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Catto Prop

Scott Hersha

Well Known Member
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.
 
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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.
 
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.
 
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
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
 
Ground Adjustable?

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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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.
 
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.
 
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.
 
I'm in the same boat

Hi Scott... I am facing the same dilemma! Virtually the same plane / engine / prop ! I was looking to get weight out of plane and even with moving battery forward of firewall and adding full Raven inverted oil I am not sure I will balance the weight reduction from prop and may have to add useless weight in form of tungsten crush plate . I will be talking to Nicole on Wednesday as I wrestle with this one . For sure though the overwhelming consensus is that Catto are quality products and people ... PS I am leaning toward 3 blade because of 0-360
 
Hi Scott... I am facing the same dilemma! Virtually the same plane / engine / prop ! I was looking to get weight out of plane and even with moving battery forward of firewall and adding full Raven inverted oil I am not sure I will balance the weight reduction from prop and may have to add useless weight in form of tungsten crush plate .

Thing of it as an opportunity to set your CG exactly where you want it.
 
Prop me up

Scott,
Being from the Jurassic RV generation where the only props available were made from trees, I am “feeling Your pain” on RPM. Like everything in life, props on a RVs are a compromise. I’ve always preferred FP as a former F16 guy, a light nose for dogfighting and acro and a lower “flywheel effect” and is a plus. Another consideration is lower cost and simplicity, something I also like. :)
I always strived to get 2700 +/- 100 RPM WOT at 10000 feet, where I normally tried to cruise XC. Down low, 2800-2900 WOT with a balanced prop/engine is ok, especially given that the 0290G as a generator ran continuously at 3200 for hours, Helicopter 0-320’s/360’s rated at 3000RPM, Reno racers much higher than that, longevity notwithstanding.

That said, I met Craig Catto in the early 90’s and installed (for testing) his first 2 blade RV prop on my RV4. Over the years I’ve tested nine different FP props on my RV4 and RV6X with many performance numbers noted. Overall it all boils down to you. Do you live in higher elevation, need better takeoff RPM on a short strip? Spend more time climbing, doing acro, or cruising XC? Personally, I like to get rated RPM (or better) if I need it up high, where MP is low and you’re not stressing the engine.

I would keep what you have, collect some data and be happy. You’re enjoying the fruits of many years of Catto beta testers (like me) helping CC perfect his masterpiece. If you want to go higher pitch, there are gains and losses as well.

It’s up to you...
V/R
Smokey
 
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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.

Scott,

That static seems a little low to me and I would think you might be pitched more for speed. Mine is around 2300-2350.

As Smokey said, live and love with what you have for now. You might have a different opinion in a year or two. I've flip flopped more than a few times in the 200+ hours of flying this over the past two years.

BTW, I recently saw the -8 that you recently donated to the Boston area. Really nice job.

Brian
 
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