Let's talk propellers.

[Tim Jodice]

Because there are so many applications for propellers lets keep this to propellers on 180/200HP piston singles. 

Why,

Are some like the one on Piper Arrows 2 blade wide square tip? 

Do the 3 blade hartzells have very pointy tips?

Is the tried and true mooney 201 2 blade Macauley elliptical tip considered by most to be the best all around prop?

Is the scimitar the thing on almost all new design propellers? 

Are there all kinds of power/rpm restrictions on aluminum propellers but composite props eliminate them? 

https://hartzellprop.com/products/top-prop/other/da-40xl-2-blade-composite/

What is the goal of the rather unique (very wide in the middle)shape of the composite hartzell found on some diamond DA40s?

https://hartzellprop.com/products/top-prop/mooney/m20a-g-m20j-2-blade/

If you go to the bottom they document that the new prop has reduced take off performance compared to a 7666-2 blade. What do you get exchange? Top speed?

Does anyone know what a 7666-2 blade is?

[carusoam]

Some things are driven by surface area... (drag)

Some are determined by number of blades... power delivery.

Other things are determined by prop material of construction...

Some times it is good to invite the prop guy @Cody Stallings to a proper prop discussion:...

Best regards,

-a-

[Hank]

Didn't Norm write his Master's Thesis on propellor efficiency? @testwest if my memory still works . . . . Now I need to look for the drawing I made of my 3-blade Hartzell prop for him; it predates this here tablet.

[N201MKTurbo]

99% of everything there is to know about propellers was known by the end of WWII. They have been trying desperately to figure out that last one percent ever sense.

[cliffy]

1 hour ago, N201MKTurbo said:

99% of everything there is to know about propellers was known by the end of WWII. They have been trying desperately to figure out that last one percent ever sense.

Maybe a "point of diminishing returns" has been reached? 

Only so much % of HP can be converted into thrust. There are limits  The curve does start to flatten.

A gain in one area means a loss in another. Aerodynamics is all about trade-offs 

"Sense"?   How about "SINCE"    :-) :-)     (auto correct spelling error for sure). 

[jaylw314]

In general, airfoils with an elliptical planform are most efficient (think Spitfire).

However, as tip speeds increase, swept-wing planforms become more efficient.

For ease of manufacturing, square tips are easiest.  Also, square tips allow you to cut down a propeller blade's length.

[0TreeLemur]

The Hartzell 2-blade HC-2CYK-1BF with that 'A' hub went in for overhaul at a reputable nearby shop because Hartzell refuses to allow ECIs on their props that haven't been opened up in decades.  They disassembled and inspected.  Both blades are "undercut", which means that they've been overhauled too many times already.

We were planning on upgrading to the 'B' hub, but doing that plus buying blades is approaching the cost of a Top Prop.  We're at a decision point.  If we do decide on a new prop, I'll have lots of time to compare performance numbers.

[Tim Jodice]

4 minutes ago, 0TreeLemur said:

If we do decide on a new prop, I'll have lots of time to compare performance numbers.

I would love to hear what you go with and why.

[0TreeLemur]

38 minutes ago, Tim Jodice said:

I would love to hear what you go with and why.

Will report back.  The calculus so far says:

$labor + $B hub +  (($cost of && time to find serviceable used blades) ||  $buy new blades) ≅ $top prop

I've read a lot on this site and others about the marginal gain of a top prop.  Maybe a couple kts faster cruise.  Not much quieter in a Mooney because of the motor mount hard connection to the tubular steel frame.  Slightly longer t/o roll.   Looks cool.  Will help sell her when that time comes.

It's just money.  Nobody owns an airplane to save money. 

[0TreeLemur]

On 9/7/2020 at 11:13 AM, Tim Jodice said:

I would love to hear what you go with and why.

The decision we made that since we were going to get a new prop anyway, we might as well go with the Top Prop.  We installed it yesterday.  Installation was a moderate pita.  Getting a torque wrench on the two studs that are behind the prop required a creative extension.  

First flight report:

1.  Definitely quieter.  Because I had to fly 2.5 h near the airfield to break in a new cylinder, I had ample opportunity to listen.   Objective proof.  Even with ANC headset, I had never before noticed that closing the cowl flaps reduces cabin noise.   I noticed it yesterday.  Novel finding.  There is a lot of low frequency rumble associated with open cowl flaps on our C.   Another data point: on this morning's flight, my co-pilot and I took off our David Clamps, and were able to actually have a conversation.  Never even wanted to try that with the old prop.  With the old prop our aircraft was frighteningly loud in the cabin at cruise.  With the new prop it is just loud.  The wind noise around the door seems to be the largest component of the noise budget now.

