Pitching for pro's and con's of a 3 blade conversion for a 180hp O-360. My research has yielded that the third blade requires more than 180 hp to justify the 3rd blade. Two blades are more efficient than additional blades due to disturbed air, etc. Since I'm in a taildragger clearance is less of an issue than a smaller diameter 3 blade is designed to overcome. Research has also indicated that the original Hartzell at 2700 rpm and 76" the tips are at .79 mach during take off roll. An 80" would be .83 mach, well below the .92 cavitating and sonic threshold disturbance for noise abatement. Maybe I'm missing something. Anyone here with experience with converting to a 3 blade prop from a 2 blade?

Long 2 blade.

3 are for looks. And extra weight, more expense, and less performance.

UtahMaule wrote:Long 2 blade.

3 are for looks. And extra weight, more expense, and less performance.

You hinted at sharing your reasoning and empirical data on this a while back when you unveiled the new 11ZA. Can you elaborate?

I'd argue that a three blade does have some advantages: smoother balance, and shorter blades for more prop clearance are two I can think of. I got the impression though that you came to a staggering conclusion in the cons department.

Yeah. I flew both. 11ZA is RWM's badass mosheen. He can tell more. I was always in the 2 blade camp. Even more now. I flew both, same plane, same day. Hands down 2 won. I know Kevin loves his 3. But he only tested 3 blades against each other. Bill Duncan tried a 4 blade on his beast. He's back to 2. I've been flying a 300 horse CallAir. 2 blades. All the scout and husky guys have thrown rocks at the 3 blades. Less is more. Trust me.

Is 11ZA a 180hp Maule? Just would like to make sure we're apples and apples...

Edit: Tail number indicates it is 235 hp. Apples and oranges...

No. IO-540. But that's even more reason for 2 blades. Plenty of O-360 guys have done this testing for you. Hands down 2. Of course maybe you like the look. Hate money and want a heavier nose.....[emoji848]

Back when I was regularly flying my friend's 231, he asked me to look into the performance difference between a 3 blade and a 2 blade (which the airplane had). My conclusion after doing some research was that with the 2 blade, it would be about 3 knots quicker than with a 3 blade, but with a 3 blade it would climb maybe 15 fpm better at the same airspeed. Neither was enough of a performance change to justify ever changing a prop, just for the sake of changing a prop, from whatever was already on an airplane. The difference in "smoothness" wouldn't be noticeable on the average 6 cylinder engine; it might be noticeable on a 4.

That was pre-MT, of course, but I doubt that it would make any difference, whether a prop was composite or aluminum.

Of course, a 3 blade looks cooler when parked, but that cool factor goes away as soon as the engine starts.

Cary

UtahMaule wrote:No. IO-540. But that's even more reason for 2 blades. Plenty of O-360 guys have done this testing for you. Hands down 2. Of course maybe you like the look. Hate money and want a heavier nose.....[emoji848]

Just getting "steered" this direction. My research indicates you are right but being a newby I would like to make sure I make a good (albeit expensive) decision. Can't afford to make this decision more than once.

UtahMaule wrote:Yeah. I flew both. 11ZA is RWM's badass mosheen. He can tell more. I was always in the 2 blade camp. Even more now. I flew both, same plane, same day. Hands down 2 won. I know Kevin loves his 3. But he only tested 3 blades against each other. Bill Duncan tried a 4 blade on his beast. He's back to 2. I've been flying a 300 horse CallAir. 2 blades. All the scout and husky guys have thrown rocks at the 3 blades. Less is more. Trust me.

Be careful with generalizations.... If we are looking at pure physics, then one blade should be the absolute best. But in the real world everything comes at a compromise. Kevin may have only tested various three blades, but I can assure you having owned multiple MT's (both 2 and 3 bladed), they don't make a two blade that has enough blade for our (Kevin and my) combination. I ran these props back to back multiple times. George Mandes did this exact exercise with the exact same results. I will say that on this combination you can extract the same (or very close) performance out of a two blade C66, but it takes at least a 86" (3 inches longer) prop to do it.

Look at it this way, several (but not all) of the MT STC's that cover both 2 and 3 blade variants utilize the exact same blade on either hub. The only physical way for the 3 blade to produce less thrust under that circumstance is for the engine to not be able to produce enough horsepower to effectively turn the 3 blade prop. Period. When we were trying to decide between the 2 and 3 blade MT for our application, flight resource indicated that 300 hp would be the minimum horse power needed to effectively turn the bigger prop, which in our case should have been borderline, so the only choice we had was to really either guess, or try them both out (which we did).

