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Which prop to keep? another Catto VS Sensinich thread

J

j-red

Well Known Member
I need some guidance. Have two props and I like them both. They're both quite different in their performance, and I first want to understand the differences fully and second want to decide on which one to keep and be happy about it.

The plane:
RV6A, o-360, carbureted, 1 slick and 1 SDS Electronic

Started out with a Sensenich FP, which worked perfectly fine, albeit a good bit of vibration and noise which I never really noticed UNTIL... I picked up a Catto 3 blade looking to pick up some extra speed. The Catto is a 66x74 and is every bit as smooth as everyone claims. However, with this pitch, the Catto performs more like a climb prop. Climb it does, and does well. It will go almost as fast as the Sensenich, but the downside is that it does so at a considerably higher fuel burn, and tends toward a higher fuel burn at most rpm's.

Cruise Performance:
Sensenich Performance: 8kDA, 2740RPM, 168KTAS, 10gph; That is throttled back some, because it will turn faster than that. Adjusting for a fuel flow of about 8gph nets around 150-155kts@2560RPM. Yesterday I tested it at full throttle, 10kmsl and saw 2800rpm, 170KTAS, and 10gph.

The Catto: 8kDA, 2720RPM full-in, 167KTAS, 13gph flow. Adjusting for a fuel flow of about 8gph also nets around 150KTAS @2450rpm


Static RPM on the Sensi = 2150rpm, held with brakes
Static on the Catto = 2200? but brakes couldn't hold it.

Climb:
Sensi- 1kfpm at 120kts, throttle reduced to keep CHT's below 415.
Catto- seems to accelerate slower, but climbs 1.5kfpm @ 110 kts full throttle and CHT's never try to go over 400. Slighly higher fuel burn.



Conclusion:
I guess where i'm seeing the most significant difference is more subjective than the numbers might imply. A lot of it is just impression because i'm usually too busy to take photos to bring back and compare.

+ & - for the Sensinich=
Better top speed at a lower fuel burn at almost every altitude. Better acceleration after leveling off. This is the big one, as most of my flying is done in the local area down low. I can hit 1500agl and almost immediately be flying at 140kts indicated, which allows me to throttle way back for a pleasurable sightseeing flight with a minimal fuel burn. Push it in, and immediately the airspeed climbs up. I'm based at sea level, and usually do lower altitude local flights, so climb performance isn't really an issue. Basically this prop does exactly what I want it to do, but with two major consequences: RPM and engine temps on climbout. I don't fully understand the way manifold pressure fits into the equation, but this prop burns less fuel at a higher rpm and lower manifold pressure than the catto. That seems to tell me the engine isn't working as hard. Still, it almost always operates at around 2700rpm which i've been told will reduce the life of the engine.

+ & - for the Catto
Smoothness, lower rpm for engine longevity, great climb ability and lower temps on climb out. Looks great!:D
The main frustration when flying it has been the time it takes to speed up. When leveling out from a climb at 110kts, i've got to leave the throttle in for considerably longer to get it up to speed, thus burning more fuel per local hop than the Sensenich assuming the same speeds.



Interesting observation in case anyone cares: there is a difference in the way I have to approach final with each prop. The Catto seems to lose energy faster and thus speed drops off quickly before touchdown than the sensenich does. My supposition is that the flywheel effect of the sensi keeps it spinning and generating some forward thrust even with the throttle out. Thus, short field landings are a snap with the catto while the sensi, at the same approach speed, just wants to float forever...

Do these observations make sense to anyone else? Can anyone think of some pro's/cons that might help sway me one way or the other that I haven't thought of yet? Am I crazy?

I'm outta money, so I need to sell one of them, and having either of them modified is really out of the question right now as is changing to a CS.
 
I am not questioning your numbers. But I don't understand them. If both get the same speed at the same density altitude, I don't understand the difference in fuel burn. It would seem that same speed at same altitude would require the same amount of thrust on the same plane. If the thrust is the same but fuel consumption is 18% higher, the Catto would seem to be 18% less efficient. That would certainly surprise me
 
Me either.
Your test procedure could be flawed. You would need to follow a rigid procedure to account for the variables between test periods. Kevin Horton has a great right up on that if you do a quick search.

Both companies have great reputations. Craig and family are RV people and having met them and seen how they do business first hand, I know what my choice would be.

You will always have some trade offs with a fixed pitch prop.
 
j-red said:
. Snip.

Cruise Performance:
Sensenich Performance: 8kDA, 2740RPM, 168KTAS, 10gph; That is throttled back some, because it will turn faster than that. Adjusting for a fuel flow of about 8gph nets around 150-155kts@2560RPM. Yesterday I tested it at full throttle, 10kmsl and saw 2800rpm, 170KTAS, and 10gph.

The Catto: 8kDA, 2720RPM full-in, 167KTAS, 13gph flow. Adjusting for a fuel flow of about 8gph also nets around 150KTAS @2450rpm
.....SNIP
Click to expand...

To be blunt - your data demonstrates both props as poor performers.
Shoot fire - I cruise at 171 kts and 11.5 GPH fuel burn in the RV-10! The 8A was 7.5 GPH for that speed.

My recommendation - sell the Catto, save your pennies and then sell the Sensenich and buy a nice shiney new Hartzell BA CS prop.

The biggest mistake I made on my first RV was installing a FP prop. I replaced it at 300 hours with the Hartzell. The performance improvement was simply amazing.
Carl
 
I appreciate the replies. I don't really understand the data myself:eek:, which was one of the reasons for the post! The props were tested in very similar conditions, and altitude adjusted for density so that a comparison would be accurate. My thought about the difference in fuel burn for the same speed was that one prop had to work harder to get there which is evidence by a higher manifold pressure for the same rpm.

