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  #1  
Old 11-23-2019, 07:45 PM
Scott Hersha Scott Hersha is offline
 
Join Date: Jan 2005
Location: Cincinnati, OH
Posts: 1,755
Default Catto Prop

Not wanting to hijack someone else’s thread, I’ll start my own thread.

I have an RV4 (purchased) with a Lycoming O-360-A1A, carbureted with a Sensenich 72-FM8S9-1-85 (85” pitch). If I set wide open throttle (WOT) at just about any altitude I’m seeing 2850-2900 RPM. I don’t do this normally, but after discussing with Nicole at Catto, she recommended I do it once more to collect some data. What I found:
7500’ DA
37* OAT
174 Knots TAS
2870 RPM

What I would like to see is 2700 - 2750 RPM at WOT. Seems like I need more pitch. I’m not too worried about loosing some runway performance, because with my current under pitched ‘cruise prop’ I still get off the ground in less than 500’ and climb at 1500 - 2000 FPM once the speed increases to about 110 and RPM has accelerated to about 2400 - 2500 RPM, which happens very quickly.

I don’t have very much experience with fixed pitch props, so I am seeking advice from those more knowledgeable about my choices relative to Catto. 2-blade? 3-blade? What kind of performance differences am I likely to see? Is a prop change warranted or worthwhile in your experience? Please explain. I’m used to cruising at 23-2400 RPM in my RV8 (former) with it’s constant speed prop, and cruising at 2600 RPM in my new RV4 seems a little uncomfortable, but if I set 2400, I’m at less than 55% power usually. I can get 75% power at 7500’, but to do so, I’m north of 2700 RPM, and I don’t want to do that.

Nicole is working on a quote/recommendation for me, but the 2-blade, 3-blade choice is mine, and I don’t want to chase after something that won’t make much difference. Maybe what I have is almost as good as it gets with a FP prop.

I know I can install a CS prop with this engine, but to do so I’ll have to pull the engine to modify the firewall for a governor installation, and then spend a minimum of $11K to make it all happen. I really don’t want to do that.

Advice/experience appreciated.
__________________
SH
RV6/2001 built/sold 2005
RV8 Fastback/2008 built/sold 2015
RV4/bought 2016/sold/2017
RV8/2018 built/Sold(sadly)
RV4/bought 2019 Flying
Cincinnati, OH/KHAO
JAN2021

Last edited by Scott Hersha : 11-23-2019 at 07:48 PM.
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  #2  
Old 11-23-2019, 09:47 PM
Ed_Wischmeyer's Avatar
Ed_Wischmeyer Ed_Wischmeyer is offline
 
Join Date: May 2005
Location: Savannah, GA
Posts: 1,378
Default

Opinions:
* You've already got a heavy engine, don't need a heavy prop. On my RV-9A, when I went to a c/s, the handling was definitely different. I'm used to it now, though. Work some sample W&B to see what a c/s prop would do. I agree with you, modifying the firewall would be way too much fun... :-(
* One potential problem with a three bladed prop is getting the cowling on and off. (On the -9A, when I went to a c/s, I needed a spacer and now have a huge gap between spinner and cowling. An unexpected benefit is that it is now ever so much easier to take the cowling on and off.)
* Also consider landing distance. With a coarser, fixed pitched prop, you'll have even less prop drag / greater residual thrust on landing, and less deceleration and descent capability.
* Double check the RPM limit on the Sensenich. Mine had a 2600 RPM limit.
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Previously RV-4, RV-8, RV-8A, AirCam, Cessna 175
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  #3  
Old 11-23-2019, 10:10 PM
crabandy crabandy is offline
 
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Location: Ottawa, Ks
Posts: 2,213
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Just talk, but when I spoke to Craig I asked him what prop he would run on my RV7. With an O-320 he recommended a 2 blade, he recommended the 3 blade with an O-360. The extra blade balanced the pulses of the O-360 engine better.

It?s defenitely worth your time to provide the current data for your airplane, average the data from multiple runs. More data can?t hurt:

Catto was able to match my RV7 perfectly before first flight on my 3 blade. 2100 seems like a low static RPM but it builds RPM steadily and I end up at 2750ish firewalled and 75% power.

