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2 blade prop VS 3 blade Prop.

LUKLA

Active Member
Folks, What are the pros and cons of 3blade VS 2blade in RV12. Rotax 912 ULS engine. price ,performance ETC. your valuable input will be appreciate. I am trying to make up my mind, which one I want go with.

I LIKE TO HEAR FORM SOME ONE WHO ACTUALLY INSTALL AND FLY RV12 WITH 3 BLADE PROP.

Lukla
RV 12 80% completed.
 
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Props...

I've heard it said "three for show, two for go". ;)

True statement, up to a point. More blades equals more drag. The most efficient prop would be a single bladed prop, but impractical. However, as horsepower goes up, the ability to apply the force generated to the air requires more blade surface area. Take a look at a C130 and note the number and size of blades per engine it has; however, its turbine engines make about 4,300 hp.

For the 912, it doesn't make enough horsepower to cavitate the 2-bladed OEM prop in cruise (think about a boat at idle, run the engine up quickly, note the foaming water behind the boat and that's cavitation) and will be more efficient, hence faster, with it than a three bladed prop.

Consider that as power goes up, you put bigger blades on. At some point, you will not have ground clearance, so you go to a three bladed prop in order to utilize the power. It will have more drag, but the ability to apply power is much greater, so it makes sense to have more blades.

Another aspect of a three bladed prop is that with more surface area, you'll have more "bite" or ability to grab the air; therefore you will tend to have better climb power - especially in thinner air, when compared to a two bladed prop.

Overall, fixed pitch props are a compromise, which leads to the question - do you want to climb fast or cruise fast? This, of course, was the reason constant speed props were invented - to have both.

The other aspect is that some folks like the appearance of a three bladed prop over a two (the "Show"). Not the deciding factor I'd recommend, but to each his own.
 
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3 blade virtues

Excellent comments by Ron. Something not mentioned yet is noise and balance. I am told that the 3 blade is more quiet and generally has less vibration than a two blade. I hope so since Catto just built one for my project.
 
You should love the Catto prop. All of the customer's for whom I have installed a Catto prop have seen increased performance in climb, cruise, and smoothness.

Vic
 
Cowling

Three-blade props sometimes makes removing/reinstalling lower cowls difficult. Any real world RV-12 experience to share?
 
True statement, up to a point. More blades equals more drag. The most efficient prop would be a single bladed prop, but impractical. However, as horsepower goes up, the ability to apply the force generated to the air requires more blade surface area. Take a look at a C130 and note the number and size of blades per engine it has; however, its turbine engines make about 4,300 hp.

For the 912, it doesn't make enough horsepower to cavitate the 2-bladed OEM prop in cruise (think about a boat at idle, run the engine up quickly, note the foaming water behind the boat and that's cavitation) and will be more efficient, hence faster, with it than a three bladed prop.

Consider that as power goes up, you put bigger blades on. At some point, you will not have ground clearance, so you go to a three bladed prop in order to utilize the power. It will have more drag, but the ability to apply power is much greater, so it makes sense to have more blades.

Another aspect of a three bladed prop is that with more surface area, you'll have more "bite" or ability to grab the air; therefore you will tend to have better climb power - especially in thinner air, when compared to a two bladed prop.

Overall, fixed pitch props are a compromise, which leads to the question - do you want to climb fast or cruise fast? This, of course, was the reason constant speed props were invented - to have both.

The other aspect is that some folks like the appearance of a three bladed prop over a two (the "Show"). Not the deciding factor I'd recommend, but to each his own.

You might want to run those theories past Tom Aberle, I think 10 time winner of the Reno Biplane class using a 4 blade prop and outright record holder...

http://www.phantomairracing.com/News-or-Reviews.html

It's the details of the prop design and matching it to the engine/ airframe for it's prime mission rather than the number of blades. In this case, clearly, more blades does not equal more drag.
 
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Although NOT RV-12 or Rotax-related, I've been fortunate to live a real side-by-side comparison between two- and three-bladed props. In this instance the aircraft are Davis DA2's, both powered by Continental C85-12F engines. One aircraft has a 2-blade Warp Drive ground adjustable prop, while the other aircraft (mine) has a 3-blade Warp Drive with tapered tips. We can't really compare blade angles because of the difference in the number of blades. It is safe to assume the 3-blade is pitched something like a couple of degrees flatter than the 2-blade. The 3-blade can hit redline RPM in cruise flight quite easily while the 2-blade is pitched such that it can barely make redline in low-level (2500' MSL) cruise flight.

Many of the comments made by previous posters have been borne out in our comparison. The 2-blade runs slightly better cruise numbers - about 3mph. The 3-blade gets off the ground faster and definitely out-climbs the 2-blade by a significant margin (at least 100 fpm better with similar load on a hot day). The 3 blade is quieter and smoother on these direct-drive engines. The 2-blade makes for easier removal of the lower cowl, but in honesty, not by very much.