I do feel that it is a little slow when compared with the numbers others are posting. Or rather, I have to burn more fuel to get those numbers than they do. That was one reason I bought the new prop: hoping for more top end speed. Mind you, my 6A isn't fat. In fact, it weighed in at around 980lbs empty. It may be a little dirtier than some others: gear leg fairings are the older all-aluminum variety, and I have a couple of exposed comm antennas, and older style wheelpants.

I can see where the constant speed prop would increase climb ability while maximizing cruise efficiency, but I don't see how it would increase cruise speed at all given that I currently have two props at the opposite end of the spectrum giving roughly the same speed. Wouldn't the CS land somewhere in-between?
 
One major problem with your data is it never mentions your test altitude other than to say that both were tested at the same D.A.

A fixed pitch prop is a compromise and will only be optimized for speed it one specific altitude range.

A fixed pitch prop pitched for better climb is also usually a great performing cruise prop at higher altitudes (11K - 12K) as long as you are willing to run the engine at the upper end of the RPM band. But it will be sub par for cruise at middle altitudes (6K - 8K).

A prop pitched for good cruise at 6 -8K will cause poorer takeoff/climb performance and wont do very well at the higher altitudes.

Knowing your test altitude (DA) will help answer your question.......
 
For comparison, my two bladed Catto, bolted to an O-360 on my RV-9 will run it up to 175 knots TAS at 8,000' DA while burning around 10.8 GPH and spinning 2840 RPM.

It makes a great climb prop and I can see between 1600 and 2100 FPM, depending on load and DA at takeoff. However, in cruise, I typically run it between 150 and 155 knots and burn around 7 GPH +/-.
 
Rvbuilder,
You make an interesting point. Tests were done at 8k DA, but I took the sensenich up to 11k da yesterday and noticed that the performance dropped off. I was able to get 170kts true at about the same 10gph fuel burn. I may try the same thing with the catto and see what happens.
 
humptybump said:
Carl, you had a very efficient RV-8A. Was that with a constant speed propeller? If so do you recall the MP and RPM for that performance? SNIP.
Click to expand...

Standard cruise for both the RV-8A and RV-10 is about 2400 RPM and 24" (or WOT if high) MP, LOP. Both planes have the Hartzell BA prop (74" on the 8A, 80" on the RV-10). The 8A has dual pMag ignitions. The RV-10 still has these #*!^ mags, but I expect that to finally end next month with delivery of a set of six cylinder pMags.

Note - both the RV-8A and RV-10 have new homes. Selling the RV-10 was a big mistake but sometimes life throws curve balls at you. At least the new owners of both planes let me fly them from time to time.

I also have a brand new 74" Hartzell BA prop that arrived last week for the new RV-8 project.

High efficiently cross country cruise has always been the driving considerations for my projects. That translates to:
- fuel injected parallel valve Lycoming engines
- cylinder injector nozzles balance to support smooth LOP operation
- pMags
- Hartzell BA props
- a reasonably low empty weight

Others may have different design objectives.
Carl
 
Thanks Carl. I realized after posting that you were probably running fuel injections and optimized electronic ignition. Combine those with the CS propeller gives you a lot of control and optimization.
 
Prop

I believe that most find the Catto three blade gives up around 3 m/h cruise compared to the Catto two blade.
MANIFOLD PRESSURE without this your data is not useful. If you had a manifold pressure you would find that it is higher to turn the Catto at the same or similar r/m. You stated that the Sensenich data is with the throttle backed out "some". The throttle is likely backed out a lot with the Sens., hence the much lower fuel flow.
Also does the Catto have metal leading edge?? This it reported to cost ANOTHER 3 m/h.
What generation Catto? There have been a lot of recent changes, not sure there is even such a thing as a "standard" Catto.
 
j-red said:
Rvbuilder,
You make an interesting point. Tests were done at 8k DA, but I took the sensenich up to 11k da yesterday and noticed that the performance dropped off. I was able to get 170kts true at about the same 10gph fuel burn. I may try the same thing with the catto and see what happens.
Click to expand...

My RV-6A with O-360 and Sensenich prop does about the same speed at that altitude but at a fuel flow in the 8.1 - 8.3 GPH range running just slightly lean of peak.
Turns about 2620 RPM WOT at 11,500 with that mixture setting.
 
j-red said:
. SNIP
I can see where the constant speed prop would increase climb ability while maximizing cruise efficiency, but I don't see how it would increase cruise speed at all given that I currently have two props at the opposite end of the spectrum giving roughly the same speed. Wouldn't the CS land somewhere in-between?
Click to expand...

Short answer - no.

I offer that a propeller's efficiency to transform engine power to thrust is dependent on many factors besides pitch. There is a lot of art involved as well.

Anytime you are pushing a engine to 2800 RPM and you can still go higher you have clear example of a prop that is not doing what it should. RVs have such a wide speed range that any FP prop will fall short in delivering what the airplane is capable of doing. On my 8A I went up to 12,500' and still had to pull throttle to keep it below 2800 RPM. I never did find out the top speed of that plane until after I replace the original prop with the Hartzell BA.

They cost more and weigh more - so just another decision for what you want on your airplane.

Carl
 
krw5927 said:
Wait.... WHAT?! The 6-cyl Pages are finally being delivered??? :eek:
Click to expand...

Well you know how that works.

While I would not be surprised if Brad slipped another month, I think a few will soon finally go out the door. I'm guessing he will have a better shipment schedule at Oshkosh.

If interested, Brad just posted a "close to final" installation and operating manual on the eMag website.

Carl
 
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