MT four blade prop

[A64Pilot]

You remind me of an Aeronautical Engineer I hired who pretty much immediately wanted to spend a whole lot of money on a computer system, saying you just cant design an aircraft without a computer.

We met in the middle, he got his computers, but not to the level he wanted, we couldn’t afford that.

So I asked him how Kelly Johnson designed the SR-71?

Don't discount the old guys and the old designs, they were actually awful smart and I believe some just had a knack for design, they could literally look and know if it would work or not, they were artists.

CAD and it’s brother CAM just took the art out is all.

‘Google why is a metal aircraft propellor batter than a wooden one instead of listening to me. 

‘Many of those detriments were solved with fiberglass covering the blades, but stiff blades are desired for propellors, my guess would be because if they flex determine how much and when etc and designing for thst gets tough, real tough, but that’s a guess.

‘Prop design is tough, it’s not a solved science believe it or not. I Certified GE’s first and likely only turboprop aircraft. By far the absolute best performing propellor for that engine was Avia’s 106” three blade, Joe Brown came down with some Engineers and we discussed that, he took it personally, he didn’t like another company having a better performing prop, so we tested several props over a month or so, we had no diameter limitations and a max RPM or 2080 meant we cold turn some long props too. Well nothing Hartzell could come up with could match the Avia, The Avia was just a real performer.

The owner of Avia is a great guy and I really wanted to go with his prop, but there was no where in the US that you could get it overhauled, and Hartzell shops are everywhere.

Anyway Hartzell Engineers studied the Avia prop and determined that they couldn’t build it, the blade profile made a blade that due to weight was beyond Hartzell’s hub’s centrifugal force limit,  so they went back and designed from scratch a four blade 108” prop that was heavily tip loaded, meaning of course that the tips carried a lot more thrust than normal. and it really woke up that aircraft, it significantly outperformed the computer models, for whatever reason they lucked into a winner.

‘You can believe me or not, but I doubt any propellor company has better computer modeling than Hartzell, so computer modeling is great, but it’s not always perfect.

First  pic is the four blade Hartzell, second is the three blade Avia.

Now while I said in general the less blades the better performing, that’s not always the case, in this case a four blade significantly outperforms a three blade.

‘It’s not always about number of blades, Hartzell could likely have built a better performing three blade, but unfortunately they didn’t have a three blade hub that could handle the centrifugal force required, so sometimes limits exist that we don’t even know about, and those limits drive design.  

 

Edited April 22, 2021 by A64Pilot

[A64Pilot]

Metal blades are enormously strong too and have a tendency to stay in one piece even when stupid foirces are applied.

This is what that four blade Hartzell looks like when the aircraft impacts the ground at just below 200 MPH and pulling in excess of 6 G’s, with 800 SHP applied.

Of course that’s ridiculous force, but I don’t worry about whether my metal prop will take a hit from a Buzzard etc either, I’ll do the strike inspection after I land.

[gsxrpilot]

JD and I have been in regular communication with Mike Trudeau at Hartzell. I'm ready to put a lighter, possibly composite prop on my 252/Encore. But according to Mike, they haven't come up with anything that out performs the canoe paddle prop I have now, at cruise in the flight levels. So I'll keep waiting.

I'd love a Scimitar Top Prop on my Mooney, but not if it's not at faster in cruise than what I've got.

[aviatoreb]

1 hour ago, A64Pilot said:

You remind me of an Aeronautical Engineer I hired who pretty much immediately wanted to spend a whole lot of money on a computer system, saying you just cant design an aircraft without a computer.

We met in the middle, he got his computers, but not to the level he wanted, we couldn’t afford that.

 

You are stereotyping.   And you are attempting to insult two different people with one sentence.  Him and me.  Its not becoming.  I think it is wonderful that you are a manager engineer.  Better you stick with just insulting the people who work for you instead of also random people you don't know on the internet.

You are presuming if I google something I will become as enlightened as you are and then my opinion will become just like yours.

I am a PhD mathematician - not an aeronautical engineer.  I don't use cad or cfd.  I make mathematics that is the underpinnings of what would go into cad.  I am a maker of algorithms by trade.