The Mac 401 smokes the Mac 2 blades (any flavor) out of the hole, the reason many back country guys poo-poo the big 401 prop is simply the weight (more the cg effect than actual pounds). I *think* that if you could get a longer MT, it would work for our application, but that's just pure speculation...

The fact that you Callair works best with a 2 blade is as anecdotal of any of this. Ever see any working turbine AT or Thrush with a two blade on it? In fact on that note, all the 500 gallon -34 powered guys are going from 3 blade to 4 We have already converted two of our airplane, and there is no comparison, it takes a crippled combination, and turns it into a pocket rocket. In most cases it's proved a 10% increase in hauling ability, in my admittedly piggish combination it makes almost 1,000# hauling difference But again that has little to no bearing on what might work best on an O-360 powered M4.

I personally don't care for the looks of any MT, but my mission dictated a better hole shot than I could get out of the shorter C66s, but not at the weight penalty of the 401's. So for me the best compromise was a 3 blade MT. Believe me when I say, I really wanted the lighter more economical 2 blade to work, but the truth is, it just left too much horsepower lying on the table. There is only one reason to build more horsepower into your airplane, and that is to be able to turn more prop.

Also as I alluded to RWM when we spoke about this, I have had conflicting results running the same two props on two different physically airframe/engine combinations even when they are the same model. We see this all the time in our work fleet, as we have multiple props in the mix to keep from having an airplane down while a prop needs service. Some engines are peppier (which affects it's ability to turn the bigger prop), some airframes are draggier, it all adds up.

Lastly, I would have to say apples to apples is going to be the best barometer you're going to get short of actually running them on your own airplane. It's the only advice I could afford RWM, because as I said to him, I had no IO540 / Maule experience... Consequently just looking for O-360 / MT combinations will still leave some wiggle room when trying to nail down whats best. You really need to poll O-360/MT/Maule M4 owners... and even that's not 100%, but probably as close as your going to get short of running them yourself...

Take care, Rob

Rob wrote:

UtahMaule wrote:Yeah. I flew both. 11ZA is RWM's badass mosheen. He can tell more. I was always in the 2 blade camp. Even more now. I flew both, same plane, same day. Hands down 2 won. I know Kevin loves his 3. But he only tested 3 blades against each other. Bill Duncan tried a 4 blade on his beast. He's back to 2. I've been flying a 300 horse CallAir. 2 blades. All the scout and husky guys have thrown rocks at the 3 blades. Less is more. Trust me.

Be careful with generalizations.... If we are looking at pure physics, then one blade should be the absolute best. But in the real world everything comes at a compromise. Kevin may have only tested various three blades, but I can assure you having owned multiple MT's (both 2 and 3 bladed), they don't make a two blade that has enough blade for our (Kevin and my) combination. I ran these props back to back multiple times. George Mandes did this exact exercise with the exact same results. I will say that on this combination you can extract the same (or very close) performance out of a two blade C66, but it takes at least a 86" (3 inches longer) prop to do it.

Look at it this way, several (but not all) of the MT STC's that cover both 2 and 3 blade variants utilize the exact same blade on either hub. The only physical way for the 3 blade to produce less thrust under that circumstance is for the engine to not be able to produce enough horsepower to effectively turn the 3 blade prop. Period. When we were trying to decide between the 2 and 3 blade MT for our application, flight resource indicated that 300 hp would be the minimum horse power needed to effectively turn the bigger prop, which in our case should have been borderline, so the only choice we had was to really either guess, or try them both out (which we did).

The Mac 401 smokes the Mac 2 blades (any flavor) out of the hole, the reason many back country guys poo-poo the big 401 prop is simply the weight (more the cg effect than actual pounds). I *think* that if you could get a longer MT, it would work for our application, but that's just pure speculation...

The fact that you Callair works best with a 2 blade is as anecdotal of any of this. Ever see any working turbine AT or Thrush with a two blade on it? In fact on that note, all the 500 gallon -34 powered guys are going from 3 blade to 4 We have already converted two of our airplane, and there is no comparison, it takes a crippled combination, and turns it into a pocket rocket. In most cases it's proved a 10% increase in hauling ability, in my admittedly piggish combination it makes almost 1,000# hauling difference But again that has little to no bearing on what might work best on an O-360 powered M4.