2. Climbs faster?   The takeoff roll seems about the same- Hartzell says it increases 3% with this prop.  But once it gets going, it seems to climb better.  With old prop 600-700 fpm at 95 kias was typical.   This morning we were climbing at a bit more than 700 fpm at 100 kias.  Need more obs, but it does seem to perhaps have increased the rate of climb.

3. Faster in cruise?   Maybe 1 kt.  Yesterday during cylinder break-in I flew 1.5 h as 75% power back and forth across the field about 15 nm each way.  The GNS430W TAS calculator consistently showed 141-143 kts.  With the old prop it used to show 140-143 kts.  One flight doesn't allow this conclusion.   It isn't much faster if at all.  Hartzell doesn't advertise it as faster, they advertise it as "more efficient".   Maybe that means that we can get the same cruise speed turning it a bit slower.  I did play with that a little bit, but results were inconclusive.

4.  100's of knots faster on the ground.   The ramp appeal is undeniable.  The scimitar blade design and new pointy spinner looks high speed.

5.  Gone is the 100 h ECI AD.  Won't miss that.

6.  The striped design fits in with the OTreeLemur motif.  I think we might paint a bird chaser spiral on the spinner!

 

[Tim Jodice]

4 minutes ago, 0TreeLemur said:

Objective proof.  Even with ANC headset, I had never before noticed that closing the cowl flaps reduces cabin noise.   I noticed it yesterday.  Novel finding.  There is a lot of low frequency rumble associated with open cowl flaps on our C. 

 

I experienced the same thing. With the cowl flaps wide open i can hear it and feel it in the floor, in trail just hear it. I couldn't tell a difference with the old prop.

Any thoughts why? Up until reading your pirep I thought it was because of changing from a 2 to a 3 blade. Scimitar blade technology? 

[the_elkhartian]

Just now, Tim Jodice said:

I experienced the same thing. With the cowl flaps wide open i can hear it and feel it in the floor, in trail just hear it. I couldn't tell a difference with the old prop.

Any thoughts why? Up until reading your pirep I thought it was because of changing from a 2 to a 3 blade. Scimitar blade technology? 

I have the 2-blade McCauley B2D34C214 on my C model, and I can definitely hear and feel the cowl flaps open. I have the LASAR 201 cowling. There isn't really a trail setting, its just open or closed.

[0TreeLemur]

48 minutes ago, Tim Jodice said:

I experienced the same thing. With the cowl flaps wide open i can hear it and feel it in the floor, in trail just hear it. I couldn't tell a difference with the old prop.

Any thoughts why? Up until reading your pirep I thought it was because of changing from a 2 to a 3 blade. Scimitar blade technology? 

Maybe the McCauley is a quieter prop.  In my case, the theory is that the original Hartzell HC-C2YK-1BF was such a loud prop that it completely masked the noise of having the cowl flaps open.  Now that I'm aware of that noise as a low-frequency rumble, it indicates that the cowl flaps do indeed let a lot more air in through the nacelle, which creates a lot of turbulence inside the engine compartment.  That turbulence creates pressure fluctuations that probably cause the firewall and things like the cheek cowls to vibrate.  Like @wingtipwalker mine are just open or closed.

[EricJ]

That's the same prop that I have, but it's been on my airplane since I bought it, so I don't have anything to compare it to.

Another parameter to compare during cruise is fuel flow.   If you get the same speeds, see whether fuel flow has changed.

 

[carusoam]

Great pirep 03!

Best regards,

-a-

[testwest]

I agree, a great PIREP, O Tree (or should I say King Julien?)

For Hank, my thesis was on efficient climb, and I utilized the propeller models in Benchmark to predict the climb performance of several alternative profiles. The propeller performance algorithm in Benchmark is a marvelous bit of programming that makes the Boeing General Propeller Chart (a three dimensional surface chart, published in the Journal of Aeronautical Sciences in January 1943) a dynamic model that can be manipulated. Today's prop manufacturers all use proprietary CFD models to do the same function, but the Boeing Chart (and its Benchmark representation) is still surprisingly accurate even today.