I opted to go with the 3-blade Warp Drive in hopes it would help in reducing noise and vibration while returning a good compromise on performance. It has delivered on all of these goals with the added bonus of better climb performance. In consideration of these benefits I would opt for a 3-blade again if presented with the same choice to make.
 
You might want to run those theories past Tom Aberle, I think 10 time winner of the Reno Biplane class using a 4 blade prop and outright record holder...

http://www.phantomairracing.com/News-or-Reviews.html

It's the details of the prop design and matching it to the engine/ airframe for it's prime mission rather than the number of blades. In this case, clearly, more blades does not equal more drag.

Sorry to disagree with you, but I'm not talking theory; it's physics. The physical property of friction in play here is simply more wetted area equals more friction, aka "drag". I think you may have missed my point to the concept of matching the engine power to the propeller. You need more wetted, i.e. blade area, to take advantage of more horsepower. Yes, there are some very fast propeller driven aircraft with many blades. I gave the example of a C130, which is the highest horspower propeller driven aircraft in production that I know of - the latest Hercules has nearly 5,000 horsepower per engine with 4 large blades per prop. I could have used any number of WWII aircraft as examples as well. However, that doesn't detract from the fact that more blades have more drag - the engine driving those blades simply has much more power to take advantage of the extra surface area.
 
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Sorry to disagree with you, but I'm not talking theory; it's physics. The physical property of friction in play here is simply more wetted area equals more friction, aka "drag". I think you may have missed my point to the concept of matching the engine power to the propeller. You need more wetted, i.e. blade area, to take advantage of more horsepower. Yes, there are some very fast propeller driven aircraft with many blades. I gave the example of a C130, which is the highest horspower propeller driven aircraft in production that I know of - the latest Hercules has nearly 5,000 horsepower per engine with 4 large blades per prop. I could have used any number of WWII aircraft as examples as well. However, that doesn't detract from the fact that more blades have more drag - the engine driving those blades simply has much more power to take advantage of the extra surface area.

I think Tom would still be using a 2 or 3 blade if it was faster since this is Reno and it's all about speed. Every mph counts. Theory is great but it's always trumped by real world experience and results. 284mph average speed around the course with a 360 Lycoming.
 
We can't really compare blade angles because of the difference in the number of blades. It is safe to assume the 3-blade is pitched something like a couple of degrees flatter than the 2-blade. The 3-blade can hit redline RPM in cruise flight quite easily while the 2-blade is pitched such that it can barely make redline in low-level (2500' MSL) cruise flight.

Many of the comments made by previous posters have been borne out in our comparison. The 2-blade runs slightly better cruise numbers - about 3mph. The 3-blade gets off the ground faster and definitely out-climbs the 2-blade by a significant margin (at least 100 fpm better with similar load on a hot day). The 3 blade is quieter and smoother on these direct-drive engines. The 2-blade makes for easier removal of the lower cowl, but in honesty, not by very much.

I opted to go with the 3-blade Warp Drive in hopes it would help in reducing noise and vibration while returning a good compromise on performance. It has delivered on all of these goals with the added bonus of better climb performance. In consideration of these benefits I would opt for a 3-blade again if presented with the same choice to make.

You make a good point, so let's look at this. Without getting into blade shape and a comparison of wetted area, the shorter the blade, the slower the tip speed for the same RPM, therefore the farther from sonic speed (the point at which the blade becomes louder and ultimately start breaking the sound barrier). For fun, listen to an Apache chopper in a high speed descent - at high speeds, the rotor sounds like a high speed cannon going off as each blade comes forward braking the sound barrier in rotation; which is why those pilots aren't supposed to do that....so a three bladed prop with shorter blades than a two bladed prop will be quieter for the same RPM.

Additionally, more blades increases the balance around the crankshaft rotation, due to the distributed weight, making it smoother - in much the same way a heavier flywheel smooths out a car engine. But you don't get balance for free.

Optimizing the propeller for the airframe and engine is why good folks, like Craig Catto, are successful. It's all about modeling for not only what works well, but what you want for your airplane (climb, smoothness, speed, looks, etc...).
 
I think Tom would still be using a 2 or 3 blade if it was faster since this is Reno and it's all about speed. Every mph counts. Theory is great but it's always trumped by real world experience and results. 284mph average speed around the course with a 360 Lycoming.

You should probably talk to Tom about this then. My guess is a 2 bladed prop sized to take advantage of his power and rpm would either be supersonic at the tips or too long to provide safe ground clearance.

This really isn't theoretical. Physics doesn't change. What does change is the implementation of those physics. Note Tom's blade design.
 
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Ron,

In Subs we used to get cavitation at high screw RPM running shallow, but it was due to the water flashing to vapor in the low pressure regions around the blade and then the bubbles collapsed as they were shed from the blades. It was a phase change phenomenon. It made a lot of distinctive noise, so we always tried to avoid it. How do you get cavitation in air if there is no phase change?