I personally don't care for the looks of any MT, but my mission dictated a better hole shot than I could get out of the shorter C66s, but not at the weight penalty of the 401's. So for me the best compromise was a 3 blade MT. Believe me when I say, I really wanted the lighter more economical 2 blade to work, but the truth is, it just left too much horsepower lying on the table. There is only one reason to build more horsepower into your airplane, and that is to be able to turn more prop.

Also as I alluded to RWM when we spoke about this, I have had conflicting results running the same two props on two different physically airframe/engine combinations even when they are the same model. We see this all the time in our work fleet, as we have multiple props in the mix to keep from having an airplane down while a prop needs service. Some engines are peppier (which affects it's ability to turn the bigger prop), some airframes are draggier, it all adds up.

Lastly, I would have to say apples to apples is going to be the best barometer you're going to get short of actually running them on your own airplane. It's the only advice I could afford RWM, because as I said to him, I had no IO540 / Maule experience... Consequently just looking for O-360 / MT combinations will still leave some wiggle room when trying to nail down whats best. You really need to poll O-360/MT/Maule M4 owners... and even that's not 100%, but probably as close as your going to get short of running them yourself...

Take care, Rob

Good points Rob. You misunderstood me some. I flew the SAME plane same day both props. Same N number...... Less than two hours apart.

The OP didn't ask about an AT packing 500 gallons. He's got well less than 300 horses. And I think he'd be foolish to put three blades on it. North of 300 horses it works for you and Kevin. But many scout and husky guys have found the three blade to suck. Not just a little either. I can agree with you that as HP goes up blade number will as well. Not many on here have that kind of power. And definitely not the OP.

Hey, Utah

Yep! and thanks. Your notes on the Husky / Scouts got me looking out of curiosity and the results were not terribly surprising.

In those applications the 3 blade models are a full 5" shorter that the 2 blade models, beyond that they are narrower in chord as well . It doesn't surprise me at all the in those cases the 3 blade owners are discouraged. In fact the 3 blade is even smaller diameter than the Hartzell they're likely replacing, conversely the MT 2 blade used in those apps is a bigger disk Coincidentally the 2 blade Husky / Scout MT's are using the same blade they use for C180-/185's.

In our case it's the same blade for either hub, so again the deciding factor in those two props was A) whether or not you had the hp. to turn it, and B) will you run up against CG issues choosing one over the other.

The Maule STC's on the other hand utilize a shorter smaller chorded blade when you elect to go 3 blade. If I am not mistaken your blades on the 2 blade are the exact same as the 180/185... So again no surprise that you guys found the 3 blade inferior to the fat long paddle the MT 2 blade is. But again, neither case adds much of value for the OP

Looks to me like the OP's prop selections will probably end up mimicking the Husky / Scout STC's which suggest his experience will be the same, but that is pure speculation...

Lastly, I am of the opinion that the boon docking C180/185 crowd would really benefit from a longer 2 blade MT. Something on the order of 86"-88". Not being an engineer, I can't say weather it's cost effective or even doable to produce such blades or the more robust hub they'd likely require, but we can certainly hope

Meanwhile I have recently been made aware of an NOS 2A34C66 90 AT-2 (88" C66) and am seriously considering going back to all metal $15,700.00 for yesteryears prop is the only reason I've stumbled so far

Good to hear your up and running ag wise! We need to catch up sometime!

Take care, Rob

Agreed on all. A true long MT would be the ticket. Ag flying around here is pretty small scale. But still fun to learn. And a wire is a wire...... Take care

16k vs. 12k?

Paying 4k for a heavier prop with some extra clearance and no improved performance?

It's the 2-blade for my O-360

I have a 2-blade prop on my C180.
I always turn it vertical when in the hangar so avoid running into it.
But I turn it horizontal when outside to minimize that someone will taxi by too close and whack it with their wing.
Don't poo-poo the chances of that, I've seen it happen. With a 3-blade, at least one blade will always be in harm's way.
A minor issue, but one that should be factored in when there's no clear-cut choice.

There are probably a few other considerations that should be looked at before choosing which MT you want to run. This piece probably behooves any potential MT buyer, not just the OP.

One of the reasons I elected to settle on the 3 blade MT vs the 2 blade, was that on the STC for an IO or O-520 motivated C180/5, The 2 blade prop has a TBO of 1800 hrs or 72 months vs 2400 hrs. or 72 months for the 3 blade. I know many will say 'we're part 91 so who cares' ...we'll get to that...