I do plenty paper and pencil and the idea of scheduling a twist with respect to radius to attain the right pitch when under load is something that can be done to a large degree paper and pencil.  It can be done with more detail and more accurately with a CAD interacting with a structural mechanics and fluid model considering shape optimization.  I bet there are a few more percentage points to eek out.

Given some time, and motivation, I could solve for a rudimentary and reasonable lay out a curve schedule for prop twist considering the bending loads, all by paper and pencil.  That is in my skill set.  I know it would be ballpark since to work the problem by hand would require some simplifying assumptions which might not be quite true to the really physical object.  I don't know how to use the modern tools or even which/what is most trending today.  I am more than confident someone does and I can walk downstairs and knock on the door of 2 or 3 other faculty in that department if we really need that answer.  If I were buying a prop, spending my hard earned money, I would purchase the one from the company that used the modern tools rather than the cranky old engineer who says stick with me kids, Ill do the whole thing paper and pencil.

I have no doubt that if a compliant composite wrapped wood prop were a thing in the 1960s that those fabulous engineers would do exactly what i am thinking of which is to paper and pencil to schedule the twist according to the computed deformation under load, rather than to schedule the twist assuming a rigid beam prop.  They did not because compliant props weren't a thing. Ok there were all wood props but only on tiny airplanes with little engines, so it wasn't a thing.  Nonetheless it would be a rough good ball park estimate and we can do better today.

I took a paper and pencil draftsmen course when I was in high school - I bet they don't even offer that anymore.  It was beginners draftsmanship but we drew rudimentary things on big pieces of paper on big draftsmen's tables.  

I look at a 1000hp Wright R-3350 twin row and super charged radial engine like on the B29 bomber as designed and flown during WWII and to realize how many parts big and small are in that big thing, and they all are there for a reason, and they are all shaped and fitted just so or the engine won't work.  Designed and drawn by I can't imagine how many engineers and engineering draftsmen, and it boggles my mind that it actually works!  And work it did!

We can do better today - not to say we were at the height of optimal during the era of paper and pencil - modern engineers who build cell phone cases with a kajillion little parts, chips with a kajillion semiconductor elements layer out in a particular way for particular reasons, carefully selecting materials and layout, and car engines, car shapes, and should be in the aero industry too - there is a lot to be gained by using the modern tools.

I am amazed by the SR71 that was built in the slide rule era and I have many times also used that example to contrast the old way and the new way.  They built a super sonic airplane designed on draftsmen's tables with pencils.  The properties of shock and what it would do to the flow into the engine for example were only understood in rudimentary ways.  Today it is still a trending problem to model these details.  Back then they built a big nose cone that would go in and out by a lever that was at the pilots hand who by feel would learn how to position it to make the flow into the engine subsonic - or so I am told when I was at Udvar Huzay one day and there was an old retired pilot-cfi acting as docent who was describing how that worked to me in some detail and I was amazed.  Today they would make that thing automatic and with lots of sensors to find the optimal position. And it would be more optimal.  Somehow they got it to work then.  Or another more famous thing about the sr71.  It leaks on the ground because it is designed to tighten up at speed with the temps at speed- and they did that design build on paper and pencil.   And lets talk about the fuels - its a special grade of jet fuel capable of operating at 70,000 feet where combustion is harder - but those chemical engineers had their own magic.  So many specialists and smart people built that airplane and it worked.

The old school engineers were amazing.  The best of the new wave engineers are also amazing and "on the shoulders of giants" their technologies are better than attainable back then.  Bad engineers of today are button pushers who don't think and just know how to use software.  Lets talk about what good engineers of today can and should do. They have some bits of the best of the old school guys with a great deal of knowledge and skills with many new tools.

[A64Pilot]

 A very large reason why aviation has been so stagnant for seemingly forever is that long ago we lost the bottomless pockets of the Federal government.

‘The US taxpayer paid for pretty much all of the aviation advances and standards back in the day because were were in a Global war, since then of course the taxpayer is still paying for advancements, unfortunately most aren’t applicable for our little slow airplanes with piston engines and propellors.

‘So that means of course that the end users, meaning us have to pay for whatever we get, and the companies supplying the products have to make a profit or they don’t stay in business.