Rich
 
Cavitation

Ron,

In Subs we used to get cavitation at high screw RPM running shallow, but it was due to the water flashing to vapor in the low pressure regions around the blade and then the bubbles collapsed as they were shed from the blades. It was a phase change phenomenon. It made a lot of distinctive noise, so we always tried to avoid it. How do you get cavitation in air if there is no phase change?

Rich

Rich, it's all fluid dynamics.

I'm quite familiar with submarine propellers, which are just fancy pumps. Whether a propeller on an airplane, a propeller on a submarine or a house fan, the mechanics are all the same. Air and water are just fluids. Whenever pressure on the outlet of the pump is less than the pressure on the inlet, Net Positive Suction Head (NPSH), goes to 0 pounds, and cavitation starts to occur. The goal is to create a higher pressure on the outlet than the inlet. You can do this several ways, but in the case of a submarine, a smaller sub-set (pun intended) of blades is inserted between the larger blades to increase the overall surface area, hence wetted area, of the propeller and therefore the force exerted to the water is greater, keeping the pressure up and reducing cavitation. The fancy schmancy submarine propellers are also why a cover is always kept over the sub's screw when brought into dry dock to keep prying eyes from the classified design.

When you say phase change, you imply going from a physical state of liquid to a gas, solid or plasma state, however in cavitation, the water isn't going through a phase change, but rather the gas in solution is expanding rapidly due to the sudden pressure reduction behind the eye of the impeller. Interesting fact: this is also why ice forms at the center of the propeller first - it's the lowest pressure, hence coldest, region of the propeller.

The noise you hear in cavitation of a water driving screw (propeller) is a result of the gas bubble suddenly collapsing as it passes into the slip stream behind the screw. It's all a function of pressure transients. And power, and the force applied as a result of that power is what causes that transient.

To your question, you get cavitation in air the same as you do in water. As an experiment, take a home fan, turn it on high speed with your ear next to the center of it. It will be loud immediately, but quiet slightly as the fan motor settles at speed and the air flow stabilizes. This phenomena is cavitation. The difference is that air is less dense than water, so less of a pressure transient occurs.
 
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Ron, got this from Engineering Toolbox. It describes the phenomenon I'm familiar with in water systems, but I wonder if in aerodynamics it has a different meaning since there is no phase change. I'd like to understand what is physically going on when the aircraft prop blade number is increased. I have heard it described as the blades "getting in each other's way" with regard to air motion, but that doesn't really explain it.

"What is Cavitation?
Cavitation may occur when local static pressure in a fluid reach a level below the vapor pressure of the liquid at the actual temperature. According the Bernoulli Equation this may happen when a fluid accelerates in a control valve or around a pump impeller.

The vaporization itself does not cause the damage - the damage happens when the vapor almost immediately after evaporation collapses when velocity decreases and pressure increases."
 
"Whenever pressure on the outlet of the pump is less than the pressure on the inlet, Net Positive Suction Head (NPSH), goes to 0 pounds, and cavitation starts to occur. The goal is to create a higher pressure on the outlet than the inlet."

You might have meant to say ? ..........

NPSH Net Positive Suction Head is the minimum pressure required at the suction port of the pump to keep the pump from cavitating.
 
Ron, got this from Engineering Toolbox. It describes the phenomenon I'm familiar with in water systems, but I wonder if in aerodynamics it has a different meaning since there is no phase change. I'd like to understand what is physically going on when the aircraft prop blade number is increased. I have heard it described as the blades "getting in each other's way" with regard to air motion, but that doesn't really explain it.

Rich, it's still just a fluid process. The only difference is the density of the fluid, which is why a water propeller will erode, or "pit", as a result of continuous cavitation and aircraft propellers don't (if you find pitting on your blades, that's from solid objects, such as dirt or other debris that went airborne). The air is already in a gaseous state, so it doesn't collapse to the extent that a air bubble in water will, but it does undergo a pressure transient just the same.

Blades "getting in each other's way" is one way of saying that turbulent air exists between the blades, causing a low pressure area that the next blade cavitates through. Imagine a blade turning in a vacuum; there is no friction of the blade on air, therefore no force applied, therefore no thrust occurs. To a lesser extent, this is the condition that occurs when a blade is cavitating - it's not making thrust. More correctly, it's not making full contact with dense air, but rather moving through "bubbles" or pockets of high and low pressure air. At the risk of way over simplifying, it's much like a tire spinning on mud - it's not getting traction. When cavitating, the blade isn't getting traction on solid air.

This will happen all the time if the blade is too small for the application. Friction, i.e. drag, is an essential part of propeller function. Without it, the prop would just spin and do nothing. This is the main reason I have to take pause when someone says a propeller doesn't have drag. The key is having the right amount. Just as having too large a blade exerts excessive drag and reduces efficiency, too small a blade creates excessive cavitation - insufficient friction, and also obviously inefficient. All of these phenomena can be solved with correct blade size, count and shape for the power, rpm and airframe.