The swept, thin tip is a really good shape for reducing noise and transonic drag. CNC machining and very high fidelity computational fluid dynamic modeling made the manufacture of these new props possible.

Climb speed has an ENORMOUS effect on propeller efficiency. Let's say you are in a climb at 88 KIAS in your 200hp Mooney with this Hartzell Blended Airfoil prop, passing 3000 feet on a standard day. Your engine is putting about 180hp into the prop hub at this point, about 27"MP and 2700 RPM. (No 25 square OWTs please). The prop is only about 76% efficient here, so you are getting about 137hp out of the prop.

Now, without changing ANYTHING else, simply nose over a little and then climb at about 115 KIAS instead:

Notice the prop efficiency is now about 83% efficient! There is about 12hp more coming out of the prop. (Sharp eyes will note the thrust force goes down, remember that power is a force per velocity function, see here for more details: http://www.epi-eng.com/propeller_technology/selecting_a_propeller.htm )

Now, the airplane won't have a higher VVI at this faster speed because the drag is going up a little faster than the excess power. But you are getting down range quite a bit faster, on essentially the same fuel burn.

The magnitude of propeller thrust hp change with increased speed during climb has not been well understood outside of fairly small flight test engineering circles until recently.

For the OP, those square tips were easy to manufacture in the old days, but very bad for blade loading, noise and transonic drag. The three-bladed Hartzell prop is still the old 7282 blade section, meaning the airfoil along the blade span is fairly consistent. The McCauley elliptical prop is a pretty good design and is hard to beat from a performance standpoint, but it is noisier and has more rpm restrictions, at least on the J with its A3 and B6 dynamic counterweights. The Hartzell ASC-II composite prop for the DA40 cited has a wide chord to help get back some of that lost efficiency at the slower speeds that I showed above, but that chord is a little wide for an airplane with a higher speed range, such as ours.

Hartzell makes a 3 blade composite prop for the 200hp Van's airplanes, 74 inch diameter with a narrower chord that the Diamond prop, and is better suited for our speed range. See here:

The neat thing is that this prop is stunningly light, only 42 lb due to their new light weight Raptor^TM hub (the 3 bladed MT for the same application is 46lb.) Would love to see the Raptor on an E or a J.

[cliffy]

2 hours ago, testwest said:

I agree, a great PIREP, O Tree (or should I say King Julien?)

For Hank, my thesis was on efficient climb, and I utilized the propeller models in Benchmark to predict the climb performance of several alternative profiles. The propeller performance algorithm in Benchmark is a marvelous bit of programming that makes the Boeing General Propeller Chart (a three dimensional surface chart, published in the Journal of Aeronautical Sciences in January 1943) a dynamic model that can be manipulated. Today's prop manufacturers all use proprietary CFD models to do the same function, but the Boeing Chart (and its Benchmark representation) is still surprisingly accurate even today.

The swept, thin tip is a really good shape for reducing noise and transonic drag. CNC machining and very high fidelity computational fluid dynamic modeling made the manufacture of these new props possible.

Climb speed has an ENORMOUS effect on propeller efficiency. Let's say you are in a climb at 88 KIAS in your 200hp Mooney with this Hartzell Blended Airfoil prop, passing 3000 feet on a standard day. Your engine is putting about 180hp into the prop hub at this point, about 27"MP and 2700 RPM. (No 25 square OWTs please). The prop is only about 76% efficient here, so you are getting about 137hp out of the prop.

Now, without changing ANYTHING else, simply nose over a little and then climb at about 115 KIAS instead:

Notice the prop efficiency is now about 83% efficient! There is about 12hp more coming out of the prop. (Sharp eyes will note the thrust force goes down, remember that power is a force per velocity function, see here for more details: http://www.epi-eng.com/propeller_technology/selecting_a_propeller.htm )

Now, the airplane won't have a higher VVI at this faster speed because the drag is going up a little faster than the excess power. But you are getting down range quite a bit faster, on essentially the same fuel burn.

The magnitude of propeller thrust hp change with increased speed during climb has not been well understood outside of fairly small flight test engineering circles until recently.

For the OP, those square tips were easy to manufacture in the old days, but very bad for blade loading, noise and transonic drag. The three-bladed Hartzell prop is still the old 7282 blade section, meaning the airfoil along the blade span is fairly consistent. The McCauley elliptical prop is a pretty good design and is hard to beat from a performance standpoint, but it is noisier and has more rpm restrictions, at least on the J with its A3 and B6 dynamic counterweights. The Hartzell ASC-II composite prop for the DA40 cited has a wide chord to help get back some of that lost efficiency at the slower speeds that I showed above, but that chord is a little wide for an airplane with a higher speed range, such as ours.

