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  #11  
Old 03-31-2011, 06:54 PM
humptybump humptybump is offline
 
Join Date: Feb 2011
Location: USA
Posts: 3,179
Default 72" option

I'm working an RV-8 with only 150hp and Craig said, "I can run up to a 72" on the 150hp with the 2 bladed and this will give you better takeoff performance."

The 72" may or may not be an option on the -4 depending on ground clearance.
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  #12  
Old 04-01-2011, 08:53 AM
Christopher Murphy Christopher Murphy is offline
 
Join Date: Feb 2007
Location: colorado
Posts: 873
Default catto prop

I have an RV-4 160hp. Has a Catto 2 blade 68dia 76 pitch that I sent back as underpitched and Craig reworked it. ( I think he widened the cord )

It is still underpitched.

Sensi 70cm 81 pitch gave me 165kts TAS at 2600 rpm
Catto gives me 155 kts TAS at 2600 rpm

10 kt difference at each dens. alt tested. Sorry , no MP pressure gage.

The Catto clocked over 190 kts at less than full power ( at about standard atmosphere.)( more than 2700rpm)

Airplane weighs about 950 empty.

Chris M RACE 34
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  #13  
Old 04-01-2011, 07:26 PM
elippse elippse is offline
 
Join Date: Dec 2006
Location: Arroyo Grande, CA
Posts: 938
Default

Say what you want from things you have heard, but the more blades you have of a similar planform outline, diameter, and pitch distribution, the more static thrust and the more rate of climb you will have. Science wins every time it's tried. Do an internet search on the 8-blade, narrow tip, NP2000 propeller that the Air force is trying on its C-130 and the Navy on its twin COD. The Air Force says that with the increased static and take-off thrust that it can probably do away with the Jato bottles that it sometimes has to use for short fields or overloads. We really need to get everybody into the new century on propeller technology and leave all of those old wives tales behind.
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  #14  
Old 04-01-2011, 07:38 PM
pmnewlon pmnewlon is offline
 
Join Date: Jun 2010
Location: Columbus, OH
Posts: 113
Default

There's a couple guys on the Ohio Valley RVators Yahoo Group running Catto props. I believe one of the -4's is (Dan H.) Join and post to OhioValleyRVators@yahoogroups.com
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  #15  
Old 04-01-2011, 11:14 PM
ratc's Avatar
ratc ratc is offline
 
Join Date: Jan 2006
Location: North Yorkshire UK
Posts: 152
Default Catto Prop Data?

Elippse, I don't question the efficiency of a propeller with 3 (or more) blades in the static thrust/ROC phase of flight and clearly the 8-blade, narrow tip, NP2000 propeller is a great example. Since this is a C/S unit it can also be optimized for the cruise, my question relates to Fixed Pitch Propellers.
How efficient is a FP 3 (or more) blade propeller, pitched for optimum static thrust in cruise conditions?
I hope it's not just me that's getting an education out of this thread, hopefully we'll all get dragged into the 21st Century!
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Andy
RV-4
#4411
G-RATC
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  #16  
Old 04-02-2011, 11:10 AM
elippse elippse is offline
 
Join Date: Dec 2006
Location: Arroyo Grande, CA
Posts: 938
Default

The thing that makes the difference is the amount of mass flow through the prop. More mass flow, more thrust, less delta-v, more efficiency. I designed Jim Smith's three-blade for best cruise. It had less static thrust beacause of the planform of my design, but higher ROC and cruise than his 68-72 Aymar DeMuth. At 8000' dalt the three-blade gave 190.5 mph GPS-determined TAS vs 186 mph for the A-D, even though the A-D was turning an average 100 rpm more. The speed increase was worth 7.5% and when you throw in the 2800 rpm/2700 rpm that gives an efficiency increase of 11.4%. Keep in mind that I said that multi-blade propellers with the same diameter, pitch distribution, and planform shape, that is, chord distribution but with reduced chords, will have more static thrust and ROC, whether FP or CS. BTW, with his new wingtips, Jim is doing 193.5 mph at 8000'dalt! You really need to read the articles I have written in Contact! magazine that go discuss planform, pitch, and multi-blades. I think you will learn a lot from them.

Last edited by elippse : 04-02-2011 at 11:12 AM. Reason: Added ending
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