So, back to the OP's question: it depends on your application and desires.
 
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"Whenever pressure on the outlet of the pump is less than the pressure on the inlet, Net Positive Suction Head (NPSH), goes to 0 pounds, and cavitation starts to occur. The goal is to create a higher pressure on the outlet than the inlet."

You might have meant to say ? ..........

NPSH Net Positive Suction Head is the minimum pressure required at the suction port of the pump to keep the pump from cavitating.

Read what you said, then reread my statement and see if it makes sense. I simply stated it in basic terms. NPSH is the net pressure difference between suction and discharge. When NPSH is less than or equal to 0 - you no longer have positive suction head, cavitation occurs, and ultimately the pump doesn't discharge; you might say it needs priming...
 
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Back to reality

I hate to stop this submariner party but lets talk about propellers.
Since we are talking about subs and I know nothing about them, except they are cool, the idea that three blades are smoother than two I see differently. With thre blades or two, the moment of inertia determides the flywheel effect, not the number of blades; one may argue three blades have one more blades worth of inertia thou. I think three blades will tend to be smoother because of another reason too. With a propeller, each blade nevers sees the same angle of attach as it rotates around, mainly due to pitch angle, flow field differences, etc. with two blades each blade will go in and out of this area on each cycle and might be synced to a 2x rpm harmonic. With three blades, there is a higher probability that at least one blade would be in each different flow field at a given time, making for smoother operation. Similar to how 3 phase AC works. Similar to why a Hughes 300 is smoother than the old Bell 206 Jet rangers. JMHO. Now let me get my beer and enjoy the rest of this blog.
 
In basic terms it might be less confusing and more accurate if we leave out the discharge pressure, and say.... NPSH is the difference between inlet pressure and the lowest pressure level inside the pump. More simply put, if there's not enough positive pressure on an operating pump inlet, the pump will cavitate. Doesn't matter the fluid, or the pump design.

I'm trying to understand how 3 blade airfoil performance can be explained with 3 phase current? I'm confused.
 
Ron,

OK, I see what you are saying. If I paraphrase: each blade disrupts the air as it passes with a low pressure in front of it and high pressure behind it. The next blade passes through the disrupted air hitting the low pressure area and decreases it's efficiency. The fewer the blades or lower the RPM the longer the disrupted air has to return to a uniform pressure. Has that got it in Sesame Street fashion?😁

Rich
 
In basic terms it might be less confusing and more accurate if we leave out the discharge pressure, and say.... NPSH is the difference between inlet pressure and the lowest pressure level inside the pump. More simply put, if there's not enough positive pressure on an operating pump inlet, the pump will cavitate. Doesn't matter the fluid, or the pump design.

I'm trying to understand how 3 blade airfoil performance can be explained with 3 phase current? I'm confused.

Hmm...I'm not sure how best to respond to you, but essentially it depends on the type of pump - and there are many. I'm thinking this discussion is outside the scope of this topic and should likely be in a different forum, but briefly - if you're talking about radial flow pumps, what you're saying is correct. However, an aircraft propeller for an RV-12 is a single stage, axial flow pump - which doesn't have an internal pressure; only inlet and outlet. You could talk in terms of the pressure just prior to the prop compared to pressure at the blade edge, but that would just be more complicated.

What's in front of the prop is the suction (inlet) and the backside of the prop is the discharge (outlet), and if the prop has turbulence on the outlet, it's cavitating...and that's simple.

As for your 3 phase AC versus 3 bladed prop. A serious response is that you can't; the potential between all three phases is explained in terms of the square root of 3 versus line voltage where all three phases will have a different potential. The pressure at all three blades on a spinning propeller in a normal atmosphere will be the same.

The non-serious response is more like "it don't rust, don't bust, don't collect no dust and runs cheaper, lighter, faster and more efficiently".
 
Ron,

OK, I see what you are saying. If I paraphrase: each blade disrupts the air as it passes with a low pressure in front of it and high pressure behind it. The next blade passes through the disrupted air hitting the low pressure area and decreases it's efficiency. The fewer the blades or lower the RPM the longer the disrupted air has to return to a uniform pressure. Has that got it in Sesame Street fashion?😁

Rich

Close enough. :D Just know that with more power and bigger blades, you move more air undisturbed, because you're moving more of it in a single blade pass.
 
I hate to stop this submariner party but lets talk about propellers.
Since we are talking about subs and I know nothing about them, except they are cool, the idea that three blades are smoother than two I see differently. With thre blades or two, the moment of inertia determides the flywheel effect, not the number of blades; one may argue three blades have one more blades worth of inertia thou. I think three blades will tend to be smoother because of another reason too. With a propeller, each blade nevers sees the same angle of attach as it rotates around, mainly due to pitch angle, flow field differences, etc. with two blades each blade will go in and out of this area on each cycle and might be synced to a 2x rpm harmonic. With three blades, there is a higher probability that at least one blade would be in each different flow field at a given time, making for smoother operation. Similar to how 3 phase AC works. Similar to why a Hughes 300 is smoother than the old Bell 206 Jet rangers. JMHO. Now let me get my beer and enjoy the rest of this blog.