Hartzell makes a 3 blade composite prop for the 200hp Van's airplanes, 74 inch diameter with a narrower chord that the Diamond prop, and is better suited for our speed range. See here:

The neat thing is that this prop is stunningly light, only 42 lb due to their new light weight Raptor^TM hub (the 3 bladed MT for the same application is 46lb.) Would love to see the Raptor on an E or a J.

Man I can read this interesting engineering stuff all night long! And I've been flying for over 50 years. Really interesting stuff 

Mine came with a McCauly 3 blade so I have no comparisons before and after conversion. (180 HP C)

Thanks!   Waiting for more. 

[Tim Jodice]

7 hours ago, testwest said:

I agree, a great PIREP, O Tree (or should I say King Julien?)

For Hank, my thesis was on efficient climb, and I utilized the propeller models in Benchmark to predict the climb performance of several alternative profiles. The propeller performance algorithm in Benchmark is a marvelous bit of programming that makes the Boeing General Propeller Chart (a three dimensional surface chart, published in the Journal of Aeronautical Sciences in January 1943) a dynamic model that can be manipulated. Today's prop manufacturers all use proprietary CFD models to do the same function, but the Boeing Chart (and its Benchmark representation) is still surprisingly accurate even today.

The swept, thin tip is a really good shape for reducing noise and transonic drag. CNC machining and very high fidelity computational fluid dynamic modeling made the manufacture of these new props possible.

Climb speed has an ENORMOUS effect on propeller efficiency. Let's say you are in a climb at 88 KIAS in your 200hp Mooney with this Hartzell Blended Airfoil prop, passing 3000 feet on a standard day. Your engine is putting about 180hp into the prop hub at this point, about 27"MP and 2700 RPM. (No 25 square OWTs please). The prop is only about 76% efficient here, so you are getting about 137hp out of the prop.

Now, without changing ANYTHING else, simply nose over a little and then climb at about 115 KIAS instead:

Notice the prop efficiency is now about 83% efficient! There is about 12hp more coming out of the prop. (Sharp eyes will note the thrust force goes down, remember that power is a force per velocity function, see here for more details: http://www.epi-eng.com/propeller_technology/selecting_a_propeller.htm )

Now, the airplane won't have a higher VVI at this faster speed because the drag is going up a little faster than the excess power. But you are getting down range quite a bit faster, on essentially the same fuel burn.

The magnitude of propeller thrust hp change with increased speed during climb has not been well understood outside of fairly small flight test engineering circles until recently.

For the OP, those square tips were easy to manufacture in the old days, but very bad for blade loading, noise and transonic drag. The three-bladed Hartzell prop is still the old 7282 blade section, meaning the airfoil along the blade span is fairly consistent. The McCauley elliptical prop is a pretty good design and is hard to beat from a performance standpoint, but it is noisier and has more rpm restrictions, at least on the J with its A3 and B6 dynamic counterweights. The Hartzell ASC-II composite prop for the DA40 cited has a wide chord to help get back some of that lost efficiency at the slower speeds that I showed above, but that chord is a little wide for an airplane with a higher speed range, such as ours.

Hartzell makes a 3 blade composite prop for the 200hp Van's airplanes, 74 inch diameter with a narrower chord that the Diamond prop, and is better suited for our speed range. See here:

The neat thing is that this prop is stunningly light, only 42 lb due to their new light weight Raptor^TM hub (the 3 bladed MT for the same application is 46lb.) Would love to see the Raptor on an E or a J.

Do you know why more blades have better take off and low speed climb performance? Based off what you said about efficiency make me think that more blades are more efficient at low speeds. 

Why is it popular to have a long (obnoxiouly loud) 2 blade prop on float planes?

My guess is to have a big prop disc to get alot of static thust to get out of the water. 

From what I have read a 3 blade has better low speed performance in exchange for top speed efficiency. 

[testwest]

A couple more quick answers, a 3 blade prop has a little better power loading and efficiency (~77.5% instead of 76% as above, for example) at the low speeds, so under the same 88 KIAS climb above you are seeing about 139 hp out of the prop instead of 137 from the BA. Will post the Benchmark model for a Mooney-Hartzell three blade here later today.