Tell Catto about the engine and the Rv and they?ll tell you the prop.
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  #4  
Old 11-24-2019, 06:38 AM
Kyle Boatright Kyle Boatright is offline
 
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Location: Atlanta, GA
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Why not have the existing prop repitched?
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  #5  
Old 11-24-2019, 08:31 PM
Scott Hersha Scott Hersha is offline
 
Join Date: Jan 2005
Location: Cincinnati, OH
Posts: 1,755
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Re-pitching a Sensenich has resulted in some bad prop failure stories - from what I?ve heard from the past. The 85? pitch on mine is the maximum pitch that Sensenich makes it these RV compatible props. I might just have to live with what I have for now anyway. I just can?t use full throttle in cruise, so I?m leaving some power/performance on the table. I?ll see what Nicole at Catto tells me about the data I sent her.
My first RV4 had a two blade Catto and a 170hp O-320. That one would spin all the way to 3000 RPM in cruise, even at 12,000?. I sent it to Catto and had him re-pitch it as much as he could, but I still would get about 2850 wide open. There?s only so much he can do to change the pitch on a composite prop.
__________________
SH
RV6/2001 built/sold 2005
RV8 Fastback/2008 built/sold 2015
RV4/bought 2016/sold/2017
RV8/2018 built/Sold(sadly)
RV4/bought 2019 Flying
Cincinnati, OH/KHAO
JAN2021
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  #6  
Old 11-24-2019, 08:49 PM
RV-4 RV-4 is offline
 
Join Date: Oct 2007
Location: St-Jerome,Quebec,Canada
Posts: 1,147
Thumbs up Catto Prop

SH
As part of your crusade toward getting the optimum prop for your -4, you may want to check that your RPM gauge is reading properly before going thru all the hassles of getting a new prop..

For reference: I have a RV-4 with a Catto 3 bladded prop reving around 2750 at WOT...My prevoius one ( also a Catto was underpitch with numbers close to 3000 rpm if I let it be..after a re-pitched I got it down to 2800 and gain 9-10 knots in the process..

Best of luck

Bruno
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  #7  
Old 11-25-2019, 05:20 AM
Northernliving Northernliving is online now
 
Join Date: May 2005
Location: Boston, MA
Posts: 496
Default Ground Adjustable?

Quote:
Originally Posted by Scott Hersha View Post
Not wanting to hijack someone else’s thread, I’ll start my own thread.

I have an RV4 (purchased) with a Lycoming O-360-A1A, carbureted with a Sensenich 72-FM8S9-1-85 (85” pitch). If I set wide open throttle (WOT) at just about any altitude I’m seeing 2850-2900 RPM. I don’t do this normally, but after discussing with Nicole at Catto, she recommended I do it once more to collect some data. What I found:
7500’ DA
37* OAT
174 Knots TAS
2870 RPM

What I would like to see is 2700 - 2750 RPM at WOT. Seems like I need more pitch. I’m not too worried about loosing some runway performance, because with my current under pitched ‘cruise prop’ I still get off the ground in less than 500’ and climb at 1500 - 2000 FPM once the speed increases to about 110 and RPM has accelerated to about 2400 - 2500 RPM, which happens very quickly.

I don’t have very much experience with fixed pitch props, so I am seeking advice from those more knowledgeable about my choices relative to Catto. 2-blade? 3-blade? What kind of performance differences am I likely to see? Is a prop change warranted or worthwhile in your experience? Please explain. I’m used to cruising at 23-2400 RPM in my RV8 (former) with it’s constant speed prop, and cruising at 2600 RPM in my new RV4 seems a little uncomfortable, but if I set 2400, I’m at less than 55% power usually. I can get 75% power at 7500’, but to do so, I’m north of 2700 RPM, and I don’t want to do that.

Nicole is working on a quote/recommendation for me, but the 2-blade, 3-blade choice is mine, and I don’t want to chase after something that won’t make much difference. Maybe what I have is almost as good as it gets with a FP prop.

I know I can install a CS prop with this engine, but to do so I’ll have to pull the engine to modify the firewall for a governor installation, and then spend a minimum of $11K to make it all happen. I really don’t want to do that.