John, John, John...

...for the record, I'm not a submariner - although I did a lot of engineering work on them many years ago (think Rickover era). But you're missing the point; a propeller on a submarine works just like a propeller on an airplane - it screws it's way through the fluid, whether water or air.

Now, your 3-phase AC comparison...that's engineering humor for me I'll have to use on Monday.
 
Back to Lycomings and propellers !

I personally experienced the conflict of theory and reality with my two blade prop. The dynamic balance guy in Indianapolis counceled that the prop and crank should be aligned for best balance and smoothness. For my 0320 with 3/8" bolts, this was not possible with the Saber extension. Because, the crank bolts and the prop bolts are offset 30 degree to provide metal for the propbolt inserts . The goal is described to be concurrence of combustion moments with propeller centrifugal forces.

Enter the three blade theory. It is my understandinding, that in addition to the pressure pulse syncronzation presented above, the power pulse moments can never coincide or harmonically differ from the 3 blade inertial forces ???
 
When I was in Navy nuclear power school one guy was having a tough time understanding the physics of a chain reaction. The instructor dumped 100 paper clips on the desk and started throwing some away, sticking some in his pocket and then adding some to illustrate each physical process on the subatomic scale. We used to call that reactor physics for Sesame Street!😜
 
When I was in Navy nuclear power school one guy was having a tough time understanding the physics of a chain reaction. The instructor dumped 100 paper clips on the desk and started throwing some away, sticking some in his pocket and then adding some to illustrate each physical process on the subatomic scale. We used to call that reactor physics for Sesame Street!😜

Having taught at NNPS, I completely agree. Thanks for the memory.
 
I personally experienced the conflict of theory and reality with my two blade prop. The dynamic balance guy in Indianapolis counceled that the prop and crank should be aligned for best balance and smoothness. For my 0320 with 3/8" bolts, this was not possible with the Saber extension. Because, the crank bolts and the prop bolts are offset 30 degree to provide metal for the propbolt inserts . The goal is described to be concurrence of combustion moments with propeller centrifugal forces.

Enter the three blade theory. It is my understandinding, that in addition to the pressure pulse syncronzation presented above, the power pulse moments can never coincide or harmonically differ from the 3 blade inertial forces ???

Ok, you've got a lot going on there... first off, if we took a three bladed prop and a two bladed prop and spun them on a shaft with some constant force, such as an electric motor, if either prop were out of balance, there would still be harmonic imbalance applied to the shaft. Once both props are properly balanced, and assuming both props weighed the same, then the issue of "smoothness" of a 3-bladed prop driven by piston engine "power pulses" comes down to the mass of the prop being evenly distributed and the force of the crank shaft being applied in three locations around the circumference of the shaft instead of just two.
 
How a 3 blade can be just as fast as a 2 blade

While in general the physics that says a three blade will climb better but be slightly slower in cruise is true in a general sense, all else being equal, there are instances where you can beat this.

I had the classic Hartzell 7666-2 two blade prop on my 200 HP. IO-360, and when it came time for overhaul, the shop told me it was too close to spec to be be overhauled again. I was faced with the need for a new prop. So, I bought one of the new Hartzell scimitar top-props, and guess what - it climbs noticeably better AND achieves the same cruise speed as the old two blade. And the reason is technology - an improved newer design that simply is more efficient.

Ironically though, while in cruise the three blade is perfectly smooth (and it is dynamically balanced to < 0.03"/sec), when dropping down to low power in approach to landing, the 3 blade is not as smooth as the two blade was, until below about <14" and 2000 rpm. Some kind of harmonic interaction with the counterbalanced engine....

Reinhard Metz
 
Beer bait

As for your 3 phase AC versus 3 bladed prop. A serious response is that you can't; the potential between all three phases is explained in terms of the square root of 3 versus line voltage where all three phases will have a different potential.

Of course 3 phase ac and propellers have nothing to do with each other. Just thought I'd pretend to know something. :)

Glad you didnt take it too seriously.
 
We need a propeller expert !

Does anyone have enough influence to get Craig Catto , Dan Horton or ?? to set us all straight for the archives ?
 
Two-blade vs. 3-blade ranks right up there with the primer wars. :)
There's lots of variables at play with our airplanes, as no 2 are EXACTLY alike. The best test is to flight test a 2-blade and a 3-blade under the same conditions (weight, temperature, altitude, etc) on the same aircraft.