You are correct on that long floatplane prop. Once out of the water a better noise and efficiency technique would be to get the RPM back off 2800 as one accelerates. If I had a float plane I would go to the trouble to model a climb RPM profile that would keep those tips off transonic as the helical tip speed (rotational speed plus forward speed basically) increases.

Benchmark does show the 2 blade BA about 1% more efficient than the 3-blade at a normal cruise, for us around 155 KTAS at 8000 feet and roughly 70% power. Tim you are also correct on that. I can post more model charts if anyone wants to see 'em.

And Cliffy thanks for the kind words. Engineering stuff is interesting, and what I try to do is keep it reasonably accurate, brief enough not to be boring, and immediately applicable by the audience in their flying.

[carusoam]

Way to go Norman!

Thanks for sharing the technical details in bite sized amounts.  
 

The TopProp has the fancy tips that you described.

Best regards,

-a-

[Tim Jodice]

1 hour ago, testwest said:

A couple more quick answers, a 3 blade prop has a little better power loading and efficiency (~77.5% instead of 76% as above, for example) at the low speeds, so under the same 88 KIAS climb above you are seeing about 139 hp out of the prop instead of 137 from the BA. Will post the Benchmark model for a Mooney-Hartzell three blade here later today.

You are correct on that long floatplane prop. Once out of the water a better noise and efficiency technique would be to get the RPM back off 2800 as one accelerates. If I had a float plane I would go to the trouble to model a climb RPM profile that would keep those tips off transonic as the helical tip speed (rotational speed plus forward speed basically) increases.

Benchmark does show the 2 blade BA about 1% more efficient than the 3-blade at a normal cruise, for us around 155 KTAS at 8000 feet and roughly 70% power. Tim you are also correct on that. I can post more model charts if anyone wants to see 'em.

And Cliffy thanks for the kind words. Engineering stuff is interesting, and what I try to do is keep it reasonably accurate, brief enough not to be boring, and immediately applicable by the audience in their flying.

I will be salivating until then.

I am unsuccessful at finding a post that I had that I have read in the past about a mooney (I think E model) owner who put a 3 blade hartzell pointy tip prop on. Saying that it was just a little bit smoother, didn’t see a climb increase and lost almost 5 knots in cruise. 

I was willing to loose top speed to get the smoother, quieter ride with the MT 3 blade yet as a learned earlier this week with a 4 way gps it with out a doubt did not loose speed. The actual numbers (154 to 156) came up a little faster but i was also lighter so I would dismiss the 2 knots. 

This is compared to what I think most consider the best 201 prop, the McCauley C214 OEM propeller.

For MT to add all the benefits of a 3 blade with out the loss how do they do it? Material? Scimitar blade? It being a smaller diameter? More modern design? 

It amazes me because it has 2 things that should be bad for efficiency (3 blades and smaller diameter) yet no loss.

Did I say I am salivating until you write back?

Thank you for taking the time to write all of this in a way the non engineers can understand. 

 

[cliffy]

Here's a question I've always had

Aluminum props- 2 blade vs 3 blade

What affect does the weight of the extra blade have in available HP to drive the plane fwd?

The extra blade weight (not drag) must use some amount of HP just for rational drive at any given RPM. 

That should take away some amount of HP available for fwd thrust

Or do we say that on any rotating solid disc weight does not factor into how much HP it takes to reach a certain RPM?

Or is it a factor only for acceleration to a given RPM?

[carusoam]

Expect the extra weight to only affect the acceleration from 0 to 2700 rpm and back to 0...

a mass/momentum issue...

With the different materials, the rigidity will play an interesting roll...

A twisting blade would cause its AOA to change...

Best regards,

-a-

[Oscar Avalle]

Very interesting discussion, I just replaced my three blade Mccauley with a MT. I am going to fly tomorrow for the first time. I heard so many things, that I am really curious, but I am trying to keep my expectations low. I will report back.

[cliffy]

7 hours ago, carusoam said:

Expect the extra weight to only affect the acceleration from 0 to 2700 rpm and back to 0...

a mass/momentum issue...

So what you are saying is that if we have a 500 lb disc and a 5,000 lb disc, once up to an arbitrary speed (say 2700 RPM) that both would take the same HP to maintain that RPM?  (Fluid drag aside)  There's no extra cost in energy expended to keep 5,000 lbs spinning as opposed to 500 lbs? (other than the drag of the spinning object)