Advice/experience appreciated.
Scott,

I’ve been through the same with an RV8 that I purchased with a carbon fiber fixed pitch prop. Mine is pitched more for climb and I can’t really get the speed that I want unless running at high RPMs. I don’t really like doing that. It’s all a compromise. My current prop is only 12lbs., so flying with a heavy passenger is quite different to say the least. I’d like a little more weight up front. I did all the same testing with Nicole to see if I should try a different prop, but in the end, decided to call this was it is; it’s a fast sports car stuck in second gear. You can pick the gear, but it's stuck there. Not much fun. I’m biting the bullet and going with a Hartzell composite CS prop. On order, to be delivered Jan 20/2020 (counting the days). If I were to stay with a FP prop, I would get one of the newer ground adjustable composites. That’s the only real way to dial in what you want for the kind of flying you are doing.

You didn't comment on your static RPM - also an important input. Perhaps a little slower than the take off RPM that you quoted. That's about where mine was.


Brian
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Boston, MA
RV8 Based at ORH - Purchased
RV8 - The Project #83313 - Under Construction

Last edited by Northernliving : 11-25-2019 at 05:31 AM.
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  #8  
Old 11-25-2019, 08:00 AM
Scott Hersha Scott Hersha is offline
 
Join Date: Jan 2005
Location: Cincinnati, OH
Posts: 1,755
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Brian,
Thanks for the input, and I like your description of being stuck in 2nd gear. I might be stuck in 3rd gear and looking for overdrive. My static RPM is 2050-2100, which is in the acceptable window according to Sensenich. I?ll look into the ground adjustable composites from Whirlwind and Sensenich. I really don?t want the expense and hassle with firewall mod required to go with a CS prop. I guess I shouldn?t complain. This airplane flys as good as any RV I?ve built or owned, is a ton of fun, and without question, the best bang for the buck I?ve ever had. I don?t like running high RPMs either, but maybe I?ll get used to it.

Bruno,
Good idea, and I?ll check that tach reading. Our chapter purchased a DynaVibe prop balancer. I?ve done 3 airplanes with it so far and when I do mine, I?ll be able to check the accuracy of my tach reading - coming from my GRT EIS.

Thanks for the inputs.
__________________
SH
RV6/2001 built/sold 2005
RV8 Fastback/2008 built/sold 2015
RV4/bought 2016/sold/2017
RV8/2018 built/Sold(sadly)
RV4/bought 2019 Flying
Cincinnati, OH/KHAO
JAN2021
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  #9  
Old 11-25-2019, 09:14 AM
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Jvon811 Jvon811 is offline
 
Join Date: Mar 2014
Location: KFNT Central Michigan
Posts: 206
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It sounds like you're just trying to get C/S performance from a fixed pitch. I just don't think it will happen.

Sounds like your chasing a speed for "cruise" and the resultant RPM is the variable. In reality, with fixed pitch, you set the RPM you want (and resultant fuel burn you want), and the variable is your cruise speed.

To me, 160hp/RV-4/2 blade fixed, your initial numbers sound awesome. Right where I'd expect a 180hp -4 to be with a cruise prop. Any more pitch and you will lose climb and takeoff performance like you suspect. That's just the nature of the beast.

Are you trying to race some buddies or something? That's a deep rabbit hole, ask me how I know, haha.
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  #10  
Old 11-25-2019, 10:56 AM
rag rag is offline
 
Join Date: Feb 2012
Location: Holmen, WI
Posts: 56
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I posted this on another thread, but it is relevant here too. RV4 - O360 180 HP Catto 2 blade, 68X76 - 2330 RPM static, 70% power, 2580-2620 RPM, 170kts. I have not compared performance to a three blade Catto, but from my research - a two blade is slightly more efficient, easier to remove the cowl, less cost, easier to ship and I have plenty of ground clearance. There are no RPM limitations other than 3200 Max. I am very happy with this combination. For me it is an excellent compromise.
I have run both the nickel leading edge and non nickel leading edge. I perfer the non-nickel leading edge - the prop pulls hard from initial throttle on takeoff. The prop with the nickel edge, would take 50 - 100 feet before it would start to pull hard on takeoff. Previous to the conversion to 180hp - I had a Catto prop on my O320 for 20 plus years. It was a noticeable performance improvement over the original Pacesetter that I installed when I built the airplane. The Catto family are great people to work with and they produce a great product.
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