That being said, I was one of the early RV-10's built and flew it out to the West Coast, stopping at the Mothership, of course. They siad it was the first RV-10 to come "home." We went flying to do some "comparison". Van flew my airplane with me in the right seat (what a pleasure to watch him fly) and Ken Krueger flew the factory RV-10. Mine had the 3-blade MT and the factory had the 2-blade Harztell (Blended airfoil I assume, but don't remember for sure). Van really noticed how much smoother the MT was. At 8500' we both went to full throttle and 2500 RPM's. We stayed neck-and-neck with the 430's having a ground speed readout within 1 knot of each other.

So did that tell us anything? Not really. It just debunked a little bit of the theory at the time that the 3-bladed props were so much slower. :)

And I had a lot of fun flying with Ken and Van that day. :)
 
Which prop

O.K. let's try this question. For a RV-10.

If I wanted a 2 blade prop, which one should I consider?

If I wanted a 3 blade prop, which one should I consider?
 
My two cents

I fly Continental O-200 powered Zenith
601XLB, originally equipped with a fixed pitch
Sensinich two blade wood prop which was dynamically balanced.
Switched over to a Warp drive three blade, absolutely less vibration, previously my oil access door would vibrate in cruise contiuosly, wore out the half turn latch. After the switch, no vibration at all in the oil door, and much smoother
overall. Take off and climb improved, most likely because of the ability to adjust
the prop on the ground. Lost some top end, 3-5 mph. I'm sure I could get that back if I adjusted for less climb.
That's my experience.
Wish I owned a RV.
Dave
 
O.K. let's try this question. For a RV-10.

If I wanted a 2 blade prop, which one should I consider?

If I wanted a 3 blade prop, which one should I consider?

My opinion from flying lots of RV-10's in various configurations:

2 Blade: Hartzell Blended Airfoil
3 Blade : MT (it was designed for the RV-10) or (if money is no object) Hartzell 3-blade composite (also designed for the RV-10), but the price will take your breath away. I wanted wanted one, but a little hard to justify to the CFO. :)

All of these seem to have great performance and reasonable TBOH periods.

There are certainly newer ones coming along, such as Whirlwind, and I hope to try their 3-blade someday, but for now the TBOH periods are too low for me, as I fly about 300-350 hours per year.

Vic
 
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Divergence from topic....TBO...Ack Thpptt!!

My opinion from flying lots of RV-10's in various configurations:

2 Blade: Hartzell Blended Airfoil
3 Blade : MT (it was designed for the RV-10) or (if money is no object) Hartzell 3-blade composite (also designed for the RV-10), but the price will take your breath away. I wanted wanted one, but a little hard to justify to the CFO. :)

All of these seem to have great performance and reasonable TBOH periods.

There are certainly newer ones coming along, such as Whirlwind, and I hope to try their 3-blade someday, but for now the TBOH periods are too low for me, as I fly about 300-350 hours per year.

Vic

Ok, you dragged me in...why do you care about stated time before overhaul? It's irrelavent to part 91 operations, let alone experimental where you are the manufacturer.

TBO's were relavent 50 years ago when monitoring technology was nowhere near what it is today. Free yourself from any stated TBO's and instead understand that you should monitor and service, repair or replace on condition. Condition based maintenance is much more efficient and cost effective way to ensure reliability. Case in point, my Baron has TBO's of 1700 hours per engine, but I have just over 2400 on the left one and it's in great condition and running very well - why would I overhaul it? There's not one regulatory or mechanical reason to do so and I'm thousands of dollars ahead by continuing it's operation.

That aside, the RV-10 blades you've listed are constant speed and have nothing to do with RV-12's, which is the point of this thread. Great topic, wrong location.
 
why do you care about stated time before overhaul? It's irrelavent to part 91 operations, let alone experimental where you are the manufacturer.

It is very relevant.

It is correct that it is not binding from a regulatory stand point, but it would be foolish to go beyond the manufacturers recommendations for a non-certified propeller (or any other critical component on an airplane).

The majority of the time, non-certified means the end users are doing the extended durability testing for the manufacturer.

If the manufacturer is not prepared to bet their company on a longer time recommendation, it would be foolish for an end user to bet their life on it.....
 
It is very relevant.

It is correct that it is not binding from a regulatory stand point, but it would be foolish to go beyond the manufacturers recommendations for a non-certified propeller (or any other critical component on an airplane).

The majority of the time, non-certified means the end users are doing the extended durability testing for the manufacturer.

If the manufacturer is not prepared to bet their company on a longer time recommendation, it would be foolish for an end user to bet their life on it.....

I can't believe you said this, but ok, we disagree. Stated overhaul times are a legal basis to limit liability for a manufacturer, but don't provide much in the way of reliability - rather it provides a false sense of security for those don't participate in CBM. Just look at the NTSB for engine failures and you'll find most accidents occur with the first 100 hours of operation or just following maintenance events. In my industry, we've completely moved to condition based maintaince, which sometimes dictates overhaul earlier than you'd expect, but often much later. If you follow a good inspection program, you'll be much safer - and that's not foolish.

