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  #1  
Old 07-06-2017, 08:10 PM
LUKLA LUKLA is offline
 
Join Date: Apr 2016
Location: Phoenix,AZ
Posts: 34
Default 2 blade prop VS 3 blade Prop.

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.

Last edited by LUKLA : 07-11-2017 at 01:32 PM.
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  #2  
Old 07-06-2017, 08:20 PM
rgmwa rgmwa is offline
 
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Location: Perth, Western Australia
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Default

I've heard it said "three for show, two for go".
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  #3  
Old 07-06-2017, 08:52 PM
rongawer's Avatar
rongawer rongawer is offline
 
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Location: Brentwood, CA
Posts: 164
Default Props...

Quote:
Originally Posted by rgmwa View Post
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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Ron Gawer

- RV-12 N975G, SN 120840, Build in progress...finally on the finishing kit, so, something like 90% done and 90% left to go.
- 1975 B58 Baron, N1975G (a bottomless money pit that makes building an RV look like lunch money, but it's a great airplane, hauls the family and my wife likes two engines...go figure)
- 1961 A33 Debonair, N433JC (R.I.P.)
- RV7A; didn't finish it and donated to kid's club
- Zenith CH601XL; flying somewhere in Louisiana https://youtu.be/wa_Y_A_rP_8

Last edited by rongawer : 07-06-2017 at 08:58 PM.
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  #4  
Old 07-06-2017, 10:49 PM
rv9builder rv9builder is offline
 
Join Date: Jan 2005
Location: Irvine, CA
Posts: 551
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Has anybody seen any performance figures for the Catto 3-blade for the RV-12?

http://www.cattoprops.com/rv-12-3-bl...t-spinner-kit/

http://www.cattoprops.com/3-blade-rv...-instructions/
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RV-12 Project: Working on Empennage
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  #5  
Old 07-07-2017, 03:07 AM
Larry DeCamp's Avatar
Larry DeCamp Larry DeCamp is offline
 
Join Date: Apr 2010
Location: Clinton, Indiana
Posts: 464
Default 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.
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  #6  
Old 07-07-2017, 04:50 AM
vic syracuse vic syracuse is offline
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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
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Built RV-4, RV-6, 2-RV-10's, RV-7A, RV-8, Prescott Pusher, Kitfox Model II, Kitfox Speedster, Kitfox 7 Super Sport, DAR, A&P, EAA Tech Counselor/Flight Advisor, CFII-ASMEL/ASES
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  #7  
Old 07-07-2017, 07:18 AM
bruceflys bruceflys is offline
 
Join Date: Aug 2014
Location: Ocala, FL (Leeward Air Ranch)
Posts: 77
Default Cowling

Three-blade props sometimes makes removing/reinstalling lower cowls difficult. Any real world RV-12 experience to share?
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RV-10 - 8/16 project resumed after -12 completed
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  #8  
Old 07-07-2017, 07:47 AM
rv6ejguy's Avatar
rv6ejguy rv6ejguy is offline
 
Join Date: Mar 2005
Location: Calgary, Canada
Posts: 3,744
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Quote:
Originally Posted by rongawer View Post
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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Turbo Subaru EJ22, Marcotte M-300, IVO, RV6A C-GVZX flying from CYBW- 414.3 hrs. on the Hobbs,
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http://www.sdsefi.com/aircraft.html
http://sdsefi.com/cpi.htm



Last edited by rv6ejguy : 07-07-2017 at 08:01 AM.
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  #9  
Old 07-07-2017, 07:57 AM
Canadian_JOY Canadian_JOY is offline
 
Join Date: Aug 2007
Location: Ontario, Canada
Posts: 1,275
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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.
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  #10  
Old 07-07-2017, 09:33 AM
rongawer's Avatar
rongawer rongawer is offline
 
Join Date: Dec 2007
Location: Brentwood, CA
Posts: 164
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Quote:
Originally Posted by rv6ejguy View Post
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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Ron Gawer

- RV-12 N975G, SN 120840, Build in progress...finally on the finishing kit, so, something like 90% done and 90% left to go.
- 1975 B58 Baron, N1975G (a bottomless money pit that makes building an RV look like lunch money, but it's a great airplane, hauls the family and my wife likes two engines...go figure)
- 1961 A33 Debonair, N433JC (R.I.P.)
- RV7A; didn't finish it and donated to kid's club
- Zenith CH601XL; flying somewhere in Louisiana https://youtu.be/wa_Y_A_rP_8

Last edited by rongawer : 07-07-2017 at 09:45 AM.
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