with that. It's one of the things I noticed during evaluation of the plane but no one, either here on the forum or others I talked to, felt like it was any big deal. Either balancing the prop, or ensuring the rubber panel mounts are in good shape, or most likely both, should clear it up.

My plane's W&B also shows it being more nose heavy than when she came from the factory, but I checked all the logs and weights and the 3-blade prop seemed like an almost exact match for the weight of the original McCauley, so that wasn't a factor. Probably just all the fancy avionics gew-gaws that have gone in over time, since it was pretty bare-bones coming from the factory as an AT model.

[ToddDPT]

Thanks again for everyone's input.  And Eric, that is great advice.  I am definitely looking into the possibility of damage history.  The overhauls seem to match the time closely to the airframe total time.

[Rustler]

Todd--

While a prop strike or other sudden stopage is always a suspicion, it may not always be the reason for a prop replacement.

I am just finishing installation of an MT 3-blade on my '80 J because of a rather sizeable chunk of propeller taken out by a rock last summer. It was flyable, but I had pretty mich lost confidence in it, and my A&P/AI wasn't sure that it would be overhaulable. Rather than worry about it, on goes the 3-blade.

About weight, here's what I found in my research. The Hartzell 3-blade weight about 71# and the McCauley about 72#. If I remember correctly, the prop that came on the plane weighs in the vicinity of 56#. There may be the cause for your W&B being so far forward. A principal reason why I opted for the MT 3-blade is that it is about 9# lighter than the original 2-blade that came on the airplane.

[RJBrown]

The Hartzell 3 blade is sexy to look at but slows the plane. Mooney actually increased the speed of the Ovation when they went back to a two blade from the 3. A 3 blade is generally smoother, if not it may need balanced. They also accelerate better.

[Kwixdraw]

I was looking through an old copy of Light Plane Maintenence today and noticed a question about a vibration after a change to a three blade prop on a Cessna . The vibration was described just as you did at about 2400 rpm. They suggested dismaounting the prop and turning it 180 degrees to remount it. Apparently there is a proprer orientation relative to the crankshaft. just thought you might want to check into it further.

[KSMooniac]

Michael, please post a PIREP on the MT when you get it done!  I'm *very* interested in one to replace my doggy '77 square-tip McCauley 2-blader.

IMO, the metal 3-bladers on 4 cylinder Mooneys are  waste.  Slower cruise, higher potential for vibration problems, no additional ground clearance, and of course heavier weight.  Only positive is subjective ramp appeal.  I wouldn't rule a candidate plane out for having a 3-blade prop, but it would be a deduction in my book.  YMMV.

[Ned Gravel]

One data point - and anecdotal only.  Take it for what it is worth (exactly what you paid for it)

My friend owns a '66 E model and he owns an MSC in Canada.  During my overhaul last year, he was trying out his new MT and wanted to figure out why he was not going as fast as he thought he should in cruise.  So he took his new MT off his, and put my 15 year old two-bladed Hartzell on in its place.  According to him, he gained about 5 mph in cruise.  Ran comparison tests for a week. 

In the end, he decided to go with the Hartzell Top Prop.

Just one data point.

[seebruce]

Has anyone noticed if the 3 bladed prop cycles quite a bit slower than a 2 blade at run-up?

[Seth]

I have a three blade prop on my 1967 M20F and it too vibrates a bit more around 2400 RPM.  Also, it does take longer than a two blade to cycle.  I never knew this fact, as it was the main constant speed prop I've ever flown (except for a 182 once every now and then), and an instructor told me to have it looked into.  The annual was a few weeks later, and they said three blade props cycle slower than two blade props.  Expecailly when returning to speed - its especially noticible during run-up.

[Jeff_S]

Nor do I have anything to compare it to since this is the first CS prop I've ever owned. But when I was doing my sign-off work with the CFI, which as you can imagine included more Touch n' Gos than I can remember, there was a noticeable lag between when I added power and the prop bit in.  And during runup, I'd say it takes about 2-3 seconds before the prop cycles. But it's always passed annual so I assume it's fine.

[Ned Gravel]

Change to my previous post on the 3-bladed MT and the Top Prop for my friend and his '66 E model.  He decided to put every worthy speed mod on instead, and keep the MT.  Now it flies almost as fast as it did with the 2-bladed prop (1 or 2 mph below his previous numbers). 

In fact, this past weekend, he told me he was in level flight within 12 miles per hour or so of the 189 mph VNE at 4500 feet and 25 squared.  I told him that was wonderful, I was at the same altitude over Ottawa, also at 25 squared - within 9 mph of VNE. 

Two blades are still faster.  Er... ...assuming, of course, that absolutely everything else between our two birds is the same - which is not the case.

[Parker_Woodruff]

I just test-flew an M20C with 3-blade hartzell.  Could definitely tell the harmonics difference.  Great looking and it climbed well but it would get old on longer flights.

[Scopes]

I'm currently looking at replacing my prop with top prop conversion (still have AD hub and the cost of overhaul with replacement of hub was quoted higher than the top prop) and am leaning towards the 2-blade (8500) over the 3-blade (9700) but my concern is the rpm restriction on the M20E application:

2-blade - "no cont. ops above 24" manifold pressure between 2350 and 2550 rpm"

3-blade - "avoid cont. ops below 15" between 1950 and 2350 rpm"

what do people think? Does the more permissive operation of the 3-blade cancel out some of the disadvantages of 3-blade on io360 (weight and cruise speed) - I guess you would run the 2-blade above 2550 on climb out to altitude where you won't make 24" 

 

 

[jetdriven]

You run these airplanes at 2700 rpm for all climbs.  

[mike_elliott]

3 blade props on 4 cyl Lycoming's are not the best idea IMO. The extra 17# hanging in front of the thrust bearing, the 60 deg orientation of the blades vs the 180 degree firing pulse set up a vibration that cannot be balanced out. Hartzell sure tried for me.

Some swear how smooth their 3 blade/4cyl. combo is. Maxwell had just such a customer recently. He had his guys hang a 2 blade on it while the owner and Don went to lunch. When they came back, Don and the owner went up in it. When they landed, the owner ordered a 2 blade.

I had both on my F, also a IO360A1A. Lost 5 kts cruise, a lot more vibration, better climb, chop power and its like putting speed brakes out. The 2 blade was a far better fit, besides being less costly to maintain.

[Scopes]

Great thanks guys - my training at our aerodrome was to climb out at 2500 for noise abatement but it's just a guideline so I will go with the 2-blade and climb out louder and faster!

[Guest]

Another thing wth the Hartzell 3 blapde prop is the spinner is too small in diameter, leaving a ring of flat cowl exposed to the air flow.

Clarence

Edited June 1, 2016 by M20Doc

[carusoam]

There is some dissapointment with that little mis-match that Clarence described.

Best regards,

-a-

[bradp]

I've heard there are potential issues with the counterweights on the IO-360 and the 3- blades. Is this just an OWT?  

@Scopes Uh that's right where most of us cruise below whatever altitude I can't make 24" of MP WOT (want to say 6/7k, no POH in front of me).  Down low it's often 25/25. McCauley two blades on the 360 have the later limitation you referenced.  

Another advantage to 2-blades comes to the pocket book at overhaul time.  

Byron is correct that it makes little sense to climb at 2500 rpm.  

[Hank]

I climb my C with 3-blade Hartzell at WOT/2700, but my restrictions are different:  "no continuous operation below 15" manifold pressure between 1950-2350 RPM" and red zone of 1900-2250. I don't think it vibrates much, but it was dynamically balanced; probably time to have it checked again, if I'm ever out Arkansas way or Cody ever swings through LA.

Many people poo-poo the idea of 3 blades with 4 cylinders. Some engines just won't run smoothly with it; some do. Don't know how to tell without mounting one and doing a dynamic balance.

[mike_elliott]

The three blade sure looks cool, but I have yet to be in a 4 cyl lyc that is smoother with one than a 2 blade. (Hartzell only, never have been behind a MT composite or McCauley 3 blade and a 4 cyl lyc). Hartzell's shop in Piqua Oh, tried 3 different times to get my short lived 3 blade balanced. While it would show some very low ips numbers, there was a harmonic and thrust vibration they could not account for. They took it back within the 90 days they gave me to be delighted and I plunked down the extra dough for a 2 blade. It was cheaper from LASAR than from Hartzell, but I picked it up at Hartzell and they hung it and balanced it. The engineers there said it was possibly because of the extra weight hanging in front of the main thrust bearing and the firing order of a 4 cyl vs a 6.

Now the 6 cylinder engines are smooth as glass with a well balanced Hartzell 3 blade that I have been behind.

[Jeff_S]

I had the 3-blade Top Prop on my J and I really liked it. Of course, I never flew it with a 2-blade so I can't make comparisons, but when I had the prop dynamically balanced it was already at a "good" level (roughly .2 IPS) and we got it down to .07 IPS (as I recall..doing that from memory). I never felt like there was undue vibration, and this is compared to my buddy's J that had the McCauley 3-blade. I didn't notice any difference between the two planes.

I do think climb was improved, as I never had any of the early sluggishness in climb that some folks complain about in a J. As for cruise speed, I routinely was able to get 150 KTAS on about 9.5-10.5 gph LOP at standard cruise altitudes, so I may have suffered a bit there but not too much. I found it comforting to have the extra oomph to get off the ground even in hot and heavy situations.