Why I’m bringing this is up is yes, a whole lot more can be done than is done, more isn’t done because by the time you amortize out the expense of doing more over the relatively few products that are sold, you have to only spend on development what you can afford, so it’s not been a can it be done thing for a longtime, for decades it’s been a can we do it and make money?

But bottom line is, are you happy with the product, does it meet your expectations? If the answer is yes, then it doesn’t matter if super computers were used to calculate loads for each kt in flight over a range or RPM’s and air density and engine torques or not.

I Think you woud be surprised at how much design by eye is done, and how much the old adage of it looks good, it will fly good holds true.

The thing that I get back to when people think that because of all the super computers etc that exist now and there just isn’t any room for Jim Bob to have a flash of inspiration is the Gurney flap, Boeing and I believe Bell with their helicopters have become enamored with it, because it works. So every once in a while some common guy with little or no training comes up with something that works.

 

Edited April 22, 2021 by A64Pilot

[ZuluZulu]

I wonder if a four-blade MT prop would be any good on a stock M20J/MSE with stock IO-360 (no Missile conversion).  I'm intrigued by the increased ground clearance, considering how hard I have to pucker every time I taxi over the rough parts of Catalina's Airport in the Sky.

[A64Pilot]

30 minutes ago, ZuluZulu said:

I wonder if a four-blade MT prop would be any good on a stock M20J/MSE with stock IO-360 (no Missile conversion).  I'm intrigued by the increased ground clearance, considering how hard I have to pucker every time I taxi over the rough parts of Catalina's Airport in the Sky.

I doubt it’s Certified for us, engine HP is significantly different, and I doubt it’s much if any more clearance, the big motors need more prop than us.

[Tim Jodice]

20 hours ago, Alan Maurer said:

Hello Everyone, I saw a photo of an M20R today with an MT propeller. Very good-looking. Anyone have any experience with this prop? 

Any actual difference in performance?

 

 

Getting back to the original question. @FoxMike (who did a nice write up on his MT here) myself and a somewhat lurker member I forget he user name but his real name is Scott S. have MT propellers. There are many others but I have not met or spoken to them so I won't speak for them.

I was interested in the MT for noise and vibration reduction. Most would agree that a 4 cylinder Lycoming is not the smoothest engine.

Before dropping $14,000 on a propeller I wanted real opinions. One of my pet peeves is "I heard from a friend " so I wanted to speak to people who actually owned one.

Scott and I have 201s Fox Mike has a Bravo. 201s go from two to three blade and Bravos go from three to four blade.

The three of us have the same opinion and that is that they are smoother, quieter, beter takeoff and climb performance. The climb performance is most noticeable when at VX/VY speeds, the faster you go the less the gain.

I personally was expecting to loose speed because it does make sense that swinging another blade through the air takes energy and historically on a low 200HP airplane a 3 blade does cost a few knots.

Cruise speed is unchanged. I did a 4 way GPS before and after. The MT came out a few (2) knots faster but it was a little cooler so I gave the credit of the few knots to the engine make a little more power. 

On the 201 it is 3 inches shorter and with Mooneys having a small amount of ground clearance I consider having a shorter propeller a plus.

Anyone who would like to see and hear side by side on the ground inside, outside and flying a 201 with a MT and a M20F with the stock Hartzell 7666 2 blade is welcome to call me and stop by. 6 zero 3 five seven 1 seven 1 one one.

A little technical stuff. I was told bt the MT propeller shop in Deland, FL that MT propellers are designed to be flexible some models more than others. The propeller that goes on a 201 on one of the most flexible and because of that it likely will never have a nickel leading edge because nickel doesn't flex like steel. 

 

[carusoam]

My bad... I should have invited @KSMooniac Scott from Kansas... 

Scott had put an MT on his bird many years ago...

 

ZZ, as far as blades vs. HP goes... 1 blade for each 100hp is a nice rule of thumb.... for defining thrust vs. drag issues...

C150s don’t care about speed... so they aren’t going to push the one bladed prob idea...

Some people place ground clearance on a pretty high level of importance... so... their choices have other compromises...

Best regards,

-a-

This is for an IO550(N), from Hartzell...  extra clearance for some reason... composite and super scimitar... probably have to crane your neck to look around it while flying...