Furthermore, the propeller manufacturer mentioned in the post I responded to, Whirlwind, clearly states in their manual:

"NOTE: There is no specified overhaul time. The propeller parts are removed from service when they can no longer meet the Continued Airworthiness Requirements."

So, in this context, the comment could mislead someone away from Whirlwind without being fully informed.
 
Wow. Replies like this are why I sometimes hesitate to give advice to those who are just asking for an opinion.
My apologies for missing that it is for an RV-12. Been running too fast. :)

Obivously we are all entitled to our opinion. But since someone has to make an entry in a logbook once per year stating that the airplane is in a condition for safe operation, I wouldn't think it would be wise to go past a manufacturer's recomended time before overhaul. Yes, I really do understand part 91 and it is a recommendation. :)

I just couldn't look myself in the mirror if someone got hurt because I thought I knew better than the manufacturer who must have some reason for the time specified.

Everyone's bar is different for risk. I clearly stated it was my opinion. :) But I stand by it.

Since you mentioned Whirlwind, I happen to like their product. But their current recommended overhaul periods won't work for me. I can't afford the downtime every 2 years or less. Someone who only flies 50 hours per year may find it works well.
 
Ok, you dragged me in...why do you care about stated time before overhaul? It's irrelavent to part 91 operations, let alone experimental where you are the manufacturer.

TBO's were relavent 50 years ago when monitoring technology was nowhere near what it is today. Free yourself from any stated TBO's and instead understand that you should monitor and service, repair or replace on condition. Condition based maintenance is much more efficient and cost effective way to ensure reliability. Case in point, my Baron has TBO's of 1700 hours per engine, but I have just over 2400 on the left one and it's in great condition and running very well - why would I overhaul it? There's not one regulatory or mechanical reason to do so and I'm thousands of dollars ahead by continuing it's operation.

That aside, the RV-10 blades you've listed are constant speed and have nothing to do with RV-12's, which is the point of this thread. Great topic, wrong location.


Ron, you are wrong on the inspection requirements for the Whirlwinds. They CLEARLY state on their website that a teardown inspection is every 400 hours or 3 years for the 3-blade and 650 hours and 5 years for the 2 blade for an RV-10.

BTW, I appreciate their short time periods while more time in the field is put on their props. Eventually I have no doubt they will be longer.

Vic
 
Ron, you are wrong on the inspection requirements for the Whirlwinds. They CLEARLY state on their website that a teardown inspection is every 400 hours or 3 years for the 3-blade and 650 hours and 5 years for the 2 blade for an RV-10.

BTW, I appreciate their short time periods while more time in the field is put on their props. Eventually I have no doubt they will be longer.

Vic

Vic, I didn't read the website, and it's obvious to me now that you are referring to a different prop model from Whirlwind Aviation, not Whirlwind Propellers [fun fact: Whirlwind Propellers makes the blades for Whirlwind Aviation folks], but the quote I provided earlier was directly from my Whirlwind manual for the GA-UL350-3B, that I am using on my RV-12 (relevant to this thread), in the maintenance and inspection requirements. It's not wrong.

I'm sure this topic will continue, as it has for years. Some people choose to adhere directly to the time recommendation and I won't argue that it's your option to do so, but it's wrong to say that it's unsafe or foolish to continue operation beyond TBO times - nor is it unwise; this only propogates fear, uncertainty and doubt for those who may not be technically informed. Quite the opposite, I consider it wise to fully evaluate a components condition for it's remaining service life and spend your money where it's needed.
 
Back to the question about a propeller for the RV-12. I have lots of hours behind 912's, with many different props. I have to say I am REALLY pleased with the Sensenich ground adjustable propeller that Van's sells for the 12. It is quite and smooth, and seems to perform really well.

I haven't flown a 3-blade on an RV-12 yet, so won't venture an opinion there.

Vic
 
In my industry, we've completely moved to condition based maintaince, which sometimes dictates overhaul earlier than you'd expect, but often much later. If you follow a good inspection program, you'll be much safer - and that's not foolish.

Furthermore, the propeller manufacturer mentioned in the post I responded to, Whirlwind, clearly states in their manual:

"NOTE: There is no specified overhaul time. The propeller parts are removed from service when they can no longer meet the Continued Airworthiness Requirements."

So, in this context, the comment could mislead someone away from Whirlwind without being fully informed.

Ok, it appears you are arguing semantics here....

Whether you call it an overhaul or an inspection, the only way to evaluate the condition of a Whirlwind propeller, which it seems you agree is the appropriate way to evaluate condition, is to disassemble it.
I believe that is what Whirlwind recommends at every 400 hours (not specifically an overhaul). Then decisions on part replacement would be made based on condition.

I have been in this business along time and have seen a lot of products for experimental aircraft come to market without having to go through a certification test program. Often times at the expense of the users.
Whirlwind has had their share of development problems just like many others. In this instance, calling for inspections at low service times is not because of lawyers, it is because it is the right thing to do with a critical component that they don't have any long term service history for.
It is false that any TBO limit is set by lawyers. It is based on in service experience, and testing, and then the limit is set conservatively to be sure to cover all scenarios.

As far as being fully informed..... People have bought W.W. propellers without knowing that it has a recommended 400 hour inspection interval. Even if you don't care, and you would be satisfied with an external visual inspection at each condition inspection after passing 400 hours in service (against the manufacturers recommendations), not everyone would.


In an attempt to get this thread back on topic......

It is not possible to say which is better (two blade or three blade) because in some instances a three blade is, and in some a two blade is. It depends on what airplane, what engine, which propeller, etc. There especially is no way to compare best prop choice for an RV-12 with a Rotax, to what is best for other airplanes with Lycomings.


Early in the RV-12 development program the 3 blade ground adjustable from Sensenich was tested to compare performance to their two blade. The two blade out performed it by a large enough margin that the decision was made to not offer it as an option (even though the tooling and plans pages for installing it had even been mostly completed).

Fast fwd a few years.....
Sensenich now has a new design 3 blade for the 912 Rotax. It has been tested by us only a small amount of time but the performance compared to the 2 blade looks to be more promising. Hopefully we will be able to provide a more detailed comparison in the future.

Hopefully this makes it clear that you can't just categorically say whether a 2 blade or a 3 blade is the best choice.
 
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Roger Lee did a bunch of testing of props, 2 and 3 blade - he found that as long as you set for 5500 WOT in flat and level there was no difference

As I said already in my other post, it is not possible to generalize that all 2 blades and 3 blades will be the same.

In the past, Roger's recommendations for prop pitch didn't agree with what you have posted so he has either changed his opinion or there was a typo.

I strongly recommend RV-12 owners not set their prop pitch for 5500 RPM WOT in level flight without using a specific altitude for the check. If you do this for any altitude lower than about 10,000, you will likely setting to course of a pitch. This will cause higher oil temps, poor take-off and climb performance, etc.
 
Ok, it appears you are arguing semantics here....

Whether you call it an overhaul or an inspection, the only way to evaluate the condition of a Whirlwind propeller, which it seems you agree is the appropriate way to evaluate condition, is to disassemble it. I believe that is what Whirlwind recommends at every 400 hours (not specifically an overhaul). Then decisions on part replacement would be made based on condition.

I have been in this business along time and have seen a lot of products for experimental aircraft come to market without having to go through a certification test program. Often times at the expense of the users.
Whirlwind has had their share of development problems just like many others. In this instance, calling for inspections at low service times is not because of lawyers, it is because it is the right thing to do with a critical component that they don't have any long term service history for.
It is false that any TBO limit is set by lawyers. It is based on in service experience, and testing, and then the limit is set conservatively to be sure to cover all scenarios.

As far as being fully informed..... People have bought W.W. propellers without knowing that it has a recommended 400 hour inspection interval. Even if you don't care, and you would be satisfied with an external visual inspection at each condition inspection after passing 400 hours in service (against the manufacturers recommendations), not everyone would.

It's not just a matter of semantics to "inspect" versus "overhaul". However you are using both terms in the same context. One refers to measuring and evaluating for remaining service life, the other requires repairing or replacement of parts that are outside of service limits to restore the component; these are different processes, both physically - and legally in a certified aircraft. I do highly advocate inspecting and doing so on a recurring basis, at least annually and then only overhauling when the inspection condition dictates. Let me put this in context of Continental engines, which I am intimately familiar with; the manual requires an inspection on various times of 50, 100, 500 hours and so on, and then states to overhaul at another time, which varies widely with the engine model.

Having been part of the process myself, I'll just have to agree to disagree with you about how the final times are set - which is really irrelavent at this point. I do agree with you that they are established on a conservative basis.

And again, your discussion of Whirlwind Propellers brings confusion - it should be applied to Whirlwind Aviation, not Whirlwind Propellers - these are two different companies and propellers. The quote I provided previously is from the WWP maintenance section of their provided manual, not a website; it's related to their fixed pitch propeller and it has NO SPECIFIC TBO listed. This thread was about fixed pitch propellers for RV-12's, not constant speed propellers.

In the end, I simply want to encourage folks to perform inspections and not blindly replace components when a timer pops up.
 
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I think Tom would still be using a 2 or 3 blade if it was faster since this is Reno and it's all about speed. Every mph counts. Theory is great but it's always trumped by real world experience and results. 284mph average speed around the course with a 360 Lycoming.

Most of the racers at Reno spin their engines well beyond 2700 RPM. Many exceed 3200 RPM. A two blade prop is unusable at those speeds because the tips are supersonic killing efficiency. With a IO360 using 2700 RPM a two blade should be more efficient.
 
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