The main reason I went to the higher TBO'd prop was because there had been reports of 2 blade MT's experiencing hub chatter when hung on higher HP engines. Since in the propellors I was concerned with, the exact same blade is utilized, I could only come to the conclusion that the 3 blade hub must be more robust for the propellor to have a higher TBO. Will the more robust hub relieve me of the potential for a chattering hub? I honestly don't know, but based on the research I've done, it's almost unheard of in the 3 blade hub. Not so for the 2 blade. Either way, this is not something I want to hash out vacationing in The Brooks, western Alaska trout fishing, or some other remote piece of realty with ice/rocks on one side and ice/ocean on the other.... I can deal with changing out a busted tailwheel etc.. in the boonies... changing out a prop I'd like to avoid

Returning back to the TBO subject... I don't want to be the rain on this parade, but not many people are talking about this, so either not many folks have looked at the TC, or they're just choosing to lay low and ignore it. Before anyone looks into an MT propellor they owe it to themselves to look at the TC, and then consult their IA.

In the TC covering most of the MT props this thread has wandered through you will find the following 'for continued airworthiness' under Note 10;

(a) Aircraft installations must be approved as part of the aircraft type certificate and demonstrate compliance with the applicable aircraft airworthiness requirements.
(b) All MTV-9 propellers are to be operated within the limits of MT-Propeller Operation and Installation Manual No.E-124 for non reversible propellers and No. E-504 for reversible propellers, and adhere to the TBO-limits shown in Service Bulletin No. 1( ).
(c) Propeller maintenance, on overhaul, and airworthiness limitations shall be accomplished in accordance with MT-Propeller Overhaul Manual No. E-220 for non reversible propellers and No. E-519 for reversible propellers, latest revision.

It had been my intention all along to just let it roll in hopes that I was mis reading this, or that maybe since the TC was referring us to an SB (which normally wouldn't be considered regulatory for part 91, we could just slide by, but it does say ALL MTV-9 propellors
and as more than one IA has already pointed out to me, that's going to be pretty hard to argue... Will anyone ever question it? probably not... Will your IA keep annualing it? well I guess that's between you and him

I would really like to hear from Hailstorm or one of the other MT savvy IA's on the site about how they interpret this

Take care, Rob

DeltaRomeo wrote:Pitching for pro's and con's of a 3 blade conversion for a 180hp O-360. ....

Sounds like you have a 76" hartzell now?
I've never had one, but it seems like all those Hartzells have AD's.
Often they are replaced with newer model Hartzellss-- which soon get AD's put out on them.
What options are there other than an MT?
I'm sue they're fine props but they sure are spendy.
Does Mccauley make a suitable prop?
Seems like an 80-84" (or more?) might be about right for 180hp--
I believe the fixed pitch borer prop for a 360 is an 84".

Rob,

Regarding TBO on prop, the STC covering the airplane has specific language about overhaul. I know for the Husky under Part 91, the overhaul time does not have to be strictly adhered to.

I'm not sure the answer if the prop is on the TC and not installed with an STC. I think installs relating to the discussion at hand will be covered by an STC.

Joe

Hotrod;

Yes, the current Hartzell has the AD and an rpm range limitation (2000 to 2250; yeah, big area to have to avoid...)
Hartzell does not have an STC for any of their different prop models for this airframe (really, no one does)
MT is installing them via 337.
Maule's TC says 72 to 76" prop; I think a greater diameter can be used if noise levels are comparable, which I think is the case since it is a different airfoil design.
And Hartzell has pushed the liability for future maintenance on the prop shops; makes most of them leary about dealing with them any further, if there is any question at all they have the option to condemn it at any time. Same model prop from Hartzell can be had new and doesn't have the AD (yet) but still has the rpm limitation. With that kind of product support I'm glad to have a better option available.

I would think a field approval for a prop wouldn't care too much about noise, but would instead depend on compatibility with the engine and also ground clearance. I believe they want 9" ground clearance with the airplane loaded to gross, in level flying attitude on greased plates.

Not sure which model O-360 you have, but I believe Mac has a 3-blade prop approved for the 360.
Heavier than the MT but probably cheaper, and maybe without the TBO issues being discussed.
Mac might also make a longer-than-76" 2-blader that's suitable for an O-360.

What about the new Hartzell Trailblazer 80" composite? Approved for O-360 through IO-390. No RPM restrictions. 10-14lbs lighter than the aluminum Hartzell. I second the notion of the 3-blade Hartzell being the wrong prop for almost every airplane. We have one on a Cessna Cardinal, it is quicker out of the hole than the 2-blade, but everything else is worse. I'm working slowly to try to get the 2-blade scimitar models approved on